Photoacoustic-mediated ultrasound therapy (PUT) is a novel anti-vascular therapeutic modality based on cavitation-induced bioeffects. During PUT, the synergistic combination of laser pulses and ultrasound bursts is used to precisely remove microvessels and stop local blood perfusion. Due to its high precision on microvessel removal, PUT holds great potential in ophthalmology as an alternative treatment modality for retinal/choroidal neovascularization.
To further improve the safety and efficiency of PUT in removing the ocular vasculature, we developed an integrated PUT and spectral domain optical coherence tomography (SD-OCT) system that can monitor cavitation in real-time during PUT. The capability of this integrated system in detecting cavitation activity was first investigated on a blood vessel-mimicking phantom in-vitro and compared with the detection results from a passive cavitation detector (PCD). The synchronizations between PCD, SD-OCT, and PUT were precisely controlled by a pulse-delay generator. The in-vitro experiments suggested that SD-OCT, by detecting signal washout, was comparable to PCD in detecting relatively large bubbles driven by 0.25 MHz ultrasound frequency. The performance of the integrated PUT and SD-OCT system was then evaluated in a rabbit eye model in-vivo. The preliminary in-vivo study indicated that micro-hemorrhage on choroid vessels typically happened after a large cavitation cloud was detected on OCT. Further in-vivo studies tested the feasibility of using real-time SD-OCT as an alert system to stop PUT once large bubble clouds were detected. The findings indicate that, by monitoring cavitation activities during PUT treatment, real-time SD-OCT monitoring could help to avoid micro-hemorrhage in the retina during PUT. Real-time OCT monitoring can thus improve the safety and efficiency of PUT in removing the retinal and choroidal microvasculature.