MRI measurement of hippocampal volumes in early stage Alzheimer's disease

Abstract

Background: Alzheimer’s disease (AD) is the most common cause of memory loss in the world today. Non-invasive neuroimaging techniques have been explored to help diagnose and perhaps predict AD before the onset of symptoms. Early AD is associated with pathologic changes in the hippocampus (HC), a structure within the cerebral cortex important in memory processes. MRI scans have proven useful in measuring the atrophy associated with these changes. Objectives: To establish reliable and accurate methods of measuring hippocampal volume on MRI and to assess hippocampal volume differences between early stage AD and nondemented controls. Methods: We assessed 63 individuals, all older than 65 years of age, using the Clinical Dementia Rating (CDR) scale and separated them into two groups: 1) early Alzheimer’s patients with a CDR score of 0.5 or 1.0 (n=32) and, 2) cognitively normal individuals with a CDR score of 0 (n= 31). Each individual underwent an MP-RAGE MRI scan on which tracing and volume analysis was performed using the software suite Analyze 6.0. A standard set of rules and hippocampal volume tracing procedures were developed and used by two trained raters. An initial reliability trial was followed by randomly inserting duplicates among the untraced images to measure continued reliability. Results: The total hippocampal volume (THCV) of the non-demented group and demented group respectively was 9,119mm3 and 6914mm3. Analysis showed a strong statistical difference between the two groups with THCV (p<0.001). Inter-rater reliability ICC was 0.974 (coefficient of variation 2.4%), intra-rater reliability ICC for rater 1 was 0.980 (coefficient of variation 4.4%) and 0.987 (coefficient of variation 1.8%) for rater 2. Conclusion: The hippocampal volume tracing procedures provide a reliable measurement for both the individual raters and measurements between two individuals. The increased atrophy of the HC was found to correlate very well with early stage AD which is consistent with current literature providing a measure of validity to our measures.