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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. 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. 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

Objective. Existing clinical C-arm interventional systems use scintillator-based energy-integrating flat panel detectors (FPDs) to generate cone-beam CT (CBCT) images. Despite its volumetric coverage, FPD-CBCT does not provide sufficient low-contrast detectability desired for certain interventional procedures. The purpose of this work was to develop a C-arm photon counting detector (PCD) CT system with a step-and-shoot data acquisition method to further improve the tomographic imaging performance of interventional systems. Approach. As a proof-of-concept, a cadmium telluride-based 51 cm × 0.6 cm PCD was mounted in front of a FPD in an Artis Zee biplane system. A total of 10 C-arm sweeps (5 forward and 5 backward) were prescribed. A motorized patient table prototype was synchronized with the C-arm system such that it translates the object by a designated distance during the sub-second rest time in between gantry sweeps. To evaluate whether this multi-sweep step-and-shoot acquisition strategy can generate high-quality and volumetric PCD-CT images without geometric distortion artifacts, experiments were performed using physical phantoms, a human cadaver head, and an in vivo swine subject. Comparison with FPD-CT was made under matched narrow beam collimation and radiation dose conditions. Main results. Compared with FPD-CT images, PCD-CT images had lower noise and improved visualization of low-contrast lesion models, as well as improved visibility of small iodinated blood vessels. Fine structures were visualized more clearly by the PCD-CT than the highest-available resolution provided by FPD-CBCT and MDCT. No perceivable geometric distortion artifacts were observed in the multi-planar PCD-CT images. Significance. This work is the first demonstration of the feasibility of high-quality and multi-planar (volumetric) PCD-CT imaging with a rotating C-arm gantry.

We propose dielectric tissue property models dependent on both water and air content covering the microwave frequency range. Water is the largest constituent of biological tissues, and its effect on the dielectric properties of biological tissue has been studied. However, dehydration effects due to thermal heating have not been fully characterized. We combined 1) Maxwell–Fricke mixture theory with a four-pole Cole–Cole equation to include water and air content dependence and, as the second approach, a different 2) Maxwell mixture model was coupled with a Debye function. The proposed approaches (1 and 2) were able to predict the permittivity ( ϵ’ ) and conductivity ( σ ) of bovine liver and swine lung tissues at different hydration and inflation states from 1 to 15 GHz. A second approach coupling Maxwell and Debye models required fewer assumptions and modeled tissue properties with higher accuracy (less than 15% mean percent error in all tissue types). These models may help improve the accuracy of microwave ablation simulation when tissue water content changes as a result of vaporization and may facilitate personalized treatment planning.

Purpose To evaluate the feasibility and efficacy of ultrasound-guided microwave ablation for the treatment of inguinal neuralgia. Materials and Methods A retrospective review of 12 consecutive ultrasound-guided microwave ablation procedures was performed of 10 consecutive patients (8 men, 2 women; mean age, 41 years [range, 15–64 years]), between August 2012 and August 2016. Inclusion criteria for inguinal neuralgia included clinical diagnosis of chronic inguinal pain (average, 17.3 months [range, 6–46 months]) refractory to conservative treatment and a positive nerve block. Pain response—reduction of pain level and duration and percent pain reduction using a 10-point visual analog scale (VAS) at baseline and up to 12 months after the procedure—was measured. Nine patients had pain after the inguinal hernia repair, and 1 patient had pain from the femoral artery bypass procedure. The microwave ablation procedure targeted the ilioinguinal nerve in 7 cases, the genitofemoral nerve in 4 cases, and the iliohypogastric nerve in 1 case. Results Average baseline VAS pain score was 6.1 (standard deviation, 2.5). Improved pain levels immediately after the procedure and at 1, 6, and 12 months were statistically significant (P = .0037, .0037, .0038, .0058, respectively). Also, 91.7% (11/12) of the procedures resulted in immediate pain relief and at 1 month and 6 months. At 12 months, 83.3% (10/12) of patients had an average of 69% ± 31% pain reduction. Percent maximal pain reduction was 93% ± 14% (60%–100%), and the average duration of clinically significant pain reduction was 10.5 months (range, 0–12 months.). No complications or adverse outcomes occurred. Conclusions Ultrasound-guided microwave ablation is an effective technique for the treatment of inguinal neuralgia after herniorrhaphy.

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 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.

Purpose To evaluate potential biologic and thermal mechanisms of the observed differences in thrombosis rates between hepatic vessels during microwave (MW) ablation procedures. Materials and Methods MW ablation antennae were placed in single liver lobes of 2 in vivo porcine liver models (n = 3 in each animal; N = 6 total) in the proximity of a large (> 5 mm) portal vein (PV) and hepatic veins (HVs). Each ablation was performed with 100 W for 5 minutes. Conventional ultrasound imaging and intravascular temperature probes were used to evaluate vessel patency and temperature changes during the ablation procedure. Vascular endothelium was harvested 1 hour after ablation and used to characterize genes and proteins associated with thrombosis in PVs and HVs. Results Targeted PVs within the MW ablation zone exhibited thrombosis at a significantly higher rate than HVs (54.5% vs 0.0%; P = .0046). There was a negligible change in intravascular temperature in PVs and HVs during the ablation procedure (0.2°C ± 0.4 vs 0.6°C ± 0.9; P = .46). PVs exhibited significantly higher gene expression than HVs in terms of fold differences in thrombomodulin (2.9 ± 2.0; P = .0001), von Willebrand factor (vWF; 7.6 ± 1.5; P = .0001), endothelial protein C receptor (3.50 ± 0.49; P = .0011), and plasminogen activator inhibitor (1.46 ± 0.05; P = .0014). Western blot analysis showed significantly higher expression of vWF (2.32 ± 0.92; P = .031) in PVs compared with HVs. Conclusions Large PVs exhibit thrombosis more frequently than HVs during MW ablation procedures. Biologic differences in thrombogenicity, rather than heat transfer, between PVs and HVs may contribute to their different rates of thrombosis.

