Quantitative 2D Digital Subtraction Venography for Venous Interventions: Validation in Phantom and In Vivo Porcine Models.

PURPOSE: To determine the feasibility of using a 2D quantitative digital subtraction venography (qDSV) technique that employs a temporally modulated contrast injection to quantify blood velocity in phantom, normal, and stenotic porcine iliac vein models. MATERIALS AND METHODS: Blood velocity was calculated using qDSV following temporally-modulated, pulsed injections of iodinated contrast medium, and compared to Doppler ultrasound (US) measurements (phantom: in-line sensor, in vivo: diagnostic linear probe). Phantom evaluation was performed in a compliant polyethylene tube phantom with simulated venous flow. In vivo evaluation of qDSV was performed in normal (n=7) and stenotic (n=3) iliac vein models. Stenoses were created using endovenous radiofrequency ablation and blood velocities were determined at baseline, post-stenosis, post-venoplasty and post-stent placement. RESULTS: In the phantom model, qDSV-calculated blood velocities (12-50 cm/s) had very strong correlations with US-measured velocities (13-51 cm/s) across a range of baseline blood velocities and injection protocols (slope=[1.01-1.13], R2=[0.96-0.99]). qDSV velocities were similar to US regardless of injection method: custom injector, commercial injector, or hand injection. In the normal in vivo model, qDSV-calculated velocities (5-18 cm/s) had strong correlation (slope=1.22, R2=0.90) with US (3-20 cm/s). In the stenosis model, blood velocity at baseline, post-stenosis, post-venoplasty, and post-stent placement were similar on qDSV and US at all time points. CONCLUSION: Venous blood velocity was accurately quantified in a venousphantom and in vivo porcine models using qDSV. Intra-procedural changes in porcine iliac vein blood velocity were quantified with qDSV after creation of a stenosis and subsequently treating it with venoplasty and stent placement.

Microwave Ablation of the Pig Growth Plate: Proof of Concept for Minimally Invasive Epiphysiodesis.

BACKGROUND: Different surgical methods for epiphysiodesis of limb length discrepancy (LLD) have been described. Although these methods are variably effective, they are associated with morbidity (pain and limp) and potential complications. Microwave ablation is a less-invasive opportunity to halt growth by selectively destroying the growth plate via thermal energy to treat LLD in children. QUESTIONS/PURPOSES: In this proof-of-concept study using an in vivo pig model, we asked: (1) What is the durability of response 2 to 4 months after microwave ablation of the tibial growth plate as measured by length and angulation of the tibia via a CT scan? (2) Was articular cartilage maintained as measured by standard histologic staining for articular cartilage viability? METHODS: To develop an in vivo protocol for microwave ablation, we placed microwave antennas adjacent to the proximal tibia growth plate in the cadaveric hindlimbs of 18 3-month-old pigs. To determine the suitable time, we varied ablation from 90 to 270 seconds at 65-W power settings. After sectioning the tibia, we visually assessed for discoloration (implying growth plate destruction) that included the central growth plate but did not encroach into the epiphysis in a manner that could disrupt the articular surface. Using this information, we then performed microwave ablation on three live female pigs (3.5 to 4 months old) to evaluate physiologic changes and durability of response. A postprocedure MRI was performed to ensure the intervention led to spatial growth plate alterations similar to that seen in cadavers. This was followed by serial CT, which was used to assess the potential effect on local bone and growth until the animals were euthanized 2 to 4 months after the procedure. We analyzed LLD, angular deformity, and bony deformity using CT scans of both tibias. The visibility of articular cartilage was compared with that of the contralateral tibia via standard histologic staining, and growth rates of the proximal tibial growth plate were compared via fluorochrome labeling. RESULTS: Eighteen cadaveric specimens showed ablation zones across the growth plate without visual damage to the articular surface. The three live pigs did not exhibit changes in gait or require notable pain medication after the procedure. Each animal demonstrated growth plate destruction, expected limb shortening (0.8, 1.2, and 1.5 cm), and bony cavitation around the growth plate. Slight valgus bone angulation (4º, 5º, and 12º) compared with the control tibia was noted. No qualitatively observable articular cartilage damage was encountered from the histologic comparison with the contralateral tibia for articular cartilage thickness and cellular morphology. CONCLUSION: A microwave antenna placed into a pig's proximal tibia growth plate can slow the growth of the tibia without apparent pain and alteration of gait and function. CLINICAL RELEVANCE: Further investigation and refinement of our animal model is ongoing and includes shorter ablation times and comparison of dynamic ablation (moving the antennae during the ablation) as well as static ablation of the tibia from a medial and lateral portal. These refinements and planned comparison with standard mechanical growth arrest in our pig model may lead to a similar approach to ablate growth plates in children with LLD.

