-
[show abstract]
[hide abstract]
ABSTRACT: 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.
American Journal of Roentgenology 03/2012; 198(3):W260-5. · 2.78 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: To evaluate the performance of a gas-cooled, high-powered microwave system.
Investigators performed 54 ablations in ex vivo bovine livers using three devices-a single 17-gauge cooled radiofrequency(RF) electrode; a cluster RF electrode; and a single 17-gauge, gas-cooled microwave (MW) antenna-at three time points (n = 6 at 4 minutes, 12 minutes, and 16 minutes). RF power was applied using impedance-based pulsing with maximum 200 W generator output. MW power of 135 W at 2.45 GHz was delivered continuously. An approved in vivo study was performed using 13 domestic pigs. Hepatic ablations were performed using single applicators and the above-mentioned MW and RF generator systems at treatment times of 2 minutes (n = 7 MW, n = 6 RF), 5 minutes (n = 23 MW, n = 8 RF), 7 minutes (n = 11 MW, n = 6 RF), and 10 minutes (n = 7 MW, n = 9 RF). Mean transverse diameter and length of the ablation zones were compared using analysis of variance (ANOVA) with post-hoc t tests and Wilcoxon rank-sum tests.
Single ex vivo MW ablations were larger than single RF ablations at all time points (MW mean diameter range 3.5-4.8 cm 4-16 minutes; RF mean diameter range 2.6-3.1 cm 4-16 minutes) (P < .05). There was no difference in mean diameter between cluster RF and MW ablations (RF 3.3-4.4 cm 4-16 minutes; P = .4-.9). In vivo lesion diameters for MW (and RF) were as follows: 2.6 cm ± 0.72 (RF 1.5 cm ± 0.14), 3.6 cm ± 0.89 (RF 2.0 cm ± 0.4), 3.4 cm ± 0.87 (RF 1.8 cm ± 0.23), and 3.8 cm ± 0.74 (RF 2.1 cm ± 0.3) at 2 minutes, 5 minutes, 7 minutes, and 10 minutes (P < .05 all time points).
Gas-cooled, high-powered MW ablation allows the generation of large ablation zones in short times.
Journal of vascular and interventional radiology: JVIR 03/2012; 23(3):405-11. · 1.81 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We describe our experience using an iodinated contrast solution to hydrodissect adjacent structures before percutaneous renal cryoablation. Hydrodissection was performed before cryoablation with placement of a 20-gauge, 15-cm introducer needle into the retroperitoneum under CT or ultrasonographic guidance followed by infusion of 5% dextrose in water and 2% iodinated contrast between the kidney and the adjacent organ. Ten patients underwent hydrodissection with an iodinated contrast solution at our institution. The mean tumor size was 3.1 ± 1.2 cm. The organs displaced included colon (n=7), small bowel (n=1), pancreas (n=1), and in one case, both the colon and ureter were displaced. The average displacement of all organs from the kidney was 2.8 cm (range 2.2-3.5 cm). There were no complications and no injuries to any adjacent structures. The injection of iodinated contrast allows for safe mobilization and differentiation of adjacent structures from the renal tumor and parenchyma leading to potentially safer cryoablation.
Journal of endourology / Endourological Society 02/2012; 26(5):463-6. · 1.75 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: CT radiation exposure has come under increasing scrutiny because of dramatically increased utilization. Multiphase CT studies (repeated scanning before and after contrast injection) are a potentially important, overlooked source of medically unnecessary radiation because of the dose-multiplier effect of extra phases. The purpose of this study was to determine the frequency of unindicated multiphase scanning and resultant excess radiation exposure in a sample referral population.
Abdominal and pelvic CT examinations (n = 500) performed at outside institutions submitted for tertiary interpretation were retrospectively reviewed for (1) the appropriateness of each phase on the basis of clinical indication and ACR Appropriateness Criteria(®) and (2) per phase and total radiation effective dose.