Thermal ablation of soft tissue changes the tissue microstructure, and consequently induces changes to its acoustic properties. While B-mode ultrasound provides high-resolution and high-frame-rate images of ablative therapeutic procedures, it is not particularly effective at delineating boundaries of ablated regions due to poor contrast in echogenicity between ablated and surrounding normal tissue. Quantitative Ultrasound (QUS) techniques can provide quantitative estimates of acoustic properties such as backscatter and attenuation coefficients and differentiate ablated and unablated regions more effectively, with the potential for monitoring minimally invasive thermal therapies. In this study, a previously introduced attenuation estimation method was used to create quantitative attenuation coefficient maps for 11 microwave ablation procedures performed on refrigerated ex-vivo bovine liver. The attenuation images correlate well with the pathological images of the ablated region. The mean attenuation coefficient for regions of interest (ROIs) drawn inside and outside the ablated zones were 0.9 (±0.2) and 0.45 (±0.15) dB/cm/MHz, respectively. These estimates agree with reported values in the literature and establish the usefulness of noninvasive attenuation imaging for monitoring therapeutic procedures in the liver.

Purpose The detection of small parenchymal hepatic lesions identified by preoperative imaging remains a challenge for traditional pathologic methods in large specimens. We developed a magnetic resonance imaging (MRI) compatible localization device for imaging of surgical specimens aimed to improve identification and localization of hepatic lesions ex vivo. Materials and methods The device consists of two stationary and one removable MR-visible grids lined with silicone gel, creating an orthogonal 3D matrix for lesion localization. To test the device, five specimens of swine liver with a random number of lesions created by microwave ablation were imaged on a 3 T MR scanner. Two readers independently evaluated lesion coordinates and size, which were then correlated with sectioning guided by MR imaging. Results All lesions ( n = 38) were detected at/very close to the expected localization. Inter-reader agreement of lesion localization was almost perfect (0.92). The lesion size estimated by MRI matched macroscopic lesion size in cut specimen (± 2 mm) in 34 and 35, respectively, out of 38 lesions. Conclusion Use of this MR compatible device for ex vivo imaging proved feasible for detection and three-dimensional localization of liver lesions, and has potential to play an important role in the ex vivo examination of surgical specimens in which pathologic correlation is clinically important.

Purpose To determine how close to the heart pulmonary microwave ablation can be performed without causing cardiac tissue injury or significant arrhythmia. Materials and Methods The study was performed with approval from the institutional animal care and use committee. Computed tomographic fluoroscopically guided microwave ablation of the lung was performed in 12 swine. Antennas were randomized to either parallel (180° ± 20°) or perpendicular (90° ± 20°) orientation relative to the heart surface and to distances of 0-10 mm from the heart. Ablations were performed at 65 W for 5 minutes or until a significant arrhythmia (asystole, heart block, bradycardia, supraventricular or ventricular tachycardia) developed. Heart tissue was evaluated with vital staining and histologic examination. Data were analyzed with mixed effects logistic regression, receiver operating characteristic curves, and the Fisher exact test. Results Thirty-four pulmonary microwave ablations were performed with the antenna a median distance of 4 mm from the heart in both perpendicular (n = 17) and parallel (n = 17) orientation. Significant arrhythmias developed during six (18%) ablations. Cardiac tissue injury occurred with 17 ablations (50%). Risk of arrhythmia and tissue injury decreased with increasing antenna distance from the heart with both antenna orientations. No cardiac complication occurred with a distance of greater than or equal to 4.4 mm from the heart. The ablation zone extended to the pleural surface adjacent to the heart in 71% of parallel and 17% of perpendicular ablations performed 5-10 mm from the heart. Conclusion Microwave lung ablations performed more than or equal to 5 mm from the heart were associated with a low risk of cardiac complications. © RSNA, 2016.

Purpose To determine whether variable hepatic microwave ablation (MWA) can induce local inflammation and distant pro-oncogenic effects compared with hepatic radiofrequency ablation (RFA) in an animal model. Materials and Methods In this institutional Animal Care and Use Committee-approved study, F344 rats (150 gm, n = 96) with subcutaneous R3230 breast adenocarcinoma tumors had normal non-tumor-bearing liver treated with RFA (70°C × 5 minutes), rapid higher-power MWA (20 W × 15 seconds), slower lower-power MWA (5 W × 2 minutes), or a sham procedure (needle placement without energy) and were sacrificed at 6 hours to 7 days (four time points; six animals per arm per time point). Ablation settings produced 11.4 mm ± 0.8 of coagulation for all groups. Distant tumor growth rates were determined to 7 days after treatment. Liver heat shock protein (HSP) 70 levels (at 72 hours) and macrophages (CD68 at 7 days), tumor proliferative indexes (Ki-67 and CD34 at 7 days), and serum and tissue levels of interleukin 6 (IL-6) at 6 hours, hepatocyte growth factor (HGF) at 72 hours, and vascular endothelial growth factor (VEGF) at 72 hours after ablation were assessed. All data were expressed as means ± standard deviations and were compared by using two-tailed t tests and analysis of variance for selected group comparisons. Linear regression analysis of tumor growth curves was used to determine pre- and posttreatment growth curves on a per-tumor basis. Results At 7 days, hepatic ablations with 5-W MWA and RFA increased distant tumor size compared with 20-W MWA and the sham procedure (5-W MWA: 16.3 mm ± 1.1 and RFA: 16.3 mm ± 0.9 vs sham: 13.6 mm ± 1.3, P < .01, and 20-W MWA: 14.6 mm ± 0.9, P < .05). RFA and 5-W MWA increased postablation tumor growth rates compared with the 20-W MWA and sham arms (preablation growth rates range for all arms: 0.60-0.64 mm/d; postablation: RFA: 0.91 mm/d ± 0.11, 5-W MWA: 0.91 mm/d ± 0.14, P < .01 vs pretreatment; 20-W MWA: 0.69 mm/d ± 0.07, sham: 0.56 mm/d ± 1.15; P = .48 and .65, respectively). Tumor proliferation (Ki-67 percentage) was increased for 5-W MWA (82% ± 5) and RFA (79% ± 5), followed by 20-W MWA (65% ± 2), compared with sham (49% ± 5, P < .01). Likewise, distant tumor microvascular density was greater for 5-W MWA and RFA (P < .01 vs 20-W MWA and sham). Lower-energy MWA and RFA also resulted in increased HSP 70 expression and macrophages in the periablational rim (P < .05). Last, IL-6, HGF, and VEGF elevations were seen in 5-W MWA and RFA compared with 20-W MWA and sham (P < .05). Conclusion Although hepatic MWA can incite periablational inflammation and increased distant tumor growth similar to RFA in an animal tumor model, higher-power, faster heating protocols may potentially mitigate such undesired effects. © RSNA, 2016.

