Abstract
Apparent transverse-relaxation rate constants (R 2 = 1/T 2) were measured in various regions of the healthy human brain using a multiecho adiabatic spin-echo sequence at five different magnetic fields, 1.5, 1.9, 3, 4.7, and 7 T. The R 2 values showed a clear dependence on magnetic field strength (B 0). The regional distribution of the R 2 was well explained by the sum of three components: (1) regional nonhemin iron concentration ([Fe]), (2) regional macromolecular mass fraction (fM), and (3) a region-independent factor. Accordingly, R 2 = α[Fe] + βfM + γ, where coefficients α, β, and γ were experimentally determined at each magnetic field by a least square fitting method using multiple regression analysis. Although the coefficient α linearly increased with B0, β showed a quadratic dependence on top of a field-independent component. The coefficient γ also increased slightly with B0 on top of a field-independent component. The linear dependence of α on B0 was consistent with that observed for the transverse-relaxation rate of water protons in ferritin solutions as found previously by others. The quadratic dependence of β on B0 was accounted for by isochronous and anisochronous exchange mechanisms using intrinsic-relaxation parameters obtained from the literature.
Original language | English (US) |
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Pages (from-to) | 947-953 |
Number of pages | 7 |
Journal | Magnetic resonance in medicine |
Volume | 68 |
Issue number | 3 |
DOIs | |
State | Published - Sep 2012 |
Keywords
- field dependence
- human brain
- iron
- macromolecule
- transverse relaxation