On the pursuit of emissions-free clean mobility - Electric vehicles versus e-fuels.

With the passing of every second we get closer to a society that is more cognizant of the effect carbon dioxide emissions are having on our planet, and that is more willing to take part in sustainable efforts to combat this and ever more interested in investing in cleaner technologies like electric vehicles (EVs). EVs are marching strongly into a market that is currently dominated by internal combustion engine vehicles, the current main fuel of which is a known contributor to most of the emission related climate problems that we now find ourselves in. Moving ahead, it is important that any move from internal combustion engines to more nascent technologies like EVs is sustainable and not detrimental to the environment. There is an ongoing debate between proponents of so-called e-fuels (being synthetic fuels made from atmospheric carbon dioxide, water, and renewable energy) and EVs wherein e-fuels are largely accused of being a half-measure while EVs are thought to contribute more in terms of brake and tire emissions than the ICE vehicles. This raises the question of whether there should even be a complete replacement of the combustion engine vehicle fleet or that should there be a 'mobility mix' similar to how we currently refer to an energy mix with power grids. This article offers some perspectives by critically analyzing and diving deeper into these pressing concerns to answer some of these questions.

A hybrid deformable registration method to generate motion-compensated 3D virtual MRI for fusion with interventional real-time 3D ultrasound.

PURPOSE: Ultrasound is often the preferred modality for image-guided therapy or treatment in organs such as liver due to real-time imaging capabilities. However, the reduced conspicuity of tumors in ultrasound images adversely impacts the precision and accuracy of treatment delivery. This problem is compounded by deformable motion due to breathing and other physiological activity. This creates the need for a fusion method to align interventional US with pre-interventional modalities that provide superior soft-tissue contrast (e.g., MRI) to accurately target a structure-of-interest and compensate for liver motion. METHOD: In this work, we developed a hybrid deformable fusion method to align 3D pre-interventional MRI and 3D interventional US volumes to target the structures-of-interest in liver accurately in real-time. The deformable multimodal fusion method involved an offline alignment of a pre-intervention MRI with a pre-intervention US volume using a traditional registration method, followed by real-time prediction of deformation using a trained deep-learning model between interventional US volumes across different respiratory states. This framework enables motion-compensated MRI-US image fusion in real-time for image-guided treatment. RESULTS: The proposed hybrid deformable registration method was evaluated on three healthy volunteers across the pre-intervention MRI and 20 US volume pairs in the free-breathing respiratory cycle. The mean Euclidean landmark distance of three homologous targets in all three volunteers was less than 3 mm for percutaneous liver procedures. CONCLUSIONS: Preliminary results show that clinically acceptable registration accuracies for near real-time, deformable MRI-US fusion can be achieved by our proposed hybrid approach. The proposed combination of traditional and deep-learning deformable registration techniques is thus a promising approach for motion-compensated MRI-US fusion to improve targeting in image-guided liver interventions.

Advanced CT techniques for hepatic microwave ablation zone monitoring and follow-up.

