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Objective To investigate the relationship between metabolic syndrome (MetS) and lower urinary tract symptoms (LUTS) with functional and anatomic changes of the lower urinary tract with MRI. Materials and Methods The bladder and prostate of 95 subjects (56M, 39F) were segmented on T2-weighted pelvic MRI using Materialize Mimics 3D software. Bladder wall volume (BWV), post-void residual (PVR) and prostate volume (PV) were quantified from the 3D renderings. LUTS were quantified using validated questionnaires administered at the time of MRI. Wilcoxin rank sum, win ratio and chi-square tests were used to correlate symptom scores, BWV, PVR and PV in patients 1) without vs with MetS, 2) with mild (IPSS or UDI-6: 0-7) vs moderate-severe (IPSS: 8-35 or UDI-6: ≥8) and 3) normal vs enlarged prostates (>40cm3). Multivariate linear regression was used to determine predictors for BWV, PVR and PV. Results Men with MetS had increased BWV (66.8 vs 51.1cm3, P = .003), higher PVR (69.1 vs 50.5cc, P= .05) and increased PV (67.2 vs 40.1cm3, P= .01). Women without and with MetS had similar BWV, PVR and LUTS (P= .3-.78). There was no difference in prevalence of MetS, BWV, PVR or PV in men or women with mild vs moderate-severe LUTS (P = .26-.97). Men with enlarged prostates were more likely to have MetS (P = .003). There was no difference in BWV, PVR and LUTS for men with normal vs enlarged prostates (P= .44-.94). In men, BWV was highly correlated with MetS (P = .005) on regression analysis. Conclusion MetS leads to detrusor hypertrophy and may contribute to impaired bladder function, likely related to the effect on the prostate.

Purpose Intra-procedural monitoring and post-procedural follow-up is necessary for a successful ablation treatment. An imaging technique which can assess the ablation geometry accurately is beneficial to monitor and evaluate treatment. In this study, we developed an automated ablation segmentation technique for serial low-dose, noisy ablation computed tomography (CT) or contrast-enhanced CT (CECT). Methods Low-dose, noisy temporal CT and CECT volumes were acquired during microwave ablation on normal porcine liver (four with non-contrast CT and eight with CECT). Highly constrained backprojection (HYPR) processing was used to recover ablation zone information compromised by low-dose noise. First-order statistic features and normalized fractional Brownian features (NBF) were used to segment ablation zones by fuzzy c-mean clustering. After clustering, the segmented ablation zone was refined by cyclic morphological processing. Automatic and manual segmentations were compared to gross pathology with Dice's coefficient (morphological similarity), while cross-sectional dimensions were compared by percent difference. Results Automatic and manual segmentations of the ablation zone were very similar to gross pathology (Dice Coefficients: Auto.-Path. = 0.84 ± 0.02; Manu.-Path. = 0.76 ± 0.03, P = 0.11). The differences in ablation area, major diameter and minor diameter were 17.9 ± 3.2%, 11.1 ± 3.2% and 16.2 ± 3.4%, respectively, when comparing automatic segmentation to gross pathology, which were lower than the differences of 32.9 ± 16.8%, 13.0 ± 9.8% and 21.8 ± 5.8% when comparing manual segmentation to gross pathology. Manual segmentations tended to overestimate gross pathology when ablation area was less than 15 cm2 , but the automated segmentation tended to underestimate gross pathology when ablation zone is larger than 20 cm2 . Conclusion Fuzzy c-means clustering may be used to aid automatic segmentation of ablation zones without prior information or user input, making serial CT/CECT has more potential to assess treatments intra-procedurally.

Measurements of tissue permittivity with small open-ended coaxial probes during microwave tissue heating have been plagued by high variability as tissue water becomes vaporized. Analysis of such variability has been hampered by a lack of direct visualization of the measurement volume. The objective of this study was to determine if X-ray computed tomography (CT) could be used to visualize the measurement volume and then predict dielectric permittivity based on the visualized tissue composition.CT attenuation at 120 kVp was measured at the end of an open-ended coaxial probe during microwave ablation of ex vivo liver (2.45 GHz at 50 W delivered for 5 minutes). Tissue composition was estimated from attenuation maps and used to predict dielectric properties based on established mixture equations. Predicted permittivity was then compared to measured values using error metrics and linear regression.There was a good agreement between measured and modeled permittivity during 5-minute ablations at 2.45 GHz (r = 0.94, p.001). Normalized root mean squared errors were below 17% in permittivity modeling at 2.45 GHz.CT-based model predictions of dielectric properties are feasible in ex vivo liver. The models may facilitate real-time imaging-based permittivity mapping.

