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Temporal spatial differences observed by functional MRI and
human intraoperative optical imaging
Source: Cerebral Cortex 2001 Aug;11(8):773-782.
Author: Cannestra AF, Pouratian N, Bookheimer SY, Martin NA, Beckerand DP, Toga AW.
PubMed ID: 11459767
Abstract:
Pre-operative functional MRI (fMRI), cortical evoked potentials (EP’s) and intraoperative optical imaging of intrinsic signals (iOIS) were employed to relate the temporal-spatial characteristics of sensori-motor responses in human brain. fMRI (at 3T). Peripheral somasthetic stimulation (2s) was provided either by a 110Hz finger vibrator or transcutaneous median nerve stimulation. Each technique provided unique spatial patterns and temporal response profiles. Spatially, all modalities localized at the level of the superior genu of the central sulcus. EP’s and iOIS activities were observed over the surface of pre- and post-central gyri with very similar spatial distributions. In contrast, fMRI primarily localized within the central sulcus. fMRI did not demonstrate large signal changes over the pre- and post central gyri (areas with iOIS/EP activity). Temporally, responses to single stimuli differed between the fMRI and iOIS techniques. Response curves had similar shape and duration, however, the total fMRI response was delayed by 2-3s relative to the iOIS. When fMRI time courses were examined over pixels colocalizing with iOIS activation, the fMRI temporal profile included an initial decrease in signal (an initial “dip”) that closely resembled the time course of iOIS response. The spatial/temporal differences in this study likely reflect the arterial versus venous contributions of iOIS and fMRI, respectively. Additionally, differences may result from volumetric versus surface acquisition of fMRI and iOIS/SSEP’s, respectively. The temporal/spatial colocalization of the iOIS signal and the fMRI initial dip suggests the initial fMRI dip and the iOIS signal may result from similar physiologic events. Introduction: Many modern functional neuroimaging techniques including functional MRI, PET, OIS, and near infra-red spectroscopy exploit changes in cerebral perfusion to produce maps of brain function. A full characterization of perfusion related cortical signals therefore is critical for the quantification and understanding of cortical activity using these methods. Methods: We measured functional magnetic resonance, evoked potential, and optical reflectance changes over sensori-motor cortex in 8 patients undergoing surgical resection of fronto-parietal masses (tumors or arterial-venous malformations). Informed consent was obtained from all patients prior to preoperative imaging. fMRI was performed pre-operatively 24-72 hours before surgery. During surgery, the patient's head was fixed, via a Mayfield apparatus, to the operating table. After site localization (via a frameless sterotaxic system), the craniotomy and reflection of the dura was performed. SSEP's and iOIS recordings were obtained. Results: Spatial and temporal statistics were compiled from iOIS,fMRI, and SSEP's maps in eight human subjects undergoing neurosurgical procedures. Different spatial patterns and temporal response profiles were observed. Although overall fMRI,iOIS and SSEP activities were observed with very similar spatial distributions, the fMRI and iOIS centers of mass (COM) were separated by statistically significant distances. Temporally, the total fMRI response statistical correlation analysis was delayed by 2-3s relative to the iOIS. However, this relationship became more similar when only colocalizing pixels were examined. Discussion: In this study we measured fMRI, optical and evoked potential changes in patients undergoing intracranial neurosurgery. We found good correlation between SSEP's and iOIS. fMRI localized near the SSEP responses, however was deep and superior with statistically significant differences in COM location. Temporal differences were observed between the iOIS and fMRI responses. However, when responses over co-localizing pixels were measured, fMRI revealed an earlier response with similar temporal characteristics to iOIS.
Source: Cerebral Cortex 2001 Aug;11(8):773-782.
Author: Cannestra AF, Pouratian N, Bookheimer SY, Martin NA, Beckerand DP, Toga AW.
PubMed ID: 11459767
Abstract:
Pre-operative functional MRI (fMRI), cortical evoked potentials (EP’s) and intraoperative optical imaging of intrinsic signals (iOIS) were employed to relate the temporal-spatial characteristics of sensori-motor responses in human brain. fMRI (at 3T). Peripheral somasthetic stimulation (2s) was provided either by a 110Hz finger vibrator or transcutaneous median nerve stimulation. Each technique provided unique spatial patterns and temporal response profiles. Spatially, all modalities localized at the level of the superior genu of the central sulcus. EP’s and iOIS activities were observed over the surface of pre- and post-central gyri with very similar spatial distributions. In contrast, fMRI primarily localized within the central sulcus. fMRI did not demonstrate large signal changes over the pre- and post central gyri (areas with iOIS/EP activity). Temporally, responses to single stimuli differed between the fMRI and iOIS techniques. Response curves had similar shape and duration, however, the total fMRI response was delayed by 2-3s relative to the iOIS. When fMRI time courses were examined over pixels colocalizing with iOIS activation, the fMRI temporal profile included an initial decrease in signal (an initial “dip”) that closely resembled the time course of iOIS response. The spatial/temporal differences in this study likely reflect the arterial versus venous contributions of iOIS and fMRI, respectively. Additionally, differences may result from volumetric versus surface acquisition of fMRI and iOIS/SSEP’s, respectively. The temporal/spatial colocalization of the iOIS signal and the fMRI initial dip suggests the initial fMRI dip and the iOIS signal may result from similar physiologic events. Introduction: Many modern functional neuroimaging techniques including functional MRI, PET, OIS, and near infra-red spectroscopy exploit changes in cerebral perfusion to produce maps of brain function. A full characterization of perfusion related cortical signals therefore is critical for the quantification and understanding of cortical activity using these methods. Methods: We measured functional magnetic resonance, evoked potential, and optical reflectance changes over sensori-motor cortex in 8 patients undergoing surgical resection of fronto-parietal masses (tumors or arterial-venous malformations). Informed consent was obtained from all patients prior to preoperative imaging. fMRI was performed pre-operatively 24-72 hours before surgery. During surgery, the patient's head was fixed, via a Mayfield apparatus, to the operating table. After site localization (via a frameless sterotaxic system), the craniotomy and reflection of the dura was performed. SSEP's and iOIS recordings were obtained. Results: Spatial and temporal statistics were compiled from iOIS,fMRI, and SSEP's maps in eight human subjects undergoing neurosurgical procedures. Different spatial patterns and temporal response profiles were observed. Although overall fMRI,iOIS and SSEP activities were observed with very similar spatial distributions, the fMRI and iOIS centers of mass (COM) were separated by statistically significant distances. Temporally, the total fMRI response statistical correlation analysis was delayed by 2-3s relative to the iOIS. However, this relationship became more similar when only colocalizing pixels were examined. Discussion: In this study we measured fMRI, optical and evoked potential changes in patients undergoing intracranial neurosurgery. We found good correlation between SSEP's and iOIS. fMRI localized near the SSEP responses, however was deep and superior with statistically significant differences in COM location. Temporal differences were observed between the iOIS and fMRI responses. However, when responses over co-localizing pixels were measured, fMRI revealed an earlier response with similar temporal characteristics to iOIS.