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1.  Magnetic resonance-guided focused ultrasound treatment of facet joint pain: summary of preclinical phase 
Study design
A phantom experiment, two thermocouple experiments, three in vivo pig experiments, and a simulated treatment on a healthy human volunteer were conducted to test the feasibility, safety, and efficacy of magnetic resonance-guided focused ultrasound (MRgFUS) for treating facet joint pain.
The goal of the current study was to develop a novel method for accurate and safe noninvasive facet joint ablation using MRgFUS.
Summary of background data
Facet joints are a common source of chronic back pain. Direct facet joint interventions include medial branch nerve ablation and intra-articular injections, which are widely used, but limited in the short and long term. MRgFUS is a breakthrough technology that enables accurate delivery of high-intensity focused ultrasound energy to create a localized temperature rise for tissue ablation, using MR guidance for treatment planning and real-time feedback.
We validated the feasibility, safety, and efficacy of MRgFUS for facet joint ablation using the ExAblate 2000® System (InSightec Ltd., Tirat Carmel, Israel) and confirmed the system's ability to ablate the edge of the facet joint and all terminal nerves innervating the joint. A phantom experiment, two thermocouple experiments, three in vivo pig experiments, and a simulated treatment on a healthy human volunteer were conducted.
The experiments showed that targeting the facet joint with energies of 150–450 J provides controlled and accurate heating at the facet joint edge without penetration to the vertebral body, spinal canal, or root foramina. Treating with reduced diameter of the acoustic beam is recommended since a narrower beam improves access to the targeted areas.
MRgFUS can safely and effectively target and ablate the facet joint. These results are highly significant, given that this is the first study to demonstrate the potential of MRgFUS to treat facet joint pain.
PMCID: PMC4036610  PMID: 24921048
Chronic back pain; Facet joints; MRgFUS; Pain palliation
2.  Radiofrequency Ablation of Rabbit Liver In Vivo: Effect of the Pringle Maneuver on Pathologic Changes in Liver Surrounding the Ablation Zone 
Korean Journal of Radiology  2004;5(4):240-249.
We wished to evaluate the effect of the Pringle maneuver (occlusion of both the hepatic artery and portal vein) on the pathologic changes in the hepatic vessels, bile ducts and liver parenchyma surrounding the ablation zone in rabbit livers.
Materials and Methods
Radiofrequency (RF) ablation zones were created in the livers of 24 rabbits in vivo by using a 50-W, 480-kHz monopolar RF generator and a 15-gauge expandable electrode with four sharp prongs for 7 mins. The tips of the electrodes were placed in the liver parenchyma near the porta hepatis with the distal 1 cm of their prongs deployed. Radiofrequency ablation was performed in the groups with (n=12 rabbits) and without (n=12 rabbits) the Pringle maneuver. Three animals of each group were sacrificed immediately, three days (the acute phase), seven days (the early subacute phase) and two weeks (the late subacute phase) after RF ablation. The ablation zones were excised and serial pathologic changes in the hepatic vessels, bile ducts and liver parenchyma surrounding the ablation zone were evaluated.
With the Pringle maneuver, portal vein thrombosis was found in three cases (in the immediate [n=2] and acute phase [n=1]), bile duct dilatation adjacent to the ablation zone was found in one case (in the late subacute phase [n=1]), infarction adjacent to the ablation zone was found in three cases (in the early subacute [n=2] and late subacute [n=1] phases). None of the above changes was found in the livers ablated without the Pringle maneuver. On the microscopic findings, centrilobular congestion, sinusoidal congestion, sinusoidal platelet and neutrophilic adhesion, and hepatocyte vacuolar and ballooning changes in liver ablated with Pringle maneuver showed more significant changes than in those livers ablated without the Pringle maneuver (p < 0.05)
Radiofrequency ablation with the Pringle maneuver created more severe pathologic changes in the portal vein, bile ducts and liver parenchyma surrounding the ablation zone compared with RF ablation without the Pringle maneuver. Therefore, we suggest that RF ablation with the Pringle maneuver should be performed with great caution in order to avoid unwanted thermal injury.
PMCID: PMC2698168  PMID: 15637474
Animals; Liver, interventional procedure; Radiofrequency (RF) ablation
3.  Radiofrequency Ablation at Low Frequencies for Targeted Tumor Heating: In-vitro and computational modeling results 
Radiofrequency (RF) ablation uses RF current to heat and kill cancer applied via an electrode inserted under image-guidance. Tumor has about half the electrical resistivity of normal tissue below 20 kHz, but similar resistivity above 500 kHz. We placed normal porcine liver tissue in contact with Agar gel having similar resistivity as tumor within 20-450 kHz. A needle electrode was placed with half of the electrically active tip in each layer. We performed ablation with electric current applied for 12 min at 30W, either at 20 kHz or 450 kHz (n=7 each) while measuring temperature via thermocouples 4 and 8mm from the electrode. Mathematical heat-transfer models were created of an equivalent configuration and temperature profile determined at both frequencies. At 8 mm distance, at 450 kHz, tumor gel phantom and normal tissue obtained similar temperatures (57.5±1.4 vs 58.7±2.5°C); at 20 kHz, tumor phantom obtained significantly higher temperatures than normal tissue (65.6±2.0 vs 57.2±5.6°C, p<0.01). Computer models confirm these results, and show the ablation zone diameter to be larger within the tumor phantom at 20 kHz compared to 450 kHz. Heating at low radio frequencies may thus allow targeted heating of tumor tissue and reduced heating of normal tissue.
PMCID: PMC3108076  PMID: 20934940
radiofrequency ablation; tumor ablation; bioheat transfer
4.  Radiofrequency Cauterization with Biopsy Introducer Needle 
The principal risks of needle biopsy are hemorrhage and implantation of tumor cells in the needle tract. This study compared hemorrhage after liver and kidney biopsy with and without radiofrequency (RF) ablation of the needle tract.
Biopsies of liver and kidney were performed in swine through introducer needles modified to allow RF ablation with the distal 2 cm of the needle. After each biopsy, randomization determined whether the site was to undergo RF ablation during withdrawal of the introducer needle. Temperature was measured with a thermistor stylet near the needle tip, with a target temperature of 70°C–100°C with RF ablation. Blood loss was measured as grams of blood absorbed in gauze at the puncture site for 2 minutes after needle withdrawal. Selected specimens were cut for gross examination.
RF ablation reduced bleeding compared with absence of RF ablation in liver and kidney (P < .01), with mean blood loss reduced 63% and 97%, respectively. Mean amounts of blood loss (±SD) in the liver in the RF and no-RF groups were 2.03 g ± 4.03 (CI, 0.53–3.54 g) and 5.50 g ± 5.58 (CI, 3.33–7.66 g), respectively. Mean amounts of blood loss in the kidney in the RF and no-RF groups were 0.26 g ± 0.32 (CI, −0.01 to 0.53 g) and 8.79 g ± 7.72 (CI, 2.34–15.24 g), respectively. With RF ablation, thermal coagulation of the tissue surrounding the needle tract was observed.