Purpose To characterize vessel occlusion rates and their role in local tumor progression in patients with hepatocellular carcinoma (HCC) who underwent microwave tumor ablation. Materials and Methods This institutional review board approved, HIPAA-compliant retrospective review included 95 patients (75 men and 20 women) with 124 primary HCCs who were treated at a single center between January 2011 and March 2014. Complete occlusion of the portal veins, hepatic veins, and hepatic arteries within and directly abutting the ablation zone was identified with postprocedure contrast material-enhanced computed tomography. For each vessel identified in the ablation zone, its size and antenna spacing were recorded and correlated with vascular occlusion with logistic regression analysis. Local tumor progression rates were then compared between patent and occluded vessels for each vessel type with Fisher exact test. Results Occlusion was identified in 39.7% of portal veins (29 of 73), 15.0% of hepatic veins (six of 40), and 14.2% of hepatic arteries (10 of 70) encompassed within the ablation zone. Hepatic vein occlusion was significantly correlated with a smaller vessel size (P = .036) and vessel-antenna spacing (P = .006). Portal vein occlusion was only significantly correlated with a smaller vessel size (P = .001), particularly in vessels that were less than 3 mm in diameter. Local tumor progression rates were significantly correlated with patent hepatic arteries within the ablation zone (P = .02) but not with patent hepatic (P = .57) or portal (P = .14) veins. Conclusion During microwave ablation of HCC, hepatic veins and arteries were resistant to vessel occlusion compared with portal veins, and only arterial patency within an ablation zone was related to local tumor progression. © RSNA, 2016.

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.

To update the oncologic outcomes and safety for microwave (MW) ablation of T1a (≤4.0 cm) and T1b (4.1–7.0 cm) renal cell carcinoma (RCC) with emphasis on tumor complexity and single session treatment. Retrospective review of 29 consecutive patients (30 tumors) with localized (NOMO) RCC (23 T1a; 7 T1b) treated with percutaneous MW ablation between 3/2013 and 6/2014. Primary outcomes investigated were technical success, local tumor progression (LTP), and complications. Technical success was assessed with contrast-enhanced computed tomography (CECT) immediately after MW ablation. Presence of LTP was assessed with CECT or contrast-enhanced magnetic resonance at 6-month target intervals for the first two years and annually thereafter. Complications were categorized using the Clavien-Dindo classification system. Median tumor diameter was 2.8 cm [IQR 2.1–3.3] for T1a and 4.7 cm [IQR 4.1–5.7] for T1b tumors. Median RENAL nephrometry score was 7 [IQR 4–8] for T1a tumors and 9 [IQR 6.25–9.75] for T1b tumors. Technical success was achieved for 22 T1a (96%) and 7 T1b (100%) tumors. There were no LTP during a median imaging follow-up of 12.0 months [IQR 6–18] for the 23 patients (24 tumors) with greater than 6 months of follow-up. There were three Clavien-Dindo grade I–II complication (10%) and no Clavien-Dindo grade III–V complications (0%). All but two patients (93%) are alive without metastatic disease; two patients died after 12-month follow-up of causes unrelated to the MW ablation. Percutaneous MW ablation appears to be a safe and effective treatment option for low, moderate, and highly complex T1a and T1b RCC in early follow-up.

Purpose To compare efficacy and major complication rates of radiofrequency (RF) and microwave (MW) ablation for treatment of hepatocellular carcinoma (HCC). Materials and Methods This retrospective single-center study included 69 tumors in 55 patients treated by RF ablation and 136 tumors in 99 patients treated by MW ablation between 2001 and 2013. RF and MW ablation devices included straight 17-gauge applicators. Overall survival and rates of local tumor progression (LTP) were evaluated using Kaplan-Meier techniques with Cox proportional hazard ratio (HR) models and competing risk regression of LTP. Results RF and MW cohorts were similar in age ( P = .22), Model for End-Stage Liver Disease score ( P = .24), and tumor size (mean 2.4 cm [range, 0.6–4.5 cm] and 2.2 cm [0.5–4.2 cm], P = .09). Median length of follow-up was 31 months for RF and 24 months for MW. Rate of LTP was 17.7% with RF and 8.8% with MW. Corresponding HR from Cox and competing risk models was 2.17 (95% confidence interval [CI], 1.04–4.50; P = 0.04) and 2.01 (95% CI, 0.95–4.26; P = .07), respectively. There was improved survival for patients treated with MW ablation, although this was not statistically significant (Cox HR, 1.59 [95% CI, 0.91–2.77; P = .103]). There were few major (≥ grade C) complications (2 for RF, 1 for MW; P = .28). Conclusions Treating HCC percutaneously with RF or MW ablation was associated with high primary efficacy and durable response, with lower rates of LTP after MW ablation.