A total of 978 phases were performed in 500 patients; 52.8% (264 of 500) received phases that were not supported by ACR criteria. Overall, 35.8% of phases (350 of 978) were unindicated, most commonly being delayed imaging (272 of 350). The mean overall total radiation effective dose per patient was 25.8 mSv (95% confidence interval, 24.2-27.5 mSv). The mean effective dose for unindicated phases was 13.1 mSv (95% confidence interval, 12.3-14.0 mSv), resulting in a mean excess effective dose of 16.8 mSv (95% confidence interval, 15.5-18.3 mSv) per patient. Unindicated radiation constituted 33.3% of the total radiation effective dose in this population. Radiation effective doses exceeding 50 mSv were found in 21.2% of patients (106 of 500).
The results of this study suggest that a large proportion of patients undergoing abdominal and pelvic CT scanning receive unindicated additional phases that add substantial excess radiation dose with no associated clinical benefit.
Journal of the American College of Radiology: JACR 11/2011; 8(11):756-61.
-
[show abstract]
[hide abstract]
ABSTRACT: The objective of our study was to determine whether pleural blood patching reduces the need for chest tube placement and hospital admission for pneumothorax complicating CT-guided percutaneous lung biopsy.
We reviewed 463 CT-guided lung biopsies performed between August 2006 and March 2010 to determine whether intervention for pneumothorax was required and patient outcome. Intervention was categorized as simple aspiration, aspiration and intrapleural blood patching, or chest tube placement and hospital admission. The technique for pleural blood patching consisted of complete pneumothorax aspiration, immediate placement of up to 15 mL of peripheral autologous blood into the pleural space, and positioning the patient in the ipsilateral decubitus position for 1 hour after the procedure.
Intervention for pneumothorax was necessary in 45 of 463 patients (9.7%) and 19 of 463 patients (4.1%) required chest tube placement. Pleural blood patching as a method to treat a postbiopsy pneumothorax and avoid further intervention was associated with a significantly higher success rate than simple aspiration: 19 of 22 (86.4%) vs seven of 15 (46.7%) (odds ratio = 7.2, p = 0.03), respectively.
Aspiration with intrapleural blood patching is superior to simple aspiration to treat pneumothorax associated with CT-guided lung biopsy. Pleural blood patching reduces the need for chest tube placement and hospital admission in this patient population.
American Journal of Roentgenology 10/2011; 197(4):783-8. · 2.78 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The 5-year survival for all stages of nonsmall cell lung cancer (NSCLC) remains bleak, having increased from 13% to just 16% over the past 30 years. Despite promising results in nonoperative patients with NSCLC and pulmonary metastatic disease, thermal ablation appears to be limited by large tumor size and proximity to large vessels. This article discusses the particular challenges of performing thermal ablation in aerated lung tissue and reviews important considerations in performing ablation including treatment complications and imaging follow-up. The article compares and contrasts the three major thermal ablation modalities: radiofrequency ablation, microwave ablation, and cryoablation.
Surgical Oncology Clinics of North America 04/2011; 20(2):369-87, ix. · 1.12 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Image-guided tumor ablation with both thermal and nonthermal sources has received substantial attention for the treatment of many focal malignancies. Increasing interest has been accompanied by continual advances in energy delivery, application technique, and therapeutic combinations with the intent to improve the efficacy and/or specificity of ablative therapies. This review outlines clinical percutaneous tumor ablation technology, detailing the science, devices, techniques, technical obstacles, current trends, and future goals in percutaneous tumor ablation. Methods such as chemical ablation, cryoablation, high-temperature ablation (radiofrequency, microwave, laser, and ultrasound), and irreversible electroporation will be discussed. Advances in technique will also be covered, including combination therapies, tissue property modulation, and the role of computer modeling for treatment optimization.
Radiology 02/2011; 258(2):351-69. · 5.73 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: To determine the expected ablation zone size and associated isotherms when using clinically available percutaneous cryoprobes for pulmonary cryoablation in a porcine lung model.
Seven ablations were performed in the lungs of three adult pigs using clinically available 2.4-mm cryoprobes (Endocare, Inc, Irvine, California) and a 10-minute double-freeze protocol. Five 18-gauge thermocouples were positioned at 5-mm increments (ie, 5, 10, 15, 20, and 25 mm) from the cryoprobe. Real-time tissue temperatures were recorded during the cryoablation. The isotherms obtained during the ablation and the pathological ablation zones were measured.