PURPOSE: To evaluate utility of advanced CT techniques including HighlY constrained back-projection and dual-energy CT for intra- and post-procedure hepatic microwave ablation zone monitoring. METHODS: 8 hepatic microwave ablations were performed in 4 adult swine (5 min/65 W). Low-dose routine CECT and dual-energy CT images were obtained every 1 min during ablation. Images were reconstructed ± HYPR. Image quality and dose metrics were collected. 21 MWA were performed in 4 adult swine. Immediate post-procedure CECT was performed in the arterial, portal venous, and delayed phases using both routine and DECT imaging with full-dose weight-based IV contrast dosing. An additional 16 MWA were subsequently performed in 2 adult swine. Immediate post-procedure CT was performed with half-dose IV contrast using routine and DECT. 12 patients (10 M/2F, mean age 62.4 yrs) with 14 hepatic tumors (4 HCC, 10 metastatic lesions) treated with MWA were prospectively imaged with DECT 1 month post-procedure. 120 kV equivalent images were compared to DECT [51 keV, iodine material density]. Image quality and dose metrics were collected. RESULTS: Gas created during MWA led to high CNR in all intraprocedural CT datasets. Optimal CNRs were noted at 4 min with CNR 6.7, 15.5,15.9, and 21.5 on LD-CECT, LD-CECT + HYPR, DECT, and DECT + HYPR, respectively (p < 0.001). Image quality scores at 4 min were 1.8, 2.8, 2.4, and 3, respectively (p < 0.001). Mean radiation dose (CTDIvol) was eightfold higher for the DECT series. For swine, post-procedural DECT images (IMD/51 keV) showed improved CNR compared to routine CT at all time points with full and with reduced dose contrast (CNR 4.6, 3.2, and 1.5, respectively, at half-contrast dose, p < 0.001). For human subjects, the 51 keV and IMD images showed higher CNRs (5.8, 4.8 vs 4.0, p < 0.001) and SNRs (3.7, 5.9 vs 2.8). Ablation zone sharpness was improved with DECT (routine 3.0 ± 0.7, DECT 3.5 ± 0.5). Diagnostic confidence was higher with DECT (routine 2.3 ± 0.9, DECT 2.6 ± 0.8). Mean DLP for DECT was 905.7 ± 606 mGy-cm, CTDIvol 37.5 ± 21.2 mGy, and effective dose 13.6 ± 9.1 mSv, slightly higher than conventional CT series. CONCLUSION: Advanced CT techniques can improve CT image quality in peri-procedural hepatic microwave ablation zone evaluation.

CT and MR imaging surveillance of stage 1 renal cell carcinoma after microwave ablation.

OBJECTIVE: To describe the CT and MR imaging findings after microwave ablation of clinical stage 1 renal cell carcinoma (RCC). METHODS: This single-center retrospective study was performed under a waiver of informed consent. 49 patients (38 M/11F, mean age 66 ± 9.0) with 52 cT1a RCC and 19 patients (10M/9F, mean age 67 ± 9.7) with 19 cT1b RCC were treated with percutaneous microwave ablation between January 2012 and June 2014. The size and volume of the RCC and ablation zone were measured and the kidney, ablation zones and retroperitoneum were assessed at immediate post-procedure CT and surveillance CT and MRI. RESULTS: Median imaging follow-up was 18 months (IQR 12-28). Ablation zones were heterogeneously hyperintense on T1W and hypointense on T2W MRI and hyperdense at CT. Thin peripheral, but no internal enhancement after contrast administration signified successful ablation zones. Ablation zones decreased in size, but did not resolve during surveillance. Immediate post-procedure subcapsular gas and hematoma (5/71, 7%) resolved prior to first follow-up. Focal, enhancing soft tissue within the ablation zone, invariably along the renal margin, signified local recurrence. Local recurrence rates were higher for T1b (2/19, 11%) compared to T1a (1/52, 2%). Urinomas (4/71, 6%) decreased in size and resolved during surveillance. Retroperitoneal fat necrosis (6/71, 9%), with opposed-phase loss of T1W MRI signal, was confirmed at histology after percutaneous biopsy. CONCLUSION: CT and MR imaging features after microwave ablation of renal cell carcinoma are predictable and reliably demonstrate treatment success, early and delayed complications, and local recurrences that can guide patient management.

Quantitative 4D-Digital Subtraction Angiography to Assess Changes in Hepatic Arterial Flow during Transarterial Embolization: A Feasibility Study in a Swine Model.