The risk of electromagnetic interference between microwave (MW) ablation and cardiac implantable electronic devices (CIEDs), ie, pacemakers and defibrillators, has not been fully evaluated. Fourteen MW ablations (kidney, n = 8; liver, n = 5; lung, n = 1) were performed in 13 patients with CIEDs in normal operating mode. Electrocardiography tracings, cardiovascular complications, tumor size, tumor-to-CIED distance, and tumor-to-device lead distance were recorded. Mean tumor size was 2.9 cm, mean tumor-to-CIED distance was 26.4 cm (range, 9–30 cm), and mean tumor-to-lead distance was 12.1 cm (range, 3.5–20 cm). No device-based cardiovascular complications or class C or higher complications per Society of Interventional Radiology criteria were identified. MW ablation appears to be safe in select patients with CIEDs.

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.

Microwave (MW) ablation was used to treat 12 hepatocellular adenomas in six patients (five women and one man; mean age, 39.6 y). Mean treated tumor size was 2.7 cm ± 2.0. Tumor response was evaluated with serial cross-sectional imaging for a mean follow-up of 12.6 months ± 7.1. Primary treatment effectiveness and local tumor control were 100%. There were no instances of hemorrhage, malignant transformation, new hepatic tumors, or extrahepatic metastases. This early experience of treatment of hepatic adenomas by MW ablation demonstrates it to be a safe and feasible treatment modality at short-term follow-up. Continued investigation, including comparison with other treatment modalities, is warranted.

To compare microwave ablation zones created by using sequential or simultaneous power delivery in ex vivo and in vivo liver tissue.All procedures were approved by the institutional animal care and use committee. Microwave ablations were performed in both ex vivo and in vivo liver models with a 2.45-GHz system capable of powering up to three antennas simultaneously. Two- and three-antenna arrays were evaluated in each model. Sequential and simultaneous ablations were created by delivering power (50 W ex vivo, 65 W in vivo) for 5 minutes per antenna (10 and 15 minutes total ablation time for sequential ablations, 5 minutes for simultaneous ablations). Thirty-two ablations were performed in ex vivo bovine livers (eight per group) and 28 in the livers of eight swine in vivo (seven per group). Ablation zone size and circularity metrics were determined from ablations excised postmortem. Mixed effects modeling was used to evaluate the influence of power delivery, number of antennas, and tissue type.On average, ablations created by using the simultaneous power delivery technique were larger than those with the sequential technique (P.05). Simultaneous ablations were also more circular than sequential ablations (P = .0001). Larger and more circular ablations were achieved with three antennas compared with two antennas (P.05). Ablations were generally smaller in vivo compared with ex vivo.The use of multiple antennas and simultaneous power delivery creates larger, more confluent ablations with greater temperatures than those created with sequential power delivery.

Tumor ablation in the liver has evolved to become a well-accepted tool in the management of increasing complex oncologic patients. At present, percutaneous ablation is considered first-line therapy for very early and early hepatocellular carcinoma and second-line therapy for colorectal carcinoma liver metastasis. Because thermal ablation is a treatment option for other primary and secondary liver tumors, an understanding of the underlying tumor biology is important when weighing the potential benefits of ablation. This article reviews ablation modalities, indications, patient selection, and imaging surveillance, and emphasizes technique-specific considerations for the performance of percutaneous ablation.

To compare transarterial chemoembolization (TACE) monotherapy to combination TACE and microwave ablation (MWA) for local control of 3- to 5-cm hepatocellular carcinoma (HCC). Patients with HCC between 3 and 5 cm treated with TACE monotherapy or combination TACE + MWA at a single institution between 2007 and 2016 were retrospectively reviewed. Twenty-four HCCs (median diameter 3.8 cm) in 16 patients (13 males; median age 64 years) were treated using TACE monotherapy. Combination TACE + MWA was used to treat 23 HCCs (median diameter 4.2 cm) in 22 patients (18 males; median age 61 years). Microwave ablation was performed at a target time of two weeks following TACE. Individual tumors were followed by serial contrast-enhanced CT or MR. Response to treatment was evaluated on a tumor-by-tumor basis using mRECIST criteria with the primary outcome being local tumor progression (LTP). Data were analyzed using Fisher’s exact test for categorical variables and Wilcoxon rank sum test for continuous variables. Time to LTP was estimated with the Kaplan–Meier method. Relative to TACE monotherapy, TACE + MWA provided a trend toward both a lower rate of LTP (34.8% vs. 62.5%, p = 0.11) and a higher complete response rate (65.2% vs. 37.5%; p = 0.12). Time to LTP (22.3 months vs. 4.2 months; p = 0.001) was significantly longer in the TACE + MWA group compared to TACE monotherapy. Combination therapy with TACE and microwave ablation improves local control and increases time to LTP for 3–5 cm HCC.