RF ablation of needle biopsy tracts reduced hemorrhage after biopsy in the liver and kidney and may reduce complications of hemorrhage as well as implantation of tumor cells in the tract.
PMCID: PMC4136646  PMID: 14963187
5.  Magnetic resonance imaging (MRI)-guided transurethral ultrasound therapy of the prostate: a preclinical study with radiological and pathological correlation using customised MRI-based moulds 
BJU international  2013;112(4):10.1111/bju.12126.
To characterise the feasibility and safety of a novel transurethral ultrasound (US)-therapy device combined with real-time multi-plane magnetic resonance imaging (MRI)-based temperature monitoring and temperature feedback control, to enable spatiotemporally precise regional ablation of simulated prostate gland lesions in a preclinical canine model.
To correlate ablation volumes measured with intra-procedural cumulative thermal damage estimates, post-procedural MRI, and histopathology.
Materials and methods
Three dogs were treated with three targeted ablations each, using a prototype MRI-guided transurethral US-therapy system (Philips Healthcare, Vantaa, Finland).
MRI provided images for treatment planning, guidance, real-time multi-planar thermometry, as well as post-treatment evaluation of efficacy.
After treatment, specimens underwent histopathological analysis to determine the extent of necrosis and cell viability.
Statistical analyses (Pearson’s correlation, Student’s t-test) were used to evaluate the correlation between ablation volumes measured with intra-procedural cumulative thermal damage estimates, post-procedural MRI, and histopathology.
MRI combined with a transurethral US-therapy device enabled multi-planar temperature monitoring at the target as well as in surrounding tissues, allowing for safe, targeted, and controlled ablations of prescribed lesions.
Ablated volumes measured by cumulative thermal dose positively correlated with volumes determined by histopathological analysis (r2 0.83, P < 0.001).
Post-procedural contrast-enhanced and diffusion-weighted MRI showed a positive correlation with non-viable areas on histopathological analysis (r2 0.89, P < 0.001, and r20.91, P = 0.003, respectively).
Additionally, there was a positive correlation between ablated volumes according to cumulative thermal dose and volumes identified on post-procedural contrast-enhanced MRI (r2 0.77, P < 0.01).
There was no difference in mean ablation volumes assessed with the various analysis methods (P > 0.05, Student’s t-test).
MRI-guided transurethral US therapy enabled safe and targeted ablations of prescribed lesions in a preclinical canine prostate model.
Ablation volumes were reliably predicted by intra- and post-procedural imaging.
Clinical studies are needed to confirm the feasibility, safety, oncological control, and functional outcomes of this therapy in patients in whom focal therapy is indicated.
PMCID: PMC3816743  PMID: 23746198
thermal ablation; therapeutic ultrasound; thermotherapy; minimally invasive therapy; magnetic resonance imaging; image-guided therapy
6.  Percutaneous Radiofrequency Thermal Ablation with Hypertonic Saline Injection: In Vivo Study in a Rabbit Liver Model 
Korean Journal of Radiology  2003;4(1):27-34.
To determine whether hypertonic saline (HS, 36% NaCl) injection prior to or during radiofrequency ablation (RFA) can increase the extent of thermally mediated coagulation in in-vivo rabbit liver tissue, and also to establish the ideal injection time in relation to RFA in order to maximize its effect on the extent of radiofrequency (RF)-induced coagulation.
Materials and Methods
In 26 rabbits, 43 RFA lesions were produced using a 17-gauge internally cooled electrode with a 1-cm active tip under ultrasound (US) guidance. Rabbits were assigned to one of three groups: Group A: RFA alone (n=8); Group B: RFA after the instillation of 1 mL HS (n=8); Group C: RFA after and during the instillation of 0.5 mL HS (n=10). RF energy (30 W) was applied for 3 minutes, and changes occurring in tissue impedance, current, power output, and the temperature of the electrode tip were automatically measured. After RFA, contrast-enhanced spiral CT was performed, and in each group the maximum diameters of the thermal lesions in gross specimens were compared. Technical success and the complications arising were evaluated by CT and on the basis of autopsy findings.
All procedures were technically successful. There were six procedure-related complications (6/26; 23%), including five localized perihepatic hematomas and one thermal injury to the stomach. With instillation of HS in group B rabbits, markedly decreased tissue impedance (73Ω ± 5) and increased current (704 mA ± 41) were noted, compared to RF ablation without saline infusion (116.3Ω ± 13, 308 mA ± 80). With instillation of the solution before RFA (group B), coagulation necrosis was greater (14.9 mm ± 3.8) than in rabbits not injected (group A: 11.5 mm ± 2.4; Group A vs. B: p < .05) and in those injected before and during RFA (group C: 12.5 mm ± 3.1; Group B vs. C: p > .05).
RFA using HS instillation can increase the volume of RFA-induced necrosis of the liver with a single application, thereby simplifying and accelerating the treatment of larger lesions. In addition, HS instillation before RFA more effectively achieves coagulation necrosis than HS instillation before and during RFA.
PMCID: PMC2698055  PMID: 12679631
Experimental study; Liver, interventional procedures; Radiofrequency ablation
7.  Does Artificial Ascites Induce the Heat-Sink Phenomenon during Percutaneous Radiofrequency Ablation of the Hepatic Subcapsular Area?: an in vivo Experimental Study Using a Rabbit Model 
Korean Journal of Radiology  2009;10(1):43-50.
To evaluate the effect of the heat-sink phenomenon induced by artificial ascites on the size of the ablation zone during percutaneous radiofrequency (RF) ablation of the hepatic subcapsular area in an in vivo rabbit model.
Materials and Methods
A total of 21 percutaneous rabbit liver RF ablations were performed with and without artificial ascites (5% dextrose aqueous solution). The rabbits were divided into three groups: a) control group (C, n = 7); b) room temperature ascites group (R, n = 7); and c) warmed ascites group (W, n = 7). The tip of a 1 cm, internally cooled electrode was placed on the subcapsular region of the hepatic dome via ultrasound guidance, and ablation was continued for 6 min. Changes in temperature of the ascites were monitored during the ablation. The size of the ablation zones of the excised livers and immediate complications rates were compared statistically between the groups (Mann-Whitney U test, Kruskal-Wallis test, linear-by-linear association, p = 0.05).
One rabbit from the "W" group expired during the procedure. In all groups, the ascites temperatures approached their respective body temperatures as the ablations continued; however, a significant difference in ascites temperature was found between groups "W" and "R" throughout the procedures (39.2±0.4℃ in group W and 33.4±4.3℃ in group R at 6 min, p = 0.003). No significant difference was found between the size of the ablation zones (782.4±237.3 mL in group C, 1,172.0±468.9 mL in group R, and 1,030.6±665.1 mL in group W, p = 0.170) for the excised liver specimens. Diaphragmatic injury was identified in three of seven cases (42.9%) upon visual inspection of group "C" rabbits (p = 0.030).