Objective To explore various microwave (MW) time/power combinations to achieve maximum single-probe system performance in a live pig liver model. Methods Fifty-one microwave ablations performed in 12 female pigs using the following time/power combinations: 65 W for 10 min (65W 10MIN), ramped from 20 to 65 W (RAMPED), 95 W pulses with cooling periods (95W PULSED), 40 W for 16 min 15 s (LOW POWER), 1 min 95 W pulse then 8 min 65 W then a second 1 min 95 W pulse (BOOKEND 95W) and 65 W for 15 min (65W 15MIN). Temperatures 1.5 cm from the antenna were measured. Livers were excised, and ablations were measured and compared. Results At fixed overall energy, LOW POWER produced ablation zones with the smallest volume compared to 65W 10MIN, RAMPED and 95W PULSED. At a fixed time of 10-min, BOOKEND 95W protocol achieved wider and larger ablation zones than 65W 10MIN (p = 0.038, p = 0.008) and 95W PULSED (p = 0.049, p = 0.004). The 65W 15MIN combination had significantly larger diameters (p = 0.026), larger lengths (p = 0.014) and larger volumes (p = 0.005) versus 65W 10MIN. Maximum temperatures were highest with BOOKEND 95W (62.9 °C) and 65 W 15 MIN (63.0 °C) and lowest with LOW POWER (45.9 °C), p = 0.009. Conclusions Low power ablations, even if controlled for total energy delivery, create small ablation zones. High peak powers are associated with larger ablation zones and high margin temperatures if cooling pauses are avoided. Ramping and pulsing protocols with interleaved cooling appear to be of no benefit versus continuous 65 W for creating large ablation zones.

Purpose Deformable registration of ultrasound (US) and contrast enhanced computed tomography (CECT) images are essential for quantitative comparison of ablation boundaries and dimensions determined using these modalities. This comparison is essential as stiffness-based imaging using US has become popular and offers a nonionizing and cost-effective imaging modality for monitoring minimally invasive microwave ablation procedures. A sensible manual registration method is presented that performs the required CT-US image registration. Methods The two-dimensional (2D) virtual CT image plane that corresponds to the clinical US B-mode was obtained by "virtually slicing" the 3D CT volume along the plane containing non-anatomical landmarks, namely points along the microwave ablation antenna. The initial slice plane was generated using the vector acquired by rotating the normal vector of the transverse (i.e., xz) plane along the angle subtended by the antenna. This plane was then further rotated along the ablation antenna and shifted along with the direction of normal vector to obtain similar anatomical structures, such as the liver surface and vasculature that is visualized on both the CT virtual slice and US B-mode images on 20 patients. Finally, an affine transformation was estimated using anatomic and non-anatomic landmarks to account for distortion between the colocated CT virtual slice and US B-mode image resulting in a final registered CT virtual slice. Registration accuracy was measured by estimating the Euclidean distance between corresponding registered points on CT and US B-mode images. Results Mean and SD of the affine transformed registration error was 1.85 ± 2.14 (mm), computed from 20 coregistered data sets. Conclusions Our results demonstrate the ability to obtain 2D virtual CT slices that are registered to clinical US B-mode images. The use of both anatomical and non-anatomical landmarks result in accurate registration useful for validating ablative margins and comparison to electrode displacement elastography based images.

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: The goal of this study was to compare intra-procedural radiofrequency (RF) and microwave ablation appearance on non-contrast CT (NCCT) and ultrasound to the zone of pathologic necrosis. MATERIALS AND METHODS: Twenty-one 5-minute ablations were performed in vivo in swine liver with 1) microwave at 140 W, 2) microwave at 70 W, or 3) RF at 200 W (n=7 each). CT and US images were obtained simultaneously at 1, 3, and 5 minutes during ablation and 2, 5, and 10 minutes post-ablation. Each ablation was sectioned in the plane of the ultrasound image and underwent vital staining to delineate cellular necrosis. CT was reformatted to the same plane as the ultrasound transducer and transverse diameters of gas and hypoechoic/hypoattenuating zones at each time point were measured. CT, ultrasound and gross pathologic diameter measurements were compared using Student’s t-tests and linear regression. RESULTS: Visible gas and the hypoechoic zone on US images were more predictive of the pathologic ablation zone than on NCCT images (P

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.