OBJECTIVE. The purpose of this study was to evaluate the incidence of clinically significant diaphragmatic injuries and local tumor progression after microwave ablation of hepatic tumors abutting the diaphragm. MATERIALS AND METHODS. This retrospective study included 55 peripheral hepatic tumors abutting the diaphragm treated by microwave ablation versus a control group of 15 centrally located tumors. Treated tumors were further subdivided according to the use of artificial ascites (fluid vs no fluid) and whether instilled fluid achieved displacement of the liver surface away from the diaphragm (displaced vs nondisplaced). Measurements of tumor size, distance to the diaphragm, ablation zone size, displacement distance, length of the ablation zone along the liver capsule, diaphragm thickness, diaphragmatic hernia, and local tumor progression were made on pre- and postablation CT and MRI. The electronic medical record was reviewed for patient self-reported pain scores and other symptoms. Data were analyzed by use of the Kruskal-Wallis and Fisher exact tests. RESULTS. There were no cases of diaphragmatic hernia in peripheral or central tumors. Postablation diaphragm thickness was higher in peripheral hepatic tumors than in control tumors. Peripheral tumors had an overall higher incidence of postprocedure shoulder pain (18% vs 0%) and local tumor progression (5.5% vs 0%) compared with control tumors, but these differences did not achieve statistical significance (p = 0.2 and p = 1, respectively). CONCLUSION. Our study shows that microwave ablation of peridiaphragmatic hepatic tumors is safe, without incidence of diaphragmatic hernia, and can be performed with a low rate of local tumor progression.

To determine the size of pulmonary artery (PA) at risk for occlusion during percutaneous microwave ablation and to assess the effect of vessel diameter, number, and patency, on ablation zone volume. Computed tomography (CT) fluoroscopy-guided percutaneous microwave ablations were performed in 8 pigs under general anesthesia. All ablations were performed at 65 W for 5 min with a single 17-gauge antenna positioned in the central third of the lungs. A CT pulmonary angiogram was performed immediately after the ablations. The maximum diameter, number and patency of PA branches within each ablation zone were recorded. Ablation volumes were measured at gross dissection and with CT. Student’s t test was used to compare ablation zone volumes among groups. Twenty-one pulmonary ablations were performed. Six of the ablation zones (29%) contained at least 1 occluded PA branch. The mean diameter of the occluded PA branches in the ablation zones (2.4 mm; range, 2.0–2.8 mm) was significantly smaller than non-occluded PA branches (3.7 mm; range: 2.1–6.9 mm; p = 0.009). No PA branches ≥3 mm in size were occluded. There was no significant difference in volume of gross ablation zones that contained occluded versus non-occluded PAs (p = 0.42), one versus multiple PAs (p = 0.71), or PAs

Purpose To evaluate the effects of tumor complexity and technique on early and midterm oncologic efficacy and rate of complications for 100 consecutive biopsy-proved stage T1a renal cell carcinomas (RCCs) treated with percutaneous microwave ablation. Materials and Methods This HIPAA-compliant, single-center retrospective study was approved by the institutional review board. The requirement to obtain informed consent was waived. Ninety-six consecutive patients (68 men, 28 women; mean age, 66 years ± 9.4) with 100 stage T1a N0M0 biopsy-proved RCCs (median diameter, 2.6 cm ± 0.8) underwent percutaneous microwave ablation between March 2011 and June 2015. Patient and procedural data were collected, including body mass index, comorbidities, tumor histologic characteristics and grade, RENAL nephrometry score, number of antennas, generator power, and duration of ablation. Technical success, local tumor progression, and presence of complications were assessed at immediate and follow-up imaging. The Kaplan-Meier method was used for survival analyses. Results Technical success was achieved for all 100 tumors (100%), including 47 moderately and five highly complex RCCs. Median clinical and imaging follow-up was 17 months (range, 0-48 months) and 15 months (range, 0-44 months), respectively. No change in estimated glomerular filtration rate was noted after the procedure (P = .49). There were three (3%) procedure-related complications and six (6%) delayed complications, all urinomas. One case of local tumor progression (1%) was identified 25 months after the procedure. Three-year local progression-free survival, cancer-specific survival, and overall survival were 88% (95% confidence interval: 0.52%, 0.97%), 100% (95% confidence interval: 1.0%, 1.0%), and 91% (95% confidence interval: 0.51%, 0.99%), respectively. Conclusion Percutaneous microwave ablation is an effective and safe treatment option for stage T1a RCC, regardless of tumor complexity. Long-term follow-up is needed to establish durable oncologic efficacy and survival relative to competing ablation modalities and surgery. © RSNA, 2017.

Purpose To evaluate safety and efficacy of percutaneous hepatic microwave (MW) ablation performed near the heart. Materials and Methods This study reviewed 118 consecutive peripheral (ablation zone margins within 5 mm of liver capsule) percutaneous MW hepatic ablations performed between June 2010 and August 2015. Ablation zones of 27 tumors (22.8%) extended to ≤ 5 mm from myocardium, and these ablations comprised the study group; the remaining ablations formed the control group. The study cohort included 14 men and 10 women (mean age, 59 y) with 16 hepatocellular carcinomas, 9 metastases, and 2 hemangiomas. Periprocedural imaging was used to evaluate tumor size and distance from the heart, ablation zone size, and complications. Mean tumor size and distance to myocardium were 2.6 cm ± 1.7 and 1.1 cm ± 1.1, respectively. The electronic medical record was used to retrospectively assess local tumor progression (LTP) and electrocardiogram and hemodynamic alterations during and after ablation. Statistical analysis was performed with Fisher exact test and t test. Results Median follow-up was 13.6 months (range, 1.2–38.7 months). No arrhythmias occurred during or after ablation in the follow-up period (0/27). There was no difference between groups in frequency of alterations in periprocedural blood pressure (25.9% vs 29.6%, p=0.81) or heart rate (18.5% vs 24.2%, P = .61) or rate of LTP (12.0% vs 10.8%, P = 1.0). Conclusions Percutaneous MW ablation near the heart may be safe and effective, without increased risk of cardiac complications and with similar rates of LTP, compared with a control group of peripheral liver ablations.

