Functional MRI and 18F FDG-Positron Emission Tomography for Presurgical Planning: Comparison with Electrical Cortical Stimulation

Summary.

 Background: In patients with mass lesions near “eloquent” cortical areas different preoperative mapping techniques can be used. Two of the most widely used approaches include positron emission tomography (PET) and functional MRI (fMRI). We employed both methods in the same patients undergoing presurgical evaluation and compared the results to those obtained by direct electrical cortical stimulation (DECS).

 Method: 22 patients with tumours of different aetiology near the central region were investigated. FMRI was performed using a T2^*-weighted gradient-echo BOLD sequence at 1.5 T, PET was performed after injection of 122–301 MBq ¹⁸F-Fluorodeoxyglucose (18-FDG) under rest and activation conditions. DECS was performed in all patients with recordings of muscles primarily involved in the investigated tasks.

 Findings: In 19 patients all three modalities could be compared, 1 patient demonstrated discordance between fMRI and PET with DECS speaking in favour of fMRI, 6 patients had neighbouring results of PET and fMRI (between 1–2 cm distance), 12 patients had overlapping results.

 Interpretation: The high incidence of neighbouring results is presumably related to fMRI specific artefacts. Advantages of fMRI are: Higher spatial and temporal resolution, more and different functional runs, shorter examination time, wider availability, longitudinal examinations, non-invasiveness and cost-effectiveness, easy registration to anatomical images. Advantages of PET are: higher signal-to-noise ratio, lesser susceptibility to artefacts (motion, draining veins), evaluation of tumour metabolism. It is our opinion that the neurosurgeon has to decide on a case-by-case basis which study suits his specific needs in the presurgical evaluation of his patient.