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Histotripsy is an emerging noninvasive, nonionizing and nonthermal focal cancer therapy that is highly precise and can create a treatment zone of virtually any size and shape. Current histotripsy systems rely on ultrasound imaging to target lesions. However, deep or isoechoic targets obstructed by bowel gas or bone can often not be treated safely using ultrasound imaging alone. This work presents an alternative x-ray C-arm based targeting approach and a fully automated robotic targeting system.The approach uses conventional cone beam CT (CBCT) images to localize the target lesion and 2D fluoroscopy to determine the 3D position and orientation of the histotripsy transducer relative to the C-arm. The proposed pose estimation uses a digital model and deep learning-based feature segmentation to estimate the transducer focal point relative to the CBCT coordinate system. Additionally, the integrated robotic arm was calibrated to the C-arm by estimating the transducer pose for four preprogrammed transducer orientations and positions. The calibrated system can then automatically position the transducer such that the focal point aligns with any target selected in a CBCT image.The accuracy of the proposed targeting approach was evaluated in phantom studies, where the selected target location was compared to the center of the spherical ablation zones in post-treatment CBCTs. The mean and standard deviation of the Euclidean distance was 1:4 _ 0:5 mm. The mean absolute error of the predicted treatment radius was 0:5 _ 0:5 mm.CBCT-based histotripsy targeting enables accurate and fully automated treatment without ultrasound guidance.The proposed approach could considerably decrease operator dependency and enable treatment of tumors not visible under ultrasound.

Chronic liver disease predisposes patients to the development of hepatocellular carcinoma (HCC), and the degree of liver dysfunction helps dictate the management of patients with primary hepatic malignancy. Percutaneous ablation is an increasingly utilized treatment modality for patients with hepatocellular carcinoma who are poor surgical candidates, particularly when treatment goals include sparing hepatic parenchyma in the setting of hepatic dysfunction. Various thermal and non-thermal ablation modalities have historically been used to treat HCC. With advances in ablation technology, modern microwave (MW) ablation systems have become increasingly utilized in HCC as well as hepatic metastatic disease management due to larger and more predictable ablation zones. The evolution of ablation technology has resulted in the growth of ablation as a safe and effective treatment option for patients with primary and secondary liver tumors.

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

Microwave (MW) ablation and stereotactic body radiation therapy (SBRT) have potentially complementary advantages and limitations for treating inoperable renal cell carcinoma (RCC). Combining SBRT and MWA may optimize tumor control and toxicity for patients with larger (>5 cm) RCCs or those with vascular involvement. We retrospectively reviewed patients at our institution with RCC treated between 2014 – 2018 to identify patients treated with a combination of SBRT and MW ablation. Seven patients with RCC were treated with combination of SBRT and MW ablation, median tumor size of 6.4 cm. Local control was 100% with a median follow-up of 15 months. Four patients experienced grade 2 nausea during SBRT. Three patients experienced toxicities after MW ablation, two with grade 1 hematuria and one with grade 3 retroperitoneal bleed/collecting system injury. Median eGFR preceding and following SBRT and MW ablation was 69 mL/min/1.73m2 and 68 mL/min/1.73m2 (p=0.19) respectively. In patients who are not surgical candidates, larger RCCs or those with vascular invasion are challenging to treat. Combination treatment with SBRT and MW ablation may balance the risks and benefits of both therapies and demonstrates high local control in our series. MW ablation and SBRT have potentially complementary advantages and limitations.

PURPOSE: To evaluate outcomes of CT fluoroscopy-guided core lung biopsies with emphasis on diagnostic yield, complications, and efficacy of parenchymal and pleural blood patching to avoid chest tube placement. METHODS: This is a single-center retrospective analysis of CT fluoroscopy-guided percutaneous core lung biopsies between 2006 and 2020. Parenchymal blood patching during introducer needle withdrawal was performed in 74% of cases as a preventative measure, and pleural blood patching was the primary salvage maneuver for symptomatic or growing pneumothorax in 60/83 (72.2%) of applicable cases. RESULTS: A total of 1029 patients underwent 1112 biopsies (532 men, mean age 66 years, 38.6% history of emphysema, lesion size=16.7 mm). The diagnostic yield was 93.6% (1032/1103). Fewer complications requiring intervention were observed in patients who had undergone parenchymal blood patching (5.7 vs. 14.2%, p