The use of microwaves (MW) for thermal cancer treatment began in the late 1970s. At first, hyperthermia was induced by using single antennas applied interstitially. This was followed by arrays of multiple interstitial antennas driven synchronously at 915 or 2450 MHz. This early work focused on hyperthermia as an adjuvant therapy, but more recently has evolved into a thermally ablative monotherapy. Increased power required to thermally ablate tissues required additional developments such as internally cooled antennas. Larger tumours have also been ablated with MW antenna arrays activated synchronously or non-synchronously. Numerical modelling has provided clinical treatment planning guidance and device design insight throughout this history. MW thermal therapy systems, treatment planning, navigation and image guidance continue to evolve to provide better tools and options for clinicians and patients in order to provide targeting optimisation with the goal of improved treatment for the patient and durable cancer eradication. This paper reviews the history and related technological developments, including antenna design, of MW heating for both hyperthermia and ablation.

Thermal ablation is increasingly being utilised in the treatment of primary and metastatic liver tumours, both as curative therapy and as a bridge to transplantation. Recent advances in high-powered microwave ablation systems have allowed physicians to realise the theoretical heating advantages of microwave energy compared to other ablation modalities. As a result there is a growing body of literature detailing the effects of microwave energy on tissue heating, as well as its effect on clinical outcomes. This article will discuss the relevant physics, review current clinical outcomes and then describe the current techniques used to optimise patient care when using microwave ablation systems.

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.

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.

PURPOSE The purpose of this study was to quantitatively analyze tissue deformation during radiofrequency (RF) and microwave ablation for varying output energy levels. METHODS A total of 46 fiducial markers which were classified into outer, middle, and inner lines were positioned into a single plane around an RF or microwave ablation applicator in each ex vivo bovine liver sample (8 cm × 6 cm × 4 cm, n = 18). Radiofrequency (500 kHz; ~35 W average) or microwave (2.4 GHz; 50-100 W output, ~35-70 W delivered) ablation was performed for 10 min (n = 4-6 each setting). CT images were acquired over the entire liver volume every 15 s. Principle strain magnitude and direction were determined from fiducial marker displacement. Normal and shear strain were then calculated such that negative strain denoted contraction and positive strain denoted expansion. Temporal variations, the final magnitudes, and angles of the strain were compared across energy delivery settings, using one-way ANOVA with post hoc Tukey's tests. RESULTS On average, tissue strain rates peak at around 1 min and decayed exponentially over time. No evidence of tissue expansion was observed. The tissue strains from RF and 50 W, 75 W, and 100 W microwave ablation at 10 min were -8.5%, -38.9%, -54.4%, and -65.7%, respectively, from the inner region and -3.6%, -23.7%, -41.8%, and -44.3%, respectively, from the outer region. Negative strain magnitude was positively correlated to energy delivery in the inner region (Spearman's ρ = -0.99). Microwaves at higher powers (75-100 W) induced significantly more strain than at lower power (50 W) or after RF ablation (P

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.

Microwave ablation is a minimally invasive image guided thermal therapy for cancer that can be adapted to endoscope use in the gastrointestinal (GI) tract. Microwave ablation in the GI tract requires precise control over the ablation zone that could be guided by high resolution imaging with quantitative contrast. Optical coherence tomography (OCT) provides ideal imaging resolution and allows for the quantification of tissue scattering properties to characterize ablated tissue. Visible and near-infrared OCT image analysis demonstrated increased scattering coefficients (μs ) in ablated versus normal tissues (Vis: 347.8%, NIR: 415.0%) and shows the potential for both wavelength ranges to provide quantitative contrast. These data suggest OCT could provide quantitative image guidance and valuable information about antenna performance in vivo.

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.

