Christopher L Brace | University of Wisconsin-Madison (original) (raw)
Papers by Christopher L Brace
Medical Physics, 2019
To quantitatively analyze tissue deformation during radiofrequency (RF) and microwave ablation fo... more To quantitatively analyze tissue deformation during radiofrequency (RF) and microwave ablation for varying output energy levels. Methods A total of 46 fiducial markers which were classified into outer, middle and inner lines, were positioned into a single plane around an RF or microwave ablation applicator in each ex-vivo bovine liver sample (8×6×4 cm, n = 18). RF (500 kHz; ~35 W average) or microwave (2.4 GHz; 50-100W output, ~35-70W delivered) ablation was performed for 10 min (n = 4-6 each setting). CT images were acquired over the entire liver volume every 15s. Principle strain magnitude and direction were determined from fiducial marker displacement. Normal and shear strain were then calculated such that negative strain denoted contraction and positive strain denoted expansion. Temporal variations, the final magnitudes and angles of the strain were compared across energy delivery settings, using one-way ANOVA with post-hoc Tukey HSD tests. Results On average, tissue strain rates peak at around 1 min and decayed exponentially over time. No evidence of tissue expansion was observed. The tissue strains from RF and 50 W, 75 W, and 100 W microwave ablation at 10 min were-8.5%,-38.9%,-54.4% and-65.7%, respectively, from the inner region and-3.6%,-23.7%,-41.8% and-44.3%, respectively, from the outer region. Negative strain magnitude was positively correlated to energy delivery in the inner region (Spearman's =-0.99). Microwaves at higher powers (75-100 W) induced significantly more Accepted Article This article is protected by copyright. All rights reserved. strain than at lower power (50 W) or after RF ablation (p<0.01). Principal strain angles ranged from 0.8° to-8.1°, indicating that tissue deformed more in the direction transverse to the applicator than along the direction of the applicator. Conclusions The influence of output energy on tissue deformation during RF and microwave ablation was analyzed. Microwave ablation created significantly greater contraction than RF ablation with similar energy delivery. During microwave ablation, more contraction was noted at higher power levels and in close proximity to the antenna. Contraction primarily transverse to the antenna produces ablation zones that are more elongated than the original tissue volume.
Microwave ablation is a cutting-edge process by which microwaves are emitted through thin antenna... more Microwave ablation is a cutting-edge process by which microwaves are emitted through thin antennas at 2.45 GHz to kill cancer cells through rapid heating. Our client, Dr. Chris Brace, tests new devices in bovine liver tissue; due to the opaque nature of the liver, it is very difficult to study the size of the ablation zone. In addition, the liver is only viable for a short period of time and is associated with a high cost. Therefore, a consistent, homogeneous, transparent liver phantom with a clear ablation zone indicator is needed. Different combinations of base gels – egg white, sodium polyacrylamide, silicone, sodium alginate, and poly(vinyl alcohol) – and indicators – thermochromic dye, egg white albumin, and bovine serum albumin – at different concentrations were tested. The dielectric properties, temperature of ablation, size of the ablation zone after five minutes of ablation at approximately 50 Watts were tested and compared to values obtain for similar tests on bovine liver...
Journal of Vascular and Interventional Radiology, 2015
Journal of Vascular and Interventional Radiology, 2016
Journal of Vascular and Interventional Radiology, 2010
Journal of Vascular and Interventional Radiology, 2009
Journal of Vascular and Interventional Radiology, 2008
To determine the effect of selective intubation on ablation zone size during pulmonary cryoablati... more To determine the effect of selective intubation on ablation zone size during pulmonary cryoablation. Selective bronchial intubation and aeration was performed in three domestic swine. A total of 20 cryoablations (ventilated, n = 10; nonventilated, n = 10) were performed. The animals were immediately sacrificed, and their lungs were removed and sectioned along the axis of ablation in 5-mm intervals. The diameter and area of the ablation zone were recorded, and the isoperimetric ratio (measure of circularity) and estimated volume were calculated. There was no significant difference in maximum diameter, minimum diameter, area, circularity, or estimated volume of the ablation zones between the aerated and nonaerated groups (mean diameter, 2.4 cm vs 2.4 cm, respectively, P = .99; area, 4.6 cm(2) vs 4.8 cm(2), P = .7; circularity, 0.94 vs 0.94, P = .99; estimated volume, 11.5 cm(3) vs 11.3 cm(3), P = .99). In contrast to radiofrequency ablation, selective bronchial intubation did not have a significant effect on the resulting ablation zones. This suggests that selective intubation may not be warranted in the setting of pulmonary cryoablation.