The purpose of this study is to determine a concentration of iodinated contrast media in saline and 5% dextrose in water (D5W) for organ hydrodissection, a technique used to physically separate and protect tissues adjacent to thermal ablations.A total of 28 samples were prepared from 1:1000-1:1 iohexol or iothalamate meglumine contrast media in either normal saline or D5W. Samples alone or juxtaposed with a homogeneous liver-mimicking phantom were imaged by CT using 80-120 kVp and 10-300 mAs. Mean CT numbers and noise were measured from the fluid, background air, phantom adjacent to the fluid, and phantom distant from the fluid. Visibility was determined from the contrast-to-noise ratio between the fluid and phantom, whereas streaking artifact was quantified by relative noise in the phantom. Measures were individually fit using multiple linear regression to determine an optimal contrast-to-fluid ratio for increased visualization without streaking. Contrast media- and blood-doped saline and D5W were also tested to determine whether such doping altered their electrical conductivity.Iohexol concentration most influenced CT number; volumetric ratios of 1:1000-1:1 produced 20 HU to over 3000 HU. CT numbers were weakly dependent on x-ray tube voltage, whereas contrast-to-noise ratio and streaking artifacts were somewhat dependent on tube output. An optimal ratio of iohexol in fluid was determined to be 1:50. There was no significant difference between the electrical impedances of doped and pure saline or D5W (p0.5, all cases).A 1:50 ratio of iohexol in saline or D5W provides an optimal combination of increased visibility on CT without streaking artifacts.

This study was designed to determine the magnitude and spatial distribution of temperature elevations when using 480 kHz RF and 2.45 GHz microwave energy in ex vivo liver models. A total of 60 heating cycles (20 s at 90 W) were performed in normal, RF-ablated, and microwave-ablated liver tissues (n = 10 RF and n = 10 microwave in each tissue type). Heating cycles were performed using a 480-kHz generator and 3-cm cooled-tip electrode (RF) or a 2.45-GHz generator and 14-gauge monopole (microwave) and were designed to isolate direct heating from each energy type. Tissue temperatures were measured by using fiberoptic thermosensors 5, 10, and 15 mm radially from the ablation applicator at the depth of maximal heating. Power delivered, sensor location, heating rates, and maximal temperatures were compared using mixed effects regression models. No significant differences were noted in mean power delivered or thermosensor locations between RF and microwave heating groups (P > 0.05). Microwaves produced significantly more rapid heating than RF at 5, 10, and 15 mm in normal tissue (3.0 vs. 0.73, 0.85 vs. 0.21, and 0.17 vs. 0.09 °C/s; P

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.

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.

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.

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.

Radiofrequency (RF) ablation is becoming an accepted treatment modality for many tumors of the liver and is being explored for tumors in the lung, kidney, and bone. While RF energy is the most familiar heat source for tissue ablation, it has certain limitations that may hamper its efficacy in these new organ systems. Microwave energy may be a better source for tissue ablation but has technical hurdles that must be overcome as well. This article outlines the physics behind RF and microwave heating, discusses relevant properties of the liver, lung, kidney, and bone for thermal ablation and examines the roles of RF and microwave ablation in these tissues.

Microwave ablation is a relatively new technology under development and testing to treat the same types of cancer that can be treated with radiofrequency ablation. Microwave energy has several possible benefits over radiofrequency energy for tumor ablation but, because clinical microwave ablation systems are not widespread, the underlying principles and technologies may not be as familiar. The basic microwave ablation system contains many of the same components as a radiofrequency ablation system: a generator, a power distribution system, and an interstitial applicator. This article attempts to provide an overview of each of these components, outline their functions and roles, and provide some insight into what every potential microwave ablation user should know about systems in development.

Purpose 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. Materials and Methods 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. Results 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 Conclusions 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.

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 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.

Objectives 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. Methods 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. Results The study group consisted of 60 cirrhotic patients (M/F = 43/17; mean age 69.6 years) with 67 subcapsular HCC (mean diameter 2.3 cm ± 1.0 cm) 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. Conclusions 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.

To prospectively evaluate, in vivo in pigs, an impedance-based multiple-electrode radiofrequency (RF) ablation system for creation of confluent areas of hepatic coagulation.The study was preapproved by the institutional research animal care and use committee. A prototype multiple-electrode RF system that enables switching between three electrically independent electrodes at impedance spikes was created. Forty-two coagulation zones (18 with single, 12 with cluster, and 12 with multiple [three single electrodes spaced 2 cm apart] electrodes) were created at laparotomy in 15 female pigs. Half the ablations were performed for 12 minutes, and half were performed for 16 minutes. The coagulation zones were excised and sliced into approximately 3-mm sections for measurement. Analysis of variance and two-sample t tests (with Bonferroni correction, alpha = .0033) were used to assess for differences between groups.At 12 minutes, the mean multiple-electrode coagulation was significantly larger than the mean single-electrode coagulation (minimum diameter, 2.8 vs 1.6 cm; maximum diameter, 4.2 vs 2.0 cm; volume, 22.1 vs 6.7 cm(3); P.0033 for all comparisons). The mean maximum diameter achieved at 12 minutes with multiple electrodes was significantly larger than that achieved with the cluster electrode (4.2 vs 2.9 cm, P = .02). At 16 minutes, the mean multiple-electrode coagulation (minimum diameter, 3.2 cm; maximum diameter, 4.2 cm; volume, 29.1 cm(3)) was significantly larger than the mean single-electrode (minimum diameter, 1.7 cm; maximum diameter, 2.2 cm; volume, 7.1 cm(3); P.0033 for all comparisons) and cluster-electrode (minimum diameter: 2.3 cm, P = .007; maximum diameter: 3.2 cm, P = .005; volume: 13.1 cm(3), P = .001) coagulations.Compared with the single and cluster systems used as controls, the multiple-electrode RF ablation system enabled the creation of significantly larger coagulation zones.

