Quantification of the cortical contribution to the NIRS signal over the motor cortex using concurrent NIRS-fMRI measurements

Abstract

Near-Infrared Spectroscopy (NIRS) measures the functional hemodynamic response occuring at the surface of the cortex. Large pial veins are located above the surface of the cerebral cortex. Following activation, these veins exhibit oxygenation changes but their volume likely stays constant. The back-reflection geometry of the NIRS measurement renders the signal very sensitive to these superficial pial veins. As such, the measured NIRS signal contains contributions from both the cortical region as well as the pial vasculature. In this work, the cortical contribution to the NIRS signal was investigated using (1) Monte Carlo simulations over a realistic geometry constructed from anatomical and vascular MRI and (2) multimodal NIRS-BOLD recordings during motor stimulation. A good agreement was found between the simulations and the modeling analysis of in vivo measurements. Our results suggest that the cortical contribution to the deoxyhemoglobin signal change (ΔHbR) is equal to 16–22% of the cortical contribution to the total hemoglobin signal change (ΔHbT). Similarly, the cortical contribution of the oxyhemoglobin signal change (ΔHbO) is equal to 73–79% of the cortical contribution to the ΔHbT signal. These results suggest that ΔHbT is far less sensitive to pial vein contamination and therefore, it is likely that the ΔHbT signal provides better spatial specificity and should be used instead of ΔHbO or ΔHbR to map cerebral activity with NIRS. While different stimuli will result in different pial vein contributions, our finger tapping results do reveal the importance of considering the pial contribution.

Measuring tissue hemodynamics and oxygenation by continuous-wave functional near-infrared spectroscopy—how robust are the different calculation methods against movement artifacts?

“…This feature is particularly of interest for the detection of task-evoked brain activity (i.e. the hemodynamic response) which is accompanied by changes in hemodynamics in the superficial tissue too (Gagnon et al 2012, Kirilina et al 2012, Klaessens et al 2004, Okada and Delpy 2003. Compared to the other MD methods, MD method 3 (i.e.…”

Time-resolved multi-channel optical system for assessment of brain oxygenation and perfusion by monitoring of diffuse reflectance and fluorescence

“…A typical change with the opposite trends of the signals change which were measured at the two wave− lengths located on the opposite sides of the isobestic point in all statistical moments can be observed. These opposite changes in the motor cortex activation are caused by chan− ges of the absorption coefficients (for 687 nm and 832 nm wavelengths) which result from increase in oxyhemoglobin concentration and decrease in deoxyhemoglobin con− centration [59][60][61][62][63][64][65][66][67].…”

Method for the discrimination of superficial and deep absorption variations by time domain fNIRS

“…blood pressure or heart rate changes) might contaminate the detected signal [5,6]. These systemic phenomena typically occur in the superficial tissues (mainly the scalp) and can confound the readings of the instruments, especially when task related physiological responses happen [6,7].…”

“…blood pressure or heart rate changes) might contaminate the detected signal [5,6]. These systemic phenomena typically occur in the superficial tissues (mainly the scalp) and can confound the readings of the instruments, especially when task related physiological responses happen [6,7]. A multi-channel configuration with sensors placed at different distances from the injection point is the solution that is currently being adopted in CW fNIRS to reduce the crosstalk between the superficial systemic signal and the deep cortical signal [8][9][10].…”