International Journal of Hyperthermia, 2007
The purpose of this study was to test the feasibility and efficacy of using a high-power generato... more The purpose of this study was to test the feasibility and efficacy of using a high-power generator with nondeployable electrodes to create large zones of coagulation in an in vivo porcine liver model. With approval from our institution's research animal care and use committee, 12 female swine (mean weight = 55 kg) were anesthetized and received RF ablation at laparotomy. Twenty-nine ablations were performed in four groups using: (i) a conventional 200-W generator and cluster electrode (n = 4), or an experimental prototype 250-W generator and (ii) a single, 17-gauge electrode (n = 9), (iii) a cluster electrode (n = 8) or (iv) three electrodes spaced 2.0 cm apart in a triangular configuration (n = 8). In the three-electrode group, power was applied by switching between electrodes using a prototype switching device. All electrodes were internally cooled. Ablation zone size, shape and generator data from each group were compared using a mixed-linear model with animals modeled as random effects. The high-power generator was able to increase significantly the zone of coagulation. Mean (+/-SD) ablation diameter was largest in the switched group (4.31 +/- 0.7 cm) followed by the cluster (3.98 +/- 0.5 cm) and single-electrode (3.26 +/- 0.5 cm) groups. Mean diameter in the high-power single-electrode group was no different than the low-power cluster group (3.25 +/- 0.4 cm, p = 0.98). Circularity measures were high (>0.75) in all groups. Coupling a high-power generator and switching device is feasible. At higher powers, the switching device creates larger zones of ablation than cluster or single electrodes. Single-electrode ablations created with the prototype high-power generator were equivalent to those produced with the cluster electrode at conventional lower powers.
IEEE Transactions on Microwave Theory and Techniques, 2005
IEEE Transactions on Medical Imaging, 2009
Radio-frequency (RF) ablation is a minimally invasive treatment for tumors in various abdominal o... more Radio-frequency (RF) ablation is a minimally invasive treatment for tumors in various abdominal organs. It is effective if good tumor localization and intraprocedural monitoring can be done. In this paper, we investigate the feasibility of using an ultrasound-based Young's modulus reconstruction algorithm to image an ablated region whose stiffness is elevated due to tissue coagulation. To obtain controllable tissue deformations for abdominal organs during and/or intermediately after the RF ablation, the proposed modulus imaging method is specifically designed for using tissue deformation fields induced by the RF electrode. We have developed a new scheme under which the reconstruction problem is simplified to a 2-D problem. Based on this scheme, an iterative Young's modulus reconstruction technique with edge-preserving regularization was developed to estimate the Young's modulus distribution. The method was tested in experiments using a tissue-mimicking phantom and on ex vivo bovine liver tissues. Our preliminary results suggest that high contrast modulus images can be successfully reconstructed. In both experiments, the geometries of the reconstructed modulus images of thermal ablation zones match well with the phantom design and the gross pathology image, respectively.
IEEE Transactions on Biomedical Engineering, 2012
European Journal of Radiology, 2016
Direct puncture of subcapsular hepatocellular carcinoma (HCC) for tumor ablation has been conside... more Direct puncture of subcapsular hepatocellular carcinoma (HCC) for tumor ablation has been considered high risk due to a perceived increased incidence of hemorrhage or tumor seeding. The purpose of this retrospective multicenter study was to identify the rate of tumor seeding, hemorrhage and local tumor progression (LTP) associated with direct puncture radiofrequency (RF) and microwave (MW) ablation of subcapsular HCC. A multicenter, retrospective review of direct-puncture RF and MW performed on subcapsular HCC was conducted. Complications and local tumor progression were documented. Data was analyzed using Kaplan-Meier and log-rank tests. The study group consisted of 60 cirrhotic patients (M/F=43/17; mean age 69.6 years) with 67 subcapsular HCC (mean diameter 2.3cm±1.0cm) that were directly punctured for RF (n=40) or MW (n=27) under ultrasound (US) guidance. The mean follow-up period was 30.8 months. There were no hemorrhagic complications. The overall LTP rate was 13.4%. There was one case of tumor tract seeding in a patient who had undergone a percutaneous biopsy two weeks prior to RF. Thermal ablation of HCC by direct puncture appears safe and effective. There were no cases of intraperitoneal hemorrhage, and tumor seeding was seen in a single case in which a preceding percutaneous biopsy had been performed.