The pathologic zone of complete necrosis had a mean diameter of 2.4 + or - 0.2 cm, with a mean area of 4.6 + or - 0.6 cm(2) and a circularity of 0.95 + or - 0.04. In comparison, the mean diameter (+ or - standard deviation) of the 0 degrees C, -20 degrees C, and -40 degrees C isotherms were 3.1 + or - 0.2 cm, 2.3 + or - 0.3 cm, and 1.8 + or - 0.4 cm, respectively. The -20 degrees C isotherm was most closely related to the pathologic zone of ablation.
This study establishes the temperature isotherms and associated ablation zone size that can be expected with modern percutaneous cryoprobes in an in vivo porcine lung model.
Journal of vascular and interventional radiology: JVIR 09/2010; 21(9):1424-8. · 1.81 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: To determine the amount of tissue contraction during radiofrequency (RF) and microwave ablation.
Markers were inserted into explanted bovine liver and lung 10 mm (inner), 20 mm (middle; not used in lung), and 30 mm (peripheral) diametrically around an ablation applicator. Aside from unablated controls, RF and microwave ablations 25-30 mm in diameter were then created and sectioned to measure the distance between markers (n = 12, liver RF; n = 8, other). Total contraction was calculated by subtracting postablation measurements from controls at each position. Relative contraction was calculated by subtracting the nearest more central measurement. Sample water content was measured to determine the relationship between dehydration and relative contraction. A mixed-effects model tested for differences in diameters, total and relative contraction, and water content with energy, tissue, and marker position as independent variables.
Total contractions at the inner, middle, and peripheral positions in liver were 2.9 mm (31%), 4.8 mm (24%), and 4.5 mm (15%) for RF and 3.6 mm (38%), 6.6 mm (33%), and 9.0 mm (30%) for microwave, respectively. Significantly more contraction was noted in lung (P < .001): 5.1 mm (55%) and 14.2 mm (49%) for RF and 4.8 mm (52%) and 13.7 mm (47%) for microwave at the inner and peripheral positions, respectively. Microwaves produced more contraction than RF in liver (P < .05) but not in lung. A positive correlation between dehydration and relative contraction was observed in all cases.
Ablation-induced tissue contraction is substantial and influenced by dehydration. Contraction should be considered when testing devices and computer models or comparing pre- and postablation images.
Journal of vascular and interventional radiology: JVIR 08/2010; 21(8):1280-6. · 1.81 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Microwave ablation uses dielectric hysteresis to produce direct volume heating of tissue. Microwaves are capable of propagating through many tissue types, even those with high impedance such as lung or bone, with less susceptibility to "heat-sink" effects along vessels. Microwaves are highly conducive to the use of multiple applicators, showing the synergy seen with other energies, but also the potential capability for phasing of the electromagnetic field. As a result, larger, more customizable ablation zones may be created in less time. Although multiple microwave ablation systems are currently available, further study and continued development are needed.
Journal of vascular and interventional radiology: JVIR 08/2010; 21(8 Suppl):S192-203. · 1.81 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: To compare ablation zones created with equal amounts of 2.45 GHz microwave and 480 kHz radiofrequency (RF) energy in ex vivo liver and lung.
A total of 38 ablations were performed in ex vivo liver and lung for 10 min each. Nineteen RF ablations (nine liver, ten lung) were performed with a 480 kHz system (200 W max, impedance-based pulsing) and cooled electrode while measuring the average RF power applied. Nineteen microwave ablations (nine liver, ten lung) were then created using a cooled triaxial antenna to deliver 2.45 GHz at the same power level as in RF experiments. Ablation zones were then sectioned and measured for minimum, maximum and mean diameters, and circularity. Measurements were compared using t-tests, with P < 0.05 indicating statistical significance.
Mean diameters of microwave ablations were greater than RF ablations in both liver and lung (4.4 +/- 0.3 vs 3.3 +/- 0.2 cm in liver; 2.45 +/- 0.3 vs 1.6 +/- 0.5 cm in lungs; P < 0.0005 all comparisons). There was no significant difference in the mean power applied during microwave or RF ablations in either organ (54.44 +/- 1.71 W vs 56.4 +/- 6.7 W in liver, P > 0.05; 40 +/- 0.95 W vs 44.9 +/- 7.1 W in lung, P > 0.05).
