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1.  Workflow for the use of a high-resolution image detector in endovascular interventional procedures 
Endovascular image-guided intervention (EIGI) has become the primary interventional therapy for the most widespread vascular diseases. These procedures involve the insertion of a catheter into the femoral artery, which is then threaded under fluoroscopic guidance to the site of the pathology to be treated. Flat Panel Detectors (FPDs) are normally used for EIGIs; however, once the catheter is guided to the pathological site, high-resolution imaging capabilities can be used for accurately guiding a successful endovascular treatment. The Micro-Angiographic Fluoroscope (MAF) detector provides needed high-resolution, high-sensitivity, and real-time imaging capabilities. An experimental MAF enabled with a Control, Acquisition, Processing, Image Display and Storage (CAPIDS) system was installed and aligned on a detector changer attached to the C-arm of a clinical angiographic unit. The CAPIDS system was developed and implemented using LabVIEW software and provides a user-friendly interface that enables control of several clinical radiographic imaging modes of the MAF including: fluoroscopy, roadmap, radiography, and digital-subtraction-angiography (DSA). Using the automatic controls, the MAF detector can be moved to the deployed position, in front of a standard FPD, whenever higher resolution is needed during angiographic or interventional vascular imaging procedures. To minimize any possible negative impact to image guidance with the two detector systems, it is essential to have a well-designed workflow that enables smooth deployment of the MAF at critical stages of clinical procedures. For the ultimate success of this new imaging capability, a clear understanding of the workflow design is essential. This presentation provides a detailed description and demonstration of such a workflow design.
doi:10.1117/12.2043087
PMCID: PMC4188374  PMID: 25302003
MAF; high resolution detector; angiography; workflow; x-ray imaging; endovascular image-guided interventions; CAPIDS
2.  Region-of-Interest Micro-Angiographic Fluoroscope Detector Used in Aneurysm and Artery Stenosis Diagnoses and Treatment 
Proceedings of SPIE  2012;8313:10.1117/12.910771.
Due to the need for high-resolution angiographic and interventional vascular imaging, a Micro-Angiographic Fluoroscope (MAF) detector with a Control, Acquisition, Processing, and Image Display System (CAPIDS) was installed on a detector changer, which was attached to the C-arm of a clinical angiographic unit at a local hospital. The MAF detector provides high-resolution, high-sensitivity, and real-time imaging capabilities and consists of a 300 µm-thick CsI phosphor, a dual stage micro-channel plate light image intensifier (LII) coupled to a fiber optic taper (FOT), and a scientific grade frame-transfer CCD camera, providing an image matrix of 1024×1024 35 µm effective square pixels with 12 bit depth. The changer allows the MAF region-of-interest (ROI) detector to be inserted in front of the Image Intensifier (II) when higher resolution is needed during angiographic or interventional vascular imaging procedures, e.g. endovascular stent deployment. The CAPIDS was developed and implemented using Laboratory Virtual Instrumentation Engineering Workbench (LabVIEW) software and provides a user-friendly interface that enables control of several clinical radiographic imaging modes of the MAF including: fluoroscopy, roadmapping, radiography, and digital-subtraction-angiography (DSA). The total system has been used for image guidance during endovascular image-guided interventions (EIGI) for diagnosing and treating artery stenoses and aneurysms using self-expanding endovascular stents and coils in fifteen patient cases, which have demonstrated benefits of using the ROI detector. The visualization of the fine detail of the endovascular devices and the vessels generally gave the clinicians confidence on performing neurovascular interventions and in some instances contributed to improved interventions.
doi:10.1117/12.910771
PMCID: PMC3877313  PMID: 24386538
Neuro-imaging; neuro-endovascular image-guided interventions; x-ray imaging; fluoroscopic detector; high-resolution imaging
3.  Design considerations for a new, high resolution Micro-Angiographic Fluoroscope based on a CMOS sensor (MAF-CMOS) 
The detectors that are used for endovascular image-guided interventions (EIGI), particularly for neurovascular interventions, do not provide clinicians with adequate visualization to ensure the best possible treatment outcomes. Developing an improved x-ray imaging detector requires the determination of estimated clinical x-ray entrance exposures to the detector. The range of exposures to the detector in clinical studies was found for the three modes of operation: fluoroscopic mode, high frame-rate digital angiographic mode (HD fluoroscopic mode), and DSA mode. Using these estimated detector exposure ranges and available CMOS detector technical specifications, design requirements were developed to pursue a quantum limited, high resolution, dynamic x-ray detector based on a CMOS sensor with 50 μm pixel size. For the proposed MAF-CMOS, the estimated charge collected within the full exposure range was found to be within the estimated full well capacity of the pixels. Expected instrumentation noise for the proposed detector was estimated to be 50–1,300 electrons. Adding a gain stage such as a light image intensifier would minimize the effect of the estimated instrumentation noise on total image noise but may not be necessary to ensure quantum limited detector operation at low exposure levels. A recursive temporal filter may decrease the effective total noise by 2 to 3 times, allowing for the improved signal to noise ratios at the lowest estimated exposures despite consequent loss in temporal resolution. This work can serve as a guide for further development of dynamic x-ray imaging prototypes or improvements for existing dynamic x-ray imaging systems.
doi:10.1117/12.2006430
PMCID: PMC3864963  PMID: 24353389
MAF; CMOS; ROI; fluoroscopy; angiography; x-ray imaging; detector design; neurovascular interventions
4.  A novel Region of Interest (ROI) imaging technique for biplane imaging in interventional suites: high-resolution small field-of-view imaging in the frontal plane and dose-reduced, large field-of-view standard-resolution imaging in the lateral plane 
Endovascular-Image-Guided-Interventional (EIGI) treatment of neuro-vascular conditions such as aneurysms, stenosed arteries, and vessel thrombosis make use of treatment devices such as stents, coils, and balloons which have very small feature sizes, 10's of microns to a few 100's of microns, and hence demand a high resolution imaging system. The current state-of-the-art flat panel detector (FPD) has about a 200-um pixel size with the Nyquist of 2.5 lp/mm. For higher-resolution imaging a charge-coupled device (CCD) based Micro-Angio -Fluoroscope (MAF-CCD) with a pixel size of 35um (Nyquist of 11 lp/mm) was developed and previously reported. Although the detector addresses the high resolution needs, the Field-Of-View (FOV) is limited to 3.5 cm × 3.5 cm, which is much smaller than current FPDs. During the use of the MAF-CCD for delicate parts of the intervention, it may be desirable to have real-time monitoring outside the MAF FOV with a low dose, and lower, but acceptable, quality image.
To address this need, a novel imaging technique for biplane imaging systems has been developed, using an MAF-CCD in the frontal plane and a dose-reduced standard large FOV imager in the lateral plane. The dose reduction is achieved by using a combination of ROI fluoroscopy and spatially different temporal filtering, a technique that has been previously presented.
In order to evaluate this technique, a simulation using images acquired during an actual EIGI treatment on a patient, followed by an actual implementation on phantoms is presented.
doi:10.1117/12.2043460
PMCID: PMC4188443  PMID: 25302001
5.  Progress in the Development of a new Angiography Suite including the High Resolution Micro-Angiographic Fluoroscope (MAF), a Control, Acquisition, Processing, and Image Display System (CAPIDS), and a New Detector Changer Integrated into a Commercial C-Arm Angiography Unit to Enable Clinical Use 
Proceedings of SPIE  2010;7622(76225I):76225I (2010).
Due to the high-resolution needs of angiographic and interventional vascular imaging, a Micro-Angiographic Fluoroscope (MAF) detector with a Control, Acquisition, Processing, and Image Display System (CAPIDS) was installed on a detector changer which was attached to the C-arm of a clinical angiographic unit. The MAF detector provides high-resolution, high-sensitivity, and real-time imaging capabilities and consists of a 300 μm-thick CsI phosphor, a dual stage micro-channel plate light image intensifier (LII) coupled to a fiber optic taper (FOT), and a scientific grade frame-transfer CCD camera, providing an image matrix of 1024×1024 35 μm square pixels with 12 bit depth. The Solid-State X-Ray Image Intensifier (SSXII) is an EMCCD (Electron Multiplying charge-coupled device) based detector which provides an image matrix of 1k×1k 32 μm square pixels with 12 bit depth. The changer allows the MAF or a SSXII region-of-interest (ROI) detector to be inserted in front of the standard flat-panel detector (FPD) when higher resolution is needed during angiographic or interventional vascular imaging procedures. The CAPIDS was developed and implemented using LabVIEW software and provides a user-friendly interface that enables control of several clinical radiographic imaging modes of the MAF or SSXII including: fluoroscopy, roadmapping, radiography, and digital-subtraction-angiography (DSA). The total system has been used for image guidance during endovascular image-guided interventions (EIGI) using prototype self-expanding asymmetric vascular stents (SAVS) in over 10 rabbit aneurysm creation and treatment experiments which have demonstrated the system's potential benefits for future clinical use.
doi:10.1117/12.844909
PMCID: PMC3021378  PMID: 21243037
SYS; DA; DSA; Fluoroscope; Roadmap; LabVIEW; MAF; SSXII; Detector-Changer; CAPIDS
6.  Investigation of new flow modifying endovascular image-guided interventional (EIGI) techniques in patient-specific aneurysm phantoms (PSAPs) using optical imaging 
Effective minimally invasive treatment of cerebral bifurcation aneurysms is challenging due to the complex and remote vessel morphology. An evaluation of endovascular treatment in a phantom involving image-guided deployment of new asymmetric stents consisting of polyurethane patches placed to modify blood flow into the aneurysm is reported. The 3D lumen-geometry of a patient-specific basilar-artery bifurcation aneurysm was derived from a segmented computed-tomography dataset. This was used in a stereolithographic rapid-prototyping process to generate a mold which was then used to create any number of exact wax models. These models in turn were used in a lost-wax technique to create transparent elastomer patient-specific aneurysm phantoms (PSAP) for evaluating the effectiveness of asymmetric-stent deployment for flow modification. Flow was studied by recording real-time digitized video images of optical dye in the PSAP and its feeding vessel. For two asymmetric stent placements: through the basilar into the right-posterior communicating artery (RPCA) and through the basilar into the left-posterior communicating artery (LPCA), the greatest deviation of flow streamlines away from the aneurysm occurred for the RPCA stent deployment. Flow was also substantially affected by variations of inflow angle into the basilar artery, resulting in alternations in washout times as derived from time-density curves. Evaluation of flow in the PSAPs with real-time optical imaging can be used to determine new EIGI effectiveness and to validate computational-fluid-dynamic calculations for EIGI-treatment planning.
doi:10.1117/12.772583
PMCID: PMC2570532  PMID: 18946513
image-guided therapy; neurosurgical procedures; modeling; procedure simulation; segmentation and rendering; treatment planning
7.  Endovascular Radiofrequency Ablation for Varicose Veins 
Executive Summary
Objective
The objective of the MAS evidence review was to conduct a systematic review of the available evidence on the safety, effectiveness, durability and cost–effectiveness of endovascular radiofrequency ablation (RFA) for the treatment of primary symptomatic varicose veins.
