Deep Photoacoustic Imaging and Acoustic Cavitation Mapping in Shockwave Lithotripsy

Abstract

<p>Kidney stone disease is a major health problem worldwide. Shockwave lithotripsy (SWL), which uses high-energy shockwave pulses to break up kidney stones, is extensively used in clinic. However, SWL can produce cavitation in vivo, and the rapid expansion and violent collapse of cavitation bubbles in small blood vessels may result in renal vascular injury. Current imaging modalities used in SWL (e.g., C-arm fluoroscopy and B-mode ultrasound) are not sensitive to vascular injuries. To better understand the mechanism of tissue injury and improve treatment safety and efficiency, it is highly desirable to concurrently detect cavitation and vascular injury during SWL. Photoacoustic imaging that is sensitive to hemoglobin can be used to monitor hemorrhage during shockwave treatment. An internal illumination strategy combined with a graded scattering fiber diffuser was applied to achieve uniform light distribution and extend the imaging depth to ~10 cm. Moreover, a sliding-window passive cavitation mapping approach was developed and validated to provide accurate temporal and spatial information about cavitation bubble collapses. Finally, we have seamlessly integrated shockwave treatment, photoacoustic imaging, and cavitation detection into a single system. Our experiment results based on phantoms and in vivo animal studies have collectively demonstrated that the integrated system is capable of capturing shockwave-induced cavitation and deeply located vascular injury during the stone treatment.</p>