A tracking system has been developed to provide real-time feedback of skin dose and dose rate during interventional fluoroscopic procedures. The dose tracking system (DTS) calculates the radiation dose rate to the patient’s skin using the exposure technique parameters and exposure geometry obtained from the x-ray imaging system digital network (Toshiba Infinix) and presents the cumulative results in a color mapping on a 3D graphic of the patient. We performed a number of tests to verify the accuracy of the dose representation of this system. These tests included comparison of system–calculated dose-rate values with ionization-chamber (6 cc PTW) measured values with change in kVp, beam filter, field size, source-to-skin distance and beam angulation. To simulate a cardiac catheterization procedure, the ionization chamber was also placed at various positions on an Alderson Rando torso phantom and the dose agreement compared for a range of projection angles with the heart at isocenter. To assess the accuracy of the dose distribution representation, Gafchromic film (XR-RV3, ISP) was exposed with the beam at different locations. The DTS and film distributions were compared and excellent visual agreement was obtained within the cm-sized surface elements used for the patient graphic. The dose (rate) values agreed within about 10% for the range of variables tested. Correction factors could be applied to obtain even closer agreement since the variable values are known in real-time. The DTS provides skin-dose values and dose mapping with sufficient accuracy for use in monitoring diagnostic and interventional x-ray procedures.
skin dose; dosimetry; radiation safety; cardiac fluoroscopic procedures; fluoroscopic dose; dose tracking; real-time dosimetry; fluoroscopic interventional procedures
Scanning Beam Digital X-ray (SBDX) is a low-dose inverse geometry fluoroscopic system for cardiac interventional procedures. The system performs x-ray tomosynthesis at multiple planes in each frame period and combines the tomosynthetic images into a projection-like composite image for fluoroscopic display. We present a novel method of stereoscopic imaging using SBDX, in which two slightly offset projection-like images are reconstructed from the same scan data by utilizing raw data from two different detector regions. To confirm the accuracy of the 3D information contained in the stereoscopic projections, a phantom of known geometry containing high contrast steel spheres was imaged, and the spheres were localized in 3D using a previously described stereoscopic localization method. After registering the localized spheres to the phantom geometry, the 3D residual RMS errors were between 0.81 and 1.93 mm, depending on the stereoscopic geometry. To demonstrate visualization capabilities, a cardiac RF ablation catheter was imaged with the tip oriented towards the detector. When viewed as a stereoscopic red/cyan anaglyph, the true orientation (towards vs. away) could be resolved, whereas the device orientation was ambiguous in conventional 2D projection images. This stereoscopic imaging method could be implemented in real time to provide live 3D visualization and device guidance for cardiovascular interventions using a single gantry and data acquired through normal, low-dose SBDX imaging.
stereoscopic x-ray fluoroscopy; inverse geometry; cardiac interventional procedures
Interventional and fluoroscopic imaging procedures for pediatric patients are becoming more prevalent because of the less-invasive nature of these procedures compared to alternatives such as surgery. Flat-panel X-ray detectors (FPD) for fluoroscopy are a new technology alternative to the image intensifier/TV (II/TV) digital system that has been in use for more than two decades. Two major FPD technologies have been implemented, based on indirect conversion of X-rays to light (using an X-ray scintillator) and then to proportional charge (using a photodiode), or direct conversion of X-rays into charge (using a semiconductor material) for signal acquisition and digitization. These detectors have proved very successful for high-exposure interventional procedures but lack the image quality of the II/TV system at the lowest exposure levels common in fluoroscopy. The benefits for FPD image quality include lack of geometric distortion, little or no veiling glare, a uniform response across the field-of-view, and improved ergonomics with better patient access. Better detective quantum efficiency indicates the possibility of reducing the patient dose in accordance with ALARA principles. However, first-generation FPD devices have been implemented with less than adequate acquisition flexibility (e.g., lack of tableside controls/information, inability to easily change protocols) and the presence of residual signals from previous exposures, and additional cost of equipment and long-term maintenance have been serious impediments to purchase and implementation. Technological advances of second generation and future hybrid FPD systems should solve many current issues. The answer to the question ‘how much better are they?–is ‘significantly better– and they are certainly worth consideration for replacement or new implementation of an imaging suite for pediatric fluoroscopy.
