High-resolution in vivo measurements of transverse relaxation times in rats at 7 Tesla

A multi-echo imaging sequence suitable for high-resolution and accurate in vivo transverse relaxation time (T-2) mapping has been implemented. The sequence was tested on phantoms and was used to measure T-2 ,values 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 literature values obtained at lower field in vivo as well as high-field T-2, measurements on excised rat tissues. The reported T-2 ,values are generally smaller compared to lower-field-strength literature values. A discussion of the possible causes of these field effects on T-2,is included (dipolar interaction, fast chemical exchange, and diffusion in susceptibility gradients).