Medical Physics
PURPOSE Intra-procedural monitoring and post-procedural follow-up is necessary for a successful a... more PURPOSE Intra-procedural monitoring and post-procedural follow-up is necessary for a successful ablation treatment. An imaging technique which can assess the ablation geometry accurately is beneficial to monitor and evaluate treatment. In this study, we developed an automated ablation segmentation technique for serial low-dose, noisy ablation computed tomography (CT) or contrast-enhanced CT (CECT). METHODS Low-dose, noisy temporal CT and CECT volumes were acquired during microwave ablation on normal porcine liver (four with non-contrast CT and eight with CECT). Highly constrained backprojection (HYPR) processing was used to recover ablation zone information compromised by low-dose noise. First-order statistic features and normalized fractional brownian features (NBF) were used to segment ablation zones by fuzzy c-mean clustering. After clustering, the segmented ablation zone was refined by cyclic morphological processing. Automatic and manual segmentations were compared to gross pathology with Dice's coefficient (morphological similarity), while cross-sectional dimensions were compared by percent difference. RESULTS Automatic and manual segmentations of the ablation zone were very similar to gross pathology (Dice Coefficients: Auto.-Path. = 0.84 ± 0.02; Manu.-Path. = 0.76 ± 0.03, P=0.11). The differences in ablation area, major diameter and minor diameter were 17.9 ± 3.2%, 11.1 ± 3.2% and 16.2 ± 3.4%, respectively, when comparing automatic segmentation to gross pathology, which were lower than the differences of 32.9±16.8%, 13.0±9.8% and 21.8±5.8% when comparing manual segmentation to gross pathology. Manual segmentations tended to overestimate gross pathology when ablation area was less than 15 cm2 , but the automated segmentation tended to underestimate gross pathology when ablation zone larger than 20 cm2 . CONCLUSION Fuzzy c-means clustering may be used to aid automatic segmentation of ablation zones without prior information or user input, making serial CT/CECT has more potential to assess treatments intra-procedurally.
International Journal of Hyperthermia
Purpose: The goal of this study was to compare intra-procedural radiofrequency (RF) and microwave... more Purpose: The goal of this study was to compare intra-procedural radiofrequency (RF) and microwave ablation appearance on non-contrast CT (NCCT) and ultrasound to the zone of pathologic necrosis. Materials and methods: Twenty-one 5-min ablations were performed in vivo in swine liver with (1) microwave at 140 W, (2) microwave at 70 W, or (3) RF at 200 W (n ¼ 7 each). CT and US images were obtained simultaneously at 1, 3, and 5 min during ablation and 2, 5, and 10 min post-ablation. Each ablation was sectioned in the plane of the ultrasound image and underwent vital staining to delineate cellular necrosis. CT was reformatted to the same plane as the ultrasound transducer and transverse diameters of gas and hypoechoic/hypoattenuating zones at each time point were measured. CT, ultrasound and gross pathologic diameter measurements were compared using Student's t-tests and linear regression. Results: Visible gas and the hypoechoic zone on US images were more predictive of the pathologic ablation zone than on NCCT images (p < 0.05). The zone of necrosis was larger than the zone of visible gas on US (mean 3.2 mm for microwave, 6.4 mm for RF) and NCCT (7.6 mm microwave, 13.9 mm RF) images (p < 0.05). The zone of visible gas and hypoechoic zone on US are more predictive of pathology with microwave ablations when compared with RF ablations (p < 0.05). Conclusion: When evaluating images during energy delivery, US is more accurate than CT and microwave-more predictable than RF-ablation based on correlation with in-plane pathology.
