Alzheimer Brain Atrophy Rate Measured by Serial MRIs

Abstract & Commentary

Sources: Paling SM, et al. The application of serial MRI analysis techniques to the study of cerebral atrophy in late-onset dementia. Med Image Anal. 2004;8(1):69-79; Chan D, et al. Change in rates of cerebral atrophy over time in early-onset Alzheimer’s disease: Longitudinal MRI study. Lancet. 2003;362:1121-1122.

Techniques for accurately measuring the rates of brain atrophy from serial MRI images have improved significantly in recent years. A few of these techniques have been implemented in a partially or fully automated fashion, which is arguably a necessary precondition to their being applied clinically. Two recent studies in Great Britain examined the applicability of these techniques to the study of rates of cerebral atrophy in Alzheimer’s disease (AD).

Chan and associates used the Brain Boundary Shift Integral (BBSI) technique to quantify MRI atrophy rates in early onset Alzheimer patients in presymptomatic to early stages of dementia. They obtained T1-weighted 1.5 Tesla MRIs an average of 5 times over a median interval of 33 months in 12 subjects with genetically linked early onset forms of AD. Using BBSI analysis, they found the rate of total brain atrophy averaged between 2.2% and 3.2% per year. The rate of atrophy increased by approximately 0.3% per year as the disease progressed, correlating with decreasing Minimental State scores. Chan et al cautioned that the rate of atrophy might not be the same in the AD population at large, since their study focused exclusively on patients with an early onset, genetic form of the disease.

Paling and colleagues examined the reproducibility and validity of quantitative analysis techniques for measuring the rate of cerebral atrophy in late-onset AD. The annual rate of cerebral atrophy was found to be significantly greater in AD patients than normal age-matched controls and comparable to that observed in the Chan study. They conclude that the available MRI quantification techniques are sufficiently robust and reproducible to have applicability to future studies of dementia and other neurodegenerative conditions.

Commentary

Quantitative MRI analysis can provide a wealth of information beyond that obtained by visual inspection of images alone. Cross-sectional quantitative MRI analysis techniques have been applied to a number of neurologic disorders, such as measurement of infarct size in stroke and plaque burden in MS. Cross-sectional techniques have also been applied to the identification of patterns of regional cerebral atrophy that distinguish, for example, AD from semantic dementia.1

Atrophy rates determined by comparison of serial MRIs represent another dimension in quantitative image analysis. The rate of whole brain atrophy in normal elderly volunteers has been estimated to be about 0.5% per year. In light of the variability inherent in the MRI measurements, a minimum interval of a year or more between scans may be required to measure atrophy rates accurately. While routine dementia diagnosis does not currently require a second MRI scan, serial MRI analysis could prove useful as a diagnostic adjunct in more difficult to diagnose cases.

The findings of Chen et al suggest that serial MRI measurements may be useful in identifying patients making the transition from mild cognitive impairment to frank dementia. Serial atrophy measurements may also serve as an alternative outcome measure for AD treatment studies. These and other applications, coupled with the improvements being made in the techniques for automating MRI analyses, make it increasingly likely that quantitative MRI analysis will someday contribute to clinical characterization of a variety of neurologic disorders associated with brain atrophy. — Norman R. Relkin

Dr. Relkin, Associate Professor of Clinical Neurology and Neuroscience, New York Presbyterian Hospital- Cornell Campus is Assistant Editor of Neurology Alert.

Reference

1. Boxer AL, et al. Arch Neurol. 2003;60:949-956.