Flat-panel detectors; Fluoroscopy; Interventional radiology
X-ray fluoroscopy is widely used for image guidance during cardiac intervention. However, radiation dose in these procedures can be high, and this is a significant concern, particularly in pediatric applications. Pediatrics procedures are in general much more complex than those performed on adults and thus are on average four to eight times longer1. Furthermore, children can undergo up to 10 fluoroscopic procedures by the age of 10, and have been shown to have a three-fold higher risk of developing fatal cancer throughout their life than the general population2,3.
We have shown that radiation dose can be significantly reduced in adult cardiac procedures by using our scanning beam digital x-ray (SBDX) system4-- a fluoroscopic imaging system that employs an inverse imaging geometry5,6 (Figure 1, Movie 1 and Figure 2). Instead of a single focal spot and an extended detector as used in conventional systems, our approach utilizes an extended X-ray source with multiple focal spots focused on a small detector. Our X-ray source consists of a scanning electron beam sequentially illuminating up to 9,000 focal spot positions. Each focal spot projects a small portion of the imaging volume onto the detector. In contrast to a conventional system where the final image is directly projected onto the detector, the SBDX uses a dedicated algorithm to reconstruct the final image from the 9,000 detector images.
For pediatric applications, dose savings with the SBDX system are expected to be smaller than in adult procedures. However, the SBDX system allows for additional dose savings by implementing an electronic adaptive exposure technique. Key to this method is the multi-beam scanning technique of the SBDX system: rather than exposing every part of the image with the same radiation dose, we can dynamically vary the exposure depending on the opacity of the region exposed. Therefore, we can significantly reduce exposure in radiolucent areas and maintain exposure in more opaque regions. In our current implementation, the adaptive exposure requires user interaction (Figure 3). However, in the future, the adaptive exposure will be real time and fully automatic.
We have performed experiments with an anthropomorphic phantom and compared measured radiation dose with and without adaptive exposure using a dose area product (DAP) meter. In the experiment presented here, we find a dose reduction of 30%.
Region-of-interest (ROI) fluoroscopy takes advantage of the fact that most neurovascular interventional activity is performed in only a small portion of an x-ray imaging field of view (FOV). The ROI beam filter is an attenuating material that reduces patient dose in the area peripheral to the object of interest. This project explores a method of moving the beam-attenuator aperture with the object of interest such that it always remains in the ROI. In this study, the ROI attenuator, which reduces the dose by 80% in the peripheral region, is mounted on a linear stage placed near the x-ray tube. Fluoroscopy is performed using the Microangiographic Fluoroscope (MAF) which is a high-resolution, CCD-based x-ray detector. A stainless-steel stent is selected as the object of interest, and is moved across the FOV and localized using an object-detection algorithm available in the IMAQ Vision package of LabVIEW. The ROI is moved to follow the stent motion. The pixel intensities are equalized in both FOV regions and an adaptive temporal filter dependent on the motion of the object of interest is implemented inside the ROI. With a temporal filter weight of 5% for the current image in the peripheral region, the SNR measured is 47.8. The weights inside the ROI vary between 10% and 33% with a measured SNR of 57.9 and 35.3 when the object is stationary and moving, respectively. This method allows patient dose reduction as well as maintenance of superior image quality in the ROI while tracking the object.
Dose reduction; Region-of-interest (ROI) fluoroscopy; object tracking; adaptive temporal filtering
Recent improvements in x-ray technology have greatly contributed to the advancement of diagnostic imaging. Fluoroscopically guided neurointerventional procedures with digital subtraction angiography (DSΛ) are being performed with increasing frequency as the treatment of choice for a variety of neurovascular diseases. Radiation-induced skin injuries can occur after extended fluoroscopic exposure times, and the injuries have recently been reported. In this article, measured radiation doses at the surface of Rando Phantom with Skin Dose Monitor, and estimated and measured entrance skin doses in patients underwent neurointerventional procedures are reported as well as means of reducing radiation doses absorbed by patients and personnel to avoid occurrence of radiation-induced injuries.
fluoroscopically guided interventional procedure, digital subtraction angiography, radiation protection
To present the experience in patient dose management and the development of an online audit tool for digital radiography.
