Diffuse speckle contrast analysis for flowmetry with deep light sources

Abstract

Diffuse optical probes for monitoring various hemodynamic variables usually use tissue-contacting fiber based probes, and no practical cases exist where source location is positioned in deep tissue, as diffuse optical spectroscopy and tomography are normally regarded as a non-invasive imaging technique. There are some cases, however, where the light source is positioned in deep tissue, as in the case of recently developed laser acupuncture. In this study, we theoretically analyze the light propagation in a semi-infinite diffuse medium with a deep light source, especially in the context of blood flow measurement. A liquid phantom study with deep light sources is performed to validate the analytic solution of photon diffusion equation, and a diffuse speckle contrast analysis (DSCA) measurement from a flow phantom within a solid matrix is performed to demonstrate the feasibility of the proposed method. The results show that the flow measurement using DSCA with a deep light source is not only feasible, but also has advantages in some cases. Sensitivity analysis shows the light source with a depth of up to 2 cm can be used to provide the information on the magnitude and location of blood flow.