PURPOSE: To determine the feasibility of using time-resolved 3D-digital subtraction angiography (4D-DSA) for quantifying changes in hepatic arterial blood flow and velocity during transarterial embolization. MATERIALS AND METHODS: Hepatic arteriography and selective transarterial embolization were performed in 4 female domestic swine (mean weight, 54 kg) using 100-300-µm microspheres. Conventional 2D and 4D-DSA were performed before, during, and after each embolization. From the 4D-DSA reconstructions, blood flow and velocity values were calculated for hepatic arterial branches using a pulsatility-based algorithm. 4D-DSA velocity values were compared to those measured using an intravascular Doppler wire with a linear regression analysis. Paired t-tests were used to compare data before and after embolization. RESULTS: There was a weak-to-moderate but statistically significant correlation of flow velocities measured with 4D-DSA and the Doppler wire (r = 0.35, n = 39, P = .012). For vessels with high pulsatility, the correlation was higher (r = 0.64, n = 11, P = .034), and the relationship between 4D-DSA and the Doppler wire fit a linear model with a positive bias toward the Doppler wire (failed to reject at 95% confidence level, P = .208). 4D-DSA performed after partial embolization showed a reduction in velocity in the embolized hepatic arteries compared to pre-embolization (mean, 3.96 ± 0.74 vs 11.8 2± 2.15 cm/s, P = .006). CONCLUSION: Quantitative 4D-DSA can depict changes in hepatic arterial blood velocity during transarterial embolization in a swine model. Further work is needed to optimize 4D-DSA acquisitions and to investigate its applicability in humans.

Comparison of Conventional and Cone-Beam CT for Monitoring and Assessing Pulmonary Microwave Ablation in a Porcine Model.

PURPOSE: To compare cone-beam computed tomography (CT) with conventional CT for assessing the growth and postprocedural appearance of pulmonary microwave ablation zones. MATERIALS AND METHODS: A total of 17 microwave ablations were performed in porcine lung in vivo by applying 65 W for 5 minutes through a single 17-gauge antenna. Either CT (n = 8) or CBCT (n = 9) was used for guidance and ablation zone monitoring at 1-minute intervals. Postprocedural noncontrast images were acquired with both modalities. Three independent readers measured the length, width, cross-sectional area, and circularity of the ablation zones on gross tissue samples and CT and cone-beam CT images. The measurements were compared via linear mixed-effects models for postprocedural appearance and with a polynomial mixed effects model for ablation zone growth curves. RESULTS: On postprocedural images, the differences between cone-beam CT and CT in mean length (3.84 vs 3.86 cm; Δ = -0.02; P = .70), width (2.61 vs 2.56 cm; Δ = 0.06; P = .46), area (7.84 vs 7.65 cm2; Δ = 0.19; P = .35), and circularity (0.85 vs 0.85; Δ = 0.01; P = .62) were not statistically significant after accounting for intersubject and interrater variability. Also, there was no significant difference between CT and cone-beam CT growth curves of the ablation zones during monitoring in terms of length (pInt. = 1.00; pLin.Slope = 0.52; pQuad.Slope = 0.69); width (pInt. = 0.83; pLin.Slope = 0.98; pQuad.Slope = 0.79), area (pInt. = 0.47; pLin.Slope = 0.27; pQuad.Slope = 0.57), or circularity (pInt. = 0.54; pLin.Slope = 0.74; pQuad.Slope = 0.80). Both CT and cone-beam CT overestimated gross pathologic observations of ablation length, width, and area (P < .001 for all). CONCLUSIONS: Cone-beam CT was similar to conventional CT when assessing the growth, final size, and shape of pulmonary microwave ablation zones and may be useful for monitoring and evaluating microwave ablations in the lung.

Analysis of iodinated contrast delivered during thermal ablation: is material trapped in the ablation zone?

