Age-related changes in conventional and magnetization transfer MR imaging in elderly people: comparison with neurocognitive performance

Abstract

Objective: This study was designed to compare three different measures of the elderly human brain; the magnetization transfer ratio (MTR) histogram, the percentage of brain parenchymal volume, and the volume of T2 hyperintense areas in terms of correlations with the study subjects neurocognitive performance.

Materials and methods: Thirty-five healthy community-dwelling elderly volunteers aged 60-82 years underwent dual fast spin-echo (FSE) imaging and magnetization transfer imaging. A semi-automated technique was used to generate the MTR histogram, the brain parenchymal volume, and the T2 lesion volume. The subjects' neurocognitive performance was assessed by using the Korean-Mini Mental State Examination (K-MMSE) and additional tests. The peak height of the MTR (PHMTR), the percentage of brain parenchymal volume (PBV), and the normalized T2 lesion volume (T2LV) were compared between the normal group (Z score on the K-MMSE>/=-2, n=23) and the mild cognitive impairment group (Z score on the K-MMSE < -2, n=12), and these parameters were correlated with age and various neurocognitive performance scores.

Results: The PHMTR was significantly lower in the cognitively impaired subjects than the PHMTR in the normal subjects (