HIGH-RESOLUTION IN-VIVO MEASUREMENTS OF TRANSVERSE RELAXATION-TIMES IN RATS AT 7 TESLA

A multi-echo imaging sequence suitable for high-resolution and accurat e in vivo transverse relaxation time (T-2) mapping has been implemente d. The sequence was tested on phantoms and was used to measure T-2 ,va lues in vivo in the rat brain, muscle, and fat at 7 T. Brain T-2, maps are shown and regional variations in brain T-2 ,are reported (41.8 ms in cortex, 47.9 ms in hippocampus). Results are compared to literatur e values obtained at lower field in vivo as well as high-field T-2, me asurements on excised rat tissues. The reported T-2 ,values are genera lly smaller compared to lower-field-strength literature values. A disc ussion of the possible causes of these field effects on T-2,is include d (dipolar interaction, fast chemical exchange, and diffusion in susce ptibility gradients).