Longitudinal Magnetization Transfer Imaging in Mild to Severe Alzheimer Disease

Abstract

BACKGROUND AND PURPOSE: MTI has been proposed as a sensitive technique for studying microstructural brain tissue changes in patients with AD, but the course of these changes over time is largely unknown. We therefore used a placebo-controlled study of memantine to follow the evolution of tissue damage in AD by means of MTR measurements and investigated how MTR changes were related to brain atrophy and cognition.

Regional Analysis of the Magnetization Transfer Ratio of the Brain in Mild Alzheimer Disease and Amnestic Mild Cognitive Impairment

“…The decreased MT ratio revealed by voxelwise analysis in the left hippocampus and amygdala and in the left posterior mesial temporal cortex in patients with mild AD as compared with healthy control subjects confirms previous data obtained by means of manually drawn regions of interest or VOIs in the hippocampus 9,12,14,18 and extends to the amygdala the capability of MT ratio to detect microstructural GM changes related to AD pathology.…”

“…In all previous MT imaging studies in AD and MCI, no side evaluation of lobar or regional MT ratio was reported, and data related to the 2 sides were typically averaged. [9][10][11][12]14,18 In our study, the voxelwise analysis did not show any region exhibiting significantly different MT ratio in the group of patients with amnestic MCI with respect to healthy control subjects, and automatic VOI analysis of the hippocampus and amygdala in the patients with amnestic MCI showed values for the MT ratio that were between the values computed for healthy control subjects and patients with AD. This result is in line with the results obtained with manual segmentation of the anterior hippocampus in a prior study, 14 whereas it represents a partial discrepancy with prior investigations in which the MT ratio of the whole brain or temporal lobe was found to be significantly decreased in patients with MCI as compared with healthy control subjects.…”

“…[14][15][16] In its simplest version, MT is obtained with acquisition of a pair of images without and with a specific radiofrequency offresonance prepulse followed by image subtraction and computation of the MT ratio. MT ratio is decreased in the temporal lobe and hippocampus of patients with AD independent from atrophy [9][10][11][12]14,17,18 ; is variably correlated with clinical severity, neuropsychological measurements, and disease duration [9][10][11][12] ; and appears capable to track progression of regional GM microstructural changes in AD. 18 MT ratio was also reported to be decreased in the whole brain, whole temporal lobe, or temporal lobe GM and WM in patients with amnestic MCI as compared with agematched healthy control subjects.…”

“…MT ratio is decreased in the temporal lobe and hippocampus of patients with AD independent from atrophy [9][10][11][12]14,17,18 ; is variably correlated with clinical severity, neuropsychological measurements, and disease duration [9][10][11][12] ; and appears capable to track progression of regional GM microstructural changes in AD. 18 MT ratio was also reported to be decreased in the whole brain, whole temporal lobe, or temporal lobe GM and WM in patients with amnestic MCI as compared with agematched healthy control subjects. 10,11,19,20 However, in 2 studies that compared the MT ratio with several parameters calculated with quantitative MT approach in the hippocampus, enthorinal cortex, insula, and temporal neocortex, the former delivered the worst performance in differentiating AD, MCI, or healthy control subjects.…”

Classification of Mild Cognitive Impairment and Alzheimer Disease Using Model-Based MR and Magnetization Transfer Imaging

“…Several studies that incorporated magnetization transfer ratio revealed a widespread distribution of tissue changes in AD and MCI in the temporal lobe before gross structural changes became apparent 9,10 and a progressive MTR reduction with time. 11 While MTR is basically a phenomenologic measure that has been shown to depend both on the amount of magnetization transfer and the direct saturation of free water by the radio-frequency pulse, 12 model-based magnetization transfer imaging allows a more comprehensive analysis by investigating the exchange of magnetization between molecules of water and molecules of more solid structural components more in detail.…”