Materials and methods:
Several tools have been developed to extract the information contained in the DICOM header of digital images, collect radiographic parameters, calculate patient entrance doses and other related parameters, and audit image quality.
The tool has been used for mammography, and includes images from over 25,000 patients, over 75,000 chest images, 100,000 computed radiography procedures and more than 1,000 interventional radiology procedures. Examples of calculation of skin dose distribution in interventional cardiology based upon information of DICOM header and the results of dosimetric parameters for cardiology procedures in 2006 are presented.
Digital radiology has great advantages for imaging and patient dose management. Dose reports, QCONLINE systems and the MPPS DICOM service are good tools to optimise procedures and to manage patient dosimetry data. The implementation of the ongoing IEC-DICOM standard for patient dose structured reports will improve dose management in digital radiology.
Digital radiography; patient dose; DICOM header audit; quality assurance
Although many clinicians know about the reducing effects of the pulsed and low-dose modes for fluoroscopic radiation when performing interventional procedures, few studies have quantified the reduction of radiation-absorbed doses (RADs). The aim of this study is to compare how much the RADs from a fluoroscopy are reduced according to the C-arm fluoroscopic modes used.
We measured the RADs in the C-arm fluoroscopic modes including 'conventional mode', 'pulsed mode', 'low-dose mode', and 'pulsed + low-dose mode'. Clinical imaging conditions were simulated using a lead apron instead of a patient. According to each mode, one experimenter radiographed the lead apron, which was on the table, consecutively 5 times on the AP views. We regarded this as one set and a total of 10 sets were done according to each mode. Cumulative exposure time, RADs, peak X-ray energy, and current, which were viewed on the monitor, were recorded.
Pulsed, low-dose, and pulsed + low-dose modes showed significantly decreased RADs by 32%, 57%, and 83% compared to the conventional mode. The mean cumulative exposure time was significantly lower in the pulsed and pulsed + low-dose modes than in the conventional mode. All modes had pretty much the same peak X-ray energy. The mean current was significantly lower in the low-dose and pulsed + low-dose modes than in the conventional mode.
The use of the pulsed and low-dose modes together significantly reduced the RADs compared to the conventional mode. Therefore, the proper use of the fluoroscopy and its C-arm modes will reduce the radiation exposure of patients and clinicians.
fluoroscopy; radiation; radiation dosage; radiographic image enhancement
High-radiation exposure occurs during computed tomographic (CT) fluoroscopy. Patient and operator doses during thoracic and abdominal interventional procedures were studied in the present experiment, and a novel shielding device to reduce exposure to the patient and operator was evaluated.
MATERIALS AND METHODS
With a 16-slice CT scanner in CT fluoroscopy mode (120 kVp, 30 mA), surface dosimetry was performed on adult and pediatric phantoms. The shielding was composed of tungsten antimony in the form of a lightweight polymer sheet. Doses to the patient were measured with and without shielding for thoracic and abdominal procedures. Doses to the operator were recorded with and without phantom, gantry, and table shielding in place. Double-layer lead-free gloves were used by the operator during the procedures.
Tungsten antimony shielding adjacent to the scan plane resulted in a maximum dose reduction of 92.3% to the patient. Maximum 85.6%, 93.3%, and 85.1% dose reductions were observed for the operator’s torso, gonads, and hands, respectively. The use of double-layer lead-free gloves resulted in a maximum radiation dose reduction of 97%.
Methods to reduce exposure during CT fluoroscopy are effective and should be searched for. Significant reduction in radiation doses to the patient and operator can be accomplished with tungsten antimony shielding.
The purpose of the study was to quantify patient exposure to ionising radiation during fluoroscopic-assisted arthroscopic surgery of the hip, establish a risk profile of this exposure, and reassure patients of radiation safety during the procedure.
We retrospectively analysed the dose area products for 50 consecutive patients undergoing arthroscopic hip surgery by an experienced hip arthroscopic surgeon. The effective dose and organ dose were derived using a Monte Carlo program.
The mean total fluoroscopy time was 1.10 minutes and the mean dose area product value was 297.2 cGycm2. We calculated the entrance skin dose to be 52 mGy to the area where the beam was targeted (81 cm2). The mean effective dose for intra-operative fluoroscopy was 0.33 mSv, with a SD of 0.90 Sv.
