High spatial and temporal resolution cerebrovascular reactivity for humans and large mammals: A technological description of integrated fNIRS and niABP mapping system

Abstract

Introduction: The process of cerebral vessels maintaining cerebral blood flow (CBF) fairly constant over a wide range of arterial blood pressure is referred to as cerebral autoregulation (CA). Cerebrovascular reactivity is the mechanism behind this process, which maintains CBF through constriction and dilation of cerebral vessels. Traditionally CA has been assessed statistically, limited by large, immobile, and costly neuroimaging platforms. However, with recent technology advancement, dynamic autoregulation assessment is able to provide more detailed information on the evolution of CA over long periods of time with continuous assessment. Yet, to date, such continuous assessments have been hampered by low temporal and spatial resolution systems, that are typically reliant on invasive point estimations of pulsatile CBF or cerebral blood volume using commercially available technology.Methods: Using a combination of multi-channel functional near-infrared spectroscopy and non-invasive arterial blood pressure devices, we were able to create a system that visualizes CA metrics by converting them to heat maps drawn on a template of human brain.Results: The custom Python heat map module works in “offline” mode to visually portray the CA index per channel with the use of colourmap. The module was tested on two different mapping grids, 8 channel and 24 channel, using data from two separate recordings and the Python heat map module was able read the CA indices file and represent the data visually at a preselected rate of 10 s.Conclusion: The generation of the heat maps are entirely non-invasive, with high temporal and spatial resolution by leveraging the recent advances in NIRS technology along with niABP. The CA mapping system is in its initial stage and development plans are ready to transform it from “offline” to real-time heat map generation.

Non-Invasive Mapping of Cerebral Autoregulation Using Near-Infrared Spectroscopy: A Study Protocol

“…The software development of such an integrated CA mapping system is currently in its initial development stage, where CA heat maps can be produced in an “offline” mode with previously recorded CVR indices [ 30 ]. We expect to integrate the ability to capture real-time signal data and calculate CVR indices automatically in real-time to produce CA heat maps in “online” mode.…”

“…CVR , cerebrovascular reactivity ; GUI , graphical user interface ; HbO , oxyhemoglobin . This figure is from Sainbhi et al [ 30 ] and is used under Creative Commons Attribution License (CC BY) [ 40 ].…”

“…NIRS , near-infrared spectroscopy . This figure is from Sainbhi et al [ 30 ], is used under Creative Commons Attribution License (CC BY) [ 40 ], and is cropped from the original.…”

“…Thus, to improve the understanding of continuously assessed CA in humans, we need a tool with both improved spatial and temporal resolution. With recent advances in NIRS technology, custom multi-channel NIRS systems are available that offer sampling frequencies up to 250 Hz, enabling the simultaneous data acquisition of full cerebral pulse waveform from multiple brain regions [ 27 , 28 , 29 , 30 ]. Since these are research systems, they cannot be used in a clinical setting to direct care provision until they acquire the appropriate health safety approvals.…”

“…Bridging this existing technological gap in high spatial and temporal resolution CA monitoring system, we have recently proposed to employ an advanced multi-channel NIRS system coupled with an entirely non-invasive continuous arterial blood pressure (niABP) monitor to create a new wearable and portable imaging system that derives CA maps of the entire brain with high sampling rates at each point. Recent work from our lab has demonstrated the feasibility of developing such a system, with a functional prototype currently running ( Figure 1 ) [ 30 ].…”