Influence of probe pressure on the diffuse correlation spectroscopy blood flow signal: extra-cerebral contributions

Abstract

A pilot study explores relative contributions of extra-cerebral (scalp/skull) versus brain (cerebral) tissues to the blood flow index determined by diffuse correlation spectroscopy (DCS). Microvascular DCS flow measurements were made on the head during baseline and breath-holding/hyperventilation tasks, both with and without pressure. Baseline (resting) data enabled estimation of extra-cerebral flow signals and their pressure dependencies. A simple two-component model was used to derive baseline and activated cerebral blood flow (CBF) signals, and the DCS flow indices were also cross-correlated with concurrent Transcranial Doppler Ultrasound (TCD) blood velocity measurements. The study suggests new pressure-dependent experimental paradigms for elucidation of blood flow contributions from extra-cerebral and cerebral tissues.

Assessment of a multi-layered diffuse correlation spectroscopy method for monitoring cerebral blood flow in adults

“…Possible reasons for this discrepancy could include differences between species -the extracerebral layer of the pig has a more substantial muscle contribution, the extracerebral thickness, which was not reported by Kim et al, and possibly the effects of probe pressure, which can reduce the effects of scalp contamination [38]. Although it should be noted that the sensitivity of the homogeneous model to superficial tissues found in the current study is in agreement with others [24,25,38].…”

“…Interestingly, the disagreement between perfusion changes determined by CT and the DCS flow index obtained with the homogeneous model contradicts a previous study in which DCS was compared to CBF measurements obtained with Xenon CT [48]. Possible reasons for this discrepancy could include differences between species -the extracerebral layer of the pig has a more substantial muscle contribution, the extracerebral thickness, which was not reported by Kim et al, and possibly the effects of probe pressure, which can reduce the effects of scalp contamination [38]. Although it should be noted that the sensitivity of the homogeneous model to superficial tissues found in the current study is in agreement with others [24,25,38].…”

“…F S and F B values from the ML DCS analysis and F HM from the HM DCS analysis) were found by comparing values pre and post scalp incisions. This unexpected finding was likely due to increased variability in the DCS signal due to probe pressure effects since it was necessary to remove the fibers to perform the incisions [38]. Consequently, capnic data before and after scalp incision were grouped together in all subsequent analysis.…”

Modified Beer-Lambert law for blood flow

“…In cerebral monitoring, one way to change superficial blood flow without affecting cerebral blood flow is to vary the pressure of the optical probe against the head [83]. Initial measurements acquired during probe pressure modulation can then be used to derive the patient-specific weighting factors in the DCS Modified Beer-Lambert law.…”

Effect of a thin superficial layer on the estimate of hemodynamic changes in a two-layer medium by time domain NIRS

“…In this case, we can reach the higher value we found for the ε(t) which is around 11% for the DW layer when S UP is thicker, for SO 2 parameter. One example of real experiments where it is interesting to study physiological events occurring only in the UP layer is the study of the tissue heating when light is injected in [26], or the study of the influence of the probe pressure on the measurements [27]. Also in this case (Secs.…”