This study confirms that fluoroscopic-assisted arthroscopic surgery of the hip is safe with a low maximum radiation dose and supports its continued use in preference to alternative imaging modalities.
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.
MAF; CMOS; ROI; fluoroscopy; angiography; x-ray imaging; detector design; neurovascular interventions
The author measured levels of fluoroscopic radiation exposure to the surgeon's body based on the different beam directions during kyphoplasty.
This is an observational study. A series of 84 patients (96 vertebral bodies) were treated with kyphoplasty over one year. The patients were divided into four groups based on the horizontal and vertical directions of the X-Ray beams. We measured radiation exposure with the seven dosimetry badges which were worn by the surgeon in each group (total of 28 badges). Twenty-four procedures were measured in each group. Cumulative dose and dose rates were compared between groups.
Fluoroscopic radiation is received by the operator in real-time for approximately 50% (half) of the operation time. Thyroid protectors and lead aprons can block radiation almost completely. The largest dose was received in the chest irrespective of beam directions. The lowest level of radiation were received when X-ray tube was away from the surgeon and beneath the bed (dose rate of head, neck, chest, abdomen and knee : 0.2986, 0.2828, 0.9711, 0.8977, 0.8168 mSv, respectively). The radiation differences between each group were approximately 2.7-10 folds.
When fluoroscopic guided-KP is performed, the X-Ray tube should be positioned on the opposite side of the operator and below the table, otherwise the received radiation to the surgeon's body would be 2.7-10 times higher than such condition.
Kyphoplasty; Radiation exposure; Fluoroscopic guidance; Dosimetry; Radiation safety; Fluoroscopy
During image guided interventional procedures, superior resolution and image quality is critically important. Operating the MAF in the new High Definition (HD) fluoroscopy mode provides high resolution and increased contrast-to-noise ratio. The MAF has a CCD camera and a 300 micron cesium iodide x-ray convertor phosphor coupled to a light image intensifier (LII) through a fiber-optic taper. The MAF captures 1024 × 1024 pixels with an effective pixel size of 35 microns, and is capable of real-time imaging at 30 fps. The HD mode uses the advantages of higher exposure along with a small focal spot effectively improving the contrast-to-noise ratio (CNR) and the spatial resolution. The Control Acquisition Processing and Image Display System (CAPIDS) software for the MAF controls the LII gain. The interventionalist can select either fluoroscopic or angiographic modes using the two standard foot pedals. When improved image quality is needed and the angiography footpedal is used for HD mode, the x-ray machine will operate at a preset higher exposure rate using a small focal spot, while the CAPIDS will automatically adjust the LII gain to achieve proper image brightness. HD mode fluoroscopy and roadmapping are thus achieved conveniently during the interventional procedure. For CNR and resolution evaluation we used a bar phantom with images taken in HD mode with both the MAF and a Flat Panel Detector (FPD). It was seen that the FPD could not resolve more than 2.8 lp/mm whereas the MAF could resolve more than 5 lp/mm. The CNR of the MAF was better than that of the FPD by 60% at lower frequencies and by 600% at the Nyquist frequency of the FPD. The HD mode has become the preferred mode during animal model interventions because it enables detailed features of endovascular devices such as stent struts to be visualized clearly for the first time. Clinical testing of the MAF in HD mode is imminent.
The purpose of this study is to evaluate the radiation dose in patients undergoing liver angiographic procedure and verify the usefulness of different dose measurements to prevent deterministic effects. Gafchromic film, MicroMOSFET data and DIAMENTOR device of the X-ray system were used to characterize the examined interventional radiology (IR) procedure.
Materials and methods
A liver embolization procedure, the SIRT (Selective Internal Radiation Therapy), was investigated. The exposure parameters from the DIAMENTOR as well as patient and geometrical data were registered. Entrance skin dose map obtained using Gafchromic film (ESDGAF) in a standard phantom as well as in 12 patients were used to calculate the maximum skin dose (MSDGAF). MicroMOSFETs were used to assess ESD in relevant points/areas. Moreover, the maximum value of five MicroMOSFETs array, due to the extension of treated area and to the relative distance of 2–3 cm of two adjacent MicroMOSFETs, was useful to predict the MSD without interfering with the clinical practice. PCXMC vers.1.5 was used to calculate effective dose (E) and equivalent dose (H).
