MR imaging of human brain at 3.0 T: Preliminary report on transverse relaxation rates and relation to estimated iron content

PURPOSE: To determine the transverse relaxation rates R2 and R2' from sever al gray matter regions and from frontal cortical white matter in healthy hu man brains in vivo and to determine the relationship between relaxation rat es and iron concentration [Fe]. MATERIALS AND METHODS: Six healthy adults aged 19-42 years underwent thin-s ection gradient-echo sampling of free induction decay and echo magnetic res onance (MR) imaging at 3.0 T. Imaging covered the mesencephalon and basal g anglia. RESULTS: Relaxation rates (mean +/- SD) were highest in globus pallidus (R2 = 25.8 seconds(-1) +/- 1.1, R2' = 12.0 seconds(-1) +/- 2.1)and lowest in p refrontal cortex (R2 = 14.4 seconds(-1) +/- 1.8, R2' = 3.4 seconds(-1) +/- 1.1). Frontal white matter measurements were as follows: R2 = 18.0 seconds( -1) +/- 1.2 and R2' = 3.9 seconds(-1) +/- 1.2. For gray matter, both R2 and R2' showed a strong correlation (r = 0.92, P < .001 and r = 0.90, P < .001 , respectively) with [Fe]. Although the slopes of the regression lines for R2' versus [Fe] and for R2 versus [Fe] were similar, the iron-independent c omponent of R2' (2.2 seconds(-1) +/- 0.6), the value when [Fe] = 0, was muc h less than that of R2 (12.7 seconds(-1) +/- 0.7). CONCLUSION: The small iron-independent component of R2', as compared with t hat of R2, is consistent with the hypothesis that R2' has higher iron-relat ed specificity.