Apparent transverse relaxation rate in human brain varies linearly with tissue iron concentration at 4.7 T

Multiple pairs of adiabatic passage pulses were implemented in a spin-echo sequence to achieve accurate measurements of the apparent transverse relaxation time (T2+ in a short scan time. In experiments on agarose gel phantoms with T-2 values ranging from 30 to 105 ms, the measured T-2(t) values were in good agreement with transverse relaxation times measured with a nonselective Carr-Purcell-Meiboom-Gill sequence. In experiments on normal human brain at 4.7 T, T-2(t) values in five different gray matter regions were found to range from 38 +/- 2 ms (globus pallidus) to 64 +/- 2 ms (frontal cortex). The apparent relaxation rate (1/T-2(t)) in these five regions showed strong correlation (r = 0.97) with published levels of iron (Fe) in those regions. The linear coefficient relating 1/T2t and [Fe] at 4.7 T was measured to be 0.551 (s center dot mg Fe/100 g f.w.)(-1). When compared with the values obtained in a previous report for six different static fields (B-0) up to 1.5 T, the current measurement confirms the linear dependence of the linear coefficient on B-0 up to 4.7 T (r = 0.99). These results suggest that the T-2(t) value in the human brain is predominantly affected by the nonhemin iron distribution. The strong correlation between the obtained T-2(t) values and the regional iron concentrations suggests a role for this pulse sequence in quantifying in vivo brain iron at high magnetic field.