Purpose: Percutaneous radiofrequency ablation and cryoablation are accepted alternative treatments for small renal cell carcinomas (RCC) in high-risk patients. The recent development of high-powered microwave (MW) ablation offers theoretical advantages over existing ablation systems, including higher tissue temperatures, more reproducible ablation zones, and shorter procedural times. The purpose of this study is to review the feasibility, safety, and early efficacy of a novel high-powered percutaneous MW ablation system to treat RCC. Methods: An institutional database identified 53 consecutive patients with biopsy-proven RCC ≤4 cm (55 tumors) who were treated with percutaneous MW ablation using a novel MW ablation system. All patients had percutaneous renal mass biopsy, which identified RCC before ablation. Postprocedure follow-up imaging was performed by contrast-enhanced computed tomography or magnetic resonance imaging. Results: Mean patient age was 66 years and 81% of patients were male. RCC subtypes included clear cell (n=25), papillary (n=12), and unspecified (n=18) and Fuhrman grades 1, 2, 3, and ungraded in 15, 25, 1, and 14 patients, respectively. The mean tumor diameter was 2.6 cm (range 0.8–4.0 cm). Six low-grade complications were recorded during 53 (11.3%) procedures: five Clavien Grade 1 (urine retention, fluid overload, and atrial fibrillation) and one Grade 2 (hemorrhage requiring transfusion). The postprocedure estimated glomerular filtration rate was not significantly changed from preprocedure levels (median: −1.1%, p=0.10). Median follow-up was 8 months (interquartile range [IQR] 5–18.25) with 0/38 (0%) patients demonstrating evidence of local recurrence or metastasis during surveillance imaging. Conclusions: Use of a high-powered MW ablation system for the treatment of T1a RCC is feasible, safe, and efficacious with short-term follow-up. A longer follow-up is warranted to evaluate oncologic outcomes.

PURPOSE: Theaim of this peper was to retrospectively review our experience utilising protective fluid instillation techniques during percutaneous microwave ablation of liver tumours to determine if fluid instillation prevents non-target injuries and allows a more aggressive case selection. MATERIALS AND METHODS: This institute review board-approved, US Health Insurance Portability and Accountability Act-compliant, retrospective study reviewed percutaneous microwave ablation of 151 malignant hepatic tumours in 87 patients, comparing cases in which protective fluid instillation was performed with those where no fluid was utilised. In cases utilising hydrodisplacement for bowel protection, a consensus panel evaluated eligibility for potential ablation without hydrodisplacement. Patient age, tumour size, local tumour progression rate, length of follow-up, complications, displacement distance/artificial ascites thickness, and treatment power/time were compared. RESULTS: Fluid administration was utilised during treatment in 29/151 of cases: 10/29 for protection of bowel (8/10 cases not possible without fluid displacement), and 19/29 for body wall/diaphragm protection. Local tumour progression was higher when hydrodisplacement was used to protect bowel tissue; this may be due to lower applied power due to operator caution. Local tumour progression was not increased for artificial ascites. There was no difference in complications between the fluid group and controls. CONCLUSION: Intraperitoneal fluid administration is a safe and effective method of protecting non-target structures during percutaneous hepatic microwave ablation. While hydrodisplacement for bowel protection allows more aggressive case selection, these cases were associated with higher rates of local tumour progression.

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. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2013.

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 Intra-procedural contrast-enhanced computed tomography (CECT) has been proposed to monitor the growth of thermal ablations. The primary challenge with multiple CT acquisitions is reducing radiation dose while maintaining sufficient image quality. The purpose of this study was to evaluate the feasibility of applying local highly constrained backprojection reconstruction (HYPR-LR) on periodic CECT images acquired with low-dose protocols, and to determine whether the ablations visible on CT were commensurate to gross pathology. Methods Low-dose (CTDIvol≤1.49mGy), temporal CECT volumes were acquired during microwave ablation on normal porcine liver. HYPR processing was performed on each volume after image registration. Ablation signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were collected to evaluate the degree of enhancement of image quality and ablation zone visualization. Ablation zones were manually segmented on HYPR and non-HYPR images and compared spatially using Dice's coefficient. The dimensions of ablation zones were also compared to gross pathology by correlation and dimensional differences. Results The SNR and CNR of ablation zones were increased after HYPR processing. The manually segmented ablation zone was highly similar to gross pathology with a Dice coefficient of 0.81 ± 0.03, while the low-dose CECT had a smaller Dice coefficient of 0.72 ± 0.05. Both HYPR and low-dose CECT had high correlation to gross pathology (0.99 and 0.94, respectively), but the variance of measurements were lower after HYPR processing compared to unprocessed images. The relative difference in area, length of long axis, and length of short axis for HYPR image were 13.1 ± 5.6%, 9.7 ± 4.2%, and 15.2 ± 2.8%, which were lower than those for low-dose CECT at 37.5 ± 6.0%, 17.7 ± 2.8%, and 28.9 ± 5.4%. Conclusion HYPR processing applied to periodic CECT images can enhance ablation zone visualization. HYPR processing may potentially enable CECT in real-time ablation monitoring under strict regulation of radiation dose.

