MR-IMAGING CONTRAST IN HUMAN BRAIN-TISSUE - ASSESSMENT AND OPTIMIZATION AT 4 T

PURPOSE: To evaluate multiple magnetic resonance (MR) imaging sequence s for their ability to provide T1- and T2-weighted images at a field s trength of 4 T, and to validate previously obtained relaxation time me asurements. MATERIALS AND METHODS: Different spin-echo, inversion-reco very (IR), gradient-recalled acquisition in the steady state (GRASS), and magnetization transfer contrast-enhanced GRASS sequences were eval uated in a single section, each in at least four volunteers. Also, int erleaved echo-planar imaging (IEPI) and interleaved gradient-recalled echo (IGRE) sequences were analyzed and compared with standard sequenc es. RESULTS: Predicted contrast behavior, according to MR relaxation t ime measurements, was found to agree well with that of the validation experiments. Fair T1 contrast can be achieved on MR images at 4 T, con trary to early predictions. Under other conditions, however, such as p artially spin-density-weighted parameters, lower contrast is observed at the high field strength when compared with conventional field stren gths. CONCLUSION: The longer T1 values at higher field strengths have a substantial effect on image contrast. Depending on the sequence and parameters chosen, good image contrast can be realized at 4 T. IEPI an d hybrid IR IGRE sequences are useful in shortening the prolonged exam ination times owing to the longer T1 values at higher field strengths.