Risonanza magnetica funzionale encefalica. Razionale della metodica ed esperienze applicative su magnete per uso clinico

Functional magnetic resonance imaging (fMRI) is a new technique for imaging the <<brain at work>>, and is increasingly being used by neurophysiologists to investigate the locations and interactions between different areas of the brain activated to perform different tasks, fMRI displays signal changes in brain tissue triggered by perfusional changes and oxygenation in the grey matter during different functional states (rest/activity). These changes are displayed at MR thanks to the effect of paramagnetic enhancement in the brain vascular bed on the T2 transverse relaxation of tissue proton in the capillaries using T2 weighted gradient echo sequences.Two main study techniques were adopted. The first, the more complicated involves a bolus injection of gadolinium and echo-planar imaging of contrast uptake in the brain capillary bed. The second technique can be used with magnets for clinical use and requires desoxyhemoglobin for endogenous paramagnetic enhancement and displays changes in blood oxygenation correlated with cortical activity (BOLDc technique: blood oxygenation dependent contrast).We used a 1.5 T superconductor magnet adopting the BOLDc technique and long TE flash gradient echo sequences. We investigated 19 volunteers making 11 studies of motor cortex activation and 13 of visual cortex. Good or satisfactory signal changes were recorded in the cortical region activated in 10 studies of motor activation and 10 of visual activation One motor activation study and 3 visual activation studies were unsatisfactory a no signal changes were found, or could not be attributed to any cortical region of interest.MR currently offers neuroradiologists the best anatomostructural information on the CNS. The technique can now be applied to investigate some aspects of brain function which were once the sole domain of nuclear medicine. With respect to SPET and PET, MR is cheaper and non-invasive giving greater spatial and temporal resolution and the chance to rapidly combine functional and anatomical images.