MR Imaging of Human Brain at 3.0 T: Preliminary Report on Transverse Relaxation Rates and Relation to Estimated Iron Content

TLDR

The study aimed to measure transverse relaxation rates R2 and R2′ in various gray matter regions and frontal white matter of healthy adults at 3.0 T and to assess their correlation with brain iron concentration. Six healthy adults aged 19–42 underwent thin‑section gradient‑echo sampling of free induction decay and echo MR imaging at 3.0 T, covering the mesencephalon and basal ganglia. Relaxation rates were highest in the globus pallidus and lowest in the prefrontal cortex, with R2 and R2′ strongly correlating with iron concentration (r = 0.92 and 0.90), and the iron‑independent component of R2′ was markedly smaller than that of R2, indicating greater iron specificity of R2′.

Abstract

PURPOSE: To determine the transverse relaxation rates R2 and R2′ from several gray matter regions and from frontal cortical white matter in healthy human brains in vivo and to determine the relationship between relaxation rates and iron concentration [Fe]. MATERIALS AND METHODS: Six healthy adults aged 19–42 years underwent thin-section gradient-echo sampling of free induction decay and echo magnetic resonance (MR) imaging at 3.0 T. Imaging covered the mesencephalon and basal ganglia. 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 prefrontal 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 component of R2′ (2.2 seconds−1 ± 0.6), the value when [Fe] = 0, was much less than that of R2 (12.7 seconds−1 ± 0.7). CONCLUSION: The small iron-independent component of R2′, as compared with that of R2, is consistent with the hypothesis that R2′ has higher iron-related specificity.