Photoacoustic Imaging for Lymphatic Vein Anastomosis - Examination using small animals

The diameters and shapes of lymphatic vessels and the blood vessels which surround them provide important information used in determining the degree of progression of lymphedema and the subsequent planning of lymphatic vein anastomosis. The aim of this project is to display this information in three dimensions using photoacoustic imaging (PAI). For this study, we used a hemispherical sensor array PAI system that provides both a high resolution and a wide field of view and displays a 3D image.We used indocyanine green (ICG) to detect lymphatics using PAI. Because oxyhemoglobin, deoxyhemoglobin, and ICG have different optical absorption spectra, we were able to distinguish between lymphatic vessels and blood vessels by using two wavelengths (800 nm and 850 nm). Our PAI system performed 3D reconstruction by performing 2D scanning with a hemispherical sensor array. We injected ICG into mouse and rat fingers and imaged the lymphatic and blood vessels of the entire foot. After performing photoacoustic measurements, we confirmed the diameter and shape of lymphatic and blood vessels using dissection and ICG fluorescence imaging.For measurements of rats, lymphatic vessels containing ICG are visible on both sides of the blood vessel. In PAI of smaller mice, lymph nodes are displayed along with lymphatic vessels. It is easy to distinguish lymphatic vessels and blood vessels using PAI, and we were able to demonstrate lymphatic and blood vessels in three dimensions.