Liver cancer is a leading cause of cancer related deaths, however primary treatment options such as surgical resection and liver transplants may not be viable for many patients. Minimally invasive image-guided microwave ablation (MWA) provides a locally effective treatment option for these patients with an impact comparable to surgery for both cancer specific and overall survival. MWA efficacy is correlated with accurate image guidance, however conventional modalities such as B-mode ultrasound and computed tomography (CT) have limitations. Alternatively, ultrasound elastography has been utilized to demarcate post-ablation zones yet has limitations for pre-ablation visualization due to variability in strain contrast between cancer types. This study attempts to characterize both pre-ablation tumors and post-ablation zones using electrode displacement elastography (EDE) for 13 patients with hepatocellular carcinoma or liver metastasis. Typically, MWA ablation margins of 0.5 – 1.0 cm are desired, which are strongly correlated with treatment efficacy. Our results demonstrate an average estimated ablation margin inner quartile range of 0.54 – 1.21 cm with a median value of 0.84 cm. These treatment margins lie within or above the targeted ablative margin indicating the potential for using EDE for differentiating index tumors and ablated zones for use during clinical ablations. We also obtained a high correlation between corresponding segmented cross-sectional areas from contrast-enhanced computed tomography (CECT), the current clinical gold standard, when compared to EDE strain images with r(2) values of 0.97 and 0.98 for pre- and post-ablation regions.

BACKGROUND: The purpose of this study is to evaluate the safety and intermediate-term efficacy of percutaneous microwave (MW) ablation for the treatment of colorectal liver metastases (CRLM) at a single institution. METHODS: A retrospective review was performed of all CRLM treated with MW ablation from 3/2011 to 7/2020 (102 tumors; 72 procedures; 57 patients). Mean age was 60 years (range, 36–88) and mean tumor size was 1.8 cm (range, 0.5–5.0 cm). The patient population included 19 patients with extra-hepatic disease. Chemotherapy (pre- and/or post-ablation) was given in 98% of patients. Forty-five sessions were preceded by other focal CRLM treatments including resection, ablation, radiation, and radioembolization. Kaplan-Meier curves were used to estimate local tumor progression-free survival (LTPFS), disease-free survival (DFS), and overall survival (OS) and multivariate analysis (Cox Proportional Hazards model) was used to test predictors of OS. RESULTS: Technical success (complete ablation) was 100% and median follow-up was 42 months (range, 1–112). There was a 4% major complication rate and an overall complication rate of 8%. Local tumor progression (LTP) rate during the entire study period was 4/98 (4%), in which 2 were retreated with MW ablation for a secondary LTP-rate of 2%. LTP-free survival at 1, 3, and 5 years was 93%, 58%, and 39% and median LTP-free survival was 48 months. OS at 1, 3, and 5 years was 96%, 66%, 47% and median OS was 52 months. There were no statistically significant predictors of OS. CONCLUSIONS: MW ablation of hepatic colorectal liver metastases appears safe with excellent local tumor control and prolonged survival compared to historical controls in selected patients. Further comparative studies with other local treatment strategies appear indicated.

To determine whether histotripsy can create human-scale transcostal ablations in porcine liver without causing severe thermal wall injuries along the beam path. Histotripsy was applied to the liver using a preclinical prototype robotic system through a transcostal window in six female swine. A 3.0 cm spherical ablation zone was prescribed. Duration of treatment (75 min) was longer than a prior subcostal treatment study (24 min, 15 s) to minimize beam path heating. Animals then underwent contrast-enhanced MRI, necropsy, and histopathology. Images and tissue were analyzed for ablation zone size, shape, completeness of necrosis, and off-target effects. Ablation zones demonstrated complete necrosis with no viable tissue remaining in 6/6 animals by histopathology. Ablation zone volume was close to prescribed (13.8 ± 1.8 cm3 vs. prescribed 14.1 cm3). Edema was noted in the body wall overlying the ablation on T2 MRI in 5/5 (one animal did not receive MRI), though there was no gross or histologic evidence of injury to the chest wall at necropsy. At gross inspection, lung discoloration in the right lower lobe was present in 5/6 animals (mean size: 1 × 2 × 4 cm) with alveolar hemorrhage, preservation of blood vessels and bronchioles, and minor injuries to pneumocytes noted at histology. Transcostal hepatic histotripsy ablation appears feasible, effective, and no severe injuries were identified in an acute porcine model when prolonged cooling time is added to minimize body wall heating.

Introduction This study was performed to determine the feasibility and safety of creating superficial histotripsy treatment in a live porcine thyroid model. Methods The porcine thymus comparable in size, shape and location to the human thyroid was used for this study. This model has been used for thyroid surgery studies due to the diminutive size of the porcine thyroid. Four female swine underwent a total of eight histotripsy treatments performed with a prototype therapy system (HistoSonics, Inc., Ann Arbor, MI). Two treatments were performed in each animal: a spherical 1.0 × 1.0 × 1.0 cm and ovoid 1.0 × 1.0 × 2.0 cm treatment zones. MRI immediately post-procedure was evaluated for histotripsy treatment zone size and imaging appearance, followed immediately by sacrifice. Tissue was then reviewed for percent cellular destruction and precision. Results Treatment zones measured on post treatment MRI were similar to prescribed volumes (spherical = 0.60 (+/− 0.11) cm3, ovoid = 1.23 (+/− 0.40) cm3, p > 0.05 vs. prescribed). MRI demonstrated well demarcated treatment zones and imaging findings consistent with cellular destruction. Histology demonstrated sharp transitions to normal tissue (mean 0.33 (+/− 0.13) cm), and high degrees of cellular destruction (mean 76% (+/− 12.5), range of 50–100%) in the treated tissue. Edema within the overlying muscle was seen in 2/8 treatments. Conclusion Histotripsy is capable of safely creating precise histotripsy treatments within the superficial neck of a porcine thyroid model without evidence of considerable complications.

