Photoacoustic endomicroscopy combined with ultrasound (PAEM-US) has been a long-standing expectation for gastrointestinal tumor examination. Here, we introduce a prototype disposable PAEM-US catheter and corresponding power interface unit, featuring catheter switchability, self-internal three-dimensional scanning, and system repeatability for gastrointestinal endoscopy. By utilizing high-fluence relays, cascade insertion loss of the optical waveguide is minimized to 0.6 dB with a high performance of power resistance, and a focus-customizable acousto-optic coaxial probe is designed for high-sensitivity optical-resolution photoacoustic imaging. Imaging capability was demonstrated with in vivo anatomical imaging at 30 frames per second. Imaging results showed co-registered microscopic visualization of the microvascular and stratification of the rat colorectum with lateral resolution of 18 μm and axial resolution of 63 μm, holding great potential in the clinical detection of gastrointestinal diseases.
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.
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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