There has been a long-standing expectation that the optical-resolution embodiment of photoacoustic tomography could have a substantial impact on gastrointestinal endoscopy by enabling microscopic visualization of the vasculature based on the endogenous contrast mechanism. Although multiple studies have demonstrated the in vivo imaging capability of a developed imaging device over the last decade, the implementation of such an endoscopic system that can be applied immediately when necessary via the instrument channel of a video endoscope has been a challenge. In this study, we developed a 3.38-mm diameter catheter-based, integrated optical-resolution photoacoustic and ultrasonic mini-probe system and successfully demonstrated its intra-instrument channel workability for the standard 3.7-mm diameter instrument channel of a clinical video endoscope based on a swine model. Through the instrument channel, we acquired the first in vivo dual-mode photoacoustic and ultrasonic endoscopic images from the esophagogastric junction of a swine. Further, in a rat colorectum in vivo imaging experiment, we visualized hierarchically developed mesh-like capillary networks with a hole size as small as ~50 µm, which suggests the potential level of image details that could be photoacoustically provided in clinical settings in the future.

Despite all the expectations for photoacoustic endoscopy (PAE), there are still several technical issues that must be resolved before the technique can be successfully translated into clinics. Among these, electromagnetic interference (EMI) noise, in addition to the limited signal-to-noise ratio (SNR), have hindered the rapid development of related technologies. Unlike endoscopic ultrasound, in which the SNR can be increased by simply applying a higher pulsing voltage, there is a fundamental limitation in leveraging the SNR of PAE signals because they are mostly determined by the optical pulse energy applied, which must be within the safety limits. Moreover, a typical PAE hardware situation requires a wide separation between the ultrasonic sensor and the amplifier, meaning that it is not easy to build an ideal PAE system that would be unaffected by EMI noise. With the intention of expediting the progress of related research, in this study, we investigated the feasibility of deep-learning-based EMI noise removal involved in PAE image processing. In particular, we selected four fully convolutional neural network architectures, U-Net, Segnet, FCN-16s, and FCN-8s, and observed that a modified U-Net architecture outperformed the other architectures in the EMI noise removal. Classical filter methods were also compared to confirm the superiority of the deep-learning-based approach. Still, it was by the U-Net architecture that we were able to successfully produce a denoised 3D vasculature map that could even depict the mesh-like capillary networks distributed in the wall of a rat colorectum. As the development of a low-cost laser diode or LED-based photoacoustic tomography (PAT) system is now emerging as one of the important topics in PAT, we expect that the presented AI strategy for the removal of EMI noise could be broadly applicable to many areas of PAT, in which the ability to apply a hardware-based prevention method is limited and thus EMI noise appears more prominently due to poor SNR.

Full-field optical coherence tomography (FF-OCT) is a high-resolution interferometric imaging technique that enables label-free visualization of cellular structural changes. In this study, we employed a custom-built time-domain FF-OCT system to monitor morphological alterations in HeLa cells undergoing doxorubicin-induced apoptosis and ethanol-induced necrosis at the single-cell level. Apoptotic cells showed characteristic features such as echinoid spine formation, cell contraction, membrane blebbing, and filopodia reorganization. In contrast, necrotic cells exhibited rapid membrane rupture, intracellular content leakage, and abrupt loss of adhesion structure. These dynamic events were visualized using high-resolution tomography and three-dimensional surface topography mapping. Furthermore, FF-OCT-based interference reflection microscopy (IRM)-like imaging effectively highlighted changes in cell–substrate adhesion and cell boundary integrity during the cell death process. Our findings suggest that FF-OCT is a powerful imaging platform for distinguishing cell death pathways and assessing dynamic cellular states, with potential applications in drug toxicity testing, anticancer therapy evaluation, and regenerative medicine.

A boxer engine is a type of engine that was developed to more effectively cancel out the mechanical vibration that occurs when the engine operates by arranging a pair of slider-crank structures in a symmetrical form. In this study, inspired by that mechanical concept, we designed and implemented a new scanner device that can improve the scanning speed of conventional linear reciprocating scanners by about tenfold without compromising the scanning range. Moreover, by applying the femtosecond laser processing technology, we implemented a customized optical encoder module as well as a large aperture (9 mm dia.) focused ultrasonic ring transducer, which enabled the successful embodiment of an optical-resolution photoacoustic microscopy system along with the new scanner concept. As the linear reciprocating scanning mechanism has been applied as a central element in various mechanical systems, we expect that the presented concept could be a useful option not only in the biophotonic field but also in many areas of industry.

Achieving an accurate working distance in gradient index (GRIN) rod lens–based miniaturized imaging probes is critical for the successful implementation of imaging systems in various biophotonic applications. Although numerous commercial optical design software tools are available for such designs and simulations, they are often too expensive for typical research laboratories and require substantial time and effort for beginners to learn and use effectively. In this paper, we present a simple yet practically useful MATLAB-based simulation code and an underlying ray tracing model. Our approach is based on the principle that the trajectory of an optical ray entering a GRIN lens medium is deterministically defined by the boundary conditions at the entrance surface. We evaluated the accuracy of the developed model using a typical optical fiber and GRIN lens configuration commonly employed in miniaturized imaging probes. Notably, for the assumed probe configuration where a paraxial approximation is valid, the predicted working distances closely matched the results obtained from commercial software. Given that many laboratories lacking access to specialized software have had to rely solely on manufacturer feedback to determine the specifications of a GRIN lens—often at the cost of considerable time—this model could serve as a valuable alternative to facilitate progress in related research.