Histotripsy is the first noninvasive, non-ionizing, and non-thermal ablation technology guided by real-time imaging. Using focused ultrasound delivered from outside the body, histotripsy mechanically destroys tissue through cavitation, rendering the target into acellular debris. The material in the histotripsy ablation zone is absorbed by the body within 1-2 months, leaving a minimal remnant scar. Histotripsy has also been shown to stimulate an immune response and induce abscopal effects in animal models, which may have positive implications for future cancer treatment. Histotripsy has been investigated for a wide range of applications in preclinical studies, including the treatment of cancer, neurological diseases, and cardiovascular diseases. Three human clinical trials have been undertaken using histotripsy for the treatment of benign prostatic hyperplasia, liver cancer, and calcified valve stenosis. This review provides a comprehensive overview of histotripsy covering the origin, mechanism, bioeffects, parameters, instruments, and the latest results on preclinical and human studies.

To determine the risk of mechanical vessel wall damage resulting in hemorrhage during and after hepatic and renal histotripsy in an anticoagulated in vivo porcine model.Non-tumor-bearing pigs (n=8, mean weight=52.5kg) were anticoagulated with warfarin (initial dose 0.08 mg/kg) to a target PT of 30-50% above baseline. A total of 15 histotripsy procedures were performed (kidney n=8, 2.0 cm sphere; liver n=7, 2.5 cm sphere). Treatments were immediately followed by CT imaging. Animals were observed for 7 days while continuing anticoagulation, followed by repeat CT and necropsy.All animals survived to complete the entire protocol with no signs of disability or distress. Three animals had hematuria (pink urine without clots). Baseline prothrombin time (PT) values (mean 16.0 sec) were elevated to 22.0 sec (37.5% above baseline, p=0.003) on the day of treatment, and 28.8 sec (77.8% above baseline, p0.001) on the day of necropsy. At the time of treatment 63% (5/8) of subjects were at a therapeutic anticoagulation level, and 100% (8/8) reached therapeutic levels by the time of necropsy. There were no cases of intra-parenchymal, peritoneal, or retroperitoneal hemorrhage associated with any treatments despite 71% (5/7) of liver and 100% (8/8) of kidney treatments extending to the organ surface.Liver and kidney histotripsy appears safe with no elevated bleeding risk in this anticoagulated animal model supporting the possibility of histotripsy treatments in patients on anti-coagulation.

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.

Objective To analyze risk factors and patterns of RCC recurrence following percutaneous ablation for stage 1 tumors and develop risk-stratified follow-up imaging protocols. Method Biopsy-proven sporadic stage 1 RCC patients treated with percutaneous microwave ablation (MWA) or cryoablation (CA) from 2002 to 2017 were included. Kaplan-Meier analysis was used to estimate local and distant recurrence-free survival, cancer-specific survival and metastatic-free survival. Multivariable models were used to identify risk factors associated with recurrence. Results A total of 256 patients with stage 1 RCC (215 T1a, 41 T1b) were treated with percutaneous MWA (178 subjects) or CA (78 subjects). Recurrence was identified in 23 patients (16 local, 7 distant). Clinical T stage (HR 2.46, 95% CI 1.06-5.72, P = .04) and tumor grade (HR 4.17, 95% CI 1.17-14.76, P = .03) were independent predictors of recurrence. Recurrence was not associated with Nephrometry score, cystic tumors, ablation modality (CA vs MWA) or gender. Five-year cancer-specific survival, and metastatic-free survival were 98.6% and 97.4%, respectively. Patients were stratified into 2 groups: reduced risk stage 1 (no risk factors) or elevated risk stage 1 (≥1 risk factor). Recurrence risk was higher in the elevated-risk group (HR = 3.19, 95% CI 1.35-7.53, P = .008). Five-year overall recurrence-free survival (local + distant) was higher in reduced-risk vs elevated-risk cohorts, 88% vs 69%, P = .005. Conclusion High nuclear grade or T1b tumors have increased recurrence risk following percutaneous thermal ablation for stage 1 RCC. Current postablation follow-up protocols may be modified for individual recurrence risk to allow more frequent imaging for elevated-risk patients, while enabling less frequent imaging for reduced-risk patients.

