The current preoperative vascular imaging methods cannot achieve noninvasive high-resolution imaging of deep-localized vessels. Photoacoustic tomography (PAT) can show microvessels with centimeter depth and submillimeter diameter without the use of contrast agents. Combined with PAT and optical projection technology, the Hessian-matrix-based skin removal algorithm and the target matching method were developed to spatially align the photoacoustic data of subcutaneous blood vessels with the anatomy of real patients and to realize three-dimensional (3D) visualization of blood vessels from the body surface. The optical projection navigation system based on PAT has high spatial resolution (∼135  μm) and temporal resolution (0.1 s). In the rabbit injection experiment, 3D distributions of needle and blood vessel (>100  μm) were obtained by image segmentation, which proved that the method can guide micro plastic injection. Furthermore, healthy volunteers' forehead imaging experiments show that 3D visualization and cross-sectional images of the human forehead clearly show the vascular network and ability of the system to image submillimeter blood vessels with penetration depth (∼10.2 mm). Our work confirms that the method of integrated photoacoustic imaging and optical projection has great potential for noninvasive diagnosis and treatment of clinical blood vessels, opening a path for the application of photonics in medical esthetics.

The mechanical properties of organisms are important indicators for clinical disputes and disease monitoring, yet most existing elastography techniques are based on contact measurements, which are limited in many application scenarios. Photoacoustic remote sensing elastography (PARSE) is the first, to the best of our knowledge, elastography modality based on acoustic pressure monitoring, where elastic contrast information is obtained by using an all-optical non-contact and non-coherent intensity monitoring method through the time-response properties of laser-induced photoacoustic pressure. To validate PARSE, sections of different elastic organs were measured and this modality was applied to differentiate between bronchial cartilage and soft tissue to confirm the validity of the elasticity evaluation. PARSE, through a mathematical derivation process, has a 9.5-times greater distinction detection capability than photoacoustic remote sensing (PARS) imaging in stained bronchial sections, expands the scope of conventional PARS imaging, and has potential to become an important complementary imaging modality.

Forward-view photoacoustic (PA) endoscopy (PAE) is promising for achieving noninvasive biopsy in narrow areas of internal organs. However, current schemes that scan the proximal end of fiber bundles' core-by-cores would cause limited spatial sampling confined by the number of cores, which result in lower lateral resolution at smaller probe size. In this paper, a flexible forward-view PAE probe based on a resonant fiber scanner with a diameter of 5 mm was developed, which compactly integrated a piezoelectric (PZT) bender, a fiber cantilever, a lens, an ultrasound transducer, and a coupler inside. Phantom imaging was conducted to evaluate the performance of the flexible forward-view PAE, exhibiting a lateral resolution of 15.6  μm in a field-of-view of approximately 3 mm diameter and the imaging speed is 0.5 frames per second. In vivo imaging shows the clear vascular network of the rat gastrointestinal wall, which demonstrates the feasibility of resonant fiber scanners for photoacoustic endoscopic imaging, and indicates its potential for application as minimally invasive tools in the clinical evaluation of gastrointestinal lesions.

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