Magnetic Field And Tissue Dependencies Of Human Brain Longitudinal (H2o)-H-1 Relaxation In Vivo

Brain water proton ((H2O)-H-1)) longitudinal relaxation time constants (T-1) were obtained from three healthy individuals at magnetic field strengths (B-O) of 0.2 Tesla (T), 1.0T, 1.5T, 4.0T, and 7.0T. A 5-mm midventricular axial slice was sampled using a modified Look-Locker technique with 1.5 mm in-plane resolution, and 32 time points post-adiabatic inversion. The results confirmed that for most brain tissues, T, values increased by more than a factor of 3 between 0.2T and 7T, and over this range were well fitted by T-1 (s) = 0.583(B-0)(0.382), T-1(s) = 0.857(B-0)(0.376), and T-1(s) = 1.35(B-0)(0.340) for white matter (WM), internal GM, and blood (H2O)-H-1, respectively. The ventricular cerebrospinal fluid (CSF) (H2O)-H-1 T-1 value did not change with B0, and its average value (standard deviation (SD)) across subjects and magnetic fields was 4.3 (+/- 0.2) s. The tissue 1/T-1 values at each field were well correlated with the macromolecular mass fraction, and to a lesser extent tissue iron content. The field-dependent increases in (H2O)-H-1 T-1 values more than offset the well-known decrease in typical MR1 contrast reagent (CR) relaxivity, and simulations predict that this leads to lower CR concentration detection thresholds with increased magnetic field. Magn Reson Med 57:308-318, 2007. (c) 2007 Wiley-Liss, Inc.