Interregional variation of longitudinal relaxation rates in human brain at3.0 T: Relation to estimated iron and water contents

In a study of interregional variation of the longitudinal relaxation rate ( R-1) in human brain at 3 T, R-1 maps were acquired from 12 healthy adults u sing a multi-slice implementation of the T one by multiple readout pulses ( TOMROP) sequence. Mean R-1 values were obtained from the prefrontal cortex (0.567 +/- 0.020 sec(-1)), caudate head (0.675 +/- 0.019 sec(-1)), putamen (0.749 +/- 0.023 sec(-1)), substantia nigra (0.873 +/- 0.037 sec(-1)), glob us pallidus (0.960 +/- 0.034 sec(-1)), thalamus (0.822 +/- 0.027 sec(-1)), and frontal white matter (1.184 +/- 0.057 sec(-1)). For gray matter regions other than the thalamus, R-1 showed a strong correlation (r = 0.984, P < 0 .0001) with estimated regional nonheme iron concentrations ([Fe]). These R- 1 values also showed a strong correlation (r = 0.976, P < 0.0001) with esti mates of 1/f(w) obtained from MRI relative proton density measurements, whe re f(w) represents tissue water content. When white matter is included in t he consideration, 1/f(w) is a better predictor of R-1 than is [Fe]. An anal ysis based on the fast-exchange two-state model of longitudinal relaxation suggests that interregional differences in f(w) account for the majority of the variation of R-1 across gray matter regions. Magn Reson Med 45:71-79, 2001, (C) 2001 Wiley-Liss, Inc.