To evaluate the efficacy and safety of microwave (MW) ablation as first-line locoregional therapy (LRT) for bridging patients with hepatocellular carcinoma (HCC) to liver transplant.This retrospective study evaluated 88 patients who received percutaneous MW ablation for 141 tumors as first-line LRT for HCC and who were listed for liver transplantation at a single medical center between 2011 and 2019. The overall survival (OS) rate statuses after liver transplant, waitlist retention, and disease progression were evaluated using the Kaplan-Meier techniques.Among the 88 patients (72 men and 16 women; mean age, 60 years; Model for End-Stage Liver Disease score, 11.2) who were listed for transplant, the median waitlist time was 9.4 months (interquartile range, 5.5-18.9). Seventy-one (80.7%) patients received transplant after a median waitlist time of 8.5 months. Seventeen (19.3%) patients were removed from the waitlist; of these, 4 (4.5%) were removed because of tumors outside of the Milan criteria (HCC-specific dropout). No difference in tumor size or alpha-fetoprotein was observed in the transplanted versus nontransplanted patients at the time of ablation (2.1 vs 2.1 cm and 34.4 vs 34.7 ng/mL for transplanted vs nontransplanted, respectively; P.05). Five (5.1%) of the 88 patients experienced adverse events after ablation; however, they all recovered. There were no cases of tract seeding. The local tumor progression (LTP) rate was 7.2%. The OS status after liver transplant at 5 years was 76.7%, and the disease-specific survival after LTP was 89.6%, with a median follow-up of 61 months for all patients.MW ablation appears to be safe and effective for bridging patients with HCC to liver transplant without waitlist removal from seeding, adverse events, or LTP.

Minimally invasive treatments, namely microwave ablation (MWA), show promise in extending liver cancer patients survival particularly when surgical resection and transplantation are not viable. However, for MWA, treatment success requires an imaging modality for visualizing ablative zones and margins. Ablative margins ideally contain 5–10 mm of normal tissue surrounding the tumor to reduce recurrence, while retaining as much normal functioning liver tissue as possible. Conventionally, this role is filled by contrast enhanced computed tomography (CECT) (clinical gold standard) however some shortcomings exist. An alternative approach, electrode displacement elastography, shows potential for visualizing ablation zones, yet motion artifacts from physiological motion degrade consistent delineation. We present a Lagrangian deformation tracking (LDT) algorithm to track tissue movement thereby reducing decorrelation noise and motion artifacts. Results are shown on a single spherical inclusion phantom scanned freehand with both qualitative and quantitative comparisons. In this paper, we demonstrate greater consistency among visualized LDT strain tensor images showing a standard deviation in inclusion radius of only 0.4 mm while conventional Eulerian tracking resulted in 1.5 mm over 0.5 seconds of tracking the 1.25 cm radius inclusion. Phantom results are validated using in vivo data on human subjects where consistency of LDT strain tensor tracking is demonstrated by the improved Dice and Pearson's correlation coefficient values obtained with respect to CECT, where the Eulerian approach performs worse when compared to LDT. Additionally, as Lagrangian tracking accumulates displacements over time, LDT increased visualization success rate from 75% seen with Eulerian tracking to 100% visualization. LDT therefore provides higher confidence that clinicians can determine ablative margins for defining ablation efficacy.

Management options for small renal masses include active surveillance, partial nephrectomy, radical nephrectomy, and thermal ablation. For tumors typically ≤3 cm in size, thermal ablation is a good option for those desiring an alternative to surgery or active surveillance, especially in patients who are considered high surgical risk. We favor microwave ablation because of the more rapid heating, higher temperatures that overcome the heat sink effect of vessels, reproducible cell kill, and a highly visible ablation zone formed by water vapor that corresponds well to the zone of necrosis. For central tumors, we favor cryoablation because of the slower formation of the ablation zone and less likelihood of damage to the collecting system. With microwaves, it is important to monitor the ablation zone in real time (ultrasound is the best modality for this purpose), avoid direct punctures of the collecting system, and to place probes tangential to the collecting system to avoid burning open a persistent tract between the urothelium and extrarenal spaces or causing strictures. The surgical steps described in this video cover our use of high-frequency jet ventilation with general anesthesia to minimize organ motion, initial imaging and targeting, probe insertion, hydrodissection (a technique that enables displacement of adjacent structures), the ablation itself, and finally our dressing. Postoperative cares typically consist of observation with a same-day discharge or an overnight stay. Follow-up includes a magnetic resonance imaging abdomen with and without contrast, chest X-ray, and laboratories (basic metabolic panel, complete blood count, and C-reactive protein) 6 months postablation. Overall, percutaneous microwave ablation is an effective and safe treatment option for renal cell carcinoma in both T1a and T1b tumors in selected patients with multiple studies showing excellent oncologic outcomes when compared with partial and radical nephrectomy.

