Real-time dual-modal photoacoustic and fluorescence small animal imaging

Abstract

By combining optical absorption contrast and acoustic resolution, photoacoustic imaging (PAI) has broken the barrier in depth for high-resolution optical imaging. Meanwhile, Fluorescence imaging (FLI), owing to advantages of high sensitivity and high specificity with abundant fluorescence agents and proteins, has always been playing a key role in live animal studies. Based on different optical contrast mechanisms, PAI and FLI can provide important complementary information to each other. In this work, we uniquely designed a Photoacoustic-Fluorescence (PA-FL) imaging system that provides real-time dual modality imaging, in which a half-ring ultrasonic array is employed for high quality PA tomography and a specially designed optical window allows simultaneous whole-body fluorescence imaging. The performance of this dual modality system was demonstrated in live animal studies, including real-time monitoring of perfusion and metabolic processes of fluorescent dyes. Our study indicates that the PA-FL imaging system has unique potential for live small animal research.

Keywords: Fluorescence imaging; Multimodal imaging; Photoacoustic imaging; Real time; Small animal imaging.

Fig. 1

Dual-modal imaging system. (a) 3D schematic diagram of the system; (b) Illustration of both light and sound path ways.

Fig. 2

PAI-FI system resolution testing results. (a) Photoacoustic image of a human hair; (b) Schematic diagram of X and Y axis; (c) X-direction PA resolution; (d) Y-direction PA resolution;(e) Camera resolution chart under fluorescence imaging system;.

Fig. 3

Photoacoustic imaging of mouse body. (a) PA reconstruction imaging of mouse liver;(b) Photoacoustic imaging of mouse liver after Frangi vascular filtering; (c)Photoacoustic reconstruction imaging of mouse kidneys;(d) Photoacoustic imaging of mouse kidneys after Frangi vascular filtering; AA, abdominal aorta; In, intestinal tract; IVC, inferior vena cava; LK, left kidney; LLV, left lobe of liver; PV, portal vein; RK, right kidney; RLV, right lobe of liver; SC, spinal cord; SP, spleen; St, stomach.

Fig. 4

Fluorescence and photoacoustic images at different times in renal perfusion experiments. (a-d) After injection of ICG into the tail vein, photoacoustic and fluorescence images at t = 0.0 s, 2.7 s, 6.3 s, 8.8 s. The left side is the photoacoustic image, the right side is the fluorescence image. (e)The average photoacoustic signal of indocyanine green (ICG) within the region outlined by the blue box showed a change over time, as did the average fluorescence signal within the region designated by the yellow box.

Fig. 5

Photoacoustic and fluorescence images at different times in ICG metabolic experiments (a) Photoacoustic and fluorescence image in liver before ICG injection; (b) PA and FL image of the liver 10 min after ICG injection; (c) Photoacoustic and fluorescence image in intestines before ICG injection; (d) PA and FL image in intestines 30 min after ICG injection.

Fig. 6

Schematic diagram of dual-mode synchronous operation.