Medical Physics, 2019
To quantitatively analyze tissue deformation during radiofrequency (RF) and microwave ablation fo... more To quantitatively analyze tissue deformation during radiofrequency (RF) and microwave ablation for varying output energy levels. Methods A total of 46 fiducial markers which were classified into outer, middle and inner lines, were positioned into a single plane around an RF or microwave ablation applicator in each ex-vivo bovine liver sample (8×6×4 cm, n = 18). RF (500 kHz; ~35 W average) or microwave (2.4 GHz; 50-100W output, ~35-70W delivered) ablation was performed for 10 min (n = 4-6 each setting). CT images were acquired over the entire liver volume every 15s. Principle strain magnitude and direction were determined from fiducial marker displacement. Normal and shear strain were then calculated such that negative strain denoted contraction and positive strain denoted expansion. Temporal variations, the final magnitudes and angles of the strain were compared across energy delivery settings, using one-way ANOVA with post-hoc Tukey HSD tests. Results On average, tissue strain rates peak at around 1 min and decayed exponentially over time. No evidence of tissue expansion was observed. The tissue strains from RF and 50 W, 75 W, and 100 W microwave ablation at 10 min were-8.5%,-38.9%,-54.4% and-65.7%, respectively, from the inner region and-3.6%,-23.7%,-41.8% and-44.3%, respectively, from the outer region. Negative strain magnitude was positively correlated to energy delivery in the inner region (Spearman's =-0.99). Microwaves at higher powers (75-100 W) induced significantly more Accepted Article This article is protected by copyright. All rights reserved. strain than at lower power (50 W) or after RF ablation (p<0.01). Principal strain angles ranged from 0.8° to-8.1°, indicating that tissue deformed more in the direction transverse to the applicator than along the direction of the applicator. Conclusions The influence of output energy on tissue deformation during RF and microwave ablation was analyzed. Microwave ablation created significantly greater contraction than RF ablation with similar energy delivery. During microwave ablation, more contraction was noted at higher power levels and in close proximity to the antenna. Contraction primarily transverse to the antenna produces ablation zones that are more elongated than the original tissue volume.
Microwave ablation is a cutting-edge process by which microwaves are emitted through thin antenna... more Microwave ablation is a cutting-edge process by which microwaves are emitted through thin antennas at 2.45 GHz to kill cancer cells through rapid heating. Our client, Dr. Chris Brace, tests new devices in bovine liver tissue; due to the opaque nature of the liver, it is very difficult to study the size of the ablation zone. In addition, the liver is only viable for a short period of time and is associated with a high cost. Therefore, a consistent, homogeneous, transparent liver phantom with a clear ablation zone indicator is needed. Different combinations of base gels – egg white, sodium polyacrylamide, silicone, sodium alginate, and poly(vinyl alcohol) – and indicators – thermochromic dye, egg white albumin, and bovine serum albumin – at different concentrations were tested. The dielectric properties, temperature of ablation, size of the ablation zone after five minutes of ablation at approximately 50 Watts were tested and compared to values obtain for similar tests on bovine liver...
Journal of Vascular and Interventional Radiology, 2015
Journal of Vascular and Interventional Radiology, 2016
Journal of Vascular and Interventional Radiology, 2010
Journal of Vascular and Interventional Radiology, 2009
Journal of Vascular and Interventional Radiology, 2008
To determine the effect of selective intubation on ablation zone size during pulmonary cryoablati... more To determine the effect of selective intubation on ablation zone size during pulmonary cryoablation. Selective bronchial intubation and aeration was performed in three domestic swine. A total of 20 cryoablations (ventilated, n = 10; nonventilated, n = 10) were performed. The animals were immediately sacrificed, and their lungs were removed and sectioned along the axis of ablation in 5-mm intervals. The diameter and area of the ablation zone were recorded, and the isoperimetric ratio (measure of circularity) and estimated volume were calculated. There was no significant difference in maximum diameter, minimum diameter, area, circularity, or estimated volume of the ablation zones between the aerated and nonaerated groups (mean diameter, 2.4 cm vs 2.4 cm, respectively, P = .99; area, 4.6 cm(2) vs 4.8 cm(2), P = .7; circularity, 0.94 vs 0.94, P = .99; estimated volume, 11.5 cm(3) vs 11.3 cm(3), P = .99). In contrast to radiofrequency ablation, selective bronchial intubation did not have a significant effect on the resulting ablation zones. This suggests that selective intubation may not be warranted in the setting of pulmonary cryoablation.