Using a single cooled applicator, microwave energy at 2.45 GHz produces larger ablations than an equivalent amount of 480 kHz RF energy in normal liver and lung. This was more apparent in lung, likely due to the high baseline impedance which limits RF, but not microwave power delivery.
Medical Physics 06/2010; 37(6):2967-73. · 2.83 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The purpose of this study was to compare a double freeze-thaw protocol to a triple freeze-thaw protocol for pulmonary cryoablation utilizing an in vivo porcine lung model. A total of 18 cryoablations were performed in normal porcine lung utilizing percutaneous technique with 9 each in a double- (10-5-10) and triple-freeze (3-3-7-7-5) protocol. Serial noncontrast CT images were obtained during the ablation. CT imaging findings and pathology were reviewed. No imaging changes were identified during the initial freeze cycle with either protocol. However, during the first thaw cycle, a region of ground glass opacity developed around the probe with both protocols. Because the initial freeze was shorter with the triple freeze-thaw protocol, the imaging findings were apparent sooner with this protocol (6 vs. 13 min). Also, despite a shorter total freeze time (15 vs. 20 min), the ablation zone identified with the triple freeze-thaw protocol was not significantly different from the double freeze-thaw protocol (mean diameter: 1.67 ± 0.41 cm vs. 1.66 ± 0.21 cm, P = 0.77; area: 2.1 ± 0.48 cm(2) vs. 1.99 ± 0.62 cm(2), P = 0.7; and circularity: 0.95 ± 0.04 vs. 0.96 ± 0.03, P = 0.62, respectively). This study suggests that there may be several advantages of a triple freeze-thaw protocol for pulmonary cryoablation, including earlier identification of the imaging findings associated with the ablation, the promise of a shorter procedure time or larger zones of ablation, and theoretically, more effective cytotoxicity related to the additional freeze-thaw cycle.
CardioVascular and Interventional Radiology 05/2010; 33(6):1180-5. · 2.09 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: To retrospectively assess the local control and intermediate- and long-term survival of patients with liver metastases from breast cancer who have undergone percutaneous ultrasonography (US)-guided radiofrequency (RF) ablation.
This study was approved by the hospital ethics committee, and all patients provided written informed consent. RF ablation was used to treat 87 breast cancer liver metastases (mean diameter, 2.5 cm) in 52 female patients (median age, 55 years). Inclusion criteria were as follows: fewer than five tumors, maximum tumor diameter of 5 cm or smaller, and disease either confined to the liver or stable with medical therapy. Forty-five (90%) of 50 patients had previously undergone chemotherapy, hormonal therapy, or both, and had no response or an incomplete response to the treatment. Contrast material-enhanced computed tomography and US were performed to evaluate complications and technical success and to assess for local tumor progression during follow-up. The Kaplan-Meier method was used to assess survival, and results were compared between groups with a log-rank test. Cox regression analysis was used to assess independent prognostic factors that affected survival.
Complete tumor necrosis was achieved in 97% of tumors. Two (4%) minor complications occurred. Median time to follow-up from diagnosis of liver metastasis and from RF ablation was 37.2 and 19.1 months, respectively. Local tumor progression occurred in 25% of patients. New intrahepatic metastases developed in 53% of patients. From the time of first RF ablation, overall median survival time and 5-year survival rate were 29.9 months and 27%, respectively. From the time the first liver metastasis was diagnosed, overall median survival time was 42 months, and the 5-year survival rate was 32%. Patients with tumors 2.5 cm in diameter or larger had a worse prognosis (hazard ratio, 2.1) than did patients with tumors smaller than 2.5 cm in diameter.
Survival rates in selected patients with breast cancer liver metastases treated with RF ablation are comparable to those reported in the literature that were achieved with surgery or laser ablation.