Artificial ascites are not likely to cause a significant heat-sink phenomenon in the percutaneous RF ablation of the hepatic subcapsular region.
PMCID: PMC2647166  PMID: 19182502
Radiofrequency (RF) ablation; Liver, interventional procedure; Ascites; Carcinoma, Hepatocellular; Neoplasm, Metastasis
8.  Hepatic Radiofrequency Ablation Using Multiple Probes: Ex Vivo and In Vivo Comparative Studies of Monopolar versus Multipolar Modes 
Korean Journal of Radiology  2006;7(2):106-117.
We wanted to compare the efficiency of multipolar radiofrequency ablation (RFA) using three perfused-cooled electrodes with multiple overlapping and simultaneous monopolar techniques for creating an ablation zone in ex vivo bovine livers and in in vivo porcine livers.
Materials and Methods
In the ex vivo experiments, we used a 200 W generator (Valleylab, CC-3 model) and three perfused-cooled electrodes or internally cooled electrodes to create 30 coagulation zones by performing consecutive monopolar RFA (group A, n = 10), simultaneous monopolar RFA (group B, n = 10) or multipolar RFA (group C, n = 10) in explanted bovine livers. In the consecutive mode, three ablation spheres were created by sequentially applying 150 watts radiofrequency (RF) energy to the internally cooled electrodes for 12 minutes each for a total of 36 minutes. In the simultaneous monopolar and multipolar modes, RF energy was concurrently applied to the three perfused-cooled electrodes for 20 minutes at 150 watt with instillation of 6% hypertonic saline at 2 mL/min. During RFA, we measured the temperatures of the treated area at its center. The changes in impedance, the current and liver temperature during RFA, as well as the dimensions of the thermal ablation zones, were compared among the three groups. In the in vivo experiments, three coagulations were created by performing multipolar RFA in a pig via laparotomy with using same parameter as the ex vivo study.
In the ex vivo experiments, the impedance was gradually decreased during the RFA in groups B and C, but in group A, the impedance was increased during RFA and this induced activation by the pulsed RF technique. In groups A, B and C, the mean final-temperature values were 80±10℃, 69±18℃and 79±12℃, respectively (p < 0.05). The multipolar mode created a larger volume of ablation than did the other modes: 37.6±4.0 cm3 (group A); 44.9±12.7 cm3 (group B); and 78.9±6.9 cm3 (group C) (p < 0.05). In the in vivo experiment, the pig well tolerated the RFA procedure and no major complications occurred during the 4 days of the follow-up period. The mean volume of coagulations produced by multipolar RFA in the pig liver was 60.5±17.9 cm3.
For the multiple probe RFA, the multipolar mode with hypertonic saline instillation was more efficient in generating larger areas of thermal ablation than either the consecutive or simultaneous monopolar modes.
PMCID: PMC2667583  PMID: 16799271
Liver, interventional procedures; Radiofrequency ablation; Experimental study
9.  Ultrasound-based Relative Elastic Modulus Imaging for Visualizing Thermal Ablation Zones in a Porcine Model 
Physics in medicine and biology  2010;55(8):2281-2306.
The feasibility of using ultrasound-based elastic modulus imaging to visualize thermal ablation zones in an in vivo porcine model is reported in this article. Elastic modulus images of soft tissues are estimated as an inverse optimization problem. Ultrasonically-measured displacement data are utilized as inputs to determine an elastic modulus distribution that provides the best match to this displacement field.
A total of 14 in vivo thermal ablation zones were investigated in this study. To determine the accuracy of delineation of each thermal ablation zone using elastic modulus imaging, the dimensions (lengths of long and short axes) and the are of each thermal ablation zone obtained from an elastic modulus image was compared to the corresponding gross pathology photograph of the same ablation zone. Comparison of elastic modulus imaging measurements and gross pathology measurements showed high correlation with respect to the area of thermal ablation zones (Pearson coefficient = 0.950 and p<0.0001). The radiological-pathological correlation was slightly lower (correlation = 0.853, p<0.0001) for strain imaging among these 14 in vivo ablation zones. We also found that, on average, elastic modulus imaging can more accurately depict thermal ablation zones, when compared to strain imaging (14.7% versus 22.3% absolute percent error in area measurements, respectively). Furthermore, elastic modulus imaging also provide higher (more than a factor of two) contrast-to-noise ratios for evaluating these thermal ablation zones than those on corresponding strain images, thereby reducing inter-observer variability. Our preliminary results suggest that elastic modulus imaging might potentially enhance the ability to visualize thermal ablation zones, thereby improving assessment of ablative therapies.
PMCID: PMC3068604  PMID: 20354279
elasticity imaging; modulus reconstruction; inverse problems; elastography; optimization; elastic modulus imaging; ablation
10.  MR Imaging-Histopathologic Correlation of Radiofrequency Thermal Ablation Lesion in a Rabbit Liver Model: Observation during Acute and Chronic Stages 
Korean Journal of Radiology  2001;2(3):151-158.
To determine the ability of MR imaging to detect the pathological changes occurring in radiofrequency (RF) thermal lesions and to assess its accuracy in revealing the extent of tissue necrosis.
Materials and Methods
Using an RF electrode, thermal lesions were created in the livers of 18 rabbits. The procedure involved three phases. In the acute phase, six animals were killed the day after performing thermal ablation with RF energy, and two on day 3. In the subacute and chronic phases, eight rabbits underwent percutaneous hepatic RF ablation. After performing MR imaging, two animals were sacrificed at 1, 2, 4, and 7 weeks after the procedure, and MR-pathologic correlation was performed.
In the acute phase, the thermal ablation lesions appeared at gross examination as well-circumscribed, necrotic areas, representing early change in the coagulative necrosis seen at microscopic examination. They were hypointense on T2-weighted images, and hyperintense on T1-weighted images. Gadolinium-enhanced MR imaging showed that a thin hyperemic rim surrounded the central coagulative necrosis. In the subacute phase, ablated lesions also showed extensive coagulative necrosis and marked inflammation at microscopic examination. Beyond two weeks, the lesions showed gradual resorption of the necrotic area, with a peripheral fibrovascular rim. The size of lesions measured by MR imaging correlated well with the findings at gross pathologic examination.
MR imaging effectively demonstrates the histopathological tissue change occurring after thermal ablation, and accurately determines the extent of the target area.
