High Field 3 T Imaging of Alzheimer Disease

G. LUCCICHENTI, P. PEran, A. Cherubini, E. Giügni, T. Scarabinq, G. E. Hagberg, U. Sabatini

Alzheimer disease (AD) is a neurodegenerative disease with neuronal loss, leading to dementia and neurological impairment [1]. Metabolic alterations are the basis of histological changes, occurring several years before cognitive impairment. In mild cognitive impairment (MCI) functional disability is absent; conversely, in Alzheimer dementia, disease progression is faster and disability occurs.

Accurate assessment of AD is crucial for early treatment, proper differential diagnosis, prediction of disease progression and quantification of response to therapy. It should be emphasised that these four aspects are critical for development of new therapies. Currently, AD is assessed by defining dementia and neurological signs. However, these signs are non-specific and might be caused by several factors. Histology is invasive, and cannot be proposed routinely. Neuroimaging potentially represents a valuable tool for early diagnosis and follow-up [2]. Diagnostic imaging techniques for dementia are magnetic resonance (MR), and nuclear medicine techniques, such as single photon emission tomography (SPECT) and positron emission tomography (PET). These latter techniques allow brain metabolism to be assessed, which has been shown to be correlated with neuronal loss. Nuclear imaging techniques are expensive, invasive, with poor spatial resolution and will not be mentioned in this paper.

Interesting results have been obtained by conventional and advanced neuroimaging techniques for differential diagnosis and estimation of disease progression, although these results refer to groups of patients and cannot be transferred for assessing single patients [3]. Hence, it should be pointed out that two different approaches for discussing results of AD neuroimaging are possible. The first one is to discuss results obtained from groups of patients in experimental settings. The second approach is to discuss the clinical applications of these techniques.

Magnetic resonance represents the most practical tool for assessing dementia. MR allows quantitative estimation of brain features in a non-invasive way through conventional and advanced techniques, such as brain morphometry, volume estimation, diffusion weighted imaging (DWI), diffusion tensor imaging (DTI), magne tization transfer, relaxometry, perfusion weighted imaging (PWI), MR spectroscopy, and functional MR. These advanced techniques are affected by the amount of information which is provided by the scanner (e.g. signal to noise ratio, SNR) and require data post-processing. In MR, signal depends on the amount of protons recruited by the magnetic field. The larger the amount of recruited protons, the greater the increase in signal with higher SNR (keeping other parameters constant). The development of high-field scanners has seen increased interest in the medical community, and they have been proposed for routine clinical imaging.

The aim of this paper is to describe neuroimaging in MCI and AD and the potential role of high-field 3 T MR scanners in research and clinical applications.

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