The mean dose-area product (DAPDIAMENTOR) for SIRT procedures was 166 Gycm2, although a wide range was observed. The mean MSDGAF for SIRT procedures was 1090 mGy, although a wide range was experienced. A correlation was found between the MSDGAF measured on a patient and the DAPDIAMENTOR value for liver embolizations. MOSFET and Gafchromic data were in agreement within 5% in homogeneous area and within 20% in high dose gradient regions. The mean equivalent dose in critical organs was 89.8 mSv for kidneys, 22.9 mSv for pancreas, 20.2 mSv for small intestine and 21.0 mSv for spleen. Whereas the mean E was 3.7 mSv (range: 0.5-13.7).
Gafchromic films result useful to study patient exposure and determine localization and amplitude of high dose skin areas to better predict the skin injuries. Then, DAPDIAMENTOR or MOSFET data could offer real-time methods, as on-line dose alert, to avoid any side effects during liver embolization with prolonged duration.
Skin dose measurement; Gafchromic film dosimetry; MOSFET dosimetry; Interventional radiology; Liver embolization
Optimisation of radiation protection in fluoroscopy is important since the procedure could lead to relatively high absorbed doses both in patients and personnel resulting in acute radiation injury. Optimisation procedures include adjustment of the fluoroscopy equipment such as exposure factors as well as proper use of automatic brightness control and pulsed fluoroscopy. It is also important to gain the benefits of image processing and the higher sensitivity of flat panel detectors as compared to image intensifier-TV systems.
Proper positioning of the patient with respect to detector and X-ray tube is of fundamental importance to image quality and radiation dose to the patient. Both image quality and radiation dose are also affected by the methodology used with parameters such as magnification factor, increased filtration, use of last-image-hold and the use of a grid.
There is a direct relation between patient dose and the absorbed dose to the personnel since this is mostly due to scattered radiation from the patient. If the correct methodology and the correct radiation protection devices are used, the absorbed dose to the personnel could be minimised to acceptable levels even for those working with complex procedures.
In order to have an organised review of all aspects of optimisation, it is recommendable to have an active quality system at the department. This system should define responsibilities and tasks for persons involved.
Radiation protection; fluoroscopy; patient dose; dose reduction
Fluoroscopic systems have excellent temporal resolution, but are relatively noisy. In this paper we present a recursive temporal filter with different weights (lag) for different user selected regions of interest (ROI) to assist the neurointerventionalist during an image guided catheter procedure. The filter has been implemented on a Graphics Processor (GPU), enabling its usage for fast frame rates such as during fluoroscopy.
We first demonstrate the use of this GPU-implemented rapid temporal filtering technique during an endovascular image guided intervention with normal fluoroscopy. Next we demonstrate its use in combination with ROI fluoroscopy where the exposure is substantially reduced in the peripheral region outside the ROI, which is then software-matched in brightness and filtered using the differential temporal filter. This enables patient dose savings along with improved image quality.
The U.S. National Press has brought to full public discussion concerns regarding the use of medical radiation, specifically x-ray computed tomography (CT), in diagnosis. A need exists for developing methods whereby assurance is given that all diagnostic medical radiation use is properly prescribed, and all patients’ radiation exposure is monitored. The “DICOM Index Tracker©” (DIT) transparently captures desired digital imaging and communications in medicine (DICOM) tags from CT, nuclear imaging equipment, and other DICOM devices across an enterprise. Its initial use is recording, monitoring, and providing automatic alerts to medical professionals of excursions beyond internally determined trigger action levels of radiation. A flexible knowledge base, aware of equipment in use, enables automatic alerts to system administrators of newly identified equipment models or software versions so that DIT can be adapted to the new equipment or software. A dosimetry module accepts mammography breast organ dose, skin air kerma values from XA modalities, exposure indices from computed radiography, etc. upon receipt. The American Association of Physicists in Medicine recommended a methodology for effective dose calculations which are performed with CT units having DICOM structured dose reports. Web interface reporting is provided for accessing the database in real-time. DIT is DICOM-compliant and, thus, is standardized for international comparisons. Automatic alerts currently in use include: email, cell phone text message, and internal pager text messaging. This system extends the utility of DICOM for standardizing the capturing and computing of radiation dose as well as other quality measures.
