Real-time mapping of photo-sono therapy induced cavitation using Doppler optical coherence tomography

Abstract

Photo-sono therapy (PST) is an innovative anti-vascular approach based on cavitation-induced spallation. Currently, passive cavitation detection (PCD) is the prevalent technique for cavitation monitoring during treatment. However, the limitations of PCD are the lack of spatial information of bubbles and the difficulty of integration with the PST system. To address this, we proposed a new, to the best of our knowledge, cavitation mapping method that integrates Doppler optical coherence tomography (OCT) with PST to visualize bubble dynamics in real time. The feasibility of the proposed system has been confirmed through experiments on vascular-mimicking phantoms and in vivo rabbit ear vessels, and the results are compared to high-speed camera observations and PCD data. The findings demonstrate that Doppler OCT effectively maps cavitation in real time and holds promise for guiding PST treatments and other cavitation-related clinical applications.

Fig. 1.

Design and principle of the Doppler OCT-guided PST system. (a) Schematic of the Doppler OCT-guided PST system. (b) Timing diagram. FG, function generator, US, ultrasound. (c) Principle of PST-induced cavitation.

Fig. 2.

Cavitation observation with SS-OCT in phantom. (a) Doppler OCT image, (b) Doppler OCT image, (c) conventional OCT image under M-mode acquisition, as a function of time, (d) conventional OCT image under B-mode acquisition, as a function of space.

Fig. 3.

Cavitation detection in flow blood phantom. Color images and black-and-white images are captured by Doppler OCT (a)–(d) and high-speed camera (a’)–(d’), respectively. (a) Control group: without pulsed laser and without US, (b) pulsed laser only at 2.76 mJ/cm², (c) ultrasound only at 310 kPa, (d) with both pulsed laser and with US.

Fig. 4.

Cavitation detection during PST in a rabbit ear in vivo. (a) OCTA image captured before PST. (b) Bubble dynamics at a selected location [indicated by the yellow line in Fig. 4(a)] during PST. (c) Algorithm for estimating cavitation probability based on Doppler OCT images, consisting of (1) phase wrap correction and (2) cavitation probability estimation. Correlation between normalized power detected by PCD and normalized cavitation probability detected by Doppler OCT with varying laser energy (d) and HIFU peak pressure (e).