Monitoring of Thermal-Induced Changes in Liver Stiffness During Controlled Hyperthermia and Microwave Ablation in an Ex Vivo Bovine Model Using Point Shear Wave Elastography.

PURPOSE: To investigate liver stiffness changes-evaluated by point shear wave elastography (pSWE)-in controlled hyperthermia and microwave ablation (MWA) in an ex vivo animal model. MATERIALS AND METHODS: Five samples of ex vivo bovine liver were uniformly heated to temperatures ranging from 40 to 100 °C. B-mode ultrasound imaging and pSWE were acquired simultaneously, and shear wave velocity (SWV) was measured in a region of interest (ROI). The threshold value of SWV at 60 °C (avg60) was identified. Subsequently, MWA was performed in 11 liver samples at 60 W until avg60 + 0.5 m/s was reached. SWV was measured in ROIs at 10-40 mm from the antenna feed. The correlation of mean values of SWV with location (within, border, or outside necrotic area) at gross pathology was evaluated. RESULTS: In controlled hyperthermia experiments, a steep transition in liver stiffness was observed at 63.0 ± 2.4 °C (SWV 3.54 ± 0.68 m/s). Avg60 was of 2.5 m/s. In 8/9 MWA experiments, interrupted when SWV of 3 m/s was measured, the ROI was at the inner side of the necrotic area border at pathology (accuracy 89%). No correlation between SWV values for outside, border, and within necrosis could be identified. CONCLUSIONS: pSWE can provide a velocity threshold predictive of the presence of coagulation necrosis during MWA in ex vivo liver model. However, pSWE is not able to reliably capture changes in stiffness within, at the border, and outside the necrotic zone in this experimental model.

Tissue shrinkage in microwave ablation of liver: an ex vivo predictive model.

PURPOSE: The aim of this study was to develop a predictive model of the shrinkage of liver tissues in microwave ablation. METHODS: Thirty-seven cuboid specimens of ex vivo bovine liver of size ranging from 2 cm to 8 cm were heated exploiting different techniques: 1) using a microwave oven (2.45 GHz) operated at 420 W, 500 W and 700 W for 8 to 20 min, achieving complete carbonisation of the specimens, 2) using a radiofrequency ablation apparatus (450 kHz) operated at 70 W for a time ranging from 6 to 7.5 min obtaining white coagulation of the specimens, and 3) using a microwave (2.45 GHz) ablation apparatus operated at 60 W for 10 min. Measurements of specimen dimensions, carbonised and coagulated regions were performed using a ruler with an accuracy of 1 mm. Based on the results of the first two experiments a predictive model for the contraction of liver tissue from microwave ablation was constructed and compared to the result of the third experiment. RESULTS: For carbonised tissue, a linear contraction of 31 ± 6% was obtained independently of the heating source, power and operation time. Radiofrequency experiments determined that the average percentage linear contraction of white coagulated tissue was 12 ± 5%. The average accuracy of our model was determined to be 3 mm (5%). CONCLUSIONS: The proposed model allows the prediction of the shrinkage of liver tissues upon microwave ablation given the extension of the carbonised and coagulated zones. This may be useful in helping to predict whether sufficient tissue volume is ablated in clinical practice.

Transperineal microwave thermoablation in patients with obstructive benign prostatic hyperplasia: a phase I clinical study with a new mini-choked microwave applicator.

PURPOSE: To evaluate the tolerability and safety of a newly designed probe for trans-perineal microwave thermoablation (TPMT) of the prostate in patients with benign prostatic hyperplasia (BPH), and the in vivo microwave effects on prostatic tissue. PATIENTS AND METHODS: Nine patients with obstructive BPH who were candidates for open prostatectomy were selected for this study. Under local anesthesia and transrectal ultrasound monitoring, all patients underwent a single standardized application of TPMT. The visual analog scale (VAS) and Short Form-36 health survey (SF-36) questionnaire were administered to each patient prior to, during, and 1 month after TPMT in order to evaluate pain and quality of life. Then the International Index of Erectile Function (IIEF-5) and International Prostate Symptom Score (IPSS) questionnaires were administered to each patient at baseline and 1 month after prostatectomy in order to evaluate sexual and urinary function, respectively. Then all patients were divided into three groups and underwent open prostatectomy 7, 15, and 30 days after TPMT, respectively. The prostatic adenomas were then evaluated by a pathologist. RESULTS: No adverse events from TPMT treatment were noted. In particular, no patients reported local, pelvic, or abdominal pain during the procedure or subsequent alterations of defecation rhythm, ano-rectal/intestinal problems, or hematuria. No differences in quality of life or in sexual function were reported. The diameters of the lesions obtained with TPMT treatment ranged from 16 to 18.1 mm in all patients. Quasi-spheroid lesions with a well-defined area of complete coagulative necrosis were documented in all removed adenomas 7, 15, and 30 days after TMPT. CONCLUSIONS: The AMICA-PROBE is a safe, well-tolerated, and repeatable method to treat BPH with microwave thermotherapy. The spheroid lesions obtained demonstrated the maximal control over the radial and longitudinal coagulative effects of the therapy. Phase II studies are needed to further evaluate the efficacy of this new probe.