Purpose: Electrode vibration elastography is a new shear waveimaging 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 inex vivo bovine livertissue. 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.

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.

The purpose of this study was to develop a technique to measure the dielectric properties of biological tissues with an interstitial dipole antenna based upon previous efforts for open-ended coaxial probes. The primary motivation for this technique is to facilitate treatment monitoring during microwave tumor ablation by utilizing the heating antenna without additional intervention or interruption of the treatment. The complex permittivity of a tissue volume surrounding the antenna was calculated from reflection coefficients measured after high-temperature microwave heating by using a rational function model of the antenna’s input admittance. Three referencing liquids were needed for measurement calibration. The dielectric measurement technique was validated ex vivo in normal and ablated bovine livers. Relative permittivity and effective conductivity were lower in the ablation zone when compared to normal tissue, consistent with previous results. The dipole technique demonstrated a mean 10% difference of permittivity values when compared to open-ended coaxial cable measurements in the frequency range of 0.5–20 GHz. Variability in measured permittivities could be smoothed by fitting to a Cole–Cole dispersion model. Further development of this technique may facilitate real-time monitoring of microwave ablation treatments through the treatment applicator.

Although a surgical procedure is performed by visual inspection with histopathological assessment of the excised tumor and margins, percutaneous and noninvasive thermal ablation is performed strictly with the aid of imaging. Applicator guidance into the target zone, treatment monitoring and verification, and clinical follow-up rely on effective imaging. Detailed discussion of imaging is beyond the scope of this article, but the influence of imaging on the choice of thermal ablation or procedural approach will be discussed as needed. More information on imaging for interventional therapies can be found in other articles in this issue of IEEE Pulse.

Purpose: Design and validate an efficient dual-slot coaxial microwave ablation antenna that produces an approximately spherical heating pattern to match the shape of most abdominal and pulmonary tumor targets.Methods: A dual-slot antenna geometry was utilized for this study. Permutations of the antenna geometry using proximal and distal slot widths from 1 to 10 mm separated by 1–20 mm were analyzed using finite-element electromagnetic simulations. From this series, the most optimal antenna geometry was selected using a two-term sigmoidal objective function to minimize antenna reflection coefficient and maximize the diameter-to-length aspect ratio of heat generation. Sensitivities to variations in tissue properties and insertion depth were also evaluated in numerical models. The most optimal dual-slot geometry of the parametric analysis was then fabricated from semirigid coaxial cable. Antenna reflection coefficients at various insertion depths were recorded in ex vivo bovine livers and compared to numerical results. Ablation zones were then created by applying 50 W for 2–10 min in simulations and ex vivo livers. Mean zone diameter, length, aspect ratio, and reflection coefficients before and after heating were then compared to a conventional monopole antenna using ANOVA with post-hoc t-tests. Statistical significance was indicated for P

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.

Purpose: To compare ablation zones created with equal amounts of 2.45 GHz microwave and 480 kHz radiofrequency(RF) energy inex vivoliver and lung. Methods: A total of 38 ablations were performed inex vivoliver and lung for 10 min each. Nineteen RF ablations (nine liver, ten lung) were performed with a 480 kHz system (200 W max, impedance-based pulsing) and cooled electrode while measuring the average RF power applied. Nineteen microwaveablations (nine liver, ten lung) were then created using a cooled triaxial antenna to deliver 2.45 GHz at the same power level as in RF experiments. Ablation zones were then sectioned and measured for minimum, maximum and mean diameters, and circularity. Measurements were compared using t -tests, with P 0.05 indicating statistical significance. Results: Mean diameters of microwaveablations were greater than RF ablations in both liver and lung ( 4.4 ± 0.3 vs 3.3 ± 0.2 cm in liver; 2.45 ± 0.3 vs 1.6 ± 0.5 cm in lungs; P 0.0005 all comparisons). There was no significant difference in the mean power applied during microwave or RF ablations in either organ ( 54.44 ± 1.71 W vs 56.4 ± 6.7 W in liver, P > 0.05 ; 40 ± 0.95 W vs 44.9 ± 7.1 W in lung, P > 0.05 ). Conclusions: Using a single cooled applicator, microwave energy at 2.45 GHz produces larger ablations than an equivalent amount of 480 kHz RF energy in normal liver and lung. This was more apparent in lung, likely due to the high baseline impedance which limits RF, but not microwave power delivery.