PMCID: PMC2718113  PMID: 11752986
Liver, MR; Liver, interventional procedure; Interventional procedures, experimental
11.  Thermal Ablation for the Treatment of Abdominal Tumors 
Percutaneous thermal ablation is an emerging treatment option for many tumors of the abdomen not amenable to conventional treatments. During a thermal ablation procedure, a thin applicator is guided into the target tumor under imaging guidance. Energy is then applied to the tissue until temperatures rise to cytotoxic levels (50-60 °C). Various energy sources are available to heat biological tissues, including radiofrequency (RF) electrical current, microwaves, laser light and ultrasonic waves. Of these, RF and microwave ablation are most commonly used worldwide.
During RF ablation, alternating electrical current (~500 kHz) produces resistive heating around the interstitial electrode. Skin surface electrodes (ground pads) are used to complete the electrical circuit. RF ablation has been in use for nearly 20 years, with good results for local tumor control, extended survival and low complication rates1,2. Recent studies suggest RF ablation may be a first-line treatment option for small hepatocellular carcinoma and renal-cell carcinoma3-5. However, RF heating is hampered by local blood flow and high electrical impedance tissues (eg, lung, bone, desiccated or charred tissue)6,7. Microwaves may alleviate some of these problems by producing faster, volumetric heating8-10. To create larger or conformal ablations, multiple microwave antennas can be used simultaneously while RF electrodes require sequential operation, which limits their efficiency. Early experiences with microwave systems suggest efficacy and safety similar to, or better than RF devices11-13.
Alternatively, cryoablation freezes the target tissues to lethal levels (-20 to -40 °C). Percutaneous cryoablation has been shown to be effective against RCC and many metastatic tumors, particularly colorectal cancer, in the liver14-16. Cryoablation may also be associated with less post-procedure pain and faster recovery for some indications17. Cryoablation is often contraindicated for primary liver cancer due to underlying coagulopathy and associated bleeding risks frequently seen in cirrhotic patients. In addition, sudden release of tumor cellular contents when the frozen tissue thaws can lead to a potentially serious condition known as cryoshock 16.
Thermal tumor ablation can be performed at open surgery, laparoscopy or using a percutaneous approach. When performed percutaneously, the ablation procedure relies on imaging for diagnosis, planning, applicator guidance, treatment monitoring and follow-up. Ultrasound is the most popular modality for guidance and treatment monitoring worldwide, but computed tomography (CT) and magnetic resonance imaging (MRI) are commonly used as well. Contrast-enhanced CT or MRI are typically employed for diagnosis and follow-up imaging.
PMCID: PMC3197316  PMID: 21445029
12.  Endoscopically Guided Foraminal and Dorsal Rhizotomy for Chronic Axial Back Pain Based on Cadaver and Endoscopically Visualized Anatomic Study 
Conventional fluoroscopically guided continuous radiofrequency (CRF) and pulsed Radiofrequency (PRF) lesioning of the medial branch, dorsal ramus, a standard technique to treat facet pain, is compared to an endoscopic visually guided technique. The endoscopic technique (Figure 1) is designed to ablate a larger area of the transverse process where the medial branch crosses to innervate the facet. Endoscopically guided visualization provides confirmation of nerve ablation or transection in the most common location of the branches of the dorsal ramus innervating the facet joint.
Surgical setup for ablation of the medial, intermediate and lateral branches of the dorsal ramus.
Materials and Method
A retrospective non randomized study of 50 initial patients assessed the efficacy of endoscopic rhizotomy. Patients with lumbar spondylosis and facet arthrosis who had at least 50% pain relief by medial branch blocks met the inclusion criteria for the visualized, surgically directed endoscopic technique. A specially designed cannula and endoscope (Richard Wolf, GmBh) (Figure 2) was developed specifically for this purpose. After completion of the initial 50 patient pilot study in 2005, utilizing a low-temperature, ultra-high frequency (1.7-4.0 MHz) bipolar energy radiofrequency source (Elliquence Int, Hewlett, NY) that demonstrated efficacy, 400 subsequent patients were added to this retrospective study by May 2013. The surgical technique refinement was guided by cadaveric variations observed from additional cadaver dissections (Figure 3) and endoscopic visualization of foraminal nerves that revealed variable locations of the dorsal ramus, including the medial branch. The anatomic variations supported a need for visualized rhizotomy. The inclusion criteria also involved increasing the percentage of back pain relief from medial branch blocks to a base of 75% estimated improvement in order to overcome the variable subjectiveness of a 50% improvement threshold that served to disappoint a small percentage of patients who overestimated the reported 50% improvement in hopes that they would qualify for the endoscopic guided procedure.
Richard Wolf YESS Rhizotomy Set. The cannulas, endoscope, bitip and surgical bipolar RF probes by Elliquence are configured ergonomically to provide excellent focal length imaging to keep image in focus with the endoscope scope resting on cannula. The bitip probe cuts tissue, and the RF probe thermally ablates tissue efficiently.
Cadaver dissection of the dorsal ramus and its branches out- lining the areas where branches of the dorsal ramus may be visualized and ablated before it reaches the facet joint.
At one year follow-up in the initial study design, VAS improved 6.2-2.5, and ODI 48-28. All patients had VAS improvement equal or greater than injection. The results remained constant with additional surgical cases that continued to improve when technique and visualized rhizotomy allowed for greater surgical exploration and ablation of the targeted zone where more than just the medial branch could be ablated. Approximately 10 percent of the patients returned at one and two year follow-up with mild recurrence of their axial back pain, but none to the original level of pain. Additional rhizotomy of the upper lumbar facets provided additional relief in selected patients.
Conclusions / level of evidence 3
The cadaver studies demonstrated considerable variability in the location of the medial and lateral branches of the dorsal ramus. Variability was most common cephalad to L3-4. The dorsal ramus and its nerve branches can also be visualized in the foramen ventral to the intertransverse ligament. Neuromas and entrapment of the dorsal ramus has been identified endoscopically, and confirmed by H and E slides (Figure 4). In the upper lumbar spine, we were not able to find the medial branch to the facets consistently at same location. The nerve to the facet joint did not always cross the transverse process. Some branches enter the facet joint before crossing the transverse process adjacent to the tip of the SAP (Figure 5). The nerve can be mistaken for a furcal nerve or foraminal ligament. Nerve Ablation at above L3-4 levels may require lesioning of the dorsal ramus or targeting the nerve innervation on the facet wall, pedicle or capsule.
This H and E slide of the biopsied specimen is consistent with a peripheral nerve fiber.
This foraminal view of a branch of the dorsal ramus is in the foramen at the level of the SAP. The nerve runs along the ventral lateral aspect of the superior facet to the tip, and can also run in the vicinity of the foraminal ligament. Endoscopic rasps, trephines, kerrisons, and burrs can be used for foraminoplasty. The nerve should be preserved, if possible, but transection of a branch of the dorsal ramus contributes to axial back pain relief. Branches of the dorsal ramus originates in the foramen before exiting to traverse the transverse process. These nerves are difficult to differentiate from furcal nerves arising from the spinal nerves. Palpating the nerve using local anesthesia can sometimes demonstrate a pain response, but not always, depending on the level of sedation and anesthetic use.
