Ultrasound therapy system and ablation results utilizing miniature imaging/therapy arrays

In open surgical procedures, image-ablate ultrasound arrays performed thermal ablation and imaging on rabbit liver lobes with implanted VX2 tumor. Treatments included unfocused (bulk ultrasound ablation, N = 10) and focused (high-intensity focused ultrasound ablation, N = 13) exposure conditions. Echo decorrelation and integrated backscatter images were formed from pulse-echo data recorded during rest periods after each therapy pulse. Echo decorrelation images were corrected for artifacts using decorrelation measured prior to ablation. Ablation prediction performance was assessed using receiver operating characteristic curves. Results revealed significantly increased echo decorrelation and integrated backscatter in both ablated liver and ablated tumor relative to unablated tissue, with larger differences observed in liver than in tumor. For receiver operating characteristic curves computed from all ablation exposures, both echo decorrelation and integrated backscatter predicted liver and tumor ablation with statistically significant success, and echo decorrelation was significantly better as a predictor of liver ablation. These results indicate echo decorrelation imaging is a successful predictor of local thermal ablation in both normal liver and tumor tissue, with potential for real-time therapy monitoring.

Section: Methodsmentioning

confidence: 99%

Echo Decorrelation Imaging of Rabbit Liver and VX2 Tumor during In Vivo Ultrasound Ablation

Fosnight

Hooi

Keil

et al. 2017

“…Ultrasound imaging was performed by the Iris 2 ultrasound imaging and ablation system (Guided Therapy Systems, Mesa, AZ) (Barthe et al, 2004). Throughout each treatment, echo signals were recorded from the Iris system using a 14-bit, PC-based A/D converter (CompuScope CS 14200, Gage Applied Technologies, Montreal, Quebec, Canada) at a sampling rate of 33.3 MHz and stored.…”

Section: Methodsmentioning

confidence: 99%

In Vivo Thermal Ablation Monitoring Using Ultrasound Echo Decorrelation Imaging

Subramanian

Rudich

Alqadah

et al. 2014

Previous work has shown ultrasound echo decorrelation imaging can track and quantify changes in echo signals to predict thermal damage during in vitro radiofrequency ablation (RFA). In the in vivo studies reported here, the feasibility of using echo decorrelation imaging as a treatment monitoring tool is assessed. RFA was performed on a normal swine liver (N = 5) and ultrasound ablation using image-ablate arrays was performed on a rabbit liver implanted with VX2 tumors (N = 2). Echo decorrelation and integrated backscatter were computed from Hilbert transformed pulse-echo data acquired during RFA and ultrasound ablation treatments. Receiver operating characteristic (ROC) curves were employed to assess the ability of echo decorrelation imaging and integrated backscatter to predict ablation. Area under the ROC curves (AUROC) was determined for RFA and ultrasound ablation using echo decorrelation imaging. Ablation was predicted more accurately using echo decorrelation imaging (AUROC 0.832 and 0.776 for RFA and ultrasound ablation respectively) than using integrated backscatter (AUROC 0.734 and 0.494).

“…The Iris system provides user-programmable control of therapeutic ultrasound exposures for image-ablate arrays, as well as B-scan imaging with capabilities comparable to clinical diagnostic scanners (Barthe 2004;. The image-ablate array employed has an active surface of 2.3 × 49 mm 2 and individual element sizes of 2.3 mm in elevation and 1.5 mm in azimuth.…”

Section: Measurementsmentioning

confidence: 99%

Acoustic Emissions During 3.1 MHz Ultrasound Bulk Ablation In Vitro

Mast

Salgaonkar

Karunakaran

et al. 2008

Acoustic emissions associated with cavitation and other bubble activity have previously been observed during ultrasound ablation experiments. Since detectable bubble activity may be related to temperature, tissue state, and sonication characteristics, these acoustic emissions are potentially useful for monitoring and control of ultrasound ablation. To investigate these relationships, ultrasound ablation experiments were performed with simultaneous measurements of acoustic emissions, tissue echogenicity, and tissue temperature, on fresh bovine liver. Ex vivo tissue was exposed to 0.9-3.3 s bursts of unfocused, continuous-wave, 3.10 MHz ultrasound from a miniaturized 32-element array, which performed B-scan imaging with the same piezoelectric elements during brief quiescent periods. Exposures employed pressure amplitudes of 0.8-1.4 MPa for exposure times of 6-20 min, sufficient to achieve significant thermal coagulation in all cases. Acoustic emissions received by a 1 MHz, unfocused passive cavitation detector, beamformed Aline signals acquired by the array, and tissue temperature detected by a needle thermocouple were sampled 0.3-1.1 times per second. Tissue echogenicity was quantified by the backscattered echo energy from a fixed region of interest within the treated zone. Acoustic emission levels were quantified from the spectra of signals measured by the passive cavitation detector, including subharmonic signal components at 1.55 MHz, broadband signal components within the band 0.3-1.1 MHz, and low-frequency components within the band 10-30 kHz. Tissue ablation rates, defined as the thermally ablated volumes per unit time, were assessed by quantitative analysis of digitally imaged, macroscopic tissue sections. Correlation analysis was performed among the averaged and time-dependent acoustic emissions in each band considered, B-mode tissue echogenicity, tissue temperature, and ablation rate. Ablation rate correlated significantly with broadband and low-frequency emissions, but was uncorrelated with subharmonic emissions. Subharmonic emissions were found to depend strongly on temperature in a nonlinear manner, with significant emissions occurring within different temperature ranges for each sonication amplitude. These results suggest potential roles for passive detection of acoustic emissions in guidance and control of bulk ultrasound ablation treatments.