International Journal of Hyperthermia, 2007
The purpose of this study was to test the feasibility and efficacy of using a high-power generato... more The purpose of this study was to test the feasibility and efficacy of using a high-power generator with nondeployable electrodes to create large zones of coagulation in an in vivo porcine liver model. With approval from our institution's research animal care and use committee, 12 female swine (mean weight = 55 kg) were anesthetized and received RF ablation at laparotomy. Twenty-nine ablations were performed in four groups using: (i) a conventional 200-W generator and cluster electrode (n = 4), or an experimental prototype 250-W generator and (ii) a single, 17-gauge electrode (n = 9), (iii) a cluster electrode (n = 8) or (iv) three electrodes spaced 2.0 cm apart in a triangular configuration (n = 8). In the three-electrode group, power was applied by switching between electrodes using a prototype switching device. All electrodes were internally cooled. Ablation zone size, shape and generator data from each group were compared using a mixed-linear model with animals modeled as random effects. The high-power generator was able to increase significantly the zone of coagulation. Mean (+/-SD) ablation diameter was largest in the switched group (4.31 +/- 0.7 cm) followed by the cluster (3.98 +/- 0.5 cm) and single-electrode (3.26 +/- 0.5 cm) groups. Mean diameter in the high-power single-electrode group was no different than the low-power cluster group (3.25 +/- 0.4 cm, p = 0.98). Circularity measures were high (>0.75) in all groups. Coupling a high-power generator and switching device is feasible. At higher powers, the switching device creates larger zones of ablation than cluster or single electrodes. Single-electrode ablations created with the prototype high-power generator were equivalent to those produced with the cluster electrode at conventional lower powers.
IEEE Transactions on Microwave Theory and Techniques, 2005
IEEE Transactions on Medical Imaging, 2009
Radio-frequency (RF) ablation is a minimally invasive treatment for tumors in various abdominal o... more Radio-frequency (RF) ablation is a minimally invasive treatment for tumors in various abdominal organs. It is effective if good tumor localization and intraprocedural monitoring can be done. In this paper, we investigate the feasibility of using an ultrasound-based Young's modulus reconstruction algorithm to image an ablated region whose stiffness is elevated due to tissue coagulation. To obtain controllable tissue deformations for abdominal organs during and/or intermediately after the RF ablation, the proposed modulus imaging method is specifically designed for using tissue deformation fields induced by the RF electrode. We have developed a new scheme under which the reconstruction problem is simplified to a 2-D problem. Based on this scheme, an iterative Young's modulus reconstruction technique with edge-preserving regularization was developed to estimate the Young's modulus distribution. The method was tested in experiments using a tissue-mimicking phantom and on ex vivo bovine liver tissues. Our preliminary results suggest that high contrast modulus images can be successfully reconstructed. In both experiments, the geometries of the reconstructed modulus images of thermal ablation zones match well with the phantom design and the gross pathology image, respectively.
IEEE Transactions on Biomedical Engineering, 2012
European Journal of Radiology, 2016
Direct puncture of subcapsular hepatocellular carcinoma (HCC) for tumor ablation has been conside... more Direct puncture of subcapsular hepatocellular carcinoma (HCC) for tumor ablation has been considered high risk due to a perceived increased incidence of hemorrhage or tumor seeding. The purpose of this retrospective multicenter study was to identify the rate of tumor seeding, hemorrhage and local tumor progression (LTP) associated with direct puncture radiofrequency (RF) and microwave (MW) ablation of subcapsular HCC. A multicenter, retrospective review of direct-puncture RF and MW performed on subcapsular HCC was conducted. Complications and local tumor progression were documented. Data was analyzed using Kaplan-Meier and log-rank tests. The study group consisted of 60 cirrhotic patients (M/F=43/17; mean age 69.6 years) with 67 subcapsular HCC (mean diameter 2.3cm±1.0cm) that were directly punctured for RF (n=40) or MW (n=27) under ultrasound (US) guidance. The mean follow-up period was 30.8 months. There were no hemorrhagic complications. The overall LTP rate was 13.4%. There was one case of tumor tract seeding in a patient who had undergone a percutaneous biopsy two weeks prior to RF. Thermal ablation of HCC by direct puncture appears safe and effective. There were no cases of intraperitoneal hemorrhage, and tumor seeding was seen in a single case in which a preceding percutaneous biopsy had been performed.
