Characterization of cortical hemodynamic changes following sensory, visual, and speech activation by intraoperative optical imaging utilizing phase‐based evaluation methods

Abstract

Alterations within cerebral hemodynamics are the intrinsic signal source for a wide variety of neuroimaging techniques. Stimulation of specific functions leads due to neurovascular coupling, to changes in regional cerebral blood flow, oxygenation and volume. In this study, we investigated the temporal characteristics of cortical hemodynamic responses following electrical, tactile, visual, and speech activation for different stimulation paradigms using Intraoperative Optical Imaging (IOI). Image datasets from a total of 22 patients that underwent surgical resection of brain tumors were evaluated. The measured reflectance changes at different light wavelength bands, representing alterations in regional cortical blood volume (CBV), and deoxyhemoglobin (HbR) concentration, were assessed by using Fourier-based evaluation methods. We found a decrease of CBV connected to an increase of HbR within the contralateral primary sensory cortex (SI) in patients that were prolonged (30 s/15 s) electrically stimulated. Additionally, we found differences in amplitude as well as localization of activated areas for different stimulation patterns. Contrary to electrical stimulation, prolonged tactile as well as prolonged visual stimulation are provoking increases in CBV within the corresponding activated areas (SI, visual cortex). The processing of the acquired data from awake patients performing speech tasks reveals areas with increased, as well as areas with decreased CBV. The results lead us to the conclusion, that the CBV decreases in connection with HbR increases

Revisiting the cerebral hemodynamics of awake, freely moving rats with repeated ketamine self-administration using a miniature photoacoustic imaging system

“… 39 – 41 These differences can also be attributed to the various anesthesia methods because anesthetic agents have distinct effects on neurovascular coupling and neuronal response patterns 42 – 44 Thus, the validity of the stimuli used in in vivo studies must be carefully considered.…”

“…Various investigators have reported differences in neurovascular coupling in awake and anesthetized animals, which could be attributed to different combinations of stimulation parameters (stimulus duration, intensity, frequency, stimulation site, etc.). [39][40][41] These differences can also be attributed to the various anesthesia methods because anesthetic agents have distinct effects on neurovascular coupling and neuronal response patterns. [42][43][44] Thus, the validity of the stimuli used in in vivo studies must be carefully considered.…”