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Quantitative Magnetization Transfer Imaging in Alzheimer Disease¹

¹ From the Dementia Research Centre (B.H.R., K.C.S., E.B.L., M.M.S., M.N.R., N.C.F.), NMR Research Unit (D.J.T., D.G.M., P.S.T.), and Department of Clinical and Experimental Epilepsy (M.R.S.), Institute of Neurology, University College London, 8-11 Queen Square, London, WC1N 3BG, England. Received June 29, 2006; revision requested August 31; revision received October 25; accepted November 22; final version accepted February 7, 2007. N.C.F. and M.N.R. supported by Alzheimer's Research Trust and Medical Research Council. D.J.T. supported by Multiple Sclerosis Society of Great Britain and Northern Ireland. Address correspondence to B.H.R. (e-mail: bridha{at}dementia.ion.ucl.ac.uk).

Purpose: To prospectively measure magnetization transfer (MT) parameters, along with established atrophy parameters, in patients with Alzheimer disease (AD) and in age- and sex-matched control subjects.

Materials and Methods: Participants provided informed consent, and additional assent was obtained from next of kin of all patients with AD. The study was approved by the local ethics committee. Fourteen patients with AD (seven men; mean age, 67.2 years ± 6.5 [standard deviation]) and 14 control subjects (nine men; mean age, 65.5 years ± 9.4) underwent volumetric T1-weighted magnetic resonance and MT imaging. Whole-brain and total hippocampal volumes were adjusted for total intracranial volume. MT images were processed to derive four fundamental parameters in the hippocampal region by using the two-pool model of the MT phenomenon. Pearson correlation coefficients were used to assess the association between volumetric and MT parameters and Mini-Mental State Examination (MMSE) results. Logistic regression models were used to investigate whether combinations of parameters associated with MMSE could help provide better group discrimination.

Results: Patients with AD had significantly reduced whole-brain (P = .001) and total hippocampal (P < .001) volumes compared with those of control subjects. Two MT parameters were significantly reduced in the hippocampal region of patients: 1/(R_AT2^A)—that is, ratio of relaxation times of free proton pool, where R_A equals 1/T1^A and is the inverse of the longitudinal relaxation time of the free proton pool (P = .01)—and , which equals f_b/[R_A(1 – f_b)], where f_b is the restricted proton fraction (P < .001). Among patients with AD, whole-brain volume and hippocampal were correlated with MMSE results. When both parameters were included in a logistic regression model, only hippocampal was significantly associated with case-control status (P = .03).

Conclusion: Certain MT parameters may serve as useful biomarkers of AD.

© RSNA, 2007

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