THE QUANTITATIVE RELATION BETWEEN T1-WEIGHTED AND T2-WEIGHTED MRI OF NORMAL GRAY-MATTER AND IRON CONCENTRATION

A retrospective analysis of 158 T1-weighted and T2-weighted MRI scans of normal brains at 0.5 and 1.5 Tesla was performed. Signal intensitie s in the frontal cortex, caudate nucleus, putamen, and globus pallidus were divided by those of frontal white matter; and these gray/white r atios were correlated with iron concentration, estimated from the anat omical region and age of the patient, Intraregional plots were also ma de of gray/white ratio versus age for the 1.5 Tesla scans. The changes in both T1-weighted and T2-weighted ratios were consistent with the h ypothesis that 1/T1 and 1/T2 vary linearly with iron concentration, an d the corresponding coefficients, determined separately from the inter regional and intraregional plots, were generally in agreement, Further more, the variability of the MRI ratios at 1.5 Tesla was consistent wi th expected iron variability except for the cortex, in which partial v olume errors due to sulci and white matter caused increased variations . The MRI results agreed well with in vitro data on T1 and T2 in tissu e specimens and with other MRI studies, When compared with T1 and T2 i n ferritin solution, a significant ''tissue relaxation enhancement'' w as found, attributable to slower diffusion and clustering of ferritin in tissue.