Background
The Ontario Health Technology Advisory Committee (OHTAC) met on August 26th, 2010 to review the safety, effectiveness, durability, and cost-effectiveness of RFA for the treatment of primary symptomatic varicose veins based on an evidence-based review by the Medical Advisory Secretariat (MAS).
Clinical Condition
Varicose veins (VV) are tortuous, twisted, or elongated veins. This can be due to existing (inherited) valve dysfunction or decreased vein elasticity (primary venous reflux) or valve damage from prior thrombotic events (secondary venous reflux). The end result is pooling of blood in the veins, increased venous pressure and subsequent vein enlargement. As a result of high venous pressure, branch vessels balloon out leading to varicosities (varicose veins).
Symptoms typically affect the lower extremities and include (but are not limited to): aching, swelling, throbbing, night cramps, restless legs, leg fatigue, itching and burning. Left untreated, venous reflux tends to be progressive, often leading to chronic venous insufficiency (CVI). A number of complications are associated with untreated venous reflux: including superficial thrombophlebitis as well as variceal rupture and haemorrhage. CVI often results in chronic skin changes referred to as stasis dermatitis. Stasis dermatitis is comprised of a spectrum of cutaneous abnormalities including edema, hyperpigmentation, eczema, lipodermatosclerosis and stasis ulceration. Ulceration represents the disease end point for severe CVI. CVI is associated with a reduced quality of life particularly in relation to pain, physical function and mobility. In severe cases, VV with ulcers, QOL has been rated to be as bad or worse as other chronic diseases such as back pain and arthritis.
Lower limb VV is a very common disease affecting adults – estimated to be the 7th most common reason for physician referral in the US. There is a very strong familial predisposition to VV. The risk in offspring is 90% if both parents affected, 20% when neither affected and 45% (25% boys, 62% girls) if one parent affected. The prevalence of VV worldwide ranges from 5% to 15% among men and 3% to 29% among women varying by the age, gender and ethnicity of the study population, survey methods and disease definition and measurement. The annual incidence of VV estimated from the Framingham Study was reported to be 2.6% among women and 1.9% among men and did not vary within the age range (40-89 years) studied.
Approximately 1% of the adult population has a stasis ulcer of venous origin at any one time with 4% at risk. The majority of leg ulcer patients are elderly with simple superficial vein reflux. Stasis ulcers are often lengthy medical problems and can last for several years and, despite effective compression therapy and multilayer bandaging are associated with high recurrence rates. Recent trials involving surgical treatment of superficial vein reflux have resulted in healing and significantly reduced recurrence rates.
Endovascular Radiofrequency Ablation for Varicose Veins
RFA is an image-guided minimally invasive treatment alternative to surgical stripping of superficial venous reflux. RFA does not require an operating room or general anaesthesia and has been performed in an outpatient setting by a variety of medical specialties including surgeons and interventional radiologists. Rather than surgically removing the vein, RFA works by destroying or ablating the refluxing vein segment using thermal energy delivered through a radiofrequency catheter.
Prior to performing RFA, color-flow Doppler ultrasonography is used to confirm and map all areas of venous reflux to devise a safe and effective treatment plan. The RFA procedure involves the introduction of a guide wire into the target vein under ultrasound guidance followed by the insertion of an introducer sheath through which the RFA catheter is advanced. Once satisfactory positioning has been confirmed with ultrasound, a tumescent anaesthetic solution is injected into the soft tissue surrounding the target vein along its entire length. This serves to anaesthetize the vein, insulate the heat from damaging adjacent structures, including nerves and skin and compresses the vein increasing optimal contact of the vessel wall with the electrodes or expanded prongs of the RF device. The RF generator is then activated and the catheter is slowly pulled along the length of the vein. At the end of the procedure, hemostasis is then achieved by applying pressure to the vein entry point.
Adequate and proper compression stockings and bandages are applied after the procedure to reduce the risk of venous thromboembolism and to reduce postoperative bruising and tenderness. Patients are encouraged to walk immediately after the procedure. Follow-up protocols vary, with most patients returning 1 to 3 weeks later for an initial follow-up visit. At this point, the initial clinical result is assessed and occlusion of the treated vessels is confirmed with ultrasound. Patients often have a second follow-up visit 1 to 3 months following RFA at which time clinical evaluation and ultrasound are repeated. If required, additional procedures such as phlebectomy or sclerotherapy may be performed during the RFA procedure or at any follow-up visits.
Regulatory Status
The Closure System® radiofrequency generator for endovascular thermal ablation of varicose veins was approved by Health Canada as a class 3 device in March 2005, registered under medical device license 67865. The RFA intravascular catheter was approved by Health Canada in November 2007 for the ClosureFast catheter, registered under medical device license 16574. The Closure System® also has regulatory approvals in Australia, Europe (CE Mark) and the United States (FDA clearance). In Ontario, RFA is not an insured service and is currently being introduced in private clinics.
Methods
Literature Search
The MAS evidence–based review was performed to support public financing decisions. The literature search was performed on March 9th, 2010 using standard bibliographic databases for studies published up until March, 2010.
Inclusion Criteria
English language full-reports and human studies Original reports with defined study methodologyReports including standardized measurements on outcome events such as technical success, safety, effectiveness, durability, quality of life or patient satisfaction Reports involving RFA for varicose veins (great or small saphenous veins)Randomized controlled trials (RCTs), systematic reviews and meta-analysesCohort and controlled clinical studies involving ≥ 1 month ultrasound imaging follow-up
Exclusion Criteria
Non systematic reviews, letters, comments and editorials Reports not involving outcome events such as safety, effectiveness, durability, or patient satisfaction following an intervention with RFAReports not involving interventions with RFA for varicose veinsPilot studies or studies with small samples (< 50 subjects)
Summary of Findings
The MAS evidence search on the safety and effectiveness of endovascular RFA ablation of VV identified the following evidence: three HTAs, nine systematic reviews, eight randomized controlled trials (five comparing RFA to surgery and three comparing RFA to ELT), five controlled clinical trials and fourteen cohort case series (four were multicenter registry studies).
The majority (12⁄14) of the cohort studies (3,664) evaluating RFA for VV involved treatment with first generation RFA catheters and the great saphenous vein (GSV) was the target vessel in all studies. Major adverse events were uncommonly reported and the overall pooled major adverse event rate extracted from the cohort studies was 2.9% (105⁄3,664). Imaging defined treatment effectiveness of vein closure rates were variable ranging from 68% to 96% at post-operative follow-up. Vein ablation rate at 6-month follow-up was reported in four studies with rates close to 90%. Only one study reported vein closure rates at 2 years but only for a minority of the eligible cases. The two studies reporting on RFA ablation with the more efficient second generation catheters involved better follow-up and reported higher ablation rates close to 100% at 6-month follow-up with no major adverse events. A large prospective registry trial that recruited over 1,000 patients at thirty-four largely European centers reported on treatment success in six overlapping reports on selected patient subgroups at various follow-up points up to 5 year. However, the follow-up for eligible recruited patients at all time points was low resulting in inadequate estimates of longer term treatment efficacy.
The overall level of evidence of randomized trials comparing RFA with surgical ligation and vein stripping (n = 5) was graded as low to moderate. In all trials RFA ablation was performed with first generation catheters in the setting of the operating theatre under general anaesthesia, usually without tumescent anaesthesia. Procedure times were significantly longer after RFA than surgery. Recovery after treatment was significantly quicker after RFA both with return to usual activity and return to work with on average a one week less of work loss. Major adverse events occurring after surgery were higher [(1.8% (n=4) vs. 0.4% (n = 1) than after RFA but not significantly. Treatment effectiveness measured by imaging defined vein absence or vein closure was comparable in the two treatment groups. Significant improvements in vein symptoms and quality of life over baseline were reported for both treatment groups. Improvements in these outcomes were significantly greater in the RFA group than the surgery group in the peri-operative period but not in later follow-up. Follow-up in these trials was inadequate to evaluate longer term recurrence for either treatment. Patient satisfaction was reported to be high for both treatments but was higher for RFA.
The studies comparing endovascular treatment approaches for VV (RFA and ELT) were more limited. Three RCT studies compared RFA (two with the second generation catheter) with ELT but mainly focused on peri-procedural outcomes such as pain, complications and recovery. Vein ablation rates were not evaluated in the trials, except for one small trial involving bilateral VV. Pain responses in patients undergoing ablation were extremely variable and up to 2 weeks, mean pain levels were significantly less with RFA than ELT ablation but differences were not significant at one month. Recovery, evaluated as return to usual activity or return to work, however, was similar in the treatment groups. Vein symptom and QOL improvements were improved in both groups but were significantly better in the RFA group than the ELT group at 2 weeks, but not at one month. Vein ablation rates were evaluated in several controlled clinical studies comparing the treatments between centers or within centers between individuals or over time. Comparisons in these studies were inconsistent with vein ablation rates for RFA reported to be similar to, higher than and lower than those with ELT.
Economic Analysis
RFA and surgical vein stripping, the main comparator reimbursed by the public system, are comparable in clinical benefits. Hence a cost-analysis was conducted to identify the differences in resources and costs between both procedures and a budgetary impact analysis (BIA) was conducted to project costs over a 5- year period in the province of Ontario. The target population of this economic analysis was patients with symptomatic varicose veins and the primary analytic perspective was that of the Ministry of Health and Long-Term Care.
The average case cost (based on Ontario hospital costs and medical resources) for surgical vein stripping was estimated to be $1,799. In order to calculate a procedural cost for RFA it was assumed that the hospital cost and physician labour fees, excluding anaesthesia and surgical assistance, were the same as vein stripping surgery. The manufacturer also provided details on the generator with a capital cost of $27,500 and a lifespan of 5 years and the disposables (catheter, sheath, guidewire) with a cost of $673 per case. The average case cost for RFA was therefore estimated to be $1,356. One-way sensitivity analysis was also conducted with hospital cost of RFA varied to 60% that of vein stripping surgery (average cost per case = $627.08) to calculate an impact to the province.
Historical volumes of vein stripping surgeries in Ontario were used to project surgeries in a linear fashion up to five years into the future. Volumes for RFA and ELT were calculated based on share capture from the surgery market based on discussion with clinical expert opinion and existing private data based on discussion with the manufacturer. RFA is expected to compete with ELT and capture some of the market. If ELT is reimbursed by the public sector then numbers will continue to increase from previous private data and share capture from the conventional surgical treatment market. Therefore, RFA cases will also increase since it will be capturing a share of the ELT market. A budget impact to the province was then calculated by multiplying volumes by the cost of the procedure.
RFA is comparable in clinical benefits to vein stripping surgery. It has the extra upfront cost of the generator and cost per case for disposables but does not require an operating theater, anaesthetist or surgical assistant fees. The impact to the province is expected to be 5 M by Year 5 with the introduction of new ELT and RFA image guided endovascular technologies and existing surgery for varicose veins.
Conclusion
The conclusions on the comparative outcomes between endovascular RFA and surgical ligation and saphenous vein stripping and between endovascular RFA and laser ablation for VV treatment are summarized in the table below (ES Table 1).