Data extraction; medical informatics applications; radiation dose; database management systems; knowledge base
An integrated software package, Compartment Model Kinetic Analysis Tool (COMKAT), is presented in this report.
COMKAT is an open-source software package with many functions for incorporating pharmacokinetic analysis in molecular imaging research and has both command-line and graphical user interfaces.
With COMKAT, users may load and display images, draw regions of interest, load input functions, select kinetic models from a predefined list, or create a novel model and perform parameter estimation, all without having to write any computer code. For image analysis, COMKAT image tool supports multiple image file formats, including the Digital Imaging and Communications in Medicine (DICOM) standard. Image contrast, zoom, reslicing, display color table, and frame summation can be adjusted in COMKAT image tool. It also displays and automatically registers images from 2 modalities. Parametric imaging capability is provided and can be combined with the distributed computing support to enhance computation speeds. For users without MATLAB licenses, a compiled, executable version of COMKAT is available, although it currently has only a subset of the full COMKAT capability. Both the compiled and the noncompiled versions of COMKAT are free for academic research use. Extensive documentation, examples, and COMKAT itself are available on its wiki-based Web site, http://comkat.case.edu. Users are encouraged to contribute, sharing their experience, examples, and extensions of COMKAT.
With integrated functionality specifically designed for imaging and kinetic modeling analysis, COMKAT can be used as a software environment for molecular imaging and pharmacokinetic analysis.
kinetic modeling; imaging software; pharmacokinetics; COMKAT
Different target-filter combinations in computed radiography have different impacts on the dose and image quality in digital radiography. This study aims to evaluate the mean glandular dose (MGD) and modulation transfer function (MTF) of various target-filter combinations by investigating the signal intensities of X-ray beams.
General Electric (GE) Senographe DMR Plus mammography unit was used for MGD and MTF evaluation. The measured MGD was compared with the dose reference level (DRL), whereas the MTF was evaluated using ImageJ 1.46o software. A modified Mammography Accreditation Phantom RMI 156 was exposed using different target-filter combinations of molybdenum-molybdenum (Mo-Mo), molybdenum-rhodium (Mo-Rh) and rhodium-rhodium (Rh-Rh) at two different tube voltages, 26 kV and 32 kV with 50 mAs.
In the MGD evaluations, all target-filters gave an MGD value of < 1.5 mGy. The one-way ANOVA test showed a highly significant interaction between the MGD and the kilovoltage and target-filter material used (26 kV: F (2,12) = 49,234, P = 0.001;32 kV: F (2,12) = 89,972, P = 0.001). A Tukey post-hoc test revealed that the MGD for 26 kV and 32 kV was highly affected by the target-filter combinations. The test of homogeneity of variances indicates that the MGD varies significantly for 26 kV and 32 kV images (0.045 and 0.030 (P < 0.05), respectively). However, the one-way ANOVA for the MTF shows that no significant difference exists between the target-filter combinations used with 26 kV and 32 kV images either in parallel or perpendicular to the chest wall side F (2,189) = 0.26, P > 0.05).
Higher tube voltage and atomic number target-filter yield higher MGD values. However, the MTF is independent of the X-ray energy and the type of target-filter combinations used.
mean glandular dose (MGD); modulation transfer function (MTF); computed radiography; spatial resolution; image processing
In this article, we present GE Healthcare’s design philosophy and implementation of X-ray imaging systems with dose management for pediatric patients, as embodied in its current radiography and fluoroscopy and interventional cardiovascular X-ray product offerings. First, we present a basic framework of image quality and dose in the context of a cost–benefit trade-off, with the development of the concept of imaging dose efficiency. A set of key metrics of image quality and dose efficiency is presented, including X-ray source efficiency, detector quantum efficiency (DQE), detector dynamic range, and temporal response, with an explanation of the clinical relevance of each. Second, we present design methods for automatically selecting optimal X-ray technique parameters (kVp, mA, pulse width, and spectral filtration) in real time for various clinical applications. These methods are based on an optimization scheme where patient skin dose is minimized for a target desired image contrast-to-noise ratio. Operator display of skin dose and Dose-Area Product (DAP) is covered, as well. Third, system controls and predefined protocols available to the operator are explained in the context of dose management and the need to meet varying clinical procedure imaging demands. For example, fluoroscopic dose rate is adjustable over a range of 20:1 to adapt to different procedure requirements. Fourth, we discuss the impact of image processing techniques upon dose minimization. In particular, two such techniques, dynamic range compression through adaptive multiband spectral filtering and fluoroscopic noise reduction, are explored in some detail. Fifth, we review a list of system dose-reduction features, including automatic spectral filtration, virtual collimation, variable-rate pulsed fluoroscopic, grid and no-grid techniques, and fluoroscopic loop replay with store. In addition, we describe a new feature that automatically minimizes the patient-to-detector distance, along with an estimate of its dose reduction potential. Finally, two recently developed imaging techniques and their potential effect on dose utilization are discussed. Specifically, we discuss the dose benefits of rotational angiography and low frame rate imaging with advanced image processing in lieu of higher-dose digital subtraction.
