Portable, high speed blood flow measurements enabled by long wavelength, interferometric diffuse correlation spectroscopy (LW-iDCS)

Abstract

Diffuse correlation spectroscopy (DCS) is an optical technique that can be used to characterize blood flow in tissue. The measurement of cerebral hemodynamics has arisen as a promising use case for DCS, though traditional implementations of DCS exhibit suboptimal signal-to-noise ratio (SNR) and cerebral sensitivity to make robust measurements of cerebral blood flow in adults. In this work, we present long wavelength, interferometric DCS (LW-iDCS), which combines the use of a longer illumination wavelength (1064 nm), multi-speckle, and interferometric detection, to improve both cerebral sensitivity and SNR. Through direct comparison with long wavelength DCS based on superconducting nanowire single photon detectors, we demonstrate an approximate 5× improvement in SNR over a single channel of LW-DCS in the measured blood flow signals in human subjects. We show equivalence of extracted blood flow between LW-DCS and LW-iDCS, and demonstrate the feasibility of LW-iDCS measured at 100 Hz at a source-detector separation of 3.5 cm. This improvement in performance has the potential to enable robust measurement of cerebral hemodynamics and unlock novel use cases for diffuse correlation spectroscopy.

Combined frequency domain near-infrared spectroscopy and diffuse correlation spectroscopy system for comprehensive metabolic monitoring of inspiratory muscles during loading

“…This method has been used previously. 22,23 The two source prisms are separated by 8.5 mm and thus probe similar tissue regions as the SCM has an average width between 7 and 8 cm. 24 An avalanche photodiode (APD) (Hammatsu S11519-30) is used as the detector for the FD-NIRS system and is coupled to a fiber bundle with NA 0.66.…”

Comparing the performance potential of speckle contrast optical spectroscopy and diffuse correlation spectroscopy for cerebral blood flow monitoring using Monte Carlo simulations in realistic head geometries

“…To take advantage of this excess laser power, the input can be pulse width modulated to keep the average power at the ANSI limit while utilizing the full power of the laser during the detector-on period. 18 Alternatively, multiple source positions 14 or larger spot sizes 9,15 can be used to increase the number of photons available for detection while remaining in compliance with the ANSI limit of power delivery per unit area. Four laser delivery strategies were explored in this work: (1) continuous illumination with a single ANSI limited source with a diameter of 3.5 mm (same as in Figs.…”

“…13 While the linescan camera implementation preserves information about the full range of autocorrelation delays, the need for high-speed sampling and limited number of pixels available (hundreds to thousands) requires a heterodyne approach for coherent gain to overcome sensor noise. 14,15 Sampling the spatial speckle contrast measured in an area some distance away from the illumination point provides high SNR potential as megapixel CMOS sensors are now available with low read noise and high frame rates. The latter approach, inspired by the laser speckle contrast imaging technique used for superficial perfusion imaging, 16 has been termed speckle contrast optical spectroscopy/tomography (SCOS/SCOT) 13,17 and has recently been demonstrated to allow light collection through multi-mode fiber bundles, 18,19 and offer more than an order of magnitude improvement in SNR with a lower price for cerebral blood flow (CBF) monitoring versus DCS measurements at the same source-detector separation.…”

Comparison of diffuse correlation spectroscopy analytical models for measuring cerebral blood flow in adults

“…Limited literature suggests that the BSR should be ∼3 to 10 for healthy adults; 18 however, we observed several subjects with BSRs that were an order of magnitude greater than this expected range. Thus, we imposed a loose quality criterion that the BSR ∈ [1,25]. After applying this criterion, the median [IQR] BSR was 6.6 [3.0, 11.9] for three-layer (N ¼ 12), 5.4 [3.8, 7.9] for two-layer (N ¼ 8), and 1.5 [1.2, 1.8] for homogenous (N ¼ 15).…”

“…No correlation was observed with CBFi from the two-or three-layer model. Imposing criteria that the BSR ∈ [1,25] improved the correlation for the homogeneous model (R s ¼ 0.65, p ¼ 0.018, N ¼ 13), and the correlation became statistically significant for the two-layer model (R s ¼ 0.79, p ¼ 0.048, N ¼ 7) and trended toward significance for the three-layer model (R s ¼ 0.47, p ¼ 0.146, N ¼ 11). Correlations between TCD-measurements in the ACA and CBFi from all models were not statistically significant (data not shown).…”