Outcome comparisons of RFA vs. surgery and RFA vs ELT for varicose veins
ELT refers to endovascular laser ablation; RFA, radiofrequency ablation
The outcomes of the evidence-based review on these treatments for VV based on different perspectives are summarized below:
RFA First versus Second Generation Catheters and Segmental Ablation
Ablation with second generation catheters and segmental ablation offered technical advantages with improved ease and significant decreases in procedure time. RFA ablation with second generation catheters is also no longer restricted to smaller (< 12 mm diameter) saphenous veins. The safety profile with the new device and method of energy delivery is as good as or improved over the first generation device. No major adverse events were reported in two multicenter prospective cohort studies in 6 month follow-up with over 500 patients. Post-operative complications such as bruising and pain were significantly less with RFA ablation with second generation catheters than ELT in two RCT trials.RFA treatment with second generation catheters has ablation rates that are higher than with first generation catheters and are more comparable with the consistently high rates of ELT.
Endovascular RFA versus Surgery
RFA has a quicker recovery attributable to decreased pain and lower minor complications.RFA, in the short term was comparable to surgery in treatment effectiveness as assessed by imaging defined anatomic outcomes such as vein closure, flow or reflux. Other treatment outcomes such as symptomatic relief and HRQOL were significantly improved in both groups and between group differences in the early peri-operative period were likely influenced by pain experiences. Longer term follow-up was inadequate to evaluate recurrence after either treatment.Patient satisfaction was high after both treatments but was higher for RFA than surgery.
Endovascular RFA versus ELT
RFA has significantly less post-operative pain than ELT but differences were not significant when pain was adjusted for analgesic use and pain differences between groups did not persist at 1 month follow-up.Treatment effectiveness, measured as symptom relief and QOL improvement were similar between the endovascular treatments in the short term (within 1 month) Treatment effectiveness measured as imaging defined vein ablation was not measured in any RCT trials (only for bilateral VV disease) and results were inconsistently reported in observational trials.Longer term follow-up was not available to assess recurrence after either treatment.
System Outcomes – RFA Replacing Surgery or Competing with ELT
RFA may offer system advantages in that the treatment can be offered by several medical specialties in outpatient settings and because it does not require an operating theatre or general anaesthesia. The treatment may result in decanting of patients from OR with decreased pre-surgical investigations, demand on anaesthetists’ time, hospital stay and wait time for VV treatment. It may also provide more reliable outpatient scheduling. Procedure costs may be less for endovascular approaches than surgery but the budget impact may be greater with insurance of RFA because of the transfer of cases from the private market to the public payer system.Competition between RFA and ELT endovascular approaches is likely to continue to stimulate innovation and technical changes to advance patient care and result in competitive pricing.
PMCID: PMC3377553  PMID: 23074413
8.  Dose Reduction Technique Using a Combination of a Region of Interest (ROI) Material X-Ray Attenuator and Spatially Different Temporal Filtering for Fluoroscopic Interventions 
Proceedings of SPIE  2012;8313:831357-.
We demonstrate a novel approach for achieving patient dose savings during image-guided neurovascular interventions, involving a combination of a material x-ray region of interest (ROI) attenuator and a spatially different ROI temporal filtering technique. The part of the image under the attenuator is reduced in dose but noisy and less bright due to fewer x-ray quanta reaching the detector, as compared to the non-attenuating (or less attenuating) region. First the brightness is equalized throughout the image by post processing and then a temporal filter with higher weights is applied to the high attenuating region to reduce the noise, at the cost of increased lag; however, in the regions where less attenuation is present, a lower temporal weight is needed and is applied to preserve temporal resolution.
A simulation of the technique is first presented on an actual image sequence obtained from an endovascular image guided interventional (EIGI) procedure. Then the actual implementation of the technique with a physical ROI attenuator is presented. Quantitative analysis including noise analysis and integral dose calculations are presented to validate the proposed technique.
doi:10.1117/12.910945
PMCID: PMC3766980  PMID: 24027617
9.  MR fluoroscopy in vascular and cardiac interventions (review) 
Vascular and cardiac disease remains a leading cause of morbidity and mortality in developed and emerging countries. Vascular and cardiac interventions require extensive fluoroscopic guidance to navigate endovascular catheters. X-ray fluoroscopy is considered the current modality for real time imaging. It provides excellent spatial and temporal resolution, but is limited by exposure of patients and staff to ionizing radiation, poor soft tissue characterization and lack of quantitative physiologic information. MR fluoroscopy has been introduced with substantial progress during the last decade. Clinical and experimental studies performed under MR fluoroscopy have indicated the suitability of this modality for: delivery of ASD closure, aortic valves, and endovascular stents (aortic, carotid, iliac, renal arteries, inferior vena cava). It aids in performing ablation, creation of hepatic shunts and local delivery of therapies. Development of more MR compatible equipment and devices will widen the applications of MR-guided procedures. At post-intervention, MR imaging aids in assessing the efficacy of therapies, success of interventions. It also provides information on vascular flow and cardiac morphology, function, perfusion and viability. MR fluoroscopy has the potential to form the basis for minimally invasive image–guided surgeries that offer improved patient management and cost effectiveness.
doi:10.1007/s10554-010-9774-1
PMCID: PMC3275732  PMID: 21359519
Cardiac imaging; Magnetic resonance imaging; Vascular imaging
10.  Implementation of a high-sensitivity Micro-Angiographic Fluoroscope (HS-MAF) for in-vivo endovascular image guided interventions (EIGI) and region-of-interest computed tomography (ROI-CT) 
New advances in catheter technology and remote actuation for minimally invasive procedures are continuously increasing the demand for better x-ray imaging technology. The new x-ray high-sensitivity Micro-Angiographic Fluoroscope (HS-MAF) detector offers high resolution and real-time image-guided capabilities which are unique when compared with commercially available detectors. This detector consists of a 300 μm CsI input phosphor coupled to a dual stage GEN2 micro-channel plate light image intensifier (LII), followed by minifying fiber-optic taper coupled to a CCD chip. The HS-MAF detector image array is 1024×1024 pixels, with a 12 bit depth capable of imaging at 30 frames per second. The detector has a round field of view with 4 cm diameter and 35 microns pixels. The LII has a large variable gain which allows usage of the detector at very low exposures characteristic of fluoroscopic ranges while maintaining very good image quality. The custom acquisition program allows real-time image display and data storage. We designed a set of in-vivo experimental interventions in which placement of specially designed endovascular stents were evaluated with the new detector and with a standard x-ray image intensifier (XII). Capabilities such fluoroscopy, angiography and ROI-CT reconstruction using rotational angiography data were implemented and verified. The images obtained during interventions under radiographic control with the HS-MAF detector were superior to those with the XII. In general, the device feature markers, the device structures, and the vessel geometry were better identified with the new detector. High-resolution detectors such as HS-MAF can vastly improve the accuracy of localization and tracking of devices such stents or catheters.
doi:10.1117/12.770297
PMCID: PMC2572822  PMID: 18958294
high-resolution fluoroscopy; cone-beam computed tomography; region-of-interest micro-angiography; ROI-CT; endovascular image-guided interventions; micro-angiographic fluoroscope
11.  Motion-adapted catheter navigation with real-time instantiation and improved visualisation 
Journal of robotic surgery  2013;7(3):251-260.
The improvements to catheter manipulation by the use of robot-assisted catheter navigation for endovascular procedures include increased precision, stability of motion and operator comfort. However, navigation through the vasculature under fluoroscopic guidance is still challenging, mostly due to physiological motion and when tortuous vessels are involved. In this paper, we propose a motion-adaptive catheter navigation scheme based on shape modelling to compensate for these dynamic effects, permitting predictive and dynamic navigations. This allows for timed manipulations synchronised with the vascular motion. The technical contribution of the paper includes the following two aspects. Firstly, a dynamic shape modelling and real-time instantiation scheme based on sparse data obtained intra-operatively is proposed for improved visualisation of the 3D vasculature during endovascular intervention. Secondly, a reconstructed frontal view from the catheter tip using the derived dynamic model is used as an interventional aid to user guidance. To demonstrate the practical value of the proposed framework, a simulated aortic branch cannulation procedure is used with detailed user validation to demonstrate the improvement in navigation quality and efficiency.
doi:10.1007/s11701-013-0423-2
PMCID: PMC3987170  PMID: 24744817
Robotic surgery; Minimally invasive surgery; Endovascular intervention; Image-guided intervention; Shape modelling; Motion prediction
12.  Intravascular Ultrasound to Guide Percutaneous Coronary Interventions 
Executive Summary
Objective
The objective of this health technology policy assessment was to determine the effectiveness and cost-effectiveness of using intravascular ultrasound (IVUS) as an adjunctive imaging tool to coronary angiography for guiding percutaneous coronary interventions.
Background
Intravascular Ultrasound
Intravascular ultrasound is a procedure that uses high frequency sound waves to acquire 3-dimensional images from the lumen of a blood vessel. The equipment for performing IVUS consists of a percutaneous transducer catheter and a console for reconstructing images. IVUS has been used to study the structure of the arterial wall and nature of atherosclerotic plaques, and obtain measurements of the vessel lumen. Its role in guiding stent placement is also being investigated. IVUS is presently not an insured health service in Ontario.
Clinical Need
Coronary artery disease accounts for approximately 55% of cardiovascular deaths, the leading cause of death in Canada. In Ontario, the annual mortality rate due to ischemic heart disease was 141.8 per 100,000 population between 1995 and 1997. Percutaneous coronary intervention (PCI), a less invasive approach to treating coronary artery disease, is used more frequently than coronary bypass surgery in Ontario. The number of percutaneous coronary intervention procedures funded by the Ontario Ministry of Health and Long-term Care is expected to increase from approximately 17, 780 in 2004/2005 to 22,355 in 2006/2007 (an increase of 26%), with about 95% requiring the placement of one or more stents. Restenosis following percutaneous coronary interventions involving bare metal stents occurs in 15% to 30% of the cases, mainly because of smooth muscle proliferation and migration, and production of extracellular matrix. In-stent restenosis has been linked to suboptimal stent expansion and inadequate lesion coverage, while stent thrombosis has been attributed to incomplete stent-to-vessel wall apposition. Since coronary angiography (the imaging tool used to guide stent placement) has been shown to be inaccurate in assessing optimal stent placement, and IVUS can provide better views of the vessel lumen, the clinical utility of IVUS as an imaging tool adjunctive to coronary angiography in coronary intervention procedures has been explored in clinical studies.
Method
A systematic review was conducted to answer the following questions:
What are the procedure-related complications associated with IVUS?
Does IVUS used in conjunction with angiography to guide percutaneous interventions improve patient outcomes compared to angiographic guidance without IVUS?
Who would benefit most in terms of clinical outcomes from the use of IVUS adjunctive to coronary angiography in guiding PCIs?
What is the effectiveness of IVUS guidance in the context of drug-eluting stents?
What is the cost-effectiveness ratio and budget impact of adjunctive IVUS in PCIs in Ontario?
