The effect of iron in MRI and transverse relaxation of amyloid‐beta plaques in Alzheimer's disease

Dysregulation of neural iron is known to occur during the progression of Alzheimer's disease. The visualization of amyloid‐beta (Aβ) plaques with MRI has largely been credited to rapid proton relaxation in the vicinity of plaques as a result of focal iron deposition. The goal of this work was to determine the relationship between local relaxation and related focal iron content associated with Aβ plaques. Alzheimer's disease (n = 5) and control tissue (n = 3) sample slices from the entorhinal cortex were treated overnight with the iron chelator deferoxamine or saline, and microscopic gradient‐echo MRI datasets were taken. Subsequent to imaging, the same slices were stained for Aβ and iron, and then compared with regard to parametric R₂* relaxation maps and gradient‐echo‐weighted MR images. Aβ plaques in both chelated and unchelated tissue generated MR hypo‐intensities and showed relaxation rates significantly greater than the surrounding tissue. The transverse relaxation rate associated with amyloid plaques was determined not to be solely a result of iron load, as much of the relaxation associated with Aβ plaques remained following iron chelation. The data indicate a dual relaxation mechanism associated with Aβ plaques, such that iron and plaque composition synergistically produce transverse relaxation.Copyright © 2014 John Wiley & Sons, Ltd.