A scalable correlator for multichannel diffuse correlation spectroscopy

Abstract

Diffuse correlation spectroscopy (DCS) is a technique which enables powerful and robust non-invasive optical studies of tissue micro-circulation and vascular blood flow. The technique amounts to autocorrelation analysis of coherent photons after their migration through moving scatterers and subsequent collection by single-mode optical fibers. A primary cost driver of DCS instruments are the commercial hardware-based correlators, limiting the proliferation of multi-channel instruments for validation of perfusion analysis as a clinical diagnostic metric. We present the development of a low-cost scalable correlator enabled by microchip-based time-tagging, and a software-based multi-tau data analysis method. We will discuss the capabilities of the instrument as well as the implementation and validation of 2- and 8-channel systems built for live animal and pre-clinical settings.

A capillary-mimicking optical tissue phantom for diffuse correlation spectroscopy

“…This relationship between flow speed and a characteristic of the autocorrelation is all that is needed for DCS at its most basic level 3,5 . The phantom exhibits the pattern that it needs to replicate in order to be useful for baselining in vivo DCS experiments and instrument testing.…”

“…A solid phantom remains inert and unaltered between experiments, allowing for effective benchmarking of instruments against a standard. A variety of solid and gel phantoms have been developed, although they generally only have a singular, large tube carrying liquid through the phantom 5,6 . This is not an accurate model of human tissue, where the majority of movement is blood flowing through capillaries.…”

Novel diffuse optics system for continuous tissue viability monitoring: extended recovery in vivo testing in a porcine flap model

“…For cost-effective construction of the device, DCS employs an inexpensive laser diode (LD) with a long coherence length to cover a sample volume. Instead of the commercialized hardware correlator, the correlator is implemented using a custom PSoc time-tagger and USB logger [10]. DRS uses a white LED as a broadband source and a miniaturized spectrometer (Avantes) to acquire a reflectance spectrum (450 ~ 650 nm).…”

“…A block diagram of the PSOC operating code is shown in Figure 3. Further details on the construction, design and operation of the DCS instrument is provided in [10]. …”

“…For blood flow index, the autocorrelation plots calculated by the custom software using multi-tau approach [10] were analyzed by a simple algorithm to obtain a tau half value. Analysis using complex fitting algorithms incorporating the photon diffusion equations to arrive upon blood flow index (BFI) is not incorporated in real-time.…”