Photoacoustic imaging (PAI) combines optical contrast with ultrasound spatial resolution and can be obtained up to a depth of a few centimeters. Hand-held PAI systems using linear array usually operate in reflection mode using a dark-field illumination scheme, where the optical fiber output is attached to both sides of the elevation plane (short-axis) of the transducer. More recently, bright-field strategies where the optical illumination is coaxial with acoustic detection have been proposed to overcome some limitations of the standard dark-field approach. In this paper, a novel multiangle long-axis lateral illumination is proposed. Monte Carlo simulations were conducted to evaluate light delivery for three different illumination schemes: bright-field, standard dark-field, and long-axis lateral illumination. Long-axis lateral illumination showed remarkable improvement in light delivery for targets with a width smaller than the transducer lateral dimension. A prototype was developed to experimentally demonstrate the feasibility of the proposed approach. In this device, the fiber bundle terminal ends are attached to both sides of the transducer’s long-axis and the illumination angle of each fiber bundle can be independently controlled. The final PA image is obtained by the coherent sum of subframes acquired using different angles. The prototype was experimentally evaluated by taking images from a phantom, a mouse abdomen, forearm, and index finger of a volunteer. The system provided light delivery enhancement taking advantage of the geometry of the target, achieving sufficient signal-to-noise ratio at clinically relevant depths.

This study evaluated whether an experimental chitosan hydrogel loaded with amine-functionalized nanohydroxyapatite could reduce dentin demineralization and promote remineralization in an in vitro GERD model. A total of 176 bovine dentin specimens were initially eroded with hydrochloric acid and distributed into four treatment groups: untreated control, chitosan gel, experimental hydrogel, and 4% TiF4 varnish, with or without abrasion. The specimens were then exposed to liquid or gaseous hydrochloric acid for 6 days. Remineralization intensity and depth were assessed by swept-source OCT, surface morphology by scanning electron microscopy, and chemical changes by µ-Ramam spectroscopy.OCT showed that the experimental hydrogel produced the highest brightness and greatest mineralized depth, reaching 320–333 µm under gaseous HCl and 255–280 µm under liquid HCl, whereas the untreated control showed the lowest depth values (143–170 µm). TiF4 varnish provided the strongest surface protection, while the experimental hydrogel showed the best depth- related remineralization. Liquid hydrochloric acid caused more severe demineralization than gaseous acid, and abrasion intensified mineral loss, especially in untreated dentin. Morphological analysis showed narrower dentinal tubules and a thin deposited surface layer in the experimental hydrogel and chitosan groups, and the experimental hydrogel also showed stronger phosphate-related Raman bands under liquid acid challenge. However, none of the treatments preserved the organic matrix at the level of sound dentin. Within the limitations of this in vitro study, the experimental hydrogel and TiF4 varnish showed promising but distinct protective effects against dentin erosion: the hydrogel favored deeper remineralization, whereas TiF4 provided stronger superficial protection.