Objective and Impact Statement. This is the first longitudinal study investigating the effects of histotripsy on local tumor progression in an in vivo orthotopic, immunocompetent rat hepatocellular carcinoma (HCC) model. Introduction. Histotripsy is the first noninvasive, nonionizing, nonthermal, mechanical ablation technique using ultrasound to generate acoustic cavitation to liquefy the target tissue into acellular debris with millimeter accuracy. Previously, histotripsy has demonstrated in vivo ablation of noncancerous liver tissue. Methods. N1-S1 HCC tumors were generated in the livers of immunocompetent rats (n = 6, control; n = 15, treatment). Real-time ultrasound-guided histotripsy was applied to ablate either 100% tumor volume + up to 2mm margin (n = 9, complete treatment) or 50-75% tumor volume (n = 6, partial treatment) by delivering 1-2 cycle histotripsy pulses at 100 Hz PRF (pulse repetition frequency) with p – ≥30MPa using a custom 1MHz transducer. Rats were monitored weekly using MRI (magnetic resonance imaging) for 3 months or until tumors reached ~25mm. Results. MRI revealed effective post-histotripsy reduction of tumor burden with near-complete resorption of the ablated tumor in 14/15 (93.3%) treated rats. Histopathology showed

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 0.001). Image quality scores at 4 min were 1.8, 2.8, 2.4, and 3, respectively (p 0.001). Mean radiation dose (CTDIAdvanced CT techniques can improve CT image quality in peri-procedural hepatic microwave ablation zone evaluation.

To evaluate the impact of anterior tumor location on oncologic efficacy, complication rates, and procedure duration for 151 consecutive biopsy-proven clinical T1a renal cell carcinoma (RCC) treated with percutaneous microwave (MW) ablation. This single-center retrospective study was performed under a waiver of informed consent. One hundred forty-eight consecutive patients (103 M/45 F; median age 67 years, IQR 61–73) with 151 cT1a biopsy-proven RCC (median diameter 2.4 cm, IQR 1.9–3.0) were treated with percutaneous MW ablation between March 2011 and August 2017. Patient and procedural data collected included Charlson comorbidity index (CCI), RENAL nephrometry score (NS), use of hydrodisplacement, MW antennas/generator output/time, and procedure time (PT). Data were stratified by anterior, posterior, and midline tumor location and compared with the Kruskal–Wallis or chi-squared tests. The Kaplan–Meier method was used for survival analyses. Tumor size, NS, and use/volume of hydrodisplacement were similar for posterior and anterior tumors (p > 0.05). Patients with anterior tumors had a higher CCI (3 vs 4, p = 0.001). Median PT for posterior and anterior tumors was similar (100 vs 108 min, p = 0.26). Single session technical success and primary efficacy were achieved for all 151 tumors including 61 posterior and 67 anterior tumors. The 4 (3%) Clavien III–IV complications and 6 (4%) local recurrences were not associated with tumor location (p > 0.05). Three-year RFS, CSS, and OS were 95% (95% CI 0.87, 0.98), 100% (95% CI 1.0, 1.0), and 96% (95% CI 0.89, 0.98), respectively. The safety and efficacy of percutaneous microwave ablation for anterior and posterior RCC are similar. • The safety profile for percutaneous microwave ablation of anterior and posterior T1a renal cell carcinoma is equivalent. • Percutaneous microwave ablation of T1a renal cell carcinoma provides durable oncologic control regardless of tumor location. • Placement of additional microwave antennas and use of hydrodisplacement are associated with longer procedure times.

PURPOSE: To determine the feasibility of ultra–low-dose (ULD) CT fluoroscopy for performing percutaneous CT-guided interventions in an in vivo porcine model and to compare radiation dose, spatial accuracy, and metal artifact for conventional CT versus CT fluoroscopy. MATERIALS AND METHODS: An in vivo swine model was used (n = 4, ∼50 kg) for 20 procedures guided by 246 incremental conventional CT scans (mean, 12.5 scans per procedure). The procedures were approved by the Institutional Animal Care and Use Committee and performed by two experienced radiologists from September 7, 2017, to August 8, 2018. ULD CT fluoroscopic acquisitions were simulated by using only two of 984 conventional CT projections to locate and reconstruct the needle, which was superimposed on a previously acquired and motion-compensated CT scan. The authors (medical physicists) compared the ULD CT fluoroscopy results to those of conventional CT for needle location, radiation dose, and metal artifacts using Deming regression and generalized mixed models. RESULTS: The average distance between the needle tip reconstructed using conventional CT and ULD CT fluoroscopy was 1.06 mm. Compared with CT fluoroscopy, the estimated dose for a percutaneous procedure, including planning acquisitions, was 0.99 mSv (21% reduction) for patients (effective dose) and 0.015 µGy (97% reduction) for physicians (scattered dose in air). Metal artifacts were statistically significantly reduced (P < .001, bootstrapping), and the average registration error of the motion compensation was within 1–3 mm. CONCLUSION: Ultra–low-dose CT fluoroscopy has the potential to reduce radiation exposure for intraprocedural scans to patients and staff by a factor of approximately 500 times compared with conventional CT acquisition, while maintaining image quality without metal artifacts. © RSNA, 2019

