Study on the mathematical relationship existing between single-photon laser-Doppler flowmetry and diffuse correlation spectroscopy with static background

Abstract

In the present contribution, the theoretical relationship existing between the blood flow index measured by diffuse correlation spectroscopy and single-photon laser-Doppler flowmetry (SP-LDF) is investigated. A specific mathematical description that accounts for the properties of single-photon detectors for SP-LDP was developed. Static background has also been considered and, to the best of our knowledge, this has never been included before in SP-LDF analytical theories. The comparisons were realized for two SP-LDF implementations: for "classical" and "fast" algorithms. "Classical" SP-LDF is not sensitive to small changes on the number of detected speckles and coherence length of the laser, usually described by a unique parameter "beta." This is a strong point when assessing blood flow index, e.g., in humans, where "beta" is particularly difficult to be determined in real time. The proposed theory may be utilized, e.g., to investigate other SP-LDF setups and optical/physiological parameter ranges or, generally, to optimize real SP-LDF instrumentation.

Dynamic light scattering imaging

“…Applying the model to the g 2 (τ) measured from the mouse brain, we obtained the correlation time τ c , static scattering estimate 1 − ρ, and the dynamic scattering regime, which ranges from MU n = 0.5 to SU/MO n = 1 and from SU/MO n = 1 to SO n = 2 . Historically, SU/MO n = 1 has been assumed in LSCI ( 8 , 18 ) and MESI ( 9 , 10 ), while for LDF, either SU/MO n = 1 or SO n = 2 was used ( 7 , 28 , 30 ). DLSI, however, shows that neither is correct per se (see Fig.…”

Dynamic Laser Speckle Imaging

“…Historically, it was assumed that n = 1 in laser speckle contrast imaging 4,9,11,12 and multi-exposure speckle imaging 10,18 . For laser Doppler flowmetry, values of n = 1 and n = 2 are both used without consensus on which is better 3,6 . Our measurements of the temporal intensity correlation in the mouse brain, however, show that neither n = 1 nor n = 2 is correct per se, see Fig.4.…”

“…Until now, it was possible to obtain the full temporal sampling of speckle intensity fluctuations for single pixels (i.e. channels of data) as is done with laser Doppler flowmetry [3][4][5][6] and diffuse correlation spectroscopy 6,7 measurements of blood flow. Scanning laser Doppler flowmetry was introduced to obtain images of blood flow 8 , but the temporal and spatial resolution was limited.…”

“…The amount of dynamic scattering of light for the measurement geometries of LDF and LSCI has typically been assumed to be on average much less than one dynamic scattering event per detected photon 23 , but recent studies have suggested that at least for brain that this number is on average greater than 1 16 . For DCS, the amount of dynamic light scattering is clearly in the multiple scattering regime as the separation between the source and detector on the surface of the tissue is much larger than the scattering length of light within the tissue 6 . For DCS, despite clarity on the amount of dynamic light scattering, the type of motion has been debated with red blood cells expected to have ordered motion but measurements suggesting unordered motion.…”

Current Methods for the Assessment of Oxygen Status and Biotissue Microcirculation Condition: Diffuse Optical Spectroscopy (Review)

“…Transcutaneous oximetry provides data on oxygen tension in the tissues, but the question whether oxygen bound to hemoglobin is shunted or utilized remains unanswered [33][34][35]. Laser Doppler flowmetry does not provide visualization presenting the results of vessel examination in the digital form [36][37][38][39]. The following methods which can visualize the saturation of the tissues with oxygen are BOLD fMRT, PET with 15 O 2 isotopes and hypoxia-selective markers (such as 18 F-fluorothymidine) [40], phosphorescence imaging with oxygen-sensitive stains [41].…”