Optimized Echo Decorrelation Imaging Feedback for Bulk Ultrasound Ablation Control

Abstract

Feasibility of controlling bulk ultrasound (US) thermal ablation using echo decorrelation imaging was investigated in ex vivo bovine liver. The first of two ablation and control procedures used a sequence of constant-intensity sonication cycles, ceased when the minimum echo decorrelation within a control region of interest (ROI) exceeded a predetermined threshold. The second procedure used a variable-intensity sonication sequence, with spatially averaged decorrelation as the stopping criterion. US exposures and echo decorrelation imaging were performed by a linear image-ablate array. Based on preliminary experiments, control ROIs and thresholds for the minimum-decorrelation and average-decorrelation criteria were specified. Controlled trials for the minimum-decorrelation and average-decorrelation criteria were compared with uncontrolled trials employing 9 or 18 cycles of matching sonication sequences. Lesion dimensions, treatment times, ablation rates, and areas under receiver operating characteristic curves were statistically compared. Successfully controlled trials using both criteria required significantly shorter treatment times than corresponding 18-cycle treatments, with better ablation prediction performance than uncontrolled 9-cycle and 18-cycle treatments. Either control approach resulted in greater ablation rate than corresponding 9-cycle or 18-cycle uncontrolled approaches. A post hoc analysis studied the effect of exchanging control criteria between the two series of controlled experiments. For either group, the average time needed to exceed the alternative decorrelation threshold approximately matched the average duration of successfully controlled experimental trials. These results indicate that either approach, using minimum-decorrelation or average-decorrelation criteria, is feasible for control of bulk US ablation. In addition, use of a variable-intensity sonication sequence for bulk US thermal ablation can result in larger ablated regions compared to constant-intensity sonication sequences.

In vivo ultrasound thermal ablation control using echo decorrelation imaging in rabbit liver and VX2 tumor

“…The real-time feedback control algorithm employed here has been validated in ex vivo bovine liver experiments to control HIFU [42] and bulk US [43] ablation treatments. For better prediction and control performance, the motion and noise compensation method previously described by Hooi et al [38] was integrated with the control algorithm, such that the effect of motion-induced decorrelation was corrected in real time.…”

“…Echo decorrelation imaging has been successfully validated for controlling ex vivo US thermal ablation in bovine liver [42, 43] and in chicken breast [44]. Results from previous ex vivo studies indicate that preclinical translation of the proposed real-time control method is feasible with some considerations.…”

“…Results from previous ex vivo studies indicate that preclinical translation of the proposed real-time control method is feasible with some considerations. These considerations include necessary modifications to stopping criteria previously employed in controlled ex vivo US experiments [42, 43], for consistency with in vivo tissue acoustical and anatomical characteristics. In addition, compensating the effect of artifactual echo decorrelation due to motion and noise is an essential consideration for controlling thermal ablation in vivo .…”

“…A motion and noise correction method [38] was used to correct cumulative echo decorrelation maps computed from stored echo data. Here, the same correction method was implemented to provide corrected cumulative echo decorrelation maps in real time, and was integrated with a real-time control algorithm previously validated for ex vivo ablation [42, 43].…”

Real-Time HIFU Treatment Monitoring Using Pulse Inversion Ultrasonic Imaging

“…As a result, the experimental results imply that the proposed method enables us to confirm the focal area of HIFU and to monitor the echogenicity changes of the area due to its capability of real-time HIFU interference elimination. Additionally, this result implies that the proposed method can help the thermometry [6] and echo decorrelation [25,26] methods accurately visualize and measure the treatment area in real time because these methods require a high signal-to-noise ratio to achieve high accuracy. For this reason, the cessation of HIFU exposure is currently necessary at the time of measurement.…”