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AJNR - American Journal of Neuroradiology

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American Journal of Neuroradiology 28:965-970, May 2007
© 2007 American Society of Neuroradiology

BRAIN

Magnetization Transfer Ratio in Alzheimer Disease: Comparison with Volumetric Measurements

B.H. Ridha^a,d, M.R. Symms^b, D.J. Tozer^c, K.C. Stockton^a, C. Frost^a,e, M.M. Siddique^a, E.B. Lewis^a, D.G. MacManus^c, P.A. Boulby^b, G.J. Barker^f, M.N. Rossor^a,d, N.C. Fox^a and P.S. Tofts^c

^a Dementia Research Centre, Institute of Neurology, University College London, London, UK
^b Department of Clinical and Experimental Epilepsy, Institute of Neurology, University College London, London, UK
^c NMR Research Unit, Institute of Neurology, University College London, London, UK
^d Division of Neuroscience and Mental Health, Imperial College London, London, UK
^e Medical Statistics Unit, London School of Hygiene and Tropical Medicine, London, UK
^f King's College London, Institute of Psychiatry, Department of Clinical Neuroscience, Centre for Neuroimaging Sciences, London, UK

Please address correspondence to Dr Basil H Ridha, Dementia Research Centre, 8-11 Queen Square, Institute of Neurology, London, WC1N 3BG, UK; e-mail: bridha{at}dementia.ion.ucl.ac.uk

BACKGROUND AND PURPOSE: Alzheimer disease (AD) is accompanied by macroscopic atrophy on volumetric MR imaging. A few studies have also demonstrated reduction in magnetization transfer ratio (MTR), suggesting microstructural changes in remaining brain tissue. This study assessed the value of measuring MTR in addition to volumetric MR in differentiating patients with AD from control subjects.

MATERIALS AND METHODS: Volumetric T1-weighted images and 3D MTR maps were obtained from 18 patients with AD and 18 age-matched control subjects. Whole-brain (WB) and total hippocampal (Hc) volumes were measured using semiautomated techniques and adjusted for total intracranial volume. Mean MTR was obtained for WB and in the Hc region. Histogram analysis was performed for WB MTR. Among patients, associations between volumetric and MTR parameters and the Mini-Mental State Examination (MMSE) were explored.

RESULTS: Patients with AD had significantly reduced WB volume (P < .0001) and mean WB MTR (P = .002) and Hc volume (P < .0001) and Hc mean MTR (P < .0001) compared with control subjects. Histogram analysis of WB MTR revealed significant reduction in the 25th percentile point in patients with AD (P = .03). Both WB volume and mean MTR were independently associated with case-control status after adjusting for the other using linear regression models. However, measuring Hc mean MTR added no statistically significant discriminatory value over and above Hc volume measurement alone. Of all MR imaging parameters, only WB volume was significantly correlated with MMSE (r = 0.47, P = .048).

CONCLUSIONS: This study demonstrates the independent reduction of WB volume and mean MTR in AD. This suggests that the 2 parameters reflect complementary aspects of the AD pathologic lesion at macrostructural and microstructural levels.