Medical Physics
PURPOSE Intra-procedural monitoring and post-procedural follow-up is necessary for a successful a... more PURPOSE Intra-procedural monitoring and post-procedural follow-up is necessary for a successful ablation treatment. An imaging technique which can assess the ablation geometry accurately is beneficial to monitor and evaluate treatment. In this study, we developed an automated ablation segmentation technique for serial low-dose, noisy ablation computed tomography (CT) or contrast-enhanced CT (CECT). METHODS Low-dose, noisy temporal CT and CECT volumes were acquired during microwave ablation on normal porcine liver (four with non-contrast CT and eight with CECT). Highly constrained backprojection (HYPR) processing was used to recover ablation zone information compromised by low-dose noise. First-order statistic features and normalized fractional brownian features (NBF) were used to segment ablation zones by fuzzy c-mean clustering. After clustering, the segmented ablation zone was refined by cyclic morphological processing. Automatic and manual segmentations were compared to gross pathology with Dice's coefficient (morphological similarity), while cross-sectional dimensions were compared by percent difference. RESULTS Automatic and manual segmentations of the ablation zone were very similar to gross pathology (Dice Coefficients: Auto.-Path. = 0.84 ± 0.02; Manu.-Path. = 0.76 ± 0.03, P=0.11). The differences in ablation area, major diameter and minor diameter were 17.9 ± 3.2%, 11.1 ± 3.2% and 16.2 ± 3.4%, respectively, when comparing automatic segmentation to gross pathology, which were lower than the differences of 32.9±16.8%, 13.0±9.8% and 21.8±5.8% when comparing manual segmentation to gross pathology. Manual segmentations tended to overestimate gross pathology when ablation area was less than 15 cm2 , but the automated segmentation tended to underestimate gross pathology when ablation zone larger than 20 cm2 . CONCLUSION Fuzzy c-means clustering may be used to aid automatic segmentation of ablation zones without prior information or user input, making serial CT/CECT has more potential to assess treatments intra-procedurally.
International Journal of Hyperthermia
Purpose: The goal of this study was to compare intra-procedural radiofrequency (RF) and microwave... more Purpose: The goal of this study was to compare intra-procedural radiofrequency (RF) and microwave ablation appearance on non-contrast CT (NCCT) and ultrasound to the zone of pathologic necrosis. Materials and methods: Twenty-one 5-min ablations were performed in vivo in swine liver with (1) microwave at 140 W, (2) microwave at 70 W, or (3) RF at 200 W (n ¼ 7 each). CT and US images were obtained simultaneously at 1, 3, and 5 min during ablation and 2, 5, and 10 min post-ablation. Each ablation was sectioned in the plane of the ultrasound image and underwent vital staining to delineate cellular necrosis. CT was reformatted to the same plane as the ultrasound transducer and transverse diameters of gas and hypoechoic/hypoattenuating zones at each time point were measured. CT, ultrasound and gross pathologic diameter measurements were compared using Student's t-tests and linear regression. Results: Visible gas and the hypoechoic zone on US images were more predictive of the pathologic ablation zone than on NCCT images (p < 0.05). The zone of necrosis was larger than the zone of visible gas on US (mean 3.2 mm for microwave, 6.4 mm for RF) and NCCT (7.6 mm microwave, 13.9 mm RF) images (p < 0.05). The zone of visible gas and hypoechoic zone on US are more predictive of pathology with microwave ablations when compared with RF ablations (p < 0.05). Conclusion: When evaluating images during energy delivery, US is more accurate than CT and microwave-more predictable than RF-ablation based on correlation with in-plane pathology.
