Abstract
Conventional non-contrast Doppler ultrasound (US) techniques are limited to relatively high velocities in large, resolvable vessels. Therefore, US without contrast has historically been ineffective for evaluating transarterial chemoembolization (TACE) treatment of hepatic malignancies, which involves acute reduction in tumor perfusion. Recent advancements in power Doppler (PD) US beamforming and tissue filtering have substantially improved sensitivity to slow blood flow in small-diameter vessels, potentially making non-contrast perfusion US imaging possible. Among these are angled plane wave beamforming, adaptive tissue clutter demodulation (AD), and singular value decomposition (SVD) filtering. Here we aim to demonstrate feasibility of these advancements for immediate evaluation of TACE. This study was IRB approved. Nine patients undergoing 10 TACE procedures were included. A Verasonics C5-2 probe with a 4.2MHz frequency was used to acquire raw angled plane wave channel data immediately before and after treatment. Images were post-processed as follows: channel data were beamformed and filtered using conventional (IIR filtering and a 16-sample ensemble) and advanced (AD+SVD filtering and a 300-sample ensemble) processing methods. Tumor-to-background contrast in PD images was computed before and after TACE and averaged across acquisitions for each processing technique. Minimal change was detected in tumor blood flow between before and after TACE images when using conventional methods. With advanced processing, visible reduction in flow within tumors was clearly identifiable. On average, conventional and advanced processing methods resulted in 0.8dB (± 1.2dB) and 8.0dB (± 1.1dB) decreases in tumor-to-background contrast, respectively. Advanced non-contrast power Doppler US to detect treatment-induced changes in blood flow is feasible immediately following TACE. As post-processing becomes more efficient, on table assessment of TACE completion may be quantifiably obtained in real time. We plan on correlating these findings with gold-standard follow-up imaging as a next step.
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