Clinical Relevance
Endoscopically guided facet rhizotomy provides more consistent ablation of the medial and lateral branches of the lumbar dorsal ramus compared to radiographically guided pulsed radiofrequency. The variations in the location of facet innervation can explain the variability of clinical results in fluoroscopically guided RF lesioning. This observation dictates a need for visually guided MIS procedure for best results.
PMCID: PMC4325504
Endoscopic; rhizotomy; visualization
13.  First In Vivo Use of a Capacitive Micromachined Ultrasound Transducer Array–Based Imaging and Ablation Catheter 
The primary objective was to test in vivo for the first time the general operation of a new multifunctional intracardiac echocardiography (ICE) catheter constructed with a microlinear capacitive micromachined ultrasound transducer (ML-CMUT) imaging array. Secondarily, we examined the compatibility of this catheter with electroanatomic mapping (EAM) guidance and also as a radiofrequency ablation (RFA) catheter. Preliminary thermal strain imaging (TSI)-derived temperature data were obtained from within the endocardium simultaneously during RFA to show the feasibility of direct ablation guidance procedures.
The new 9F forward-looking ICE catheter was constructed with 3 complementary technologies: a CMUT imaging array with a custom electronic array buffer, catheter surface electrodes for EAM guidance, and a special ablation tip, that permits simultaneous TSI and RFA. In vivo imaging studies of 5 anesthetized porcine models with 5 CMUT catheters were performed.
The ML-CMUT ICE catheter provided high-resolution real-time wideband 2-dimensional (2D) images at greater than 8 MHz and is capable of both RFA and EAM guidance. Although the 24-element array aperture dimension is only 1.5 mm, the imaging depth of penetration is greater than 30 mm. The specially designed ultrasound-compatible metalized plastic tip allowed simultaneous imaging during ablation and direct acquisition of TSI data for tissue ablation temperatures. Postprocessing analysis showed a first-order correlation between TSI and temperature, permitting early development temperature-time relationships at specific myocardial ablation sites.
Multifunctional forward-looking ML-CMUT ICE catheters, with simultaneous intracardiac guidance, ultrasound imaging, and RFA, may offer a new means to improve interventional ablation procedures.
PMCID: PMC3420825  PMID: 22298868
ablation; capacitive micromachined ultrasound transducer; electroanatomic mapping; electrophysiology; intracardiac echocardiography; intracardiac imaging; microelectromechanical system; thermal strain
14.  High-Powered Gas-Cooled Microwave Ablation: Shaft Cooling Creates an Effective Stick Function Without Altering the Ablation Zone 
Ajr. American Journal of Roentgenology  2012;198(3):W260-W265.
The purpose of our study was to validate the ability of a new gas-cooled microwave device to secure antennas into tissue before ablation via shaft cooling and to verify that such cooling does not compromise the intended ablation.
The force required to extract several types of applicators from ex vivo bovine liver before and after ablation was measured. Six groups were compared: cooled needle and multitined radiofrequency electrodes, secured and unsecured cryoprobes, and gas-cooled microwave antennas (n = 6 each). Ablations were next created in in vivo porcine livers for 2 and 10 minutes (n = 6 each) using the gas-cooled microwave system at 140 W. Extraction force was again measured before and after ablation and compared between groups using analysis of variance with post hoc Student t tests. Histologic analysis of the ablation zone was performed to evaluate cellular necrosis along the antenna shaft.
Ex vivo, the secured cryoprobe and microwave antenna required significantly more force to remove than unsecured radiofrequency, cryoprobe, and microwave applicators (p < 0.05, all comparisons). The multitined radiofrequency electrode and cooled radiofrequency electrode required significantly more force to remove after ablation than before ablation (p = 0.006 and 0.02, respectively). In vivo, the secured antenna required significantly more force to remove before ablation than after ablation at both 2 (p < 0.0001) and 10 minutes (p < 0.0001). There was no histologic evidence of cell preservation along the antenna shaft.
The gas cooling used in this microwave device can effectively secure antennas into tissue without altering ablation shape or reducing the intended thermal damage.
PMCID: PMC3298039  PMID: 22358023
cryogenic cooling; microwave ablation; thermal ablation
15.  CT and MR Imaging Appearance of Renal Neoplasms after Radiofrequency Ablation and Cryoablation 
Thermal ablation procedures including radiofrequency ablation and cryoablation have been increasingly utilized for treatment for small renal cell carcinoma. Currently, CT and MR imaging are usually used to assess residual or recurrent disease after thermal ablation of renal tumor. After thermal ablation, the zone of ablation is usually seen as an area of hypoattenuation on computed tomography (CT) and is generally hypointense at T2-weighted magnetic resonance (MR) imaging and iso- to hyperintense at T1-weighted imaging relative to renal parenchyma. The ablation zone frequently involutes over time. Residual tumor after thermal ablation is most common at the margin of the ablation zone and often seen as nodular or crescent-shaped areas of contrast enhancement. Accurate assessment of ablated tumors at postprocedural imaging is essential for evaluating the adequacy of treatment and guiding further management. Complications are uncommon and usually minor, but should be detected on post-procedural imaging studies.
PMCID: PMC3047393  PMID: 19358438
16.  Monitoring Radiofrequency Ablation Using Real-Time Ultrasound Nakagami Imaging Combined with Frequency and Temporal Compounding Techniques 
PLoS ONE  2015;10(2):e0118030.
Gas bubbles induced during the radiofrequency ablation (RFA) of tissues can affect the detection of ablation zones (necrosis zone or thermal lesion) during ultrasound elastography. To resolve this problem, our previous study proposed ultrasound Nakagami imaging for detecting thermal-induced bubble formation to evaluate ablation zones. To prepare for future applications, this study (i) created a novel algorithmic scheme based on the frequency and temporal compounding of Nakagami imaging for enhanced ablation zone visualization, (ii) integrated the proposed algorithm into a clinical scanner to develop a real-time Nakagami imaging system for monitoring RFA, and (iii) investigated the applicability of Nakagami imaging to various types of tissues. The performance of the real-time Nakagami imaging system in visualizing RFA-induced ablation zones was validated by measuring porcine liver (n = 18) and muscle tissues (n = 6). The experimental results showed that the proposed algorithm can operate on a standard clinical ultrasound scanner to monitor RFA in real time. The Nakagami imaging system effectively monitors RFA-induced ablation zones in liver tissues. However, because tissue properties differ, the system cannot visualize ablation zones in muscle fibers. In the future, real-time Nakagami imaging should be focused on the RFA of the liver and is suggested as an alternative monitoring tool when advanced elastography is unavailable or substantial bubbles exist in the ablation zone.