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 Ω 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 cm 3 ± 3.7, 7.4 cm 3 ± 3.8, and 7.8 cm 3 ± 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.

To evaluate the safety and efficacy of US-guided percutaneous microwave (MW) ablation in the treatment of renal angiomyolipoma (AML). From January 2011 to April 2014, seven patients (5 females and 2 males; mean age 51.4) with 11 renal AMLs (9 sporadic type and 2 tuberous sclerosis associated) with a mean size of 3.4 ± 0.7 cm (range 2.4–4.9 cm) were treated with high-powered, gas-cooled percutaneous MW ablation under US guidance. Tumoral diameter, volume, and CT/MR enhancement were measured on pre-treatment, immediate post-ablation, and delayed post-ablation imaging. Clinical symptoms and creatinine were assessed on follow-up visits. All ablations were technically successful and no major complications were encountered. Mean ablation parameters were ablation power of 65 W (range 60–70 W), using 456 mL of hydrodissection fluid per patient, over 4.7 min (range 3–8 min). Immediate post-ablation imaging demonstrated mean tumor diameter and volume decreases of 1.8 % (3.4–3.3 cm) and 1.7 % (27.5–26.3 cm3), respectively. Delayed imaging follow-up obtained at a mean interval of 23.1 months (median 17.6; range 9–47) demonstrated mean tumor diameter and volume decreases of 29 % (3.4–2.4 cm) and 47 % (27.5–12.1 cm3), respectively. Tumoral enhancement decreased on immediate post-procedure and delayed imaging by CT/MR parameters, indicating decreased tumor vascularity. No patients required additional intervention and no patients experienced spontaneous bleeding post-ablation. Our early experience with high-powered, gas-cooled percutaneous MW ablation demonstrates it to be a safe and effective modality to devascularize and decrease the size of renal AMLs.

To compare dual-energy computed tomography (CT) with conventional CT for the detection of small-bowel ischemia in an experimental animal model.The study was approved by the animal care and use committee and was performed in accordance with the Guide for Care and Use of Laboratory Animals issued by the National Research Council. Ischemic bowel segments (n = 8) were created in swine (n = 4) by means of surgical occlusion of distal mesenteric arteries and veins. Contrast material-enhanced dual-energy CT and conventional single-energy CT (120 kVp) sequences were performed during the portal venous phase with a single-source fast-switching dual-energy CT scanner. Attenuation values and contrast-to-noise ratios of ischemic and perfused segments on iodine material-density, monospectral dual-energy CT (51 keV, 65 keV, and 70 keV), and conventional 120-kVp CT images were compared. Linear mixed-effects models were used for comparisons.The attenuation difference between ischemic and perfused segments was significantly greater on dual-energy 51-keV CT images than on conventional 120-kVp CT images (mean difference, 91.7 HU vs 47.6 HU; P.0001). Conspicuity of ischemic segments was significantly greater on dual-energy iodine material-density and 51-keV CT images than on 120-kVp CT images (mean contrast-to-noise ratios, 4.9, 4.3, and 2.1, respectively; P.0001). Although attenuation differences on dual-energy 65- and 70-keV CT images were not significantly different from those on 120-kVp images (55.0 HU, 45.8 HU, and 47.6 HU, respectively; 65 keV vs 120 kVp, P = .15; 70 keV vs 120 kVp, P = .46), the contrast-to-noise ratio was greater for the 65- and 70-keV images than for the 120-kVp images (4.4, 4.1, and 2.1 respectively; P.0005).Dual-energy CT significantly improved the conspicuity of the ischemic bowel compared with conventional CT by increasing attenuation differences between ischemic and perfused segments on low-kiloelectron volt and iodine material density images.

To evaluate whether thermoreversible poloxamer 407 15.4 % in water (P407) can protect non-target tissues adjacent to microwave (MW) ablation zones in a porcine model.MW ablation antennas were placed percutaneously into peripheral liver, spleen, or kidney (target tissues) under US and CT guidance in five swine such that the expected ablation zones would extend into adjacent diaphragm, body wall, or bowel (non-target tissues). For experimental ablations, P407 (a hydrogel that transitions from liquid at room temperature to semi-solid at body temperature) was injected into the potential space between target and non-target tissues, and the presence of a gel barrier was verified on CT. No barrier was used for controls. MW ablation was performed at 65 W for 5 min. Thermal damage to target and non-target tissues was evaluated at dissection.Antennas were placed 7 ± 3 mm from the organ surface for both control and gel-protected ablations (p = 0.95). The volume of gel deployed was 49 ± 27 mL, resulting in a barrier thickness of 0.8 ± 0.5 cm. Ablations extended into non-target tissues in 12/14 control ablations (mean surface area = 3.8 cm(2)) but only 4/14 gel-protected ablations (mean surface area = 0.2 cm(2); p = 0.0005). The gel barrier remained stable at the injection site throughout power delivery.When used as a hydrodissection material, P407 protected non-targeted tissues and was successfully maintained at the injection site for the duration of power application. Continued investigations to aid clinical translation appear warranted.

