In vivo photoacoustic/ultrasonic dual‐modality endoscopy with a miniaturized full field‐of‐view catheter

Abstract

Endoscopy is an essential clinical tool for the diagnosis of gastrointestinal (GI) tract cancer. A photoacoustic system that elegantly combines optical and ultrasound endoscopy advantages by providing high-sensitivity functional information and large imaging depth is a potentially powerful tool for GI tract imaging. Recently, several photoacoustic endoscopic imaging systems have been proposed and developed. However, the relatively large size and rigid length of the catheter make it difficult to translate them into wide clinical applications; while the existing system of a relatively small catheter, capable of in vivo animal imaging, is unable to acquire full (360°) field-of-view cross-section images. In this study, we developed a photoacoustic/ultrasonic dual-modality endoscopic system and a corresponding miniaturized, encapsulated imaging catheter, which provides a full 360° field-of-view. The diameter of the catheter is 2.5 mm, which is compatible with the 2.8-mm instrumental channel of a conventional clinical optical endoscope. Using this system, we demonstrate in vivo 3-dimensional endoscopic photoacoustic/ultrasonic imaging of the colorectum of a healthy Sprague Dawley rat, by depicting vasculature and morphology of the GI tract. The significantly improved imaging field of view, reduced catheter size, high-quality imaging results suggest that the developed photoacoustic/ultrasonic dual-modality endoscopy has a great potential to be translated into a broad range of clinical applications in gastroenterology.

Miniature probe for dual‐modality photoacoustic microscopy and white‐light microscopy for image guidance: A prototype toward an endoscope

“…The prototype should be further developed to become a practical endoscope by integrating scanning capability so as to facilitate clinical PAE applications. One could consider integrating a torque coil to realize rotational scanning . In this scheme, multiple MMFs can be used to deliver the white‐light source for WLE mode .…”

“…As for the rotational scanning (by a torque coil) and raster scanning (by the imaging fiber bundle) mentioned above, their scanning speed is discussed as follows. For the former, a motor can be used to realize rotational scanning of the torque coil , while for the latter, a galvanometer mirror can be adopted to realize fast raster scanning. Thus, for the two scanning approaches, the scanning speed will be restricted by the PRF of a laser and the speed of the integrated scanner.…”

“…Thus, for the two scanning approaches, the scanning speed will be restricted by the PRF of a laser and the speed of the integrated scanner. According to previous studies , the B‐scan rate of 5 and 100 Hz for the rotational scanning and raster scanning, respectively, should be technically possible. High imaging speed would facilitate clinical PAE applications, such as minimizing the issue of peristalsis of the gastrointestinal tract during PAE image acquisition.…”

“…The former is termed as optical‐resolution PAM (OR‐PAM) , and the latter acoustic‐resolution PAM (AR‐PAM) . Over the past few years, many attempts have been made to implement PAM as miniature probes, also called photoacoustic endoscopy (PAE) , which enables PAM of internal organs. PAE is desired for minimally invasive interventional procedures.…”

“…Recently, many PAE applications have been demonstrated, such as gastrointestinal tract , intravascular and urogenital system imaging . Similar to PAM, PAE can be categorized into OR‐PAE and AR‐PAE , also depending on how resolution is determined. OR‐PAE typically employs a single‐mode optical fiber and a gradient‐index (GRIN) lens to provide high resolution up to several micrometers despite sacrificing imaging depth.…”