PMCID: PMC4320093  PMID: 25658424
17.  A comparison of direct heating during radiofrequency and microwave ablation in ex vivo liver 
To determine the magnitude and spatial distribution of temperature elevations when using 480 kHz RF and 2.45 GHz microwave energy in ex vivo liver models.
Materials and Methods
A total of sixty heating cycles (20 s at 90 W) were performed in normal, RF ablated and microwave ablated liver tissues (n=10 RF and n=10 microwave in each tissue type). Heating cycles were performed using a 480 kHz generator and 3 cm cooled-tip electrode (RF) or a 2.45 GHz generator and 14-gauge monopole (microwave) and designed to isolate direct heating from each energy type. Tissue temperatures were measured using fiberoptic thermosensors 5, 10 and 15 mm radially from the ablation applicator at the depth of maximal heating. Power delivered, sensor location, heating rates and maximal temperatures were compared using mixed effects regression models.
No significant differences were noted in mean power delivered or thermosensor locations between RF and microwave heating groups (P>0.05). Microwaves produced significantly more rapid heating than RF at 5, 10 and 15mm in normal tissue (3.0 vs. 0.73, 0.85 vs. 0.21 and 0.17 vs. 0.09 °C/s; P<.05); and at 5 and 10mm in ablated tissues (2.3 ± 1.4 vs. 0.7 ± 0.3, 0.5 ± 0.3 vs. 0.2 ± 0.0 C/s, P<.05). The radial depth of heating was approximately 5mm greater for microwaves than RF.
Direct heating obtained with 2.45 GHz microwave energy using a single needle-like applicator is faster and covers a larger volume of tissue than 480 kHz RF energy. Keywords: microwave ablation, direct heating, thermal ablation
PMCID: PMC3437379  PMID: 22572764
microwave ablation; direct heating; thermal ablation
18.  Acoustic emissions during 3.1 MHz ultrasound bulk ablation in vitro 
Ultrasound in medicine & biology  2008;34(9):10.1016/j.ultrasmedbio.2008.02.007.
Acoustic emissions associated with cavitation and other bubble activity have previously been observed during ultrasound ablation experiments. Since detectable bubble activity may be related to temperature, tissue state, and sonication characteristics, these acoustic emissions are potentially useful for monitoring and control of ultrasound ablation. To investigate these relationships, ultrasound ablation experiments were performed with simultaneous measurements of acoustic emissions, tissue echogenicity, and tissue temperature, on fresh bovine liver. Ex vivo tissue was exposed to 0.9–3.3 s bursts of unfocused, continuous-wave, 3.10 MHz ultrasound from a miniaturized 32-element array, which performed B-scan imaging with the same piezoelectric elements during brief quiescent periods. Exposures employed pressure amplitudes of 0.8–1.4 MPa for exposure times of 6–20 min, sufficient to achieve significant thermal coagulation in all cases. Acoustic emissions received by a 1 MHz, unfocused passive cavitation detector, beamformed A-line signals acquired by the array, and tissue temperature detected by a needle thermocouple were sampled 0.3–1.1 times per second. Tissue echogenicity was quantified by the backscattered echo energy from a fixed region of interest within the treated zone. Acoustic emission levels were quantified from the spectra of signals measured by the passive cavitation detector, including subharmonic signal components at 1.55 MHz, broadband signal components within the band 0.3–1.1 MHz, and low-frequency components within the band 10–30 kHz. Tissue ablation rates, defined as the thermally ablated volumes per unit time, were assessed by quantitative analysis of digitally imaged, macroscopic tissue sections. Correlation analysis was performed among the averaged and time-dependent acoustic emissions in each band considered, B-mode tissue echogenicity, tissue temperature, and ablation rate. Ablation rate correlated significantly with broadband and low-frequency emissions, but was uncorrelated with subharmonic emissions. Subharmonic emissions were found to depend strongly on temperature in a nonlinear manner, with significant emissions occurring within different temperature ranges for each sonication amplitude. These results suggest potential roles for passive detection of acoustic emissions in guidance and control of bulk ultrasound ablation treatments.
PMCID: PMC3845361  PMID: 18420337
ultrasound ablation; therapy; acoustic emissions; passive cavitation detection
19.  Moving-Shot versus Fixed Electrode Techniques for Radiofrequency Ablation: Comparison in an Ex-Vivo Bovine Liver Tissue Model 
Korean Journal of Radiology  2014;15(6):836-843.
To compare the ablation characteristics of the moving-shot technique (MST) and the fixed electrode technique (FET) for radiofrequency (RF) ablation in an ex-vivo bovine liver tissue model.
Materials and Methods
We performed RF ablation using FET in 110 bovine liver blocks using 11 different ablation times ranging from 5 seconds to 5 minutes (10 blocks per each time duration). Ten bovine liver blocks at each ablation time of 1- or 2-minute, were ablated with MST, which treated conceptual ablation units by moving the electrode tip. We evaluated the ablation volume obtained with FET across ablation time lengths. The results of FET and MST performed with the same ablation time lengths, i.e., 1- and 2-minute ablation time were also compared.
The ablation volume achieved with FET gradually increased with increasing ablation time; however, the pair-wise statistical comparison between 2 neighboring ablation time lengths was not significant after 30 seconds. MST with either 1- or 2-minute ablation time achieved larger ablation volumes (1.1 ± 0.2 mL vs. 2.7 ± 0.3 mL, p < 0.001; and 1.4 ± 0.2 mL vs. 5.6 ± 0.4 mL, p < 0.001, respectively), longer true RF times (46.7 ± 4.6 seconds vs. 60 seconds, p < 0.001; and 64.8 ± 4.6 seconds vs. 120 seconds, p < 0.001, respectively), fewer numbers of RF cut-offs (1.6 ± 0.5 vs. 0, p < 0.001; and 5.5 ± 0.5 vs. 0, p < 0.001, respectively), and greater energy deposition (2050.16 ± 209.2 J vs. 2677.76 ± 83.68 J, p < 0.001; and 2970.64 ± 376.56 J vs. 5564.72 ± 5439.2 J, p < 0.001, respectively), than FET.
The MST can achieve a larger ablation volume by preventing RF cut-off, compared with the FET in an ex-vivo bovine liver model.
PMCID: PMC4248641  PMID: 25469097
Radiofrequency ablation; Moving shot technique; Fixed electrode technique; Thyroid nodule; Intervention
20.  A Comparative Experimental Study of the In-vitro Efficiency of Hypertonic Saline-Enhanced Hepatic Bipolar and Monopolar Radiofrequency Ablation 
Korean Journal of Radiology  2003;4(3):163-169.
To compare the in-vitro efficiency of a hypertonic saline (HS)-enhanced bipolar radiofrequency (RF) system with monopolar RF applications by assessing the temperature profile and dimensions of RF-created coagulation necrosis in bovine liver.