Hepatocellular carcinoma and liver metastases are common hepatic malignancies presenting with high mortality rates. Minimally invasive microwave ablation (MWA) yields high success rates similar to surgical resection. However, MWA procedures require accurate image guidance during the procedure and for post-procedure assessments. Ultrasound electrode displacement elastography (EDE) has demonstrated utility for non-ionizing imaging of regions of thermal necrosis created with MWA in the ablation suite. Three strategies for displacement vector tracking and strain tensor estimation, namely coupled subsample displacement estimation (CSDE), a multilevel 2-D normalized cross-correlation method, and quality-guided displacement tracking (QGDT) have previously shown accurate estimations for EDE. This paper reports on a qualitative and quantitative comparison of these three algorithms over 79 patients after an MWA procedure. Qualitatively, CSDE presents sharply delineated, clean ablated regions with low noise except for the distal boundary of the ablated region. Multilevel and QGDT contain more visible noise artifacts, but delineation is seen over the entire ablated region. Quantitative comparison indicates CSDE with more consistent mean and standard deviations of region of interest within the mass of strain tensor magnitudes and higher contrast, while Multilevel and QGDT provide higher CNR. This fact along with highest success rates of 89% and 79% on axial and lateral strain tensor images for visualization of thermal necrosis using the Multilevel approach leads to it being the best choice in a clinical setting. All methods, however, provide consistent and reproducible delineation for EDE in the ablation suite.

Primary liver cancers and liver metastases are malignancies resulting in high mortality rates [1, 2]. As a treatment method, microwave ablation (MWA) presents with treatment success similar to surgical resection while significantly reducing morbidity and mortality for patients, requiring ablative margins of 0.5 – 1.0 cm verified using medical imaging. Unfortunately, traditional imaging modalities used namely, contrast enhanced computed tomography and B-mode ultrasound have limitations in providing visualization for validating MWA efficacy. Alternatively, electrode displacement elastography (EDE) has shown potential in visualizing MWA post ablation regions. However, EDE has not been used previously for comparing the pre and post ablation cross-sectional area measurements for ablative margin estimation and treatment of liver cancers. This work shows that EDE can achieve ablative margin estimation by comparing pre- and post- ablation EDE strain imaging for use in determining MWA efficacy.

To determine whether histotripsy can create human-scale transcostal ablations in porcine liver without causing severe thermal wall injuries along the beam path.Histotripsy was applied to the liver using a preclinical prototype robotic system through a transcostal window in six female swine. A 3.0 cm spherical ablation zone was prescribed. Duration of treatment (75 min) was longer than a prior subcostal treatment study (24 min, 15 s) to minimize beam path heating. Animals then underwent contrast-enhanced MRI, necropsy, and histopathology. Images and tissue were analyzed for ablation zone size, shape, completeness of necrosis, and off-target effects.Ablation zones demonstrated complete necrosis with no viable tissue remaining in 6/6 animals by histopathology. Ablation zone volume was close to prescribed (13.8 ± 1.8 cmTranscostal hepatic histotripsy ablation appears feasible, effective, and no severe injuries were identified in an acute porcine model when prolonged cooling time is added to minimize body wall heating.

There is currently no consensus regarding preferred clinical outcome measures following image-guided tumor ablation or clear definitions of oncologic end points. This consensus document proposes standardized definitions for a broad range of oncologic outcome measures with recommendations on how to uniformly document, analyze, and report outcomes. The initiative was coordinated by the Society of Interventional Oncology in collaboration with the Definition for the Assessment of Time-to-Event End Points in Cancer Trials, or DATECAN, group. According to predefined criteria, based on experience with clinical trials, an international panel of 62 experts convened. Recommendations were developed using the validated three-step modified Delphi consensus method. Consensus was reached on when to assess outcomes per patient, per session, or per tumor; on starting and ending time and survival time definitions; and on time-to-event end points. Although no consensus was reached on the preferred classification system to report complications, quality of life, and health economics issues, the panel did agree on using the most recent version of a validated patient-reported outcome questionnaire. This article provides a framework of key opinion leader recommendations with the intent to facilitate a clear interpretation of results and standardize worldwide communication. Widespread adoption will improve reproducibility, allow for accurate comparisons, and avoid misinterpretations in the field of interventional oncology research. Published under a CC BY 4.0 license. Online supplemental material is available for this article. See also the editorial by Liddell in this issue.

Histotripsy has been used for tumor ablation, through controlled, non-invasive acoustic cavitation. This is the first study to evaluate the impact of partial histotripsy ablation on immune infiltration, survival outcomes, and metastasis development, in an in vivo orthotopic, immunocompetent rat HCC model (McA-RH7777). At 7–9 days post-tumor inoculation, the tumor grew to 5–10 mm, and ~50–75% tumor volume was treated by ultrasound-guided histotripsy, by delivering 1–2 cycle histotripsy pulses at 100 Hz PRF (focal peak negative pressure P– >30 MPa), using a custom 1 MHz transducer. Complete local tumor regression was observed on MRI in 9/11 histotripsy-treated rats, with no local recurrence or metastasis up to the 12-week study end point, and only a

