Ex vivo photoacoustic imaging of atherosclerotic carotid plaques

Vulnerability assessment of carotid plaques is vital to prevent atherosclerosis-related mortality and disability. Photoacoustic imaging (PAI) in combination with plane-wave ultrasound (PUS) may have the ability to reveal the composition and the anatomical structure of the plaque, which infers its mechanical properties and vulnerability. In this study, we used PAI and PUS imaging to scan endarterectomy samples ex vivo, targeting intraplaque hemorrhage, and compared the results with those obtained in healthy (porcine) carotids and histology. A fully integrated hand-held photoacoustic probe was used, consisting of a pulsed diode laser (t_p = 130 ns, E_p = 1 mJ, λ = 808 nm) and a linear array transducer (f_c = 7.5 MHz). Three porcine carotid arteries and six carotid plaque samples were obtained from a local slaughterhouse and hospital respectively, and were mounted to the imaging setup. Data of endarterectomy samples revealed that PAI of carotid plaques at 808 nm wavelength is capable of detecting blood clots, which can be extensions of vasculature in the plaque, intra-plaque hemorrhage, or the result of trauma inflicted on the medial vascularization. Due to calcification and the limited optical penetration, imaging depth was mostly limited to the proximal wall of the samples. The porcine carotids revealed no hemorrhaging, which was corroborated by the lack of PAI contrast.