In vivo Detection of Lesion and Hemorrhage in Mouse Brain using Noninvasive Photoacoustic Imaging

Photoacoustic imaging (PAI) is a noninvasive imaging procedure that uses laser light to visualize internal organs, blood vessels, and other tissues with great clarity. The main advantage of it, compared to existing optical imaging techniques, is that PAI overcomes the overwhelming scattering of light in biological tissues by utilizing ultrasonic wave to translate the signal, thus can provide higher spatial resolution. Moreover, the 532-nm laser light used in the experiments is predominantly absorbed by hemoglobin in blood. Therefore, the PAI can be used as a sensitive blood detector. The 532-nm laser light with the repetition rate of 15 Hz and the pulse width of 10 ns used as the excitated source. A needle hydrophone was used to capture signal. The orthogonal mode was adapted to excitated and received the photoacoustic signals. A custom-built tank was coupled the photoacoustic signals between the hydrophone and the mouse head. Here we present a clearly vascular distribution of mouse cerebral cortex surface with the skip and skull intact in vivo. Furthermore, a trauma lesion on the mouse cerebral cortex is accurately mapped with our system. The hemorrhage around the lesion region also is visualized by PAI images. Photoacoustic technique with its unique characteristic can provide satisfactory imaging quality on the brain of small animals. Experimental results demonstrate that PAI can supply information regarding the changes in morphologic and physiology of brain. This noninvasive PAI holds promise for applications in detecting cerebrovascular disease.