Bi-exponential Na T * component analysis in the human brain.

The purpose of this study was to measure the sodium transverse relaxation time T * in the healthy human brain. Five healthy subjects were scanned with 18 echo times (TEs) as short as 0.17 ms. T * values were fitted on a voxel-by-voxel basis using a bi-exponential model. Data were also analysed using a continuous distribution fit with a region of interest-based inverse Laplace transform. Average T * values were 3.4 ± 0.2 ms and 23.5 ± 1.8 ms in white matter (WM) for the short and long components, respectively, and 3.9 ± 0.5 ms and 26.3 ± 2.6 ms in grey matter (GM) for the short and long components, respectively, using the bi-exponential model. Continuous distribution fits yielded results of 3.1 ± 0.3 ms and 18.8 ± 3.2 ms in WM for the short and long components, respectively, and 2.9 ± 0.4 ms and 17.2 ± 2 ms in GM for the short and long components, respectively. Na T * values of the brain for the short and long components for various anatomical locations using ultra-short TEs are presented for the first time.