A systematic search of databases OVID MEDLINE, EMBASE, MEDLINE In-Process & Other Non-Indexed Citations, The Cochrane Library, and the International Agency for Health Technology Assessment (INAHTA) database for the period beginning in May 2001 until the day of the search, November 4, 2005 yielded 2 systematic reviews, 1 meta-analysis, 6 randomized controlled trials, and 2 non-randomized studies on left main coronary arteries. The quality of the studies ranged from moderate to high. These reports were combined with reports from a previous systematic review for analysis. In addition to qualitative synthesis, pooled analyses of data from randomized controlled studies using a random effect model in the Cochrane Review Manager 4.2 software were conducted when possible.
Findings of Literature Review & Analysis
Safety
Intravascular ultrasound appears to be a safe tool when used in coronary interventions. Periprocedural complications associated with the use of IVUS in coronary interventions ranged from 0.5% in the largest study to 4%. Coronary rupture was reported in 1 study (1/54). Other complications included prolonged spasms of the artery after stenting, dissection, and femoral aneurysm.
Effectiveness
Based on pooled analyses of data from randomized controlled studies, the use of intravascular ultrasound adjunctive to coronary intervention in percutaneous coronary interventions using bare metal stents yielded the following findings:
For lesions predominantly at low risk of restenosis:
There were no significant differences in preintervention angiographic minimal lumen diameter between the IVUS-guided and angiography-guided groups.
IVUS guidance resulted in a significantly larger mean postintervention angiographic minimal lumen diameter (weighted mean difference of 0.11 mm, P = .0003) compared to angiographic guidance alone.
The benefit in angiographic minimal lumen diameter from IVUS guidance was not maintained at 6-month follow-up, when no significant difference in angiographic minimal lumen diameter could be detected between the two arms (weighted mean difference 0.08, P = .13).
There were no statistically significant differences in angiographic binary restenosis rates between IVUS-guidance and no IVUS guidance (Odds ratio [OR] 0.87 in favour of IVUS, 95% Confidence Interval [CI] [0.64–1.18], P = 0.37).
IVUS guidance resulted in a reduction in the odds of target lesion revascularization (repeat percutaneous coronary intervention or coronary bypass graft) compared to angiographic guidance alone. The reduction was statistically significant at a follow-up period of 6 months to 1 year, and at a follow-up period of 18 month to 2 years (OR 0.52 in favour of IVUS, 95% CI [0.33–0.81], P = .004).
Total revascularization rate (either target lesion or target vessel revascularization) was significantly lower for IVUS-guided patients at 18 months to 2.5 years after intervention (OR 0.43 in favour of IVUS, 95% CI [0.29–0.63], p < .0001).
There were no statistically significant differences in the odds of death (OR 1.36 in favour of no IVUS, P =0.65) or myocardial infarction (OR 0.95 in favour of IVUS, P = 0.93) between IVUS-guidance and angiographic guidance alone at up to 2.5 years of follow-up
The odds of having a major cardiac event (defined as death, myocardial infarction, and target lesion or target vessel revascularization) were significantly lower for patients with IVUS guidance compared to angiographic guidance alone during follow-up periods of up to 2.5 years (OR 0.53, 95% CI [0.36–0.78], P = 0.001). Since there were no significant reductions in the odds of death or myocardial infarction, the reduction in the odds of combined events reflected mainly the reduction in revascularization rates.
For lesions at High Risk of Restenosis:
There is evidence from one small, randomized controlled trial (n=150) that IVUS-guided percutaneous coronary intervention in long de novo lesions (>20 mm) of native coronary arteries resulted in statistically significant larger minimal lumen Diameter, and statistically significant lower 6-month angiographic binary restenosis rate. Target vessel revascularization rate and the rate of combined events were also significantly reduced at 12 months.
A small subgroup analysis of a randomized controlled trial reported no benefit in clinical or angiographic outcomes for IVUS-guided percutaneous coronary interventions in patients with diabetes compared to those guided by angiography. However, due to the nature and size of the analysis, no firm conclusions could be reached.
Based on 2 small, prospective, non-randomized controlled studies, IVUS guidance in percutaneous coronary interventions of left main coronary lesions using bare metal stents or drug-eluting stents did not result in any benefits in angiographic or clinical outcomes. These findings need to be confirmed.
Interventions Using Drug-Eluting Stents
There is presently no evidence on whether the addition of IVUS guidance during the implantation of drug-eluting stents would reduce incomplete stent apposition, or improve the angiographic or clinical outcomes of patients.
Ontario-Based Economic Analysis
Cost-effectiveness analysis showed that PCIs using IVUS guidance would likely be less costly and more effective than PCIs without IVUS guidance. The upfront cost of adjunctive use of IVUS in PCIs ranged from $1.56 million at 6% uptake to $13.04 million at 50% uptake. Taking into consideration cost avoidance from reduction in revascularization associated with the use of IVUS, a net saving of $0.63 million to $5.2 million is expected. However, since it is uncertain whether the reduction in revascularization rate resulting from the use of IVUS can be generalized to clinical settings in Ontario, further analysis on the budget impact and cost-effectiveness need to be conducted once Ontario-specific revascularization rates are verified.
Factors to be Considered in the Ontario Context
Applicability of Findings to Ontario
The interim analysis of an Ontario field evaluation that compared drug-eluting stents to bare metal stents showed that the revascularization rates in low-risk patients with bare metal stents were much lower in Ontario compared to rates reported in randomized controlled trials (7.2% vs >17 %). Even though IVUS is presently not routinely used in the stenting of low-risk patients in Ontario, the revascularization rates in these patients in Ontario were shown to be lower than those reported for the IVUS groups reported in published studies. Based on this information and previous findings from the Ontario field evaluation on stenting, it is uncertain whether the reduction in revascularization rates from IVUS guidance can be generalized to Ontario. In light of the above findings, it is advisable to validate the reported benefits of IVUS guidance in percutaneous coronary interventions involving bare metal stents in the Ontario context.
Licensing Status
As of January 16, 2006, Health Canada has licensed 10 intravascular ultrasound imaging systems/catheters for transluminal intervention procedures, most as class 4 medical devices.
Current Funding
IVUS is presently not an insured procedure under the Ontario Health Insurance Plan and there are no professional fees for this procedure. All costs related to the use of IVUS are covered within hospitals’ global budgets. A single use IVUS catheter costs approximately $900CDN and the procedure adds approximately 20 minutes to 30 minutes to a percutaneous coronary intervention procedure.
Diffusion
According to an expert consultant, current use of IVUS in coronary interventions in Ontario is probably limited to high-risk cases such as interventions in long lesions, small vessels, and bifurcated lesions for which images from coronary angiography are indeterminate. It was estimated that IVUS is being used in about 6% of all percutaneous coronary interventions at a large Ontario cardiac centre.
Expert Opinion
IVUS greatly enhances the cardiac interventionists’ ability to visualize and assess high-risk lesions such as long lesions, narrow lesions, and bifurcated lesions that may have indeterminate angiographic images. Information from IVUS in these cases facilitates the choice of the most appropriate approach for the intervention.
Conclusion
The use of adjunctive IVUS in PCIs using bare metal stents in lesions predominantly at low risk for restenosis had no significant impact on survival, myocardial infarction, or angiographic restenosis rates up to 2.5 years after intervention.
The use of IVUS adjunctive to coronary angiography in percutaneous coronary interventions using bare metal stents in lesions predominantly at low risk for restenosis significantly reduced the target lesion and target vessel revascularization at a follow-up period of 18 months to 2.5 years.
One small study suggests that adjunctive IVUS in PCIs using bare metal stents in long lesions (>20 mm) significantly improved the 6-month angiographic restenosis rate and one-year target lesion revascularization rate. These results need to be confirmed with large randomized controlled trials.
Based on information from the Ontario field evaluation on stenting, it is uncertain whether the reduction in revascularization rate resulting from the use of IVUS in the placement of bare metal stents can be generalized to clinical settings in Ontario.
There is presently insufficient evidence available to determine the impact of adjunctive IVUS in percutaneous interventions in high-risk lesions (other than long lesions) or in PCIs using drug-eluting stents.
PMCID: PMC3379536  PMID: 23074482
13.  Advanced Electrophysiologic Mapping Systems 
Executive Summary
Objective
To assess the effectiveness, cost-effectiveness, and demand in Ontario for catheter ablation of complex arrhythmias guided by advanced nonfluoroscopy mapping systems. Particular attention was paid to ablation for atrial fibrillation (AF).
Clinical Need
Tachycardia
Tachycardia refers to a diverse group of arrhythmias characterized by heart rates that are greater than 100 beats per minute. It results from abnormal firing of electrical impulses from heart tissues or abnormal electrical pathways in the heart because of scars. Tachycardia may be asymptomatic, or it may adversely affect quality of life owing to symptoms such as palpitations, headaches, shortness of breath, weakness, dizziness, and syncope. Atrial fibrillation, the most common sustained arrhythmia, affects about 99,000 people in Ontario. It is associated with higher morbidity and mortality because of increased risk of stroke, embolism, and congestive heart failure. In atrial fibrillation, most of the abnormal arrhythmogenic foci are located inside the pulmonary veins, although the atrium may also be responsible for triggering or perpetuating atrial fibrillation. Ventricular tachycardia, often found in patients with ischemic heart disease and a history of myocardial infarction, is often life-threatening; it accounts for about 50% of sudden deaths.
Treatment of Tachycardia
The first line of treatment for tachycardia is antiarrhythmic drugs; for atrial fibrillation, anticoagulation drugs are also used to prevent stroke. For patients refractory to or unable to tolerate antiarrhythmic drugs, ablation of the arrhythmogenic heart tissues is the only option. Surgical ablation such as the Cox-Maze procedure is more invasive. Catheter ablation, involving the delivery of energy (most commonly radiofrequency) via a percutaneous catheter system guided by X-ray fluoroscopy, has been used in place of surgical ablation for many patients. However, this conventional approach in catheter ablation has not been found to be effective for the treatment of complex arrhythmias such as chronic atrial fibrillation or ventricular tachycardia. Advanced nonfluoroscopic mapping systems have been developed for guiding the ablation of these complex arrhythmias.
The Technology
Four nonfluoroscopic advanced mapping systems have been licensed by Health Canada:
CARTO EP mapping System (manufactured by Biosense Webster, CA) uses weak magnetic fields and a special mapping/ablation catheter with a magnetic sensor to locate the catheter and reconstruct a 3-dimensional geometry of the heart superimposed with colour-coded electric potential maps to guide ablation.
EnSite System (manufactured by Endocardial Solutions Inc., MN) includes a multi-electrode non-contact catheter that conducts simultaneous mapping. A processing unit uses the electrical data to computes more than 3,000 isopotential electrograms that are displayed on a reconstructed 3-dimensional geometry of the heart chamber. The navigational system, EnSite NavX, can be used separately with most mapping catheters.
The LocaLisa Intracardiac System (manufactured by Medtronics Inc, MN) is a navigational system that uses an electrical field to locate the mapping catheter. It reconstructs the location of the electrodes on the mapping catheter in 3-dimensional virtual space, thereby enabling an ablation catheter to be directed to the electrode that identifies abnormal electric potential.
