Investigating the depth-sensitivity of laser speckle contrast imaging in flow phantoms

Abstract

Laser speckle contrast imaging (LSCI) is a wide-field, optical technique capable of assessing changes in flow rates of scattering fluids. In biomedical applications, LSCI has been used to quantify changes of blood perfusion in various tissue. One limitation of LSCI is its limited depth sensitivity- it can only sense blood flow in superficial layers of tissue. The goal of this study was to experimentally investigate the depth-sensitivity of LSCI for detecting fluid flow embedded in a turbid optical phantom. LSCI was used to image a flow channel buried by the scattering medium at incremental depths ranging from 0 mm to 2.4 mm. The flow measurements were successively repeated using two illumination wavelengths, 633 nm and 785 nm. Images were captured with and without flow present through the phantom for each wavelength and analyzed to develop a flow-sensitivity parameter. This provided a metric of LSCI’s ability for detecting flow as a function of channel depth. At a depth of 1.5 mm, the flow sensitivity decreased by 80% with the 633 nm illumination and 65% for the 785 nm illumination relative to a depth of 0 mm. The results demonstrate that the flow sensitivity of the 785 nm source diminished at a slower rate as the buried depth was increased than the sensitivity of the 633 nm source. This study suggests that the flow depth and illumination wavelength should be considered while using LSCI.