A fast all-optical 3D photoacoustic scanner for clinical vascular imaging

Nature Biomedical Engineering (2024 )Cite this article

The clinical assessment of microvascular pathologies (in diabetes and in inflammatory skin diseases, for example) requires the visualization of superficial vascular anatomy. Photoacoustic tomography (PAT) scanners based on an all-optical Fabry–Perot ultrasound sensor can provide highly detailed 3D microvascular images, but minutes-long acquisition times have precluded their clinical use. Here we show that scan times can be reduced to a few seconds and even hundreds of milliseconds by parallelizing the optical architecture of the sensor readout, by using excitation lasers with high pulse-repetition frequencies and by exploiting compressed sensing. A PAT scanner with such fast acquisition minimizes motion-related artefacts and allows for the volumetric visualization of individual arterioles, venules, venous valves and millimetre-scale arteries and veins to depths approaching 15 mm, as well as for dynamic 3D images of time-varying tissue perfusion and other haemodynamic events. In exploratory case studies, we used the scanner to visualize and quantify microvascular changes associated with peripheral vascular disease, skin inflammation and rheumatoid arthritis. Fast all-optical PAT may prove useful in cardiovascular medicine, oncology, dermatology and rheumatology.

Visualizing the microvasculature to sub-cm depths in tissue is required for the effective clinical management of a wide range of vascular abnormalities, including those associated with skin cancers, dermatological conditions1, the diabetic foot2 and superficial soft-tissue damage such as burns or ulcers3. Optical imaging techniques offer promise on account of their ability to visualize vascular anatomy, oxygenation and flow4,5. However, strong optical scattering by tissue limits penetration depth or spatial resolution. Conventional light microscopy, optical coherence tomography and other methods that rely on unscattered ballistic photons can provide capillary-level microvascular images but only to sub-mm depths. Laser Doppler or speckle contrast imaging techniques that exploit diffuse or semi-ballistic photons provide greater penetration depth. However, optical scattering limits spatial resolution, resulting in spatially averaged images that do not reveal microvascular architecture at the level of individual microvessels. Ultrasound (US) imaging can overcome the depth/resolution limitations of optical techniques but presents other challenges. Conventional non-contrast clinical Doppler US yields poor microvascular contrast with emerging ultrafast plane-wave US6,7, offering higher sensitivity. However, both rely on the detection of moving blood, thus limiting their sensitivity to slowly moving or static blood and precluding the measurement of blood oxygenation.

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