Functional magnetic resonance imaging in anesthetized patients: a relevant step toward real-time intraoperative functional neuroimaging.
OBJECTIVE
The introduction of intraoperative 1.5-T magnetic resonance imaging may provide up-to-date functional information in the surgical environment. However, feasible passive paradigms that allow the examination of anesthetized patients will be a precondition for intraoperative functional magnetic resonance imaging (fMRI). The aim of this study is to evaluate the feasibility of a recently developed passive fMRI paradigm for functional neuroimaging in anesthetized patients.


METHODS
We investigated four anesthetized patients with intracranial pathological conditions not related to the sensorimotor cortex. All patients had been anesthetized with standard total intravenous anesthesia for more than 24 hours before the fMRI scan. Anesthesia and monitoring were sustained during the scanning procedure. A simultaneous electrical stimulation of the median and tibial nerves was applied to elicit a cortical activation using a custom-designed magnetoelectrically shielded conductor. Statistical evaluation using Statistical Parametric Mapping software (Wellcome Department of Imaging Neuroscience, University College, London, England) and the Talairach Daemon Client (Version 1.1; Research Imaging Center, University of Texas Health Science Center, San Antonio, TX) followed.


RESULTS
Three of four patients showed a good activation of the sensorimotor cortex under anesthesia. In one patient, no significant activation was observed, presumably as a result of increased body impedance because of severe edema. Standard dosages of the narcotics did not influence the cortical response; however, stimulation intensity had to be increased compared with awake patients. We did not detect relevant interferences with magnetic resonance imaging arising from the technical setup.


CONCLUSIONS
The method presented proved to be a feasible paradigm for fMRI evaluation of the sensorimotor cortex in anesthetized patients and thus forms a relevant step toward real intraoperative functional neuroimaging.
Department of Neurosurgery, University of Essen, Essen, Germany. thomas.gasser@uni-essen.de
Thomas
T
Gasser
Erol
E
Sandalcioglu
Beate
B
Schoch
Elke
E
Gizewski
Michael
M
Forsting
Dietmar
D
Stolke
Helmut
H
Wiedemayer
D000368:Aged; D000758:Anesthesia / Q000379:methods*; D001931:Brain Mapping / Q000379:methods; D003199:Computer Systems; D005071:Evoked Potentials; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007430:Intraoperative Care / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000503:physiopathology* / Q000601:surgery*; D013003:Somatosensory Cortex / Q000503:physiopathology* / Q000601:surgery*; D025321:Surgery, Computer-Assisted / Q000379:methods*