FIP Special Student Seminar: Deep photoacoustic imaging and cavitation mapping in shockwave lithotripsy

Kidney stone disease is a major health problem worldwide. Shockwave lithotripsy (SWL), which uses high-energy shockwave pulses to break kidney stones, is extensively used in clinical practice. However, the rapid expansion and violent collapse of cavitation bubbles produced by SWL in small blood vessels may result in severe renal vascular injury. Current imaging modalities used in SWL (e.g., C-arm fluoroscopy and B-mode ultrasound) are not sensitive to vascular injury, and/or cannot detect the tissue-damaging cavitation events during SWL. By contrast, photoacoustic imaging (PAI) is a non-invasive and non-radiative imaging modality that is uniquely sensitive to blood by using hemoglobin as the endogenous contrast. Moreover, photoacoustic imaging is seamlessly compatible with passive cavitation detection (PCD) by sharing the one-way ultrasound detection. Here, we have integrated the SWL treatment, photoacoustic imaging and passive cavitation detection into a single system (SWL/PAI/PCD), which, for the first time, is capable of studying the cavitation events and monitoring the vascular injury at the same time. In addition, to achieve a large penetration depth of > 10 cm in clinical applications, we have developed internal-illumination photoacoustic imaging, in which a novel graded-scattering fiber diffuser has been designed and fabricated to achieve uniform light illumination over a large tissue volume inside the kidney. Our experimental results on tissue phantoms.l