Metabolic and electrophysiological validation of functional MRI

Objectives-Although functional MRI is widely used for preoperative planning and intraoperative neuronavigation, its accuracy to depict the site of neu ronal activity is not exactly known. Experience with methods that may valid ate fMRI data and the results obtained when coregistering fMRI with differe nt preoperative and intraoperative mapping modalities including metabolical ly based F-18-fluorodeoxyglucose PET, electrophysiologcally based transcran ial magnetic stimulation (TMS), and direct electrical cortical stimulation (DECS) are described. Methods-Fifty patients were included. PET was performed in 30, TMS in 10, a nd DECS in 41 patients. After coregistration using a frameless stereotactic system, results were grouped into overlapping (<1 cm distance), neighbouri ng (<2 cm), or contradictory (>2 cm). Results-Comparing fMRI with PET, 18 overlapping, seven neighbouring, and on e contradictory result were obtained. In four patients no comparison was po ssible (because of motion artefacts, low signal to noise ratio, and unusual high tumour metabolism in PET). The comparison of TMS and MRI showed seven overlapping and three neighbouring results. In three patients no DECS resu lts could be obtained. Of the remaining 38 patients, MRI hand motor tasks w ere compared with DECS results of the upper limb muscles in 36 patients, an d fMRI foot motor tasks were compared with DECS results of the lower limb o n 13 occasions. Of those 49 studies, overlapping results were obtained in 3 1 patients, and neighbouring in 14. On four occasions fMRI did not show fun ctional information (because of motion artefacts and low signal to noise). Conclusions-All validation techniques have intrinsic limitations that restr ict their spatial resolution. However, of 50 investigated patients, there w as only one in whom results contradictory to CAM were obtained. Although it is not thought that MRI can replace the intraoperatively updated functiona l information (DECS), it is concluded that fMRI is an important adjunct in the preoperative assessment of patients with tumours in the vicinity of the central region.