Use of T1-weighted/T2-weighted magnetic resonance ratio to elucidate changes due to amyloid β accumulation in cognitively normal subjects.

The ratio of signal intensity in T1-weighted (T1w) and T2-weighted (T2w) magnetic resonance imaging (MRI) was recently proposed to enhance the sensitivity of detecting changes in disease-related signal intensity. The objective of this study was to test the effectiveness of T1w/T2w image ratios as an easily accessible biomarker for amyloid beta (Aβ) accumulation. We performed the T1w/T2w analysis in cognitively normal elderly individuals. We applied [C] Pittsburgh Compound B (PiB)-PET to the same individuals, and Aβ deposition was quantified by its binding potential (PiB-BP). The subjects were divided into low and high PiB-BP groups, and group differences in regional T1w/T2w values were evaluated. In the regions where we found a significant group difference, we conducted a correlation analysis between regional T1w/T2w values and PiB-BP. Subjects with high global cortical PiB-BP showed a significantly higher regional T1w/T2w ratio in the frontal cortex and anterior cingulate cortex We found a significant positive relationship between the regional T1w/T2w ratio and Aβ accumulation. Moreover, with a T1w/T2w ratio of 0.55 in the medial frontal regions, we correctly discriminated subjects with high PiB-BP from the entire subject population with a sensitivity of 84.6% and specificity of 80.0%. Our results indicate that early Aβ-induced pathological changes can be detected using the T1w/T2w ratio on MRI. We believe that the T1w/T2w ratio is a prospective stable biological marker of early Aβ accumulation in cognitively normal individuals. The availability of such an accessible marker would improve the efficiency of clinical trials focusing on the initial disease stages by reducing the number of subjects who require screening by Aβ-PET scan or lumbar puncture.