An inexpensive, accurate focused ultrasound stereotactic targeting method guided by pretreatment magnetic resonance imaging (MRI) images for murine brain models is presented. An uncertainty of each sub-component of the stereotactic system was analyzed. The entire system was calibrated using clot phantoms. The targeting accuracy of the system was demonstrated with an in vivo mouse glioblastoma (GBM) model. The accuracy was quantified by the absolute distance difference between the prescribed and ablated points visible on the pre treatment and posttreatment MR images, respectively. A precalibration phantom study ( ${N} = {6}$ ) resulted in an error of 0.32 ± 0.31, 0.72 ± 0.16, and 1.06 ± 0.38 mm in axial, lateral, and elevational axes, respectively. A postcalibration phantom study ( ${N} = {8}$ ) demonstrated a residual error of 0.09 ± 0.01, 0.15 ± 0.09, and 0.47 ± 0.18 mm in axial, lateral, and elevational axes, respectively. The calibrated system showed significantly reduced ( ${p} ) error of 0.20 ± 0.21, 0.34 ± 0.24, and 0.28 ± 0.21 mm in axial, lateral, and elevational axes, respectively, in the in vivo GBM tumor-bearing mice ( ${N} = {10}$ ).

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 determine physician radiation exposure when using partial-angle computed tomography (CT) fluoroscopy (PACT) vs conventional full-rotation CT and whether there is an optimal tube/detector position at which physician dose is minimized. MATERIALS AND METHODS Physician radiation dose (entrance air kerma) was measured for full-rotation CT (360°) and PACT (240°) at all tube/detector positions using a human-mimicking phantom placed in a 64-channel multidetector CT. Parameters included 120 kV, 20- and 40-mm collimation, and 100 mA. The mean, standard deviation, and increase/decrease in physician dose compared with a full-rotation scan were reported. RESULTS Physician radiation exposure during CT fluoroscopy with PACT was highly dependent on the position of the tube/detector during scanning. The lowest PACT physician dose was when the physician was on the detector side (center view angle 116°; -35% decreased dose vs full-angle CT). The highest PACT physician dose was with the physician on the tube side (center view angle 298°; +34% increased dose vs full-angle CT), all doses P

BACKGROUND: Previous human-scale porcine liver model studies of histotripsy have resulted in ablation zones elongated in the cranial-caudal (CC) dimension due to uninterrupted respiratory motion during the ablation procedure. PURPOSE: The purpose of this study is to compensate for elongation of hepatic histotripsy ablation zones in the cranial-caudal (CC) dimension caused by respiratory motion by prescribing ellipsoid shaped ablations. METHODS: Six female swine underwent 12 hepatic histotripsy ablations using a prototype clinical histotripsy system under general anesthesia. Each animal received two ablation zones prescribed as either an ellipsoid (2.5cm (AP) x 2.5cm (ML) x 1.7cm (CC), prescribed volume=5.8cc) or a sphere (2.5cm all dimensions, prescribed volume 8.2cc). Ventilatory tidal volume was held constant at 400cc for all ablations. Post procedure MRI was followed by sacrifice and gross and microscopic histology. RESULTS: Ablations on MRI were slightly larger than prescribed in all dimensions. Ellipsoid plan ablations (2.8 × 3.0 × 3.1cm, volume 13.2cc, sphericity index 0.987) were closer to prescribed volume than spherical plan ablations (2.9 × 3.1 × 3.7cm, volume 17.1cc, sphericity index 0.953). Ellipsoid plan ablations were more spherical than sphere plan ablations, but the difference did not reach statistical significance (p=.06). Pathologic analysis confirmed complete necrosis within the center of each ablation zone with no widening of the zone of partial ablation on the superior and inferior as compared to the lateral borders (p=.22). CONCLUSION: Altering ablation zone prescription shape when performing hepatic histotripsy ablations can partially mitigate respiratory motion effects to achieve the desired ablation shape and volume.

INTRODUCTION AND OBJECTIVE:Renal angiomyolipoma (AML) are rare tumors and few data are available to compare treatments for patients with large or enlarging tumors. The objective of this project was...

Evaluate the safety and efficacy of adrenal microwave ablation performed with continuous intra-arterial blood pressure monitoring (IABPM) and without alpha-adrenergic blockade (AAB) as pretreatment. A single-center, retrospective review of all percutaneous adrenal microwave ablation performed between 2011 and 2018. Microwave ablation was completed on 11 patients, with a total of 15 adrenal tumors with a mean size of 3.3 cm (1.4–6.9 cm) treated metastatic RCC, HCC, esophageal carcinoma, adrenal adenoma. Cases were performed without prior AAB, but with continuous IABPM and rapid intervention using short-acting antihypertensive medications. There were no post-procedural episodes of hypertension, no neurological or cardiovascular complications, and no SIR moderate or worse adverse event complications. Mean intraprocedural maximum systolic blood pressure (SBP) was 211 mmHg (range: 132–288), with an average increase in SBP of 100 mmHg (range: 23–180). A hypertensive crisis (SBP ≥ 180 and/or DBP ≥ 120) occurred in 9 of the 15 procedures (60%) with a mean length of 3.0 min (range: 1–12). The technical success rate was 100% (15/15 procedures). The mean follow-up time was 2.4 years (range: 0.9–7.7 years), with primary and secondary efficacy rates of 77% and 87%, respectively, and an overall survival of 82%. In this single-center retrospective study, microwave ablation of adrenal tumors without AAB was safe and effective when performed with continuous arterial line monitoring of vital signs and the use of short-acting, rapid-onset antihypertensive medications. Level 4, Case Series.

