Off-resonance saturation as an MRI method to quantify mineral- iron in the post-mortem brain

Purpose
To employ an off-resonance saturation method to measure the mineral-iron pool in the postmortem brain, which is an endogenous contrast agent that can give information on cellular iron status.

Methods
An off-resonance saturation acquisition protocol was implemented on a 7 Tesla preclinical scanner, and the contrast maps were fitted to an established analytical model. The method was validated by correlation and Bland-Altman analysis on a ferritin-containing phantom. Mineral-iron maps were obtained from postmortem tissue of patients with neurological diseases characterized by brain iron accumulation, that is, Alzheimer disease, Huntington disease, and aceruloplasminemia, and validated with histology. Transverse relaxation rate and magnetic susceptibility values were used for comparison.

Results
In postmortem tissue, the mineral-iron contrast colocalizes with histological iron staining in all the cases. Iron concentrations obtained via the off-resonance saturation method are in agreement with literature.

Conclusions
Off-resonance saturation is an effective way to detect iron in gray matter structures and partially mitigate for the presence of myelin. If a reference region with little iron is available in the tissue, the method can produce quantitative iron maps. This method is applicable in the study of diseases characterized by brain iron accumulation and can complement existing iron-sensitive parametric methods.