Correlation of proton transverse relaxation rates (R₂) with iron concentrations in postmortem brain tissue from Alzheimer's disease patients

Iron accumulates in the Alzheimer's disease (AD) brain and is directly associated with β-amyloid pathology. The proton transverse relaxation rate (R₂) has a strong linear relationship with iron concentrations in healthy brain tissue; however, an independent test of this relationship has not been extended to AD brain tissue. In this study in vitro single spin-echo (SE) measurements were made on tissue samples from four human AD brains using a 4.7T MRI research scanner. R₂ values were calculated for 14 cortical and subcortical gray matter (GM) and white matter (WM) regions. Atomic absorption spectroscopy was used to measure iron concentrations in the corresponding excised brain regions. Significant positive linear correlations were observed between R₂ values and iron concentrations in GM regions assessed across individual tissue samples and data averaged by brain region. With the use of a predictive model for R₂, a threshold iron concentration of 55 μg Fe/g wet tissue was determined above which R₂ appears to be dominated by the affects of iron in AD brain tissue. High-field MRI may therefore be a useful research tool for assessing brain iron changes associated with AD.