Torque coil-based highly-flexible photoacoustic and ultrasonic mini-probe for use in the instrument channel of a clinical video endoscope

In order for photoacoustic endoscopy to make a significant contribution to clinical gastroenterology, the relevant probes must be implemented in a form that can pass through the instrument channel of a clinical video endoscope or one that has its own camera-based self-steering capability at its distal section to effectively approach a target point. In line with the first direction, multiple probes with a diameter smaller than standard channel sizes have been reported in biomedical photoacoustics research thus far. However, no actual in vivo image acquisition via the instrument channel has been demonstrated yet. In this study, we developed a torque coil-based highly-flexible mini-probe that can provide co-registered optical resolution photoacoustic and ultrasonic images via the standard instrument channel of a video endoscope. With the probe, we were able to acquire in vivo photoacoustic and ultrasonic endoscopic images from a swine esophagus via the instrument channel of a clinical video endoscope, which is the first demonstration in biomedical photoacoustics to the best of our knowledge. In this paper, we describe several useful aspects that we learned from this study and discuss future hardware development directions that must be pursued for the full clinical translation of the mini-probe technology.