To evaluate and model the risk of in vivo thrombosis in each hepatic vessel type during hepatic microwave ablation as a function of vessel diameter, velocity, and vessel-antenna spacing.A single microwave ablation antenna was inserted into a single porcine lobe (n = 15 total) adjacent to a hepatic artery, hepatic vein, or portal vein branch. Conventional ultrasound and Doppler ultrasound were used to measure the vessel diameter, blood flow velocity, and vessel-antenna spacing. A microwave ablation zone was created at 100 W for 5 minutes. Thrombus formation was evaluated on ultrasound performed immediately after the procedure. Logistic regression was used to evaluate the predictive value of vessel diameter, blood flow velocity, and vessel-antenna spacing on vascular thrombosis.Thrombosis was identified in 53% of portal veins, 13% of hepatic veins, and 0% of hepatic arteries. The average peak blood flow rate of the hepatic artery was significantly greater than the average peak blood flow rate of the hepatic vein and portal vein. Peak blood flow velocity12.45 cm/s, vessel diameter5.10 mm, and vessel-antenna spacing3.75 mm were strong predictors of hepatic vein thrombosis. However, these individual factors were not predictive of the more common portal vein thrombosis.Hepatic arteries do not appear to be at risk for thrombosis during microwave ablation procedures. Portal vein thrombosis was more common than hepatic vein thrombosis during microwave ablation treatments but was not as predictable based on vessel diameter, flow velocity, or vessel-antenna spacing alone.

Image-guided thermal ablation is an evolving and growing treatment option for patients with malignant disease of multiple organ systems. Treatment indications have been expanding to include benign tumors as well. Specifically, the most prevalent indications to date have been in the liver (primary and metastatic disease, as well as benign tumors such as hemangiomas and adenomas), kidney (primarily renal cell carcinoma, but also benign tumors such as angiomyolipomas and oncocytomas), lung (primary and metastatic disease), and soft tissue and/or bone (primarily metastatic disease and osteoid osteomas). Each organ system has different underlying tissue characteristics, which can have profound effects on the resulting thermal changes and ablation zone. Understanding these issues is important for optimizing clinical results. In addition, thermal ablation technology has evolved rapidly during the past several decades, with substantial technical and procedural improvements that can help improve clinical outcomes and safety profiles. Staying up to date on these developments is challenging but critical because the physical properties underlying the different ablation modalities and the appropriate use of adjuncts will have a tremendous effect on treatment results. Ultimately, combining an understanding of the physical properties of the ablation modalities with an understanding of the thermal kinetics in tissue and using the most appropriate ablation modality for each patient are key to optimizing clinical outcomes. Suggested algorithms are described that will help physicians choose among the various ablation modalities for individual patients.

Purpose To retrospectively review the results of hepatocellular carcinoma (HCC) treatment with a high-power, gas-cooled, multiantenna-capable microwave device. Materials and Methods A total of 107 HCCs in 75 patients (65 men) with a mean age of 61 years (range, 44–82 y) were treated via percutaneous approach. Combination microwave ablation and transarterial chemoembolization was performed for 22 tumors in 19 patients with tumors larger than 4 cm (n = 10), tumors larger than 3 cm with ill-defined margins (n = 7), or lesions not identified with ultrasonography (n = 5). Mean tumor size was 2.1 cm (range, 0.5–4.2 cm), with median follow-up of 14 months, for ablation alone; compared with 3.7 cm (range, 1.0–7.0 cm) and 12 months, respectively, for combination therapy. All procedures were performed with a single microwave system (Certus 140) with one to three 17-gauge antennas. Results Mean ablation time was 5.3 minutes (range, 1–11.5 min). All treatments were considered technically successful in a single session. Primary technique effectiveness rates were 91.6% (98 of 107) overall, 93.7% (89 of 95) for tumors 4 cm or smaller, and 75.0% (nine of 12) for tumors larger than 4 cm; and 91.8% (78 of 85) for ablation alone and 90.9% (20 of 22) for combination therapy. There was no major complication or procedure-related mortality. The overall survival rate was 76.0% at a median 14-month clinical follow-up, with most deaths related to end-stage liver disease (n = 11) or multifocal HCC (n = 5). Conclusions Treating HCC with a gas-cooled, multiantenna-capable microwave ablation device is safe, with promising treatment effectiveness.

Microwave ablation is an extremely promising heat-based thermal ablation modality that has particular applicability in treating hepatic malignancies. Microwaves can generate very high temperatures in very short time periods, potentially leading to improved treatment efficiency and larger ablation zones. As the available technology continues to improve, microwave ablation is emerging as a valuable alternative to radiofrequency ablation in the treatment of hepatic malignancies. This article reviews the current state of microwave ablation including technical and clinical considerations.

Image-guided tumor ablation has become a well-established hallmark of local cancer therapy. The breadth of options available in this growing field increases the need for standardization of terminology and reporting criteria to facilitate effective communication of ideas and appropriate comparison among treatments that use different technologies, such as chemical (eg, ethanol or acetic acid) ablation, thermal therapies (eg, radiofrequency, laser, microwave, focused ultrasound, and cryoablation) and newer ablative modalities such as irreversible electroporation. This updated consensus document provides a framework that will facilitate the clearest communication among investigators regarding ablative technologies. An appropriate vehicle is proposed for reporting the various aspects of image-guided ablation therapy including classification of therapies, procedure terms, descriptors of imaging guidance, and terminology for imaging and pathologic findings. Methods are addressed for standardizing reporting of technique, follow-up, complications, and clinical results. As noted in the original document from 2003, adherence to the recommendations will improve the precision of communications in this field, leading to more accurate comparison of technologies and results, and ultimately to improved patient outcomes. Online supplemental material is available for this article .