POTENTIAL PITFALLS OF FUNCTIONAL MRI USING CONVENTIONAL GRADIENT-RECALLED ECHO TECHNIQUES

The conventional gradient-recalled echo technique, FLASH, has widely b een used for functional MRI. FLASH results at 4 T with short TEs of 10 -20 ms mimic those at 1.5 T with TEs of 25-50 ms or longer. Under thes e conditions, large venous vessels dominate the activated area; howeve r, the use of longer TEs at 4 T reveals activation in gray matter area s as well as large vessels. Inflow effects of large vessels can be gre atly reduced with centric-reordering of phase-encoding steps and inter -image delay. Finger and toe movement paradigms show that functional a ctivation maps are consistent with classical somatotopic maps, and are specific to the tasks. Navigator-based motion correction generates fu nctional maps with larger activation areas by reducing physiological n oise.