Radiology 09/2009; 253(3):861-9. · 5.73 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: To determine whether microwave ablation with high-power triaxial antennas creates significantly larger ablation zones than radiofrequency (RF) ablation with 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 with 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 after ablation and ablation zone diameter, cross-sectional area, and circularity were measured. Comparisons between groups were performed with use of a mixed-effects model with P values less than .05 indicating statistical significance.
No adverse events occurred during the procedures. Three-electrode RF (mean area, 14.7 cm(2)) and single-antenna microwave (mean area, 10.9 cm(2)) ablation zones were significantly larger than single-electrode RF zones (mean area, 5.6 cm(2); 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 of 123 degrees C vs 100 degrees 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.
Journal of vascular and interventional radiology: JVIR 08/2009; 20(9):1224-9. · 1.81 Impact Factor
-
S Nahum Goldberg,
Clement J Grassi,
John F Cardella,
J William Charboneau,
Gerald D Dodd,
Damian E Dupuy,
Debra A Gervais,
Alice R Gillams,
Robert A Kane, Fred T Lee,
Tito Livraghi,
John McGahan,
David A Phillips,
Hyunchul Rhim,
Stuart G Silverman,
Luigi Solbiati,
Thomas J Vogl,
Bradford J Wood,
Suresh Vedantham,
David Sacks
[show abstract]
[hide abstract]
ABSTRACT: The field of interventional oncology with use of image-guided tumor ablation requires standardization of terminology and reporting criteria to facilitate effective communication of ideas and appropriate comparison between treatments that use different technologies, such as chemical (ethanol or acetic acid) ablation, and thermal therapies, such as radiofrequency (RF), laser, microwave, ultrasound, and cryoablation. This document provides a framework that will hopefully facilitate the clearest communication between investigators and will provide the greatest flexibility in comparison between the many new, exciting, and emerging technologies. An appropriate vehicle for reporting the various aspects of image-guided ablation therapy, including classification of therapies and procedure terms, appropriate descriptors of imaging guidance, and terminology to define imaging and pathologic findings, are outlined. Methods for standardizing the reporting of follow-up findings and complications and other important aspects that require attention when reporting clinical results are addressed. It is the group's intention that adherence to the recommendations will facilitate achievement of the group's main objective: improved precision and communication in this field that lead to more accurate comparison of technologies and results and, ultimately, to improved patient outcomes. The intent of this standardization of terminology is to provide an appropriate vehicle for reporting the various aspects of image-guided ablation therapy.
Journal of vascular and interventional radiology: JVIR 07/2009; 20(7 Suppl):S377-90. · 1.81 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: 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 medical imaging. 03/2009; 28(8):1325-34.
-
[show abstract]
[hide abstract]
ABSTRACT: To compare the performance of equivalently sized radiofrequency and microwave ablation applicators in a normal porcine lung model.
All experiments were approved by an institutional animal care and use committee. A total of 18 ablations were performed in vivo in normal porcine lungs. By using computed tomographic (CT) fluoroscopic guidance, a 17-gauge cooled triaxial microwave antenna (n = 9) and a 17-gauge cooled radiofrequency (RF) electrode (n = 9) were placed percutaneously. Ablations were performed for 10 minutes by using either 125 W of microwave power or 200 W of RF power delivered with an impedance-based pulsing algorithm. CT images were acquired every minute during ablation to monitor growth. Animals were sacrificed after the procedure. Ablation zones were then excised and sectioned transverse to the applicator in 5-mm increments. Minimum and maximum diameter, cross-sectional area, length, and circularity were measured from gross specimens and CT images. Comparisons of each measurement were performed by using a mixed-effects model; P < .05 was considered to indicate a significant difference.
Mean diameter (3.32 cm +/- 0.19 [standard deviation] vs 2.70 cm +/- 0.23, P < .001) was 25% larger with microwave ablation and mean cross-sectional area (8.25 cm(2) +/- 0.92 vs 5.45 cm(2) +/- 1.14, P < .001) was 50% larger with microwave ablation, compared with RF ablation. With microwave ablation, the zones of ablation were also significantly more circular in cross section (mean circularity, 0.90 +/- 0.06 vs 0.82 +/- 0.09; P < .05). One small pneumothorax was noted during RF ablation but stabilized without intervention.