Intra-procedural contrast-enhanced CT (CECT) has been proposed to evaluate treatment efficacy of thermal ablation. We hypothesized that contrast material delivered concurrently with thermal ablation may become trapped in the ablation zone, and set out to determine whether such an effect would impact ablation visualization. CECT images were acquired during microwave ablation in normal porcine liver with: (A) normal blood perfusion and no iodinated contrast, (B) normal perfusion and iodinated contrast infusion or (C) no blood perfusion and residual iodinated contrast. Changes in CT attenuation were analyzed from before, during and after ablation to evaluate whether contrast was trapped inside of the ablation zone. Visualization was compared between groups using post-ablation contrast-to-noise ratio (CNR). Attenuation gradients were calculated at the ablation boundary and background to quantitate ablation conspicuity. In Group A, attenuation decreased during ablation due to thermal expansion of tissue water and water vaporization. The ablation zone was difficult to visualize (CNR = 1.57 ± 0.73, boundary gradient = 0.7 ± 0.4 HU mm(-1)), leading to ablation diameter underestimation compared to gross pathology. Group B ablations saw attenuation increase, suggesting that iodine was trapped inside the ablation zone. However, because the normally perfused liver increased even more, Group B ablations were more visible than Group A (CNR = 2.04 ± 0.84, boundary gradient = 6.3 ± 1.1 HU mm(-1)) and allowed accurate estimation of the ablation zone dimensions compared to gross pathology. Substantial water vaporization led to substantial attenuation changes in Group C, though the ablation zone boundary was not highly visible (boundary gradient = 3.9 ± 1.1 HU mm(-1)). Our results demonstrate that despite iodinated contrast being trapped in the ablation zone, ablation visibility was highest when contrast is delivered intra-procedurally. Therefore, CECT may be feasible for real-time thermal ablation monitoring.

Design and validation of a thermoreversible material for percutaneous tissue hydrodissection.

Interventional oncology procedures such as thermal ablation are becoming routine for many cancers. Hydrodissection-separating tissues with fluids-protects tissues near the treatment zone to improve ablation's safety and facilitate more aggressive treatments. However, currently used fluids such as normal saline and 5% dextrose in water (D5W) migrate in the peritoneum, reducing their protective efficacy. As a hydrodissection alternative, we investigated a thermoreversible poloxamer 407 (P407) solution. Such a material can be injected as a liquid which then forms a semi-solid gel at body temperature without syneresis. The desired gelation temperature of 32°C was achieved with 15.4 wt/wt % P407. Viscosity analysis revealed the lowest viscosity and ideal injection point was at 14°C. Solution viscosity increased during gelation, to a peak of 65 kPa*s at 40°C. The electrical impedance of P407 was significantly greater than isotonic saline, but lower than D5W, indicating its potential for electrical protection. The P407 gel was similar to other hydrodissection fluids at ultrasound and CT imaging. Ex vivo liver ablations showed that P407 protects neighboring tissues, but may require a thicker barrier for comparable protection to D5W. Overall, we found that the P407 solution is a feasible alternative to traditional hydrodissection fluids and warrants additional study.

Visualizing ex vivo radiofrequency and microwave ablation zones using electrode vibration elastography.

PURPOSE: Electrode vibration elastography is a new shear wave imaging technique that can be used to visualize thermal ablation zones. Prior work has shown the ability of electrode vibration elastography to delineate radiofrequency ablations; however, there has been no previous study of delineation of microwave ablations or radiological-pathological correlations using multiple observers. METHODS: Radiofrequency and microwave ablations were formed in ex vivo bovine liver tissue. Their visualization was compared on shear wave velocity and maximum displacement images. Ablation dimensions were compared to gross pathology. Elastographic imaging and gross pathology overlap and interobserver variability were quantified using similarity measures. RESULTS: Elastographic imaging correlated with gross pathology. Correlation of area estimates was better in radiofrequency than in microwave ablations, with Pearson coefficients of 0.79 and 0.54 on shear wave velocity images and 0.90 and 0.70 on maximum displacement images for radiofrequency and microwave ablations, respectively. The absolute relative difference in area between elastographic imaging and gross pathology was 18.9% and 22.9% on shear wave velocity images and 16.0% and 23.1% on maximum displacement images for radiofrequency and microwave ablations, respectively. CONCLUSIONS: Statistically significant radiological-pathological correlation was observed in this study, but correlation coefficients were lower than other modulus imaging techniques, most notably in microwave ablations. Observers provided similar delineations for most thermal ablations. These results suggest that electrode vibration elastography is capable of imaging thermal ablations, but refinement of the technique may be necessary before it can be used to monitor thermal ablation procedures clinically.

