title: Proton NMR relaxation times of human blood samples at 1.5 T and implications for functional MRI.
abstract: To further investigate the dependency of fMRI signal changes on echo time TE, we measured T2 and T2* values, obtained from human blood samples at various oxygenation levels and used them in a simple model to calculated signal enhancement in fMRI. In addition, the longitudinal relaxation time T1 of human blood was determined for reference. All measurements were performed at 23 degrees C to reduce blood cell metabolism during the measurement procedure. At 23 degrees C T1 values of 1434 +/- 48 ms for arterial human blood were obtained after correcting for hematocrit content, as hematocrit values ranged fro 28% to 34% only. The T2 relaxation times obtained are 181 +/- 23 ms for venous and 254 +/- 26 ms for arterial human blood, T2* relaxation times corrected for inhomogeneities of the static magnetic field (B0) are 42 +/- 2.8 ms and 254 +/- 32 ms, respectively. Furthermore, absolute and relative signal changes in fMRI experiments are calculated. The results from these model calculations reveal that contrast in fMRI can be optimised by choosing an appropriate echo time.
authors.affiliation: Institute for Medical Physics, University of Vienna, Austria.
authors.forename: M
authors.initials: M
authors.lastname: Barth
authors.forename: E
authors.initials: E
authors.lastname: Moser
mesh_terms: D000328:Adult; D000368:Aged; D001790:Blood Physiological Phenomena; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D010100:Oxygen / Q000097:blood; D011522:Protons
chemical_list: D011522:Protons; D010100:Oxygen