MAGN FIELD &TISSUE DEPENDENCIES OF HUMAN BRAIN LONGITUDINAL 1H2O RELAX IN VIVO

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Brain water proton (1H2O) longitudinal relaxation time constants (T1) were obtained from three healthy individuals at magnetic field strengths (B0) 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, T1 values increased by more than a factor of 3 between 0.2T and 7T, and over this range were well fitted by T1 (s)=0.583(B0)0.382, T1(s)=0.857(B0)0.376, and T1(s)=1.35(B0)0.340 for white matter (WM), internal GM, and blood 1H2O, respectively. The ventricular cerebrospinal fluid (CSF) 1H2O T1 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/T1 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 1H2O T1 values more than offset the well-known decrease in typical MRI contrast reagent (CR) relaxivity, and simulations predict that this leads to lower CR concentration detection thresholds with increased magnetic field.