Materials and Methods
A total of 27 ablations were performed in explanted bovine livers. After placement of two 16-gauge open-perfused electrodes at an interelectrode distance of 3 cm, 5% HS was instilled into tissue at a rate of 1 mL/min through the electrode. Seventeen thermal ablation zones were created in the monopolar mode (groups A, B), and ten more were created using the two open-perfused electrodes in the bipolar mode (group C). RF was applied to each electrode for 5 mins (for a total of 10 mins, group A) or 10 mins (for a total of 20 mins, group B) at 50W in the sequential monopolar mode, or to both electrodes for 10 min in the bipolar mode (group C). During RF instillation, we measured tissue temperature at the midpoint between the two electrodes. The dimensions of the thermal ablation zones and changes in impedance and wattage during RFA were compared between the groups.
With open-perfusion electrodes, the mean accumulated energy output value was lower in the bipolar mode (group C: 26675 ± 3047 Watt·s) than in the monopolar mode (group A: 28778 ± 1300 Watt·s) but the difference was not statistically significant (p > 0.05). In the bipolar mode, there were impedance rises of more than 700 Ω during RF energy application, but in the monopolar modes, impedance did not changed markedly. In the bipolar mode, however, the temperature at the mid-point between the two probes was higher (85℃) than in the monopolar modes (65℃, 80℃ for group A, B, respectively) (p < 0.05). In addition, in HS-enhanced bipolar RFA (group C), the shortest diameter at the midpoint between the two electrodes was greater than in either of the monopolar modes: 5.4 ± 5.6 mm (group A); 28.8 ± 8.2 mm (group B); 31.2 ± 7.6 mm (group C) (p < 0.05)
Using an open perfusion system, HS-enhanced bipolar RFA more efficiently created larger areas of thermal ablation and higher tissue temperatures than monopolar RFA.
PMCID: PMC2698083  PMID: 14530645
Liver, interventional procedures; Radiofrequency ablation; Experimental study
21.  An in-vitro animal experiment on metal implants’ thermal effect on radiofrequency ablation 
To explore metal implants’ thermal effect on radiofrequency ablation (RFA) and ascertain distance-thermal relationship between the metal implants and radiofrequency (RF) electrode.
Metal implants models were established in seven in-vitro porcine livers using silver clips or 125I seeds. RFA were conducted centering the RF electrode axis1 cm away from them, with one side containing a metal implants model the test group and the other side the control group. The thermometric needles were used to measure multi-point temperatures in order to compare the time-distance-temperature difference between the two groups. The gross scopes of the ablation of the two groups were measured and the tissues were analyzed for microscopic histology.
At the ablation times of 8, 12, and 15 min, the average multi-point temperatures of the test group and the control group were 48.2±18.07°C, 51.5±19.57°C, 54.6±19.75°C, and 48.6±17.69°C, 52.2±19.73°C, 54.9±19.24°C, respectively, and the differences were not statistically significant (n=126, P>0.05). At the ablation times of 12 and 15 min, the ablation scopes of the test group and the control group were (horizontal/longitudinal diameter) 1.55/3.48 cm, 1.89/3.72 cm, and 1.56/3.48 cm, 1.89/3.72 cm, respectively, and the differences were not statistically significant (n=14, P>0.05). The two groups had the same manifestations in microscopy.
Metal implants do not cause significant thermal effect on RFA.
PMCID: PMC3704274  PMID: 23799942
Implant; Metal; Radiofrequency ablation; Thermal effect; Animal experiment; In vitro
22.  Ultrasound-guided microwave ablation for abdominal wall metastatic tumors: A preliminary study 
AIM: To evaluate the feasibility, safety and efficacy of ultrasound-guided microwave (MW) ablation for abdominal wall metastatic tumors.
METHODS: From August 2007 to December 2010, a total of 11 patients with 23 abdominal wall nodules (diameter 2.59 cm ± 1.11 cm, range 1.3 cm to 5.0 cm) were treated with MW ablation. One antenna was inserted into the center of tumors less than 1.7 cm, and multiple antennae were inserted simultaneously into tumors 1.7 cm or larger. A 21 gauge thermocouple was inserted near important organs which required protection (such as bowel or gallbladder) for real-time temperature monitoring during MW ablation. Treatment outcome was observed by contrast-enhanced ultrasound and magnetic resonance imaging (MRI) [or computed tomography (CT)] during follow-up.
RESULTS: MW ablation was well tolerated by all patients. Six patients with 11 nodules had 1 thermocouple inserted near important organs for real-time temperature monitoring and the maximum temperature was 56 °C. Major complications included mild pain (54.5%), post-ablation fever (100%) and abdominal wall edema (25%). All 23 tumors (100%) in this group were completely ablated, and no residual tumor or local recurrence was observed at a median follow-up of 13 mo (range 1 to 32 mo). The ablation zone was well defined on contrast-enhanced imaging (contrast-enhanced CT, MRI and/or contrast-enhanced ultrasound) and gradually shrank with time.
CONCLUSION: Ultrasound-guided MW ablation may be a feasible, safe and effective treatment for abdominal wall metastatic tumors in selected patients.
PMCID: PMC3380330  PMID: 22736926
Abdominal wall; Microwave ablation; Neoplasm metastasis; Thermal ablation therapy; Ultrasonography
23.  An experimental model to investigate the targeting accuracy of MR-guided focused ultrasound ablation in liver 
Magnetic Resonance-guided High Intensity Focused Ultrasound (MRgHIFU) is a hybrid technology that aims to offer non-invasive thermal ablation of targeted tumors or other pathological tissues. Acoustic aberrations and non-linear wave propagating effects may shift the focal point significantly away from the prescribed (or, theoretical) position. It is therefore mandatory to evaluate the spatial accuracy of ablation for a given HIFU protocol and/or device. We describe here a method for producing a user-defined ballistic target as an absolute reference marker for MRgHIFU ablations.
The investigated method is based on trapping a mixture of MR contrast agent and histology stain using radiofrequency (RF) ablation causing cell death and coagulation. A dedicated RF-electrode was used for the marker fixation as follows: a RF coagulation (4 W, 15 seconds) and injection of the mixture followed by a second RF coagulation. As a result, the contrast agent/stain is encapsulated in the intercellular space. Ultrasonography imaging was performed during the procedure, while high resolution T1w 3D VIBE MR acquisition was used right after to identify the position of the ballistic marker and hence the target tissue. For some cases, after the marker fixation procedure, HIFU volumetric ablations were produced by a phased-array HIFU platform. First ex vivo experiments were followed by in vivo investigation on four rabbits in thigh muscle and six pigs in liver, with follow-up at Day 7.
At the end of the procedure, no ultrasound indication of the marker’s presence could be observed, while it was clearly visible under MR and could be conveniently used to prescribe the HIFU ablation, centered on the so-created target. The marker was identified at Day 7 after treatment, immediately after animal sacrifice, after 3 weeks of post-mortem formalin fixation and during histology analysis. Its size ranged between 2.5 and 4 mm.