Pediatric dose management; Fluoroscopic equipment; Technical advances
Endoscopic retrograde cholangiopancreatography (ERCP) is associated with a considerable radiation exposure for patients and staff. While optimization of the radiation dose is recommended, few studies have been published. The purpose of this study has been to measure patient and staff radiation dose, to estimate the effective dose and radiation risk using digital fluoroscopic images. Entrance skin dose (ESD), organ and effective doses were estimated for patients and staff.
Materials and Methods:
Fifty-seven patients were studied using digital X-ray machine and thermoluminescent dosimeters (TLD) to measure ESD at different body sites. Organ and surface dose to specific radiosensitive organs was carried out. The mean, median, minimum, third quartile and the maximum values are presented due to the asymmetry in data distribution.
The mean ESD, exit and thyroid surface dose were estimated to be 75.6 mGy, 3.22 mGy and 0.80 mGy, respectively. The mean effective dose for both gastroenterologist and assistant is 0.01 mSv. The mean patient effective dose was 4.16 mSv, and the cancer risk per procedure was estimated to be 2 × 10-5
ERCP with fluoroscopic technique demonstrate improved dose reduction, compared to the conventional radiographic based technique, reducing the surface dose by a factor of 2, without compromising the diagnostic findings. The radiation absorbed doses to the different organs and effective doses are relatively low.
ERCP; radiation risk; staff exposure
The C-arm fluoroscope is an essential tool for the intervention of pain. The aim of this study was to investigate the radiation exposure experienced by the hand and chest of pain physicians during C-arm fluoroscopy-guided procedures.
This is a prospective study about radiation exposure to physicians during transforaminal epidural steroid injection (TFESI) and medial branch block (MBB). Four pain physicians were involved in this study. Data about effective dose (ED) at each physician's right hand and left side of the chest, exposure time, radiation absorbed dose (RAD), and the distance from the center of the X-ray field to the physician during X-ray scanning were
Three hundred and fifteen cases were included for this study. Demographic data showed no significant differences among the physicians in the TFESIs and MBBs. In the TFESI group, there was a significant difference between the ED at the hand and chest in all the physicians. In physician A, B and C, the ED at the chest was more than the ED at the hand. The distance from the center of the X-ray field to physician A was more than that of the other physicians, and for the exposure time, the ED and RAD in physician A was less than that of the other physicians. In the MBB group, there was no difference in the ED at the hand and chest, except for physician D. The distance from the center of the X-ray field to physician A was more than that of the other physicians and the exposure time in physician A was less than that of the other physicians.
In conclusion, the distance from the radiation source, position of the hand, experience and technique can correlate with the radiation dose.
distance; exposure time; radiation dose; radiation protection
To evaluate the feasibility of image fusion (IF) of preprocedural arterial-phase computed tomography with intraprocedural fluoroscopy for roadmapping in endovascular repair of complex aortic aneurysms, and to compare this approach versus current roadmapping methods (ie, two-dimensional [2D] and three-dimensional [3D] angiography).
Materials and Methods
Thirty-seven consecutive patients with complex aortic aneurysms treated with endovascular techniques were retrospectively reviewed; these included aneurysms of digestive and/or renal arteries and pararenal and juxtarenal aortic aneurysms. All interventions were performed with the same angiographic system. According to the availability of different roadmapping software, patients were successively placed into three intraprocedural image guidance groups: (i) 2D angiography (n = 9), (ii) 3D rotational angiography (n = 14), and (iii) IF (n = 14). X-ray exposure (dose–area product [DAP]), injected contrast medium volume, and procedure time were recorded.
