Abstract
Speckle contrast optical spectroscopy (SCOS) measures absolute blood flow in deep tissue, by taking advantage of multi-distance (previously reported in the literature) or multi-exposure (reported here) approach. This method promises to use inexpensive detectors to obtain good signal-to-noise ratio, but it has not yet been implemented in a suitable manner for a mass production. Here we present a new, compact, low power consumption, 32 by 2 single photon avalanche diode (SPAD) array that has no readout noise, low dead time and has high sensitivity in low light conditions, such as in vivo measurements. To demonstrate the capability to measure blood flow in deep tissue, healthy volunteers were measured, showing no significant differences from the diffuse correlation spectroscopy. In the future, this array can be miniaturized to a low-cost, robust, battery operated wireless device paving the way for measuring blood flow in a wide-range of applications from sport injury recovery and training to, on-field concussion detection to wearables.
Highlights
Blood flow supplies brain and other organs with oxygen and removes the by-products in order to maintain healthy functions of the organs
We show that the method is comparable to the diffuse correlation spectroscopy (DCS), where shot acquisition multi-exposure speckle contrast imaging (sMESI) SCOS method uses a CMOS single-photon avalanche diode (SPAD) array making the technique relatively low cost and fast
We mention here that the goal of the paper was to quantitatively compare the two related methods (DCS and SCOS) for measuring deep tissue blood flow on equal footing, and based on the results presented, one could conclude that there are no significant differences between SCOS and Diffuse correlation spectroscopy (DCS)
Summary
Blood flow supplies brain and other organs with oxygen and removes the by-products in order to maintain healthy functions of the organs. LSCI uses two-dimensional detector arrays (CCD or CMOS) [5,6,7,8] with a relatively long exposure time to obtain information about superficial relative blood flow This technique allows the use of a simple experimental setup with a relatively high spatio-temporal resolution, but with the use of a single exposure time it is prone to systematic error, due to deviations from the physical model in the presence of the static scatters (such as skull). This can be resolved by implementing multi-exposure speckle imaging (MESI) [9, 10]. MESI and sMESI, allow absolute blood flow measurements, they are still limited to imaging the superficial tissue (
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