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.

Purpose: Percutaneous thermal ablation is increasingly being used to destroy hepatic tumorsin situ. The success of ablative techniques is highly dependent on adequate ablation zone monitoring, and ultrasound-based strain imaging could become a convenient and cost-effective means to delineate ablation zone boundaries. This study investigates in vivo electrode displacement-based strain imaging for monitoring hepatic ablation procedures that are difficult to perform with conventional elastography. Methods: In our method, minute displacements (less than a millimeter) are applied to the unconstrained end of the ablation electrode, resulting in localized tissue deformation within the ablation zone that provides the mechanical stimuli required for strain imaging. This article presents electrode displacement strain images of radiofrequency ablation zones created in porcine liver in vivo (n=13). Results: Cross-sectional area measurements from strain images of these ablation zones were obtained using manual and automated segmentation. Area measurements from strain images were highly correlated with areas measured on histopathology images, quantitated using linear regression (R=0.894, P

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.

Interventional oncology procedures such as thermal ablation are becoming widely used for many tumours in the liver, kidney and lung. Thermal ablation refers to the focal destruction of tissue by generating cytotoxic temperatures in the treatment zone. Hydrodissection - separating tissues with fluids - protects healthy tissues adjacent to the ablation treatment zone to improve procedural safety, and facilitate more aggressive power application or applicator placement. However, fluids such as normal saline and 5% dextrose in water (D5W) can migrate into the peritoneum, reducing their protective efficacy. As an alternative, a thermo-gelable poloxamer 407 (P407) solution has been recently developed to facilitate hydrodissection procedures. We hypothesise that the P407 gel material does not provide convective heat dissipation from the ablation site, and therefore may alter the heat transfer dynamics compared to liquid materials during hydrodissection-assisted thermal ablation. The purpose of this study was to investigate the heat dissipation mechanics within D5W, liquid P407 and gel P407 hydrodissection barriers. Overall it was shown that the gel P407 dissipated heat primarily through conduction, whereas the liquid P407 and D5W dissipated heat through convection. Furthermore, the rate of temperature change within the gel P407 was greater than liquid P407 and D5W. Testing to evaluate the in vivo efficacy of the fluids with different modes of heat dissipation seems warranted for further study.

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.

The purpose of this study was to compare the impact of continuous and pulsed energy deliveries on microwave ablation growth and shape in unperfused and perfused liver models.A total of 15 kJ at 2.45 GHz was applied to ex vivo bovine liver using one of five delivery methods (n = 50 total, 10 per group): 25 W continuous for 10 min (25 W average), 50 W continuous for 5 min (50 W average), 100 W continuous for 2.5 min (100 W average), 100 W pulsed for 10 min (25 W average), and 100 W pulsed for 5 min (50 W average). A total of 30 kJ was applied to in vivo porcine livers (n = 35, 7 per group) using delivery methods similar to the ex vivo study, but with twice the total ablation time to offset heat loss to blood perfusion. Temperatures were monitored 5-20 mm from the ablation antenna, with values over 60 °C indicating acute cellular necrosis. Comparisons of ablation size and shape were made between experimental groups based on total energy delivery, average power applied, and peak power using ANOVA with post-hoc pairwise tests.No significant differences were noted in ablation sizes or circularities between pulsed and continuous groups in ex vivo tissue. Temperature data demonstrated more rapid heating in pulsed ablations, suggesting that pulsing may overcome blood perfusion and coagulate tissues more rapidly in vivo. Differences in ablation size and shape were noted in vivo despite equivalent energy delivery among all groups. Overall, the largest ablation volume in vivo was produced with 100 W continuous for 5 min (265.7 ± 208.1 cm(3)). At 25 W average, pulsed-power ablation volumes were larger than continuous-power ablations (67.4 ± 34.5 cm(3) versus 23.6 ± 26.5 cm(3), P = 0.43). Similarly, pulsed ablations produced significantly greater length (P ≤ 0.01), with increase in diameter (P = 0.09) and a slight decrease in circularity (P = 0.97). When comparing 50 W average power groups, moderate differences in size were noted (P ≥ 0.06) and pulsed ablations were again slightly more circular.Pulsed energy delivery created larger ablation zones at low average power compared to continuous energy delivery in the presence of blood perfusion. Shorter duty cycles appear to provide greater benefit when pulsing.

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.