In vivo study and imaging of blood flow changes
using diffusing wave correlation techniques
I.V. Meglinsky 
, D.A. Boas 
, A.G. Yodh 
and B. Chance 
Department of Biochemistry and Biophysics, University of Pennsylvania,
Philadelphia, PA 19104-6089;
Department of Physics and Astronomy, University of Pennsylvania,
Philadelphia, PA 19104-6089;
Department of Physics, Saratov State University, Saratov, Russia
In recent years there has been a growing interest in the study of flow phenomena in complex fluids using photon speckle correlation techniques. The best-known applications of these studies in biology and medicine are the non-invasive measurements of blood flow in large and small blood vessels, as well as the blood volume changes in capillary loops of muscles and other biological tissues. In this contribution, methods for probing the spatially varying dynamics of blood flow in heterogeneous turbid media with diffusing light are applied. We have in vivo non-invasively measured the blood flow changes using photon correlation spectroscopy with a simple correlation diffusion model to study and quantify blood flow in the human arm during cuff ischemia. The method utilizes the Doppler broadening of light that arises in a multiply scattering dynamic media, but the method is also responsive to changes in absorption and scattering coefficients. Our measurements clearly show blood flow! changes with cuff pressures, including the hyperemic overshoot after cuff release, that is qualitatively correlated to physiological behavior of the cardiovascular system. In this article, we present our method, results, and discuss the critical relevance of the technique.
This paper is organized as follows. In section 2, we experimental describe our method and our experimental setup. In section 3, we discuss the results, and in section 4 we present our theory for analyzing the experimental results. In section 5, we review model experiments for verifying the validity of our theory. The clinical relevance of our technique is discussed in section 6.