Patient characteristics were similar among groups, with no statistically significant differences (P ≥ .05). There was no statistical difference in endograft deployment success between groups (2D angiography, eight of nine patients [89%]; 3D angiography and IF, 14 of 14 patients each [100%]). The IF group showed significant reduction (P < .0001) in injected contrast medium volume versus other groups (2D, 235 mL ± 145; 3D, 225 mL ± 119; IF, 65 mL ± 28). Mean DAP values showed no significant difference between groups (2D, 1,188 Gy · cm2 ± 1,067; 3D, 984 Gy · cm2 ± 581; IF, 655 Gy · cm2 ± 457; P = .18); nor did procedure times (2D, 233 min ± 123; 3D, 181 min ± 53; IF, 189 min ± 60; P = .59).
The use of IF-based roadmapping is a feasible technique for endovascular complex aneurysm repair associated with significant reduction of injected contrast agent volume and similar x-ray exposure and procedure time.
Intracranial aneurysm (IA) embolization using Gugliemi Detachable Coils (GDC) under x-ray fluoroscopic guidance is one of the most important neuro-vascular interventions. Coil deposition accuracy is key and could benefit substantially from higher resolution imagers such as the micro-angiographic fluoroscope (MAF). The effect of MAF guidance improvement over the use of standard Flat Panels (FP) is challenging to assess for such a complex procedure. We propose and investigate a new metric, inter-frame cross-correlation sensitivity (CCS), to compare detector performance for such procedures. Pixel (P) and histogram (H) CCS’s were calculated as one minus the cross-correlation coefficients between pixel values and histograms for the region of interest at successive procedure steps. IA treatment using GDC’s was simulated using an anthropomorphic head phantom which includes an aneurysm. GDC’s were deposited in steps of 3 cm and the procedure was imaged with a FP and the MAF. To measure sensitivity to detect progress of the procedure by change in images of successive steps, an ROI was selected over the aneurysm location and pixel-value and histogram changes were calculated after each step. For the FP, after 4 steps, the H and P CCSs between successive steps were practically zero, indicating that there were no significant changes in the observed images. For the MAF, H and P CCSs were greater than zero even after 10 steps (30 cm GDC), indicating observable changes. Further, the proposed quantification method was applied for evaluation of seven patients imaged using the MAF, yielding similar results (H and P CCSs greater than zero after the last GDC deposition). The proposed metric indicates that the MAF can offer better guidance during such procedures.
Intracranial aneurysms; microangiographic fluoroscope; MAF; coil embolization; cross-correlation sensitivity
The study aimed to characterise the factors related to the X-ray dose delivered to the patient's skin during interventional cardiology procedures.
We studied 177 coronary angiographies (CAs) and/or percutaneous transluminal coronary angioplasties (PTCAs) carried out in a French clinic on the same radiography table. The clinical and therapeutic characteristics, and the technical parameters of the procedures, were collected. The dose area product (DAP) and the maximum skin dose (MSD) were measured by an ionisation chamber (Diamentor; Philips, Amsterdam, The Netherlands) and radiosensitive film (Gafchromic; International Specialty Products Advanced Materials Group, Wayne, NJ). Multivariate analyses were used to assess the effects of the factors of interest on dose.
The mean MSD and DAP were respectively 389 mGy and 65 Gy cm−2 for CAs, and 916 mGy and 69 Gy cm−2 for PTCAs. For 8% of the procedures, the MSD exceeded 2 Gy. Although a linear relationship between the MSD and the DAP was observed for CAs (r=0.93), a simple extrapolation of such a model to PTCAs would lead to an inadequate assessment of the risk, especially for the highest dose values. For PTCAs, the body mass index, the therapeutic complexity, the fluoroscopy time and the number of cine frames were independent explanatory factors of the MSD, whoever the practitioner was. Moreover, the effect of technical factors such as collimation, cinematography settings and X-ray tube orientations on the DAP was shown.
Optimising the technical options for interventional procedures and training staff on radiation protection might notably reduce the dose and ultimately avoid patient skin lesions.