Polar Constellation Advanced Mapping Catheter System (manufactured by Boston Scientific, MA) is a multielectrode basket catheter with 64 electrodes on 8 splines. Once deployed, each electrode is automatically traced. The information enables a 3-dimensional model of the basket catheter to be computed. Colour-coded activation maps are reconstructed online and displayed on a monitor. By using this catheter, a precise electrical map of the atrium can be obtained in several heartbeats.
Review Strategy
A systematic search of Cochrane, MEDLINE and EMBASE was conducted to identify studies that compared ablation guided by any of the advanced systems to fluoroscopy-guided ablation of tachycardia. English-language studies with sample sizes greater than or equal to 20 that were published between 2000 and 2005 were included. Observational studies on safety of advanced mapping systems and fluoroscopy were also included. Outcomes of interest were acute success, defined as termination of arrhythmia immediately following ablation; long-term success, defined as being arrhythmia free at follow-up; total procedure time; fluoroscopy time; radiation dose; number of radiofrequency pulses; complications; cost; and the cost-effectiveness ratio.
Quality of the individual studies was assessed using established criteria. Quality of the overall evidence was determined by applying the GRADE evaluation system. (3) Qualitative synthesis of the data was performed. Quantitative analysis using Revman 4.2 was performed when appropriate.
Quality of the Studies
Thirty-four studies met the inclusion criteria. These comprised 18 studies on CARTO (4 randomized controlled trials [RCTs] and 14 non-RCTs), 3 RCTs on EnSite NavX, 4 studies on LocaLisa Navigational System (1 RCT and 3 non-RCTs), 2 studies on EnSite and CARTO, 1 on Polar Constellation basket catheter, and 7 studies on radiation safety.
The quality of the studies ranged from moderate to low. Most of the studies had small sample sizes with selection bias, and there was no blinding of patients or care providers in any of the studies. Duration of follow-up ranged from 6 weeks to 29 months, with most having at least 6 months of follow-up. There was heterogeneity with respect to the approach to ablation, definition of success, and drug management before and after the ablation procedure.
Summary of Findings
Evidence is based on a small number of small RCTS and non-RCTS with methodological flaws.
Advanced nonfluoroscopy mapping/navigation systems provided real time 3-dimensional images with integration of anatomic and electrical potential information that enable better visualization of areas of interest for ablation
Advanced nonfluoroscopy mapping/navigation systems appear to be safe; they consistently shortened the fluoroscopy duration and radiation exposure.
Evidence suggests that nonfluoroscopy mapping and navigation systems may be used as adjuncts to rather than replacements for fluoroscopy in guiding the ablation of complex arrhythmias.
Most studies showed a nonsignificant trend toward lower overall failure rate for advanced mapping-guided ablation compared with fluoroscopy-guided mapping.
Pooled analyses of small RCTs and non-RCTs that compared fluoroscopy- with nonfluoroscopy-guided ablation of atrial fibrillation and atrial flutter showed that advanced nonfluoroscopy mapping and navigational systems:
Yielded acute success rates of 69% to 100%, not significantly different from fluoroscopy ablation.
Had overall failure rates at 3 months to 19 months of 1% to 40% (median 25%).
Resulted in a 10% relative reduction in overall failure rate for advanced mapping guided-ablation compared to fluoroscopy guided ablation for the treatment of atrial fibrillation.
Yielded added benefit over fluoroscopy in guiding the ablation of complex arrhythmia. The advanced systems were shown to reduce the arrhythmia burden and the need for antiarrhythmic drugs in patients with complex arrhythmia who had failed fluoroscopy-guided ablation
Based on predominantly observational studies, circumferential PV ablation guided by a nonfluoroscopy system was shown to do the following:
Result in freedom from atrial fibrillation (with or without antiarrhythmic drug) in 75% to 95% of patients (median 79%). This effect was maintained up to 28 months.
Result in freedom from atrial fibrillation without antiarrhythmic drugs in 47% to 95% of patients (median 63%).
Improve patient survival at 28 months after the procedure as compared with drug therapy.
Require special skills; patient outcomes are operator dependent, and there is a significant learning curve effect.
Complication rates of pulmonary vein ablation guided by an advanced mapping/navigation system ranged from 0% to 10% with a median of 6% during a follow-up period of 6 months to 29 months.
The complication rate of the study with the longest follow-up was 8%.
The most common complications of advanced catheter-guided ablation were stroke, transient ischemic attack, cardiac tamponade, myocardial infarction, atrial flutter, congestive heart failure, and pulmonary vein stenosis. A small number of cases with fatal atrial-esophageal fistula had been reported and were attributed to the high radiofrequency energy used rather than to the advanced mapping systems.
Economic Analysis
An Ontario-based economic analysis suggests that the cumulative incremental upfront costs of catheter ablation of atrial fibrillation guided by advanced nonfluoroscopy mapping could be recouped in 4.7 years through cost avoidance arising from less need for antiarrhythmic drugs and fewer hospitalization for stroke and heart failure.
Expert Opinion
Expert consultants to the Medical Advisory Secretariat noted the following:
Nonfluoroscopy mapping is not necessary for simple ablation procedures (e.g., typical flutter). However, it is essential in the ablation of complex arrhythmias including these:
Symptomatic, drug-refractory atrial fibrillation
Arrhythmias in people who have had surgery for congenital heart disease (e.g., macro re-entrant tachycardia in people who have had surgery for congenital heart disease).
Ventricular tachycardia due to myocardial infarction
Atypical atrial flutter
Advanced mapping systems represent an enabling technology in the ablation of complex arrhythmias. The ablation of these complex cases would not have been feasible or advisable with fluoroscopy-guided ablation and, therefore, comparative studies would not be feasible or ethical in such cases.
Many of the studies included patients with relatively simple arrhythmias (e.g., typical atrial flutter and atrial ventricular nodal re-entrant tachycardia), for which the success rates using the fluoroscopy approach were extremely high and unlikely to be improved upon using nonfluoroscopic mapping.
By age 50, almost 100% of people who have had surgery for congenital heart disease will develop arrhythmia.
Some centres are under greater pressure because of expertise in complex ablation procedures for subsets of patients.
The use of advanced mapping systems requires the support of additional electrophysiologic laboratory time and nursing time.
Conclusions
For patients suffering from symptomatic, drug-refractory atrial fibrillation and are otherwise healthy, catheter ablation offers a treatment option that is less invasive than is open surgical ablation.
Small RCTs that may have been limited by type 2 errors showed significant reductions in fluoroscopy exposure in nonfluoroscopy-guided ablation and a trend toward lower overall failure rate that did not reach statistical significance.
Pooled analysis suggests that advanced mapping systems may reduce the overall failure rate in the ablation of atrial fibrillation.
Observational studies suggest that ablation guided by complex mapping/navigation systems is a promising treatment for complex arrhythmias such as highly symptomatic, drug-refractory atrial fibrillation for which rate control is not an option
In people with atrial fibrillation, ablation guided by advanced nonfluoroscopy mapping resulted in arrhythmia free rates of 80% or higher, reduced mortality, and better quality of life at experienced centres.
Although generally safe, serious complications such as stroke, atrial-esophageal, and pulmonary vein stenosis had been reported following ablation procedures.
Experts advised that advanced mapping systems are also required for catheter ablation of:
Hemodynamically unstable ventricular tachycardia from ischemic heart disease
Macro re-entrant atrial tachycardia after surgical correction of congenital heart disease
Atypical atrial flutter
Catheter ablation of atrial fibrillation is still evolving, and it appears that different ablative techniques may be appropriate depending on the characteristics of the patient and the atrial fibrillation.
Data from centres that perform electrophysiological mapping suggest that patients with drug-refractory atrial fibrillation may be the largest group with unmet need for advanced mapping-guided catheter ablation in Ontario.
Nonfluoroscopy mapping-guided pulmonary vein ablation for the treatment of atrial fibrillation has a significant learning effect; therefore, it is advisable for the province to establish centres of excellence to ensure a critical volume, to gain efficiency and to minimize the need for antiarrhythmic drugs after ablation and the need for future repeat ablation procedures.
PMCID: PMC3379531  PMID: 23074499
14.  Endovascular Laser Therapy for Varicose Veins 
Executive Summary
Objective
The objective of the MAS evidence review was to conduct a systematic review of the available evidence on the safety, effectiveness, durability and cost–effectiveness of endovascular laser therapy (ELT) for the treatment of primary symptomatic varicose veins (VV).
Background
The Ontario Health Technology Advisory Committee (OHTAC) met on November 27, 2009 to review the safety, effectiveness, durability and cost-effectiveness of ELT for the treatment of primary VV based on an evidence-based review by the Medical Advisory Secretariat (MAS).
Clinical Condition
VV are tortuous, twisted, or elongated veins. This can be due to existing (inherited) valve dysfunction or decreased vein elasticity (primary venous reflux) or valve damage from prior thrombotic events (secondary venous reflux). The end result is pooling of blood in the veins, increased venous pressure and subsequent vein enlargement. As a result of high venous pressure, branch vessels balloon out leading to varicosities (varicose veins).
Symptoms typically affect the lower extremities and include (but are not limited to): aching, swelling, throbbing, night cramps, restless legs, leg fatigue, itching and burning. Left untreated, venous reflux tends to be progressive, often leading to chronic venous insufficiency (CVI).
A number of complications are associated with untreated venous reflux: including superficial thrombophlebitis as well as variceal rupture and haemorrhage. CVI often results in chronic skin changes referred to as stasis dermatitis. Stasis dermatitis is comprised of a spectrum of cutaneous abnormalities including edema, hyperpigmentation, eczema, lipodermatosclerosis and stasis ulceration. Ulceration represents the disease end point for severe CVI.
CVI is associated with a reduced quality of life particularly in relation to pain, physical function and mobility. In severe cases, VV with ulcers, QOL has been rated to be as bad or worse as other chronic diseases such as back pain and arthritis.
Lower limb VV is a common disease affecting adults and estimated to be the seventh most common reason for physician referral in the US. There is a strong familial predisposition to VV with the risk in offspring being 90% if both parents affected, 20% when neither is affected, and 45% (25% boys, 62% girls) if one parent is affected. Globally, the prevalence of VV ranges from 5% to 15% among men and 3% to 29% among women varying by the age, gender and ethnicity of the study population, survey methods and disease definition and measurement. The annual incidence of VV estimated from the Framingham Study was reported to be 2.6% among women and 1.9% among men and did not vary within the age range (40-89 years) studied.
Approximately 1% of the adult population has a stasis ulcer of venous origin at any one time with 4% at risk. The majority of leg ulcer patients are elderly with simple superficial vein reflux. Stasis ulcers are often lengthy medical problems and can last for several years and, despite effective compression therapy and multilayer bandaging are associated with high recurrence rates. Recent trials involving surgical treatment of superficial vein reflux have resulted in healing and significantly reduced recurrence rates.
Endovascular Laser Therapy for VV
ELT is an image-guided, minimally invasive treatment alternative to surgical stripping of superficial venous reflux. It does not require an operating room or general anesthesia and has been performed in outpatient settings by a variety of medical specialties including surgeons (vascular or general), interventional radiologists and phlebologists. Rather than surgically removing the vein, ELT works by destroying, cauterizing or ablating the refluxing vein segment using heat energy delivered via laser fibre.
