P-134 Non-ionizing Non-invasive Functional Intestinal Imaging of Dynamic Gut Process Using Photoacoustic Tomography

Abstract

Background: The conventional methods such as, capsule endoscopy, enteroscopy, magnetic resonance imaging (MRI), computed tomography (CT), X-rays and ultrasound (US) have been used to image the surface of the intestine and gastrointestinal (GI) conditions, which are unable to provide tomographical depth information with a remarkable resolution. These drawbacks were compensated by implementing non-invasive photoacoustic tomography (PAT) method to image the dynamic gut process of an in-vivo mouse intestine, which has not been experimented previously. Furthermore, PAT is a low cost and non-ionizing modality with deeper penetration than other optical methods. Here, we report an implementation of photoacoustic imaging with optical contrast for the small animal model to inspect the gastrointestinal tract. Method(s): A customized volumetric reflection-mode PAT that uses a single element ultrasound transducer was utilized for imaging. In concise, tunable laser pulses were obtained from an OPO laser (Surelite OPO PLUS; Continuum; wavelength tuning range, 680 to 2500 nm; pulse width, 5 ns; and pulse repetition rate, 10 Hz), which is excited using a pump laser (SLII-10; Continuum; Q-switched Nd:YAG; 532 nm) the originated laser light is passed through an custom-made set up of spherical conical lens and optical condenser with a pulse energy of approximately 5 mJ/cm2 (far less than the safety limit). As the raster scanning for volumetric imaging initiates, the acoustic coupling was improved using a custom-made water tray. A mouse (6-8 weeks old female BALB/c mouse) is placed just beneath the water tray. The induced PA signals were captured by the focused ultrasound transducer (V308; Olympus NDT; 5-MHz center frequency). For real-time and dynamic intestine monitoring, a Vevo LAZR was utilized, which is a combination of high resolution ultrasound (US) and PA 256 element transducer-array system. The Vevo LAZR PA/US imaging system was effectively utilized to produce real-time images with 21 MHz transducer frequency. Result(s): The custom-built PAT system revealed the bio-distribution of foods in the GI tract through the tomographical depth images with an axial resolution of 100 mm. In the results, the applied foods could be clearly observed through the intestine. Negligible background was detected, enabling the clear resolution of intestinal features; indeed, individual small bowel diverticula were distinguishable. Depth encoding analysis revealed further spatial details of intestinal distribution with depth mapping to 5 mm. PA/US imaging modality produced highly resolved images with dynamic functional information of intestinal movement in mice. PA obtained maximum intensity projection (MIP) of food, that illustrates intestinal transit using a single transducer PA system. Not many significant movements were observed during heavy anesthetization and clear motility was seen even after the isoflurane was removed. Conclusion(s): Real-time PAT method was implemented to image high-resolution, low-background, real-time in-vivo mouse intestinal anatomy, pathology and function. The limitations of the depth information as well as the resolution were compensated through this method. Future directions of research may include using contrast agents for targeted detection and examining multi-colour PA imaging for diagnosis of gut diseases.