Ultrasound-based relative elastic modulus imaging for visualizing thermal ablation zones in a porcine model.

The feasibility of using ultrasound-based elastic modulus imaging to visualize thermal ablation zones in an in vivo porcine model is reported. 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 area of each thermal ablation zone obtained from an elastic modulus image were 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 provides higher (more than a factor of 2) 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.

Multiple-electrode radiofrequency ablation: comparison with a conventional cluster electrode in an in vivo porcine kidney model.

PURPOSE: To compare multiple-electrode radiofrequency (RF) ablation versus RF ablation with a cluster electrode in an in vivo porcine kidney model. MATERIALS AND METHODS: Thirteen female pigs (mean weight, 45 kg) were used for the study. In each animal, RF ablations were performed for 12 minutes with a conventional cluster electrode in one kidney (controls, n = 13) and a multiple-electrode configuration in the contralateral organ. Multiple-electrode ablations were performed with electrodes 1.5 cm apart (group 1, n = 7) or 2.0 cm apart (group 2, n = 6). The mean maximum temperature at the electrode tips was determined. After each animal was euthanized, the kidneys were removed and the ablation zones were sectioned into 5-mm transverse slices. A representative slice was stained with 2,3,5-triphenyl-2H-tetrazolium chloride. Standard ablation zone metrics were measured and differences between groups were analyzed for statistical significance. RESULTS: The mean maximum ablation zone diameter was 3.0 cm +/- 0.6 (SD) for controls, compared with 5.0 cm +/- 0.5 for group 1 (P < .0001) and 4.4 cm +/- 1.0 for group 2 (P = .002). Mean ablation zone minimum diameter was higher for group 1 (P = .002) and group 2 (P = .03) than for controls. Isoperimetric ratios were lowest for group 2 (P = .04 vs controls) whereas the highest temperatures at the electrode tips were observed with group 1 (P = .02 vs controls). CONCLUSION: In normal porcine kidney, multiple-electrode RF ablation produced larger zones of ablation than a cluster electrode. Efficacy was greater when electrodes were spaced 1.5 cm apart than when they were spaced 2.0 cm apart.

Multiple-electrode radiofrequency ablation of hepatic malignancies: initial clinical experience.

OBJECTIVE: The objective of our study was to retrospectively analyze our initial clinical experience with percutaneous multiple-electrode radiofrequency ablation and evaluate its safety and efficacy for treating hepatic malignancies. MATERIALS AND METHODS: Thirty-eight malignant hepatic tumors (mean diameter, 2.7 cm; range, 0.7-10.0 cm) in 23 patients (12 men and 11 women; mean age, 65 years; range, 40-84 years) were treated in 26 radiofrequency ablation sessions with an impedance-based multiple-electrode system. One, two, or three (mean, 2.4) 17-gauge electrodes were placed, and tumors were ablated using a combination of CT and sonography for guidance and monitoring. Electrodes were placed in close proximity (mean spacing: two electrodes, 1.0 cm; three electrodes, 1.4 cm) to treat large tumors or were used independently to treat several tumors simultaneously. Contrast-enhanced CT scans were obtained immediately after ablation to determine technical success and evaluate for complications. Follow-up CT scans at 1, 3, 6, 9, and 12 months (mean, 4 months) after ablation were obtained to assess for tumor progression and new metastases. RESULTS: Local control was achieved in 37 of 38 tumors, 34 of which were treated in one session. Ablations created with closely spaced electrodes had a mean diameter of 4.9 cm. The total ablation time was reduced by approximately 54% compared with an equivalent number of ablations performed with a single-electrode system (1,014 vs 2,196 minutes). Three complications occurred: one death from a presumed postprocedure pulmonary embolus, one pneumothorax, and one asymptomatic perihepatic hemorrhage. CONCLUSION: Multiple-electrode radiofrequency ablation appears to be a safe and effective means of achieving local control in large or multiple hepatic malignancies at short-term follow-up.