Prior to ELT, colour-flow Doppler ultrasonography is used to confirm and map all areas of venous reflux to devise a safe and effective treatment plan. The ELT procedure involves the introduction of a guide wire into the target vein under ultrasound guidance followed by the insertion of an introducer sheath through which an optical fibre carrying the laser energy is advanced. A tumescent anesthetic solution is injected into the soft tissue surrounding the target vein along its entire length. This serves to anaesthetize the vein so that the patient feels no discomfort during the procedure. It also serves to insulate the heat from damaging adjacent structures, including nerves and skin. Once satisfactory positioning has been confirmed with ultrasound, the laser is activated. Both the laser fibre and the sheath are simultaneously, slowly and continuously pulled back along the length of the target vessel. At the end of the procedure, homeostasis is then achieved by applying pressure to the entry point.
Adequate and proper compression stockings and bandages are applied after the procedure to reduce the risk of venous thromboembolism, and to reduce postoperative bruising and tenderness. Patients are encouraged to walk immediately after the procedure and most patients return to work or usual activity within a few days. Follow-up protocols vary, with most patients returning 1-3 weeks later for an initial follow-up visit. At this point, the initial clinical result is assessed and occlusion of the treated vessels is confirmed with ultrasound. Patients often have a second follow-up visit 1-3 months following ELT at which time clinical evaluation and ultrasound are repeated. If required, sclerotherapy may be performed during the ELT procedure or at any follow-up visits.
Regulatory Status
Endovascular laser for the treatment of VV was approved by Health Canada as a class 3 device in 2002. The treatment has been an insured service in Saskatchewan since 2007 and is the only province to insure ELT. Although the treatment is not an insured service in Ontario, it has been provided by various medical specialties since 2002 in over 20 private clinics.
Methods
Literature Search
The MAS evidence-based review was performed as an update to the 2007 health technology review performed by the Australian Medical Services Committee (MSAC) to support public financing decisions. The literature search was performed on August 18, 2009 using standard bibliographic databases for studies published from January 1, 2007 to August 15, 2009. Search alerts were generated and reviewed for additional relevant literature up until October 1, 2009.
Inclusion Criteria
English language full-reports and human studies
Original reports with defined study methodology
Reports including standardized measurements on outcome events such as technical success, safety, effectiveness, durability, quality of life or patient satisfaction
Reports involving ELT for VV (great or small saphenous veins)
Randomized controlled trials (RCTs), systematic reviews and meta-analyses
Cohort and controlled clinical studies involving > 1 month ultrasound imaging follow-up
Exclusion Criteria
Non systematic reviews, letters, comments and editorials
Reports not involving outcome events such as safety, effectiveness, durability, or patient satisfaction following an intervention with ELT
Reports not involving interventions with ELT for VV
Pilot studies or studies with small samples ( < 50 subjects)
Summary of Findings
The MAS evidence search identified 14 systematic reviews, 29 cohort studies on safety and effectiveness, four cost studies and 12 randomized controlled trials involving ELT, six of these comparing endovascular laser with surgical ligation and saphenous vein stripping.
Since 2007, 22 cohort studies involving 10,883 patients undergoing ELT of the great saphenous vein (GSV) have been published. Imaging defined treatment effectiveness of mean vein closure rates were reported to be greater than 90% (range 93%- 99%) at short term follow-up. Longer than one year follow-up was reported in five studies with life table analysis performed in four but the follow up was still limited at three and four years. The overall pooled major adverse event rate, including DVT, PE, skin burns or nerve damage events extracted from these studies, was 0.63% (69/10,883).
The overall level of evidence of randomized trials comparing ELT with surgical ligation and vein stripping (n= 6) was graded as moderate to high. Recovery after treatment was significantly quicker after ELT (return to work median number of days, 4 vs. 17; p= .005). Major adverse events occurring after surgery were higher [(1.8% (n=4) vs. 0.4% (n = 1) 1 but not significantly. Treatment effectiveness as measured by imaging vein absence or closure, symptom relief or quality of life similar in the two treatment groups and both treatments resulted in statistically significantly improvements in these outcomes. Recurrence was low after both treatments at follow up but neovascularization (growth of new vessels, a key predictor of long term recurrence was significantly more common (18% vs. 1%; p = .001) after surgery. Although patient satisfaction was reported to be high (>80%) with both treatments, patient preferences evaluated through recruitment process, physician reports and consumer groups were strongly in favour of ELT. For patients minimal complications, quick recovery and dependability of outpatient scheduling were key considerations.
As clinical effectiveness of the two treatments was similar, a cost-analysis was performed to compare differences in resources and costs between the two procedures. A budget impact analysis for introducing ELT as an insured service was also performed. The average case cost (based on Ontario hospital costs and medical resources) for surgical vein stripping was estimated to be $1,799. Because of the uncertainties with resources associated with ELT, in addition to the device related costs, hospital costs were varied and assumed to be the same as or less than (40%) those for surgery resulting in an average ELT case cost of $2,025 or $1,602.
Based on the historical pattern of surgical vein stripping for varices a 5-year projection was made for annual volumes and costs. In Ontario in 2007/2008, 3481 surgical vein stripping procedures were performed, 28% for repeat procedures. Annual volumes of ELT currently being performed in the province in over 20 private clinics were estimated to be approximately 840. If ELT were publicly reimbursed, it was assumed that it would capture 35% of the vein stripping market in the first year and increase to 55% in subsequent years. Based on these assumptions if ELT were not publicly reimbursed, the province would be paying approximately $5.9 million and if ELT were reimbursed the province would pay $8.2 million if the hospital costs for ELT were the same as surgery and $7.1 million if the hospital costs were less (40%) than surgery.
The conclusions on the comparative outcomes between laser ablation and surgical ligation and saphenous vein stripping are summarized in the table below (ES Table 1).
Outcome comparisons of ELT vs. surgery for VV
The outcomes of the evidence-based review on these treatments based on three different perspectives are summarized below:
Patient Outcomes – ELT vs. Surgery
ELT has a quicker recovery attributable to the decreased pain, lower minor complications, use of local anesthesia with immediate ambulation.
ELT is as effective as surgery in the short term as assessed by imaging anatomic outcomes, symptomatic relief and HRQOL outcomes.
Recurrence is similar but neovascularization, a key predictor of long term recurrence, is significantly higher with surgery.
Patient satisfaction is equally high after both treatments but patient preference is much more strongly for ELT. Surgeons performing ELT are satisfied with treatment outcomes and regularly offer ELT as a treatment alternative to surgery.
Clinical or Technical Advantages – ELT Over Surgery
An endovascular approach can more easily and more precisely treat multilevel disease and difficult to treat areas
ELT is an effective and a less invasive treatment for the elderly with VV and those with venous leg ulcers.
System Outcomes – ELT Replacing Surgery
ELT may offer system advantages in that the treatment can be offered by several medical specialties in outpatient settings and because it does not require an operating theatre or general anesthesia.
The treatment may result in ↓ pre-surgical investigations, decanting of patients from OR, ↓ demand on anesthetists time, ↓ hospital stay, ↓decrease wait time for VV treatment and provide more reliable outpatient scheduling.
Depending on the reimbursement mechanism for the treatment, however, it may also result in closure of outpatient clinics with an increasingly centralization of procedures in selected hospitals with large capital budgets resulting in larger and longer waiting lists.
Procedure costs may be similar for the two treatments but the budget impact may be greater with insurance of ELT because of the transfer of the cases from the private market to the public payer system.
PMCID: PMC3377531  PMID: 23074409
15.  Remote control catheter navigation: options for guidance under MRI 
Background
Image-guided endovascular interventions have gained increasing popularity in clinical practice, and magnetic resonance imaging (MRI) is emerging as an attractive alternative to X-ray fluoroscopy for guiding such interventions. Steering catheters by remote control under MRI guidance offers unique challenges and opportunities.
Methods
In this review, the benefits and limitations of MRI-guided remote control intervention are addressed, and the tools for guiding such interventions in the magnetic environment are summarized. Designs for remote control catheter guidance include a catheter tip electromagnetic microcoil design, a ferromagnetic sphere-tipped catheter design, smart material-actuated catheters, and hydraulically actuated catheters. Remote control catheter guidance systems were compared and contrasted with respect to visualization, safety, and performance. Performance is characterized by bending angles achievable by the catheter, time to achieve bending, degree of rotation achievable, and miniaturization capacity of the design. Necessary improvements for furthering catheter design, especially for use in the MRI environment, are addressed, as are hurdles that must be overcome in order to make MRI guided endovascular procedures more accessible for regular use in clinical practice.
Conclusions
MR-guided endovascular interventions under remote control steering are in their infancy due to issues regarding safety and reliability. Additional experimental studies are needed prior to their use in humans.
doi:10.1186/1532-429X-14-33
PMCID: PMC3461467  PMID: 22655535
Interventional MRI; Remote control catheter guidance
16.  Navigation with Electromagnetic Tracking for Interventional Radiology Procedures 
PURPOSE
To assess the feasibility of the use of preprocedural imaging for guide wire, catheter, and needle navigation with electromagnetic tracking in phantom and animal models.
MATERIALS AND METHODS
An image-guided intervention software system was developed based on open-source software components. Catheters, needles, and guide wires were constructed with small position and orientation sensors in the tips. A tetrahedral-shaped weak electromagnetic field generator was placed in proximity to an abdominal vascular phantom or three pigs on the angiography table. Preprocedural computed tomographic (CT) images of the phantom or pig were loaded into custom-developed tracking, registration, navigation, and rendering software. Devices were manipulated within the phantom or pig with guidance from the previously acquired CT scan and simultaneous real-time angiography. Navigation within positron emission tomography (PET) and magnetic resonance (MR) volumetric datasets was also performed. External and endovascular fiducials were used for registration in the phantom, and registration error and tracking error were estimated.
RESULTS
The CT scan position of the devices within phantoms and pigs was accurately determined during angiography and biopsy procedures, with manageable error for some applications. Preprocedural CT depicted the anatomy in the region of the devices with real-time position updating and minimal registration error and tracking error (<5 mm). PET can also be used with this system to guide percutaneous biopsies to the most metabolically active region of a tumor.
CONCLUSIONS
Previously acquired CT, MR, or PET data can be accurately codisplayed during procedures with reconstructed imaging based on the position and orientation of catheters, guide wires, or needles. Multimodality interventions are feasible by allowing the real-time updated display of previously acquired functional or morphologic imaging during angiography, biopsy, and ablation.
doi:10.1097/01.RVI.0000148827.62296.B4
PMCID: PMC2375916  PMID: 15802449
17.  Computer-Based Route-Definition System for Peripheral Bronchoscopy 
Journal of Digital Imaging  2011;25(2):307-317.
