Diffuse Correlation Spectroscopy: A Review of Recent Advances in Parallelisation and Depth Discrimination Techniques

Abstract

Diffuse correlation spectroscopy is a non-invasive optical modality used to measure cerebral blood flow in real time, and it has important potential applications in clinical monitoring and neuroscience. As such, many research groups have recently been investigating methods to improve the signal-to-noise ratio, imaging depth, and spatial resolution of diffuse correlation spectroscopy. Such methods have included multispeckle, long wavelength, interferometric, depth discrimination, time-of-flight resolution, and acousto-optic detection strategies. In this review, we exhaustively appraise this plethora of recent advances, which can be used to assess limitations and guide innovation for future implementations of diffuse correlation spectroscopy that will harness technological improvements in the years to come.

Validation of the Openwater wearable optical system: cerebral hemodynamic monitoring during a breath-hold maneuver

“…To address this challenge, other methods have been proposed to increase SNR of intensity or electric field autocorrelation function measurements. 20,51 These methods include the use of highly parallelized homodyne single photon detection, [52][53][54][55][56] heterodyne interferometric detection, [57][58][59][60] heterodyne holographic detection, 61,62 source light with wavelength beyond the water peak, [63][64][65][66] and high coherence pulsed sources. [67][68][69][70][71][72][73] The Openwater system does not use high-SNR temporal autocorrelation function measurements to derive blood flow.…”

“…DCS measurements of the brain, however, are often confounded by low SNR, especially for large source-detector separations. To address this challenge, other methods have been proposed to increase SNR of intensity or electric field autocorrelation function measurements 20 , 51 . These methods include the use of highly parallelized homodyne single photon detection, 52 – 56 heterodyne interferometric detection, 57 – 60 heterodyne holographic detection, 61 , 62 source light with wavelength beyond the water peak, 63 – 66 and high coherence pulsed sources 67 …”