A transmissive laser speckle imaging technique for measuring deep tissue blood flow: An example application in finger joints

Background and Objective Laser speckle perfusion imaging (LSPI) is a minimally invasive optical measure of relative changes in blood flow, providing real‐time, high resolution, two‐dimensional maps of vascular structure. Standard LSI imaging uses a light‐reflective geometry that limits the measurement to a thin surface layer of 0.2–1 mm. The objective of this study was to test a new LSI instrument geometry with the laser source opposed to the image capture plane (light transmissive). Captured light then travels the entire tissue thickness (10–15 mm), sampling much deeper regions of interest than conventional optical imaging techniques. Study Design Reflective‐light (conventional) and transmissive‐light LSI modes were used to measure finger joint blood flow during a timed tourniquet occlusion of the brachial artery in volunteer participants. Results There was greatly increased visibility of vessels underlying the skin in the light‐transmissive mode LSI mode. Established LSI algorithms were shown to still work in the light‐transmissive mode, despite decorrelation due to finite laser coherence length and the light passing through a tissue thickness of 10–15 mm. Conclusion Transmissive LSI can be used to measure blood flow deep (10–15 mm) into tissues. This could be useful for non‐invasive measurements of finger joint synovial blood flow in diagnosing and treating peripheral vascular disorders, such as rheumatoid arthritis. Lasers Surg. Med. 43:21–28, 2011. © 2011 Wiley‐Liss, Inc.