Objective and Impact Statement . This is the first longitudinal study investigating the effects of histotripsy on local tumor progression in an in vivo orthotopic, immunocompetent rat hepatocellular carcinoma (HCC) model. Introduction . Histotripsy is the first noninvasive, nonionizing, nonthermal, mechanical ablation technique using ultrasound to generate acoustic cavitation to liquefy the target tissue into acellular debris with millimeter accuracy. Previously, histotripsy has demonstrated in vivo ablation of noncancerous liver tissue. Methods . N1-S1 HCC tumors were generated in the livers of immunocompetent rats ( n = 6 , control; n = 15 , treatment). Real-time ultrasound-guided histotripsy was applied to ablate either 100 % tumor volume + up to 2 mm margin ( n = 9 , complete treatment) or 50-75% tumor volume ( n = 6 , partial treatment) by delivering 1-2 cycle histotripsy pulses at 100 Hz PRF (pulse repetition frequency) with p − ≥ 30 MPa using a custom 1 MHz transducer. Rats were monitored weekly using MRI (magnetic resonance imaging) for 3 months or until tumors reached ~25 mm. Results . MRI revealed effective post-histotripsy reduction of tumor burden with near-complete resorption of the ablated tumor in 14/15 (93.3%) treated rats. Histopathology showed Conclusion . Complete and partial histotripsy ablation resulted in effective tumor removal for 14/15 rats, with no evidence of local tumor progression or recurrence.

Purpose To determine the feasibility of creating a clinically relevant hepatic ablation (ie, an ablation zone capable of treating a 2-cm liver tumor) by using robotically assisted sonic therapy (RAST), a noninvasive and nonthermal focused ultrasound therapy based on histotripsy. Materials and Methods This study was approved by the institutional animal use and care committee. Ten female pigs were treated with RAST in a single session with a prescribed 3-cm spherical treatment region and immediately underwent abdominal magnetic resonance (MR) imaging. Three pigs (acute group) were sacrificed immediately following MR imaging. Seven pigs (chronic group) were survived for approximately 4 weeks and were reimaged with MR imaging immediately before sacrifice. Animals underwent necropsy and harvesting of the liver for histologic evaluation of the ablation zone. RAST ablations were performed with a 700-kHz therapy transducer. Student t tests were performed to compare prescribed versus achieved ablation diameter, difference of sphericity from 1, and change in ablation zone volume from acute to chronic imaging. Results Ablation zones had a sphericity index of 0.99 ± 0.01 (standard deviation) (P < .001 vs sphericity index of 1). Anteroposterior and transverse dimensions were not significantly different from prescribed (3.4 ± 0.7; P = .08 and 3.2 ± 0.8; P = .29, respectively). The craniocaudal dimension was significantly larger than prescribed (3.8 ± 1.1; P = .04), likely because of respiratory motion. The central ablation zone demonstrated complete cell destruction and a zone of partial necrosis. A fibrous capsule surrounded the ablation zone by 4 weeks. On 4-week follow-up images, ablation zone volumes decreased by 64% (P < .001). Conclusion RAST is capable of producing clinically relevant ablation zones in a noninvasive manner in a porcine model. © RSNA, 2018.

Bubble-induced color Doppler (BCD) is a histotripsy therapy monitoring technique that uses Doppler ultrasound to track the motion of residual cavitation nuclei that persist after the collapse of the histotripsy bubble cloud. In this study, BCD is used to monitor tissue fractionation during histotripsy tissue therapy, and the BCD signal is correlated with the destruction of structural and non-structural components identified histologically to further understand how BCD monitors the extent of treatment. A 500-kHz, 112-element phased histotripsy array is used to generate approximately 6×6×7 mm lesions within ex vivo bovine liver tissue by scanning over 219 locations with 30–1000 pulses-per-location. A 128-element L7-4 imaging probe is used to acquire BCD signals during all treatments. The BCD signal is then quantitatively analyzed using the time-to-peak rebound velocity (t(prv)) metric. Using the Pearson correlation coefficient (PCC), the t(prv) is compared to histological analytics of lesions generated by different numbers of pulses using a significance level of 0.001. Histological analytics in this study include viable cell count, reticulin-stained type III collagen area, and trichrome-stained type I collagen area. It is found that the t(prv) metric has a statistically significant correlation with the change in reticulin-stained type III collagen area with a PCC of −0.94 (p < 0.001) indicating that changes in BCD are more likely due to destruction of the structural components of tissue.