Journal of endourology / Endourological Society, 2012
OBJECTIVE: Microwave ablation offers the potential advantages of high temperature and faster tiss... more OBJECTIVE: Microwave ablation offers the potential advantages of high temperature and faster tissue heating, but prior instrument development has been limited by overheating of the antenna shaft and supply cables. Recently, a novel gas-cooled microwave device has been developed and approved for tumor ablation by the FDA. We report the safety and preliminary effectiveness of this device in the treatment of renal tumors. METHODS: Between 1/2011 and 3/2012, renal tumors (n = 17) were treated at two medical centers with a high-powered, gascooled microwave ablation system (NeuWave Medical, Madison, WI) using ultrasound and CT-guidance. Tumors included biopsy-proven renal cell carcinoma (n = 13), oncocytoma (n = 1), insufficient tissue for diagnosis (n = 1), and angiomyolipoma (n = 2, imaging-based diagnosis). Mean patient age was 66 years. Postprocedure imaging was performed by contrast-enhanced CT or MRI to evaluate for recurrence. RESULTS: Mean tumor diameter was 3.0 cm (range: 1.9-5.4). Tumor diameter decreased by a mean of 13% (range: 0-30%; SD = 8%) as assessed on immediate post-ablation CT. The mean duration of power application was 6.1 minutes. Mean generator power was 83.0W (range: 55-140). Technical success (no residual enhancing tumor) was achieved for all tumors. No major complications were reported. Two small, asymptomatic sub-capsular hematomas were detected on post-ablation CT. Mean follow-up was 3.4 months and no local tumor progression or recurrence was identified in any case. CONCLUSIONS: Preliminary experience with high-powered, gas-cooled percutaneous renal microwave ablation demonstrates immediate technical success in treatment of small renal tumors. Further studies are warranted to demonstrate long-term oncologic outcomes and optimal surveillance protocols after ablation.
Objectives: To evaluate the feasibility, safety, and preliminary effectiveness of a high-powered,... more Objectives: To evaluate the feasibility, safety, and preliminary effectiveness of a high-powered, gas-cooled microwave ablation system for percutaneous treatment of biopsy-proven renal cell carcinoma in a retrospective, multicenter case series. Methods: Between 1/2011 and 11/2013, 89 biopsy-proven renal cell carcinomas were treated in 87 patients using ultrasound and CT-guided microwave ablation with a high-powered, gas-cooled microwave ablation system (NeuWave Medical, Madison, WI) at three academic medical centers. Histologic subtypes included clear cell (n=57), papillary (n=24), chromophobe (n=1) and unspecified (n=7). Gradable tumors included Fuhrman grades 1 (n=18), 2 (n=35), and 3 (n=1). Mean patient age was 66 years, and each patient underwent a single treatment session. Post-procedure imaging was performed by CT or MRI to evaluate for recurrence. Results: Mean tumor diameter was 2.8 cm (range: 1.0-7.1). Tumor volume decreased by a mean of 51% (IQR: 37-68%) as assessed on imm...
Objectives: To evaluate the feasibility, safety, and preliminary effectiveness of a high- powered... more Objectives: To evaluate the feasibility, safety, and preliminary effectiveness of a high- powered, gas-cooled microwave ablation system for treatment of renal tumors. Methods: Between 1/2011 and 12/2012, 35 renal tumors in 35 patients were treated at two medical centers using ultrasound and CT-guided microwave ablation with a high-powered, gas-cooled microwave ablation system (NeuWave Medical, Madison, WI). Tumors included biopsy-proven renal cell carcinoma (n=26; grade 1=6; grade 2=15, ungraded=5), angiomyolipoma (n=4, diagnosis made by imaging), oncocytoma (n=2), glomerulosclerosis (n=2), and insufficient tissue for diagnosis (n=1). Mean patient age was 63 years, with 26 males and 9 females. Post-procedure imaging was performed by CECT or MRI to evaluate for enhancement in the ablation zone at target intervals of 3, 6, and 12 months post-ablation. Results: Mean pre-treatment tumor diameter was 2.9 cm (range: 1.0-5.4). Tumor diameter decreased by a mean of 13% (range: -30 to +30%; ...
PURPOSE/AIM -Review advantages/limitations of microwave ablation (MWA). -Discuss applications of ... more PURPOSE/AIM -Review advantages/limitations of microwave ablation (MWA). -Discuss applications of gas cooled MWA and available antennas. -Use case-based review to illustrate patient selection, antenna placement, intraprocedural imaging, technical efficacy and complications of microwave ablation in the lung, liver, kidney, adrenal and retroperitoneum. CONTENT ORGANIZATION -Introduction -Potential advantages and limitations of MWA -Review of available antennas: advantages/limitations, applications. -Multi-organ (liver, kidney, lung, retroperitoneum) clinical case based pictorial review illustrating patient selection, intraprocedural monitoring, technical efficacy, complications, follow up. -Summary SUMMARY -Use of MWA enables rapid generation of very high temperatures, which can lead to decreased treatment time and decreased susceptibility to heat sink effects and high tissue resistance. -Gas cooled MWA allows for treatment at high powers with a relatively small gauge antenna. -MWA can...