Unintended thermal injuries from radiofrequency ablation: protection with 5% dextrose in water.

OBJECTIVE: Radiofrequency ablation of hepatic tumors can lead to thermal injury of surrounding structures. Both saline and 5% dextrose in water (D5) have been used to displace these surrounding structures before radiofrequency ablation. The purpose of this study was to determine the relative effectiveness of these two fluids for protecting the diaphragm and lung during radiofrequency ablation. MATERIALS AND METHODS: Ten female domestic swine (mean weight, 45 kg) underwent radiofrequency ablation at open surgery. Group 1 (n = 12 lesions) was pretreated with peritoneal D5 before radiofrequency ablation. Group 2 (n = 11 lesions) was pretreated with peritoneal 0.9% saline. A 2.7-mm spacer was placed between the liver surface and diaphragm in groups 1 and 2. Group 3 (n = seven lesions) served as a control group with no pretreatment regimen. Group 4, an additional control group (n = eight lesions), consisted of animals pretreated with D5 in which a larger spacer was used. After radiofrequency ablation, the animals were sacrificed and the liver, diaphragm, and lung were removed. The extent of thermal injury to the surface of each organ was recorded. RESULTS: The animals in the D5 and saline pretreatment groups experienced fewer diaphragm injuries than the control animals (D5, p = 0.02). The smallest lesions in the lung and diaphragm were in the D5 group, followed by the saline and control groups (diaphragm, p = 0.0001; lung, p = 0.13). Diaphragm lesions were significantly smaller in the D5 and saline groups than in the control group (p = 0.0001 and 0.01, respectively). CONCLUSION: Instillation of D5 into the peritoneal cavity before hepatic radiofrequency ablation decreases the risk and severity of diaphragm and lung injuries compared with no pretreatment or pretreatment with 0.9% saline in this animal model. Pretreatment with D5 may increase both the safety of and the number of patients eligible for treatment with thermal therapies.

Multiple-electrode radiofrequency ablation: simultaneous production of separate zones of coagulation in an in vivo porcine liver model.

PURPOSE: A multiple-electrode radiofrequency (RF) system was developed based on switching between electrodes that allows for the simultaneous use of as many as three electrically independent electrodes. The purpose of this study was to determine if each multiple-electrode ablation zone is identical to an ablation zone created with conventional single-electrode mode. MATERIALS AND METHODS: Nine female domestic pigs (mean weight, 90 kg) were used for this study. A prototype monopolar multiple-electrode RF ablation system was created with use of an RF generator and an electronic switching algorithm. A maximum of three electrodes can be used simultaneously by switching between electrodes at each impedance spike (30 omega greater than baseline levels). A total of 39 zones of ablation were created at open laparotomy in pig livers with use of a conventional single electrode (n = 9), two single electrodes simultaneously (n = 6 ablations; 12 ablation zones), or three single electrodes simultaneously (n = 6 ablations; 18 ablation zones). RF electrodes were spaced in separate lobes of the liver when multiple zones of coagulation were created simultaneously. Animals were euthanized after RF ablation, livers were removed, and ablation zones were sectioned and measured. RESULTS: Zones of coagulation created simultaneously with two or three electrodes were equivalent to ablation zones created with use of conventional single-electrode ablation. No significant differences were observed among control animals treated with a single electrode, those with two separate zones of ablation created simultaneously, and those with three simultaneously created ablation zones in terms of mean (+/-SD) minimum diameter (1.6 cm +/- 0.6, 1.6 cm +/- 0.5, and 1.7 cm +/- 0.4, respectively), maximum diameter (2.0 cm +/- 0.5, 2.3 cm +/- 0.5, 2.2 cm +/- 0.5, respectively), and volume (6.7 cm3 +/- 3.7, 7.4 cm3 +/- 3.8, and 7.8 cm3 +/- 3.9; P > .30, analysis of variance, pairwise t-test comparisons). CONCLUSIONS: A rapid-switching multiple-electrode RF system was able to simultaneously create as many as three separate ablation zones of equivalent size compared with single-electrode controls. This system would allow physicians to simultaneously treat multiple tumors, substantially reducing procedure time and anesthesia risk.