Tomographic Ultrasound and LED-Based Photoacoustic System for Preclinical Imaging

Abstract

Small animals are widely used as disease models in medical research. Noninvasive imaging modalities with functional capability play an important role in studying the disease state and treatment progress. Photoacoustics, being a noninvasive and functional modality, has the potential for small-animal imaging. However, the conventional photoacoustic tomographic systems use pulsed lasers, making it expensive, bulky, and require long acquisition time. In this work, we propose the use of photoacoustic and ultrasound tomographic imaging with LEDs as the light source and acoustic detection using a linear transducer array. We have demonstrated full-view tomographic imaging of a euthanized mouse and a potential application in liver fibrosis research.

Keywords: fibrosis; liver; photoacoustic; small animal; tomography; ultrasound.

Figure 1

Small animal tomographic imaging system. (a) Schematic of the set-up with the imaging probe scanning around the mouse in a water tank. (b) Imaging probe with linear transducer array and four LED arrays in a 3D printed holder. (c) Photograph of the imaging set-up showing mouse holder, imaging probe and the scanning stages.

Figure 2

Tomographic photoacoustic and ultrasound imaging. (a–c) Co-registered ultrasound and photoacoustic B-Scan images of mouse abdomen, acquired from three different angles. Tomographic (d) ultrasound, (e) photoacoustic, and (f) co-registered ultrasound and photoacoustic image. Several organs in the abdominal region indicated by Sc-spinal cord, K-kidney, L-liver, Sp -spleen, St-stomach, and I-intestine. Dashed lines are used to mark the organs in the photoacoustic image.

Figure 3

Tomographic imaging of the liver. (a) Tomographic photoacoustic and ultrasound images of a control mouse showing the liver at a scanning step of 2 mm. (b) Ultrasound image of the liver and (c) corresponding photoacoustic image. The green line markers the liver region. (d) Histology image of the control liver stained with Collagen I (fibrosis marker). (e) Ultrasound image of a mouse liver with fibrosis (CCl₄-treated) and (f) corresponding photoacoustic image. (g) Histology image of the fibrotic liver stained with collagen I (fibrosis marker). (h) Tomographic photoacoustic and ultrasound images of the fibrotic mouse showing liver at a scanning step of 2 mm.