Multi-detector computed tomography (MDCT) scanners produce high-resolution images of the chest. Given a patient’s MDCT scan, a physician can use an image-guided intervention system to first plan and later perform bronchoscopy to diagnostic sites situated deep in the lung periphery. An accurate definition of complete routes through the airway tree leading to the diagnostic sites, however, is vital for avoiding navigation errors during image-guided bronchoscopy. We present a system for the robust definition of complete airway routes suitable for image-guided bronchoscopy. The system incorporates both automatic and semiautomatic MDCT analysis methods for this purpose. Using an intuitive graphical user interface, the user invokes automatic analysis on a patient’s MDCT scan to produce a series of preliminary routes. Next, the user visually inspects each route and quickly corrects the observed route defects using the built-in semiautomatic methods. Application of the system to a human study for the planning and guidance of peripheral bronchoscopy demonstrates the efficacy of the system.
doi:10.1007/s10278-011-9433-7
PMCID: PMC3295963  PMID: 22083553
3D pulmonary imaging; Procedure planning; Image-guided intervention; Bronchoscopy; Lung cancer; MDCT; Virtual bronchoscopic navigation; Route planning
18.  An Event-Driven Distributed Processing Architecture for Image-Guided Cardiac Ablation Therapy 
Medical imaging data is becoming increasing valuable in interventional medicine, not only for preoperative planning, but also for real-time guidance during clinical procedures. Three key components necessary for image-guided intervention are real-time tracking of the surgical instrument, aligning the real-world patient space with image-space, and creating a meaningful display that integrates the tracked instrument and patient data. Issues to consider when developing image-guided intervention systems include the communication scheme, the ability to distribute CPU intensive tasks, and flexibility to allow for new technologies. In this work, we have designed a communication architecture for use in image-guided catheter ablation therapy. Communication between the system components is through a database which contains an event queue and auxiliary data tables. The communication scheme is unique in that each system component is responsible for querying and responding to relevant events from the centralized database queue. An advantage of the architecture is the flexibility to add new system components without affecting existing software code. In addition, the architecture is intrinsically distributed, in that components can run on different CPU boxes, and even different operating systems. We refer to this Framework for Image-Guided Navigation using a Distributed Event-Driven Database in Real-Time as the FINDER architecture. This architecture has been implemented for the specific application of image-guided cardiac ablation therapy. We describe our prototype image-guidance sytem and demonstrate its functionality by emulating a cardiac ablation procedure with a patient-specific phantom. The proposed architecture, designed to be modular, flexible, and intuitive, is a key step towards our goal of developing a complete system for visualization and targeting in image-guided cardiac ablation procedures.
doi:10.1016/j.cmpb.2009.01.009
PMCID: PMC2755259  PMID: 19285747
19.  Ultrasound-guided percutaneous drainage of infected pancreatic necrosis 
Surgical Endoscopy  2013;27(8):2841-2848.
Background
The role of percutaneous drainage in the management of infected pancreatic necrosis remains controversial, and ultrasound-guided technique is rarely used for this indication. The purpose of this study was to evaluate the safety and efficacy of sonographically guided percutaneous catheter drainage for infected pancreatic necrosis.
Methods
The patient group consisted of 16 men and 2 women. The mean age of the patients was 47 years. The median computed tomography severity index of acute pancreatitis was 10 points. Percutaneous catheter drainage was performed under sonographic guidance using preferably retroperitoneal approach, and transperitoneal access in selected cases. The medical records and imaging scans were reviewed retrospectively for each patient.
Results
Percutaneous catheter drainage resulted in a complete resolution of infected pancreatic necrosis in 6 of 18 patients (33 %). Twelve of 18 patients who were initially managed with PCD required eventually necrosectomy (67 %). The most common reason for crossover to surgical intervention was persistent sepsis (n = 7). Open necrosectomy was performed in 4 of these patients, and 3 patients underwent successful minimally invasive retroperitoneal necrosectomy. Five patients required conversion to open surgery because of procedure-related complications. In 3 cases, there was leakage of the necrotic material into the peritoneal cavity. Two other patients experienced hemorrhagic complications. Overall mortality rate was 17 %. The size of the largest necrotic collection in patients who were successfully treated with percutaneous drainage decreased by a median of 76 % shortly after the procedure, whereas it decreased only by a median of 16 % in cases of failure of percutaneous drainage.
Conclusions
Ultrasound-guided percutaneous catheter drainage used in infected pancreatic necrosis is a technique with acceptably low morbidity and mortality that may be the definitive treatment or a bridge management to necrosectomy. A negligible decrease in size of the necrotic collection predicts failure of percutaneous drainage.
doi:10.1007/s00464-013-2831-9
PMCID: PMC3710405  PMID: 23404151
Acute pancreatitis; Infected necrosis; Pancreatic necrosectomy; Pancreatic necrosis; Percutaneous catheter drainage
20.  Magnetic Resonance Imaging–guided Vascular Interventions 
Magnetic resonance imaging (MRI), which provides superior soft-tissue imaging and no known harmful effects, has the potential as an alternative modality to guide various medical interventions. This review will focus on MR-guided endovascular interventions and present its current state and future outlook. In the first technical part, enabling technologies such as developments in fast imaging, catheter devices, and visualization techniques are examined. This is followed by a clinical survey that includes proof-of-concept procedures in animals and initial experience in human subjects. In preclinical experiments, MRI has already proven to be valuable. For example, MRI has been used to guide and track targeted cell delivery into or around myocardial infarctions, to guide atrial septal puncture, and to guide the connection of portal and systemic venous circulations. Several investigational MR-guided procedures have already been reported in patients, such as MR-guided cardiac catheterization, invasive imaging of peripheral artery atheromata, selective intraarterial MR angiography, and preliminary angioplasty and stent placement. In addition, MR-assisted transjugular intrahepatic portosystemic shunt procedures in patients have been shown in a novel hybrid double-doughnut x-ray/MRI system. Numerous additional investigational human MR-guided endovascular procedures are now underway in several medical centers around the world. There are also significant hurdles: availability of clinical-grade devices, device-related safety issues, challenges to patient monitoring, and acoustic noise during imaging. The potential of endovascular interventional MRI is great because as a single modality, it combines 3-dimensional anatomic imaging, device localization, hemodynamics, tissue composition, and function.
PMCID: PMC1950261  PMID: 16924170
interventional MRI; endovascular procedures; real-time MRI
21.  Detector system comparison using relative CNR for specific imaging tasks related to neuro-endovascular image-guided interventions (neuro-EIGIs) 
Neuro-EIGIs require visualization of very small endovascular devices and small vessels. A Microangiographic Fluoroscope (MAF) x-ray detector was developed to improve on the standard flat panel detector’s (FPD’s) ability to visualize small objects during neuro-EIGIs. To compare the performance of FPD and MAF imaging systems, specific imaging tasks related to those encountered during neuro-EIGIs were used to assess contrast to noise ratio (CNR) of different objects. A bar phantom and a stent were placed at a fixed distance from the x-ray focal spot to mimic a clinical imaging geometry and both objects were imaged by each detector system. Imaging was done without anti-scatter grids and using the same conditions for each system including: the same x-ray beam quality, collimator position, source to imager distance (SID), and source to object distance (SOD). For each object, relative contrasts were found for both imaging systems using the peak and trough signals. The relative noise was found using mean background signal and background noise for varying detector exposures. Next, the CNRs were found for these values for each object imaged and for each imaging system used. A relative CNR metric is defined and used to compare detector imaging performance. The MAF utilizes a temporal filter to reduce the overall image noise. The effects of using this filter with the MAF while imaging the clinical object’s CNRs are reported. The relative CNR for the detectors demonstrated that the MAF has superior CNRs for most objects and exposures investigated for this specific imaging task.
doi:10.1117/12.2042332
PMCID: PMC4187362  PMID: 25301999
MAF; ROI; CNR; image metrics; fluoroscopy; angiography; x-ray imaging; neurovascular interventions
22.  Abdominal aortic aneurysm: Treatment options, image visualizations and follow-up procedures 
Abdominal aortic aneurysm is a common vascular disease that affects elderly population. Open surgical repair is regarded as the gold standard technique for treatment of abdominal aortic aneurysm, however, endovascular aneurysm repair has rapidly expanded since its first introduction in 1990s. As a less invasive technique, endovascular aneurysm repair has been confirmed to be an effective alternative to open surgical repair, especially in patients with co-morbid conditions. Computed tomography (CT) angiography is currently the preferred imaging modality for both preoperative planning and post-operative follow-up. 2D CT images are complemented by a number of 3D reconstructions which enhance the diagnostic applications of CT angiography in both planning and follow-up of endovascular repair. CT has the disadvantage of high cummulative radiation dose, of particular concern in younger patients, since patients require regular imaging follow-ups after endovascular repair, thus, exposing patients to repeated radiation exposure for life. There is a trend to change from CT to ultrasound surveillance of endovascular aneurysm repair. Medical image visualizations demonstrate excellent morphological assessment of aneurysm and stent-grafts, but fail to provide hemodynamic changes caused by the complex stent-graft device that is implanted into the aorta. This article reviews the treatment options of abdominal aortic aneurysm, various image visualization tools, and follow-up procedures with use of different modalities including both imaging and computational fluid dynamics methods. Future directions to improve treatment outcomes in the follow-up of endovascular aneurysm repair are outlined.
doi:10.3724/SP.J.1263.2012.00049
PMCID: PMC3390098  PMID: 22783323
Abdominal aortic aneurysm; Computed tomography; Follow-up; Stent graft; Treatment; Visualization.
23.  Remote Magnetic Navigation for Accurate, Real-time Catheter Positioning and Ablation in Cardiac Electrophysiology Procedures 
New remote navigation systems have been developed to improve current limitations of conventional manually guided catheter ablation in complex cardiac substrates such as left atrial flutter. This protocol describes all the clinical and invasive interventional steps performed during a human electrophysiological study and ablation to assess the accuracy, safety and real-time navigation of the Catheter Guidance, Control and Imaging (CGCI) system. Patients who underwent ablation of a right or left atrium flutter substrate were included. Specifically, data from three left atrial flutter and two counterclockwise right atrial flutter procedures are shown in this report. One representative left atrial flutter procedure is shown in the movie. This system is based on eight coil-core electromagnets, which generate a dynamic magnetic field focused on the heart. Remote navigation by rapid changes (msec) in the magnetic field magnitude and a very flexible magnetized catheter allow real-time closed-loop integration and accurate, stable positioning and ablation of the arrhythmogenic substrate.
doi:10.3791/3658
PMCID: PMC3665328  PMID: 23628883
Medicine; Issue 74; Anatomy; Physiology; Biomedical Engineering; Surgery; Cardiology; catheter ablation; remote navigation; magnetic; robotic; catheter; positioning; electrophysiology; clinical techniques
24.  Endovascular Repair of Descending Thoracic Aortic Aneurysm 
Executive Summary
Objective
To conduct an assessment on endovascular repair of descending thoracic aortic aneurysm (TAA).
Clinical Need
Aneurysm is the most common condition of the thoracic aorta requiring surgery. Aortic aneurysm is defined as a localized dilatation of the aorta. Most aneurysms of the thoracic aorta are asymptomatic and incidentally discovered. However, TAA tends to enlarge progressively and compress surrounding structures causing symptoms such as chest or back pain, dysphagia (difficulty swallowing), dyspnea (shortness of breath), cough, stridor (a harsh, high-pitched breath sound), and hoarseness. Significant aortic regurgitation causes symptoms of congestive heart failure. Embolization of the thrombus to the distal arterial circulation may occur and cause related symptoms. The aneurysm may eventually rupture and create a life-threatening condition.