Microwave ablation with a 17-gauge high-power triaxial antenna creates larger and more circular zones of ablation than does a similarly sized RF applicator in a preclinical animal model. Microwave ablation may be a more effective treatment of lung tumors.
Radiology 03/2009; 251(3):705-11. · 5.73 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Image-guided tumor ablation is rapidly gaining acceptance for treating many tumors. While imaging diagnosis, treatment targeting and follow-up continue to improve, little progress has been made in developing practical imaging techniques for monitoring ablation treatments. In this study we demonstrate the feasibility of using contrast-enhanced computed tomography (CECT) to monitor ablation zone growth with 2 min temporal resolution. Highly constrained back-projection (HYPR) post-processing is applied to the time-series of CECT images, improving image quality by a factor of four after acquiring ten time frames. Such improvements limit the amount of radiation and iodinated contrast material required to visualize the ablation zone, especially at early time points. Additional study of periodic CECT with HYPR processing appears warranted.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 01/2009; 2009:4299-302.
-
[show abstract]
[hide abstract]
ABSTRACT: BACKGROUND: Microwave ablation is an emerging tumor ablation modality. To date, microwave systems have generally utilized single large-diameter antennas to deliver high input powers. OBJECTIVE: To determine whether spatially distributing power through an array of multiple smaller antennas creates a more uniform thermal profile and increases peripheral tissue temperatures when compared with microwave ablation using a single larger antenna. METHODS: Microwave ablations were performed in ex vivo bovine liver using a single 2.45-GHz magnetron generator and a constant total input power (90 W) delivered through either a single 13-gauge antenna, two 17-gauge antennas, or three 18-gauge antennas. Multiple antennas were driven coherently. Temperatures were recorded at 5-mm radial distances and the resulting thermal profiles and ablation zones were compared using analysis of variance. RESULTS: Multiple-antenna configurations were less invasive (ie, the area of tissue punctured was smaller) than the single-antenna configuration; despite this, ablation zones created using multiple smaller antennas were larger and as circular when compared with those created using a single larger antenna. Multiple-antenna configurations resulted in more uniform thermal profiles and higher peripheral tissue temperatures. CONCLUSION: Distributing power evenly among multiple smaller antennas resulted in larger ablation zones with more uniform thermal profiles than more invasive ablations with a larger single antenna.
Journal of Interventional Oncology 01/2009; 2(2):65-72.
-
[show abstract]
[hide abstract]
ABSTRACT: To compare radiofrequency (RF) ablations created by using a sequential technique to those created simultaneously by using a switching algorithm in ex vivo and in vivo liver models.
RF ablation was performed by using either sequential or switched application of three cooled electrodes in a 2-cm triangular array in ex vivo bovine liver (28 total ablations) and in vivo swine liver (12 total ablations) models. For sequential ablations, electrodes were powered for 12 minutes each with a 5-minute rest interval between activations to simulate electrode repositioning. Switched ablations were created by using a multiple-electrode switching system for 12 minutes. Temperatures were measured during ex vivo experiments at four points in the ablation zone. Ablation zones were measured for minimum and maximum diameter, cross-sectional area, and isoperimetric ratio. Mann-Whitney and Wilcoxon matched pairs tests were used to identify differences between groups.
The switched application created larger and more circular zones of ablation than did the sequential application, with mean (+/-standard deviation) ex vivo cross-sectional areas of 25.4 cm(2) +/- 5 .3 and 18.8 cm(2) +/- 6.6 (P = .001), respectively, and mean in vivo areas of 17.1 cm(2) +/- 5.1 and 13.2 cm(2) +/- 4.2 (P < .05). Higher temperatures and more rapid heating occurred with the switched application; switched treatments were 74% faster than sequential treatments (12 vs 46 minutes). In the sequential group, subsequent ablations grew progressively larger due to local ischemia.
Switched application of three electrodes creates larger, more confluent ablations in less time than sequential application. Thermal synergy and ablation-induced ischemia both substantially influence multiple-electrode ablations.
Journal of vascular and interventional radiology: JVIR 11/2008; 20(1):118-24. · 1.81 Impact Factor