Experimental validation of this new ballistic marker method was performed for liver MRgHIFU ablation, free of any side effects (e.g. no edema around the marker, no infection, no bleeding). The study suggests that the absolute reference marker had ultrasound conspicuity below the detection threshold, was irreversible, MR-compatible and MR-detectable, while also being a well-established histology staining technique.
PMCID: PMC3901025  PMID: 24433332
MR guided HIFU; Ballistic marker; Tracer encapsulation; Targeting; Pre-clinical quality assurance
24.  Radio Frequency Ablation for Primary Liver Cancer 
Executive Summary
The Medical Advisory Secretariat undertook a review of the evidence on the safety, clinical effectiveness, and cost-effectiveness of radio frequency ablation (RFA) compared with other treatments for unresectable hepatocellular carcinoma (HCC) in Ontario.
Liver cancer is the fifth most common type of cancer globally, although it is most prevalent in Asia and Africa. The incidence of liver cancer has been increasing in the Western world, primarily because of an increased prevalence of hepatitis B and C. Data from Cancer Care Ontario from 1998 to 2002 suggest that the age-adjusted incidence of liver cancer in men rose slightly from 4.5 cases to 5.4 cases per 100,000 men. For women, the rates declined slightly, from 1.8 cases to 1.4 cases per 100,000 women during the same period. Most people who present with symptoms of liver cancer have a progressive form of the disease. The rates of survival in untreated patients in the early stage of the disease range from 50% to 82% at 1 year and 26% to 32% at 2 years. Patients with more advanced stages have survival rates ranging from 0% to 36% at 3 years. Surgical resection and transplantation are the procedures that have the best prognoses; however, only 15% to 20% of patients presenting with liver cancer are eligible for surgery. Resection is associated with a 50% survival rate at 5 years.
The Technology: Radio Frequency Ablation
RFA is a relatively new technique for the treatment of small liver cancers that cannot be treated with surgery. This technique applies alternating high-frequency electrical currents to the cancerous tissue. The intense heat leads to thermal coagulation that can kill the tumour. RFA is done under general or local anesthesia and can be done percutaneously (through the skin with a small needle), laparoscopically (microinvasively, using a small video camera), or intraoperatively. Percutaneous RFA is usually a day procedure.
The leading international organizations for health technology assessments, including the Canadian Coordinating Office for Health Technology Assessment (CCOHTA) and the International Network of Agencies for Health Technology Assessment (INAHTA), were scanned for previous systematic reviews on RFA. The Cochrane Library Database was also scanned. The most recent systematic review examined the literature up to October 2003. Five previous health technology assessments were found.
To update the international systematic reviews, the Medical Advisory Secretariat systematically reviewed the literature from January 1, 2003 to the third week of April 2004. Peer-reviewed literature from EMBASE, MEDLINE (including in-process and other nonindexed citations) and the Cochrane Library Database were searched for the following search terms:
Catheter ablation
Radiofrequency or radio-frequency or radio frequency or RFA or RFTA
Liver neoplasms or liver cancer or hepatocellular or hepatocellular or hepatic
The inclusion criteria were as follows:
Population: patients with primary hepatocellular carcinoma
Procedure: RFA used as the only treatment (not as an adjunct)
Language: publication in English
Published health technology assessments, guidelines, and peer-reviewed literature (abstracts and in-progress manuscripts)
Outcomes: therapeutic response (% complete ablation), mortality, survival, and tumour recurrence
Grey literature, where relevant, was also reviewed.
Summary of Findings
The Medical Advisory Secretariat included 5 previous health technology assessments from 2002 to 2004 and 9 peer-reviewed studies from January 2003 to April 2004 in its review. The health technology assessments suggested that RFA is as safe and effective for treating up to 3 or 4 small (< 4 to 5 cm), unresectable liver tumours in the short term (2 years). One small randomized controlled trial (RCT) that compared RFA with percutaneous ethanol injection (PEI), another ablative technique, suggested that RFA is at least as safe and effective for small unresectable primary liver tumours compared to PEI. However, the patient populations and comparison technologies in the peer-reviewed literature and the previous health technology assessments were heterogeneous; therefore, meta-analyses could not be performed.
RFA has also been used to treat colorectal and neuroendocrine liver metastases and kidney, lung, breast, and bone cancer. Although this report did not focus on these indications because of a paucity of published evidence of effectiveness, some individual patients with the above indications may benefit from RFA; therefore, RFA may quickly diffuse into these areas. Various clinical trials focussing on these indications are underway.
Level 2 evidence suggests RFA is as safe and perhaps more effective than percutaneous ethanol injection to treat HCC.
RFA and percutaneous ethanol injection are more effective and more cost-effective than transcatheter arterial chemoembolization.
RFA is marginally more expensive, yet more cost-effective than percutaneous ethanol injection.
Complications are few, but experienced interventional radiologists should do RFA.
RFA may benefit some patients with liver metastases or other primary cancers, although published evidence of effectiveness has not yet been established.
PMCID: PMC3387776  PMID: 23074458
25.  Microwave ablation versus radiofrequency ablation in the kidney: high-power triaxial antennas create larger ablation zones than similarly sized internally cooled electrodes 
To determine whether microwave ablation with high-power triaxial antennas creates significantly larger ablation zones than RF ablation using similarly sized internally cooled electrodes.
Twenty-eight 12-minute ablations were performed in an in vivo porcine kidney model. RF ablations were performed with a 200-W pulsed generator and either a single 17-gauge cooled electrode (n = 9) or three switched electrodes spaced 1.5 cm apart (n = 7). Microwave ablations were performed using one (n = 7), two (n = 3), or three (n = 2) 17-gauge triaxial antennas to deliver 90 W continuous power per antenna. Multiple antennas were powered simultaneously. Temperatures 1 cm from the applicator were measured during two RF and microwave ablations each. Animals were euthanized post-ablation and ablation zone diameter, cross-sectional area and circularity were measured. Comparisons between groups were performed using a mixed effects model with P < .05 indicating statistical significance.
No adverse events occurred during the procedures. Three-electrode RF (mean area, 14.7 cm2) and single-antenna microwave (mean area, 10.9 cm2) ablation zones were significantly larger than single-electrode RF (mean area, 5.6 cm2; P = .001 and P = .0355, respectively). No significant differences were detected between single-antenna microwave and multiple-electrode RF. Ablation zone circularity was similar across groups (P > .05). Tissue temperatures were higher during microwave ablation (maximum temperature, 123 °C; versus 100 °C for RF).
Microwave ablation with high-power triaxial antennas created larger ablation zones in normal porcine kidneys than RF ablation with similarly sized applicators.
PMCID: PMC3309457  PMID: 19616970

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