The overall incidence rate of TAA is about 10 per 100,000 person-years. The descending aorta is involved in about 30% to 40% of these cases.
The prognosis of large untreated TAAs is poor, with a 3-year survival rate as low as 25%. Intervention is strongly recommended for any symptomatic TAA or any TAA that exceeds twice the diameter of a normal aorta or is 6 cm or larger. Open surgical treatment of TAA involves left thoracotomy and aortic graft replacement. Surgical treatment has been found to improve survival when compared with medical therapy. However, despite dramatic advances in surgical techniques for performing such complex operations, operative mortality from centres of excellence are between 8% and 20% for elective cases, and up to 50% in patients requiring emergency operations. In addition, survivors of open surgical repair of TAAs may suffer from severe complications. Postoperative or postprocedural complications of descending TAA repair include paraplegia, myocardial infarction, stroke, respiratory failure, renal failure, and intestinal ischemia.
The Technology
Endovascular aortic aneurysm repair (EVAR) using a stent graft, a procedure called endovascular stent-graft (ESG) placement, is a new alternative to the traditional surgical approach. It is less invasive, and initial results from several studies suggest that it may reduce mortality and morbidity associated with the repair of descending TAAs.
The goal in endovascular repair is to exclude the aneurysm from the systemic circulation and prevent it from rupturing, which is life-threatening. The endovascular placement of a stent graft eliminates the systemic pressure acting on the weakened wall of the aneurysm that may lead to the rupture. However, ESG placement has some specific complications, including endovascular leak (endoleak), graft migration, stent fracture, and mechanical damage to the access artery and aortic wall.
The Talent stent graft (manufactured by Medtronic Inc., Minneapolis, MN) is licensed in Canada for the treatment of patients with TAA (Class 4; licence 36552). The design of this device has evolved since its clinical introduction. The current version has a more flexible delivery catheter than did the original system. The prosthesis is composed of nitinol stents between thin layers of polyester graft material. Each stent is secured with oversewn sutures to prevent migration.
Review Strategy
Objectives
To compare the effectiveness and cost-effectiveness of ESG placement in the treatment of TAAs with a conventional surgical approach
To summarize the safety profile and effectiveness of ESG placement in the treatment of descending TAAs
Measures of Effectiveness
Primary Outcome
Mortality rates (30-day and longer term)
Secondary Outcomes
Technical success rate of introducing a stent graft and exclusion of the aneurysm sac from systemic circulation
Rate of reintervention (through surgical or endovascular approach)
Measures of Safety
Complications were categorized into 2 classes:
Those specific to the ESG procedure, including rates of aneurysm rupture, endoleak, graft migration, stent fracture, and kinking; and
Those due to the intervention, either surgical or endovascular. These include paraplegia, stroke, cardiovascular events, respiratory failure, real insufficiency, and intestinal ischemia.
Inclusion Criteria
Studies comparing the clinical outcomes of ESG treatment with surgical approaches
Studies reporting on the safety and effectiveness of the ESG procedure for the treatment of descending TAAs
Exclusion Criteria
Studies investigating the clinical effectiveness of ESG placement for other conditions such as aortic dissection, aortic ulcer, and traumatic injuries of the thoracic aorta
Studies investigating the aneurysms of the ascending and the arch of the aorta
Studies using custom-made grafts
Literature Search
The Medical Advisory Secretariat searched The International Network of Agencies for Health Technology Assessment and the Cochrane Database of Systematic Reviews for health technology assessments. It also searched MEDLINE, EMBASE, Medline In-Process & Other Non-Indexed Citations, and Cochrane CENTRAL from January 1, 2000 to July 11, 2005 for studies on ESG procedures. The search was limited to English-language articles and human studies.
One health technology assessment from the United Kingdom was identified. This systematic review included all pathologies of the thoracic aorta; therefore, it did not match the inclusion criteria. The search yielded 435 citations; of these, 9 studies met inclusion criteria.
Summary of Findings
Mortality
The results of a comparative study found that in-hospital mortality was not significantly different between ESG placement and surgery patients (2 [4.8%] for ESG vs. 6 [11.3%] for surgery).
Pooled data from case series with a mean follow-up ranging from 12 to 38 months showed a 30-day mortality and late mortality rate of 3.9% and 5.5%, respectively. These rates are lower than are those reported in the literature for surgical repair of TAA.
Case series showed that the most common cause of early death in patients undergoing endovascular repair is aortic rupture, and the most common causes of late death are cardiac events and aortoesophageal or aortobronchial fistula.
Technical Success Rate
Technical success rates reported by case series are 55% to 100% (100% and 94.4% in 2 studies with all elective cases, 89% in a study with 5% emergent cases, and 55% in a study with 42% emergent cases).
Surgical Reintervention
In the comparative study, 3 (7.1%) patients in the ESG group and 14 (26.5%) patients in the surgery group required surgical reintervention. In the ESG group, the reasons for surgical intervention were postoperative bleeding at the access site, paraplegia, and type 1 endoleak. In the surgical group, the reasons for surgery were duodenal perforation, persistent thoracic duct leakage, false aneurysm, and 11 cases of postoperative bleeding.
Pooled data from case series show that 9 (2.6%) patients required surgical intervention. The reasons for surgical intervention were endoleak (3 cases), aneurysm enlargement and suspected infection (1 case), aortic dissection (1 case), pseudoaneurysm of common femoral artery (1 case), evacuation of hematoma (1 case), graft migration (1 case), and injury to the access site (1 case).
Endovascular Revision
In the comparative study, 3 (7.1%) patients required endovascular revision due to persistent endoleak.
Pooled data from case series show that 19 (5.3%) patients required endovascular revision due to persistent endoleak.
Graft Migration
Two case series reported graft migration. In one study, 3 proximal and 4 component migrations were noted at 2-year follow-up (total of 5%). Another study reported 1 (3.7%) case of graft migration. Overall, the incidence of graft migration was 2.6%.
Aortic Rupture
In the comparative study, aortic rupture due to bare stent occurred in 1 case (2%). The pooled incidence of aortic rupture or dissection reported by case series was 1.4%.
Postprocedural Complications
In the comparative study, there were no statistically significant differences between the ESG and surgery groups in postprocedural complications, except for pneumonia. The rate of pneumonia was 9% for those who received an ESG and 28% for those who had surgery (P = .02). There were no cases of paraplegia in either group. The rate of other complications for ESG and surgery including stroke, cardiac, respiratory, and intestinal ischemia were all 5.1% for ESG placement and 10% for surgery. The rate for mild renal failure was 16% in the ESG group and 30% in the surgery group. The rate for severe renal failure was 11% for ESG placement and 10% for surgery.
Pooled data from case series show the following postprocedural complication rates in the ESG placement group: paraplegia (2.2%), stroke (3.9%), cardiac (2.9%), respiratory (8.7%), renal failure (2.8%), and intestinal ischemia (1%).
Time-Related Outcomes
The results of the comparative study show statistically significant differences between the ESG and surgery group for mean operative time (ESG, 2.7 hours; surgery, 5 hours), mean duration of intensive care unit stay (ESG, 11 days; surgery, 14 days), and mean length of hospital stay (ESG, 10 days; surgery, 30 days).
The mean duration of intensive care unit stay and hospital stay derived from case series is 1.6 and 7.8 days, respectively.
Ontario-Based Economic Analysis
In Ontario, the annual treatment figures for fiscal year 2004 include 17 cases of descending TAA repair procedures (source: Provincial Health Planning Database). Fourteen of these have been identified as “not ruptured” with a mean hospital length of stay of 9.23 days, and 3 cases have been identified as “ruptured,” with a mean hospital length of stay of 28 days. However, because one Canadian Classification of Health Interventions code was used for both procedures, it is not possible to determine how many were repaired with an EVAR procedure or with an open surgical procedure.
Hospitalization Costs
The current fiscal year forecast of in-hospital direct treatment costs for all in-province procedures of repair of descending TAAs is about $560,000 (Cdn). The forecast in-hospital total cost per year for in-province procedures is about $720,000 (Cdn). These costs include the device cost when the procedure is EVAR (source: Ontario Case Costing Initiative).
Professional (Ontario Health Insurance Plan) Costs
Professional costs per treated patient were calculated and include 2 preoperative thoracic surgery or EVAR consultations.
The professional costs of an EVAR include the fees paid to the surgeons, anesthetist, and surgical assistant (source: fee service codes). The procedure was calculated to take about 150 minutes.
The professional costs of an open surgical repair include the fees of the surgeon, anesthetist, and surgical assistant. Open surgical repair was estimated to take about 300 minutes.
Services provided by professionals in intensive care units were also taken into consideration, as were the costs of 2 postoperative consultations that the patients receive on average once they are discharged from the hospital. Therefore, total Ontario Health Insurance Plan costs per treated patient treated with EVAR are on average $2,956 (ruptured or not ruptured), as opposed to $5,824 for open surgical repair and $6,157 for open surgical repair when the aneurysm is ruptured.
Conclusions
Endovascular stent graft placement is a less invasive procedure for repair of TAA than is open surgical repair.
There is no high-quality evidence with long-term follow-up data to support the use of EVAR as the first choice of treatment for patients with TAA that are suitable candidates for surgical intervention.
However, short- and medium-term outcomes of ESG placement reported by several studies are satisfactory and comparable to surgical intervention; therefore, for patients at high risk of surgery, it is a practical option to consider. Short- and medium-term results show that the benefit of ESG placement over the surgical approach is a lower 30-day mortality and paraplegia rate; and shorter operative time, ICU stay, and hospital stay.
PMCID: PMC3382300  PMID: 23074469
25.  Electromagnetic tracking for abdominal interventions in computer aided surgery 
Electromagnetic tracking has great potential for assisting physicians in precision placement of instruments during minimally invasive interventions in the abdomen, since electromagnetic tracking is not limited by the line-of-sight restrictions of optical tracking. A new generation of electromagnetic tracking has recently become available, with sensors small enough to be included in the tips of instruments. To fully exploit the potential of this technology, our research group has been developing a computer aided, image-guided system that uses electromagnetic tracking for visualization of the internal anatomy during abdominal interventions. As registration is a critical component in developing an accurate image-guided system, we present three registration techniques: 1) enhanced paired-point registration (time-stamp match registration and dynamic registration); 2) orientation-based registration; and 3) needle shape-based registration. Respiration compensation is another important issue, particularly in the abdomen, where respiratory motion can make precise targeting difficult. To address this problem, we propose reference tracking and affine transformation methods. Finally, we present our prototype navigation system, which integrates the registration, segmentation, path-planning and navigation functions to provide real-time image guidance in the clinical environment. The methods presented here have been tested with a respiratory phantom specially designed by our group and in swine animal studies under approved protocols. Based on these tests, we conclude that our system can provide quick and accurate localization of tracked instruments in abdominal interventions, and that it offers a user friendly display for the physician.
doi:10.3109/10929080600751399
PMCID: PMC4136656  PMID: 16829506
Image-guided systems; optical tracking; electromagnetic tracking; computer aided surgery; registration; respiratory motion compensation; navigation

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