Time-domain algorithm for single-photon laser-Doppler flowmetry at large interoptode spacing in human bone

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

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.

Probability density function of the electric field in diffuse correlation spectroscopy of human bone in vivo

Diffuse correlation spectroscopy (DCS) is the technique of choice for non-invasive assessments of human bone blood flow. However, DCS classical algorithms are based on the fundamental assumption that the electric field of the light reaching the DCS photodetector is a zero-mean complex Gaussian variable. The non-validity of this hypothesis might produce inaccurate blood flow estimations. It is shown that for the human tibia, the "Gaussian hypothesis" holds for interoptode distances ≥20  mm. This lower boundary seems to depend on the type of investigated tissue.

Near-infrared photons: a non-invasive probe for studying bone blood flow regulation in humans

The study of bone blood flow regulation in humans has always represented a difficult task for the clinician and the researcher. Classical measurement techniques imply the presence of ionizing radiation or contrast agents, or they are slow or cannot be repeated too often in time. In the present review, we would like to give a perspective on how the optical approach might overcome some of these problems and give unique solutions to the study of bone blood flow regulation. We hope that the present contribution will encourage the scientific community to put a greater attention on this approach.