Magnetization transfer imaging in normal aging, mild cognitive impairment, and Alzheimer's disease
Van Der Flier WM, J. Van Den Heuvel DM, Weverling-Rijnsburger AWE, Bollen ELEM, Westendorp GJ, Van Buchem MA, Middelkoop HAM.;
Commented by , 19 Aug 2002
Background
Effort has been made to find early paraclinical measurements to distinguish patients with Alzheimer’s Disease (AD) from normally-aged persons. Mild Cognitive Impairment (MCI) is considered to be a transitional stage between old age and AD and therefore interest has focused on diagnostic markers in this context.
Aim
To assess whether structural changes are present on magnetization transfer imaging (MTI) in AD and MCI patients. Furthermore the study aimed to show whether these abnormalities are global in character or restricted to the temporal lobe.
Method
25 consecutive probable AD and 13 MCI patients were selected. For all patients a standard dementia screening and a routine blood examination was completed. MRI was performed on a 1,5 tesla scanner, conventional T1 spin echo, proton density and T2-weighted dual fast spin-echo and fast FLAIR images were obtained.
Furthermore MTI were obtained. The MTI postprocessing included estimation of the cerebral volume, tracing of the frontal and temporal lobe and calculation of magnetization transfer ratios (MTR) providing quantitative estimates of structural brain damage.
Results
In AD patients compared to controls, structural changes and atrophy were found using analysis of variance in the whole brain and in the frontal and temporal lobes. In MCI patients, results were comparable although structural changes occurred in the frontal lobes without evidence of atrophy. Both MTI measurements and atrophy correlated with MMSE score.
Discussion
The authors state that the MTI analysis is regarded as a sensitive measure of brain damage in AD, which is reflected in the strong correlation between MTR and MMSE. Structural changes were detected in a preclinical disease stage, and it was possible to distinguish quantitatively between MCI and AD.
It was demonstrated that structural brain changes in MCI and AD is a widespread phenomenon that is not restricted to the temporal lobes. Furthermore it was concluded that the structural changes precede atrophy since it was observed outside the temporal lobes without evidence of atrophy in MCI patients.
The authors suggest that volumetric MTI may serve as a surrogate marker in prospective clinical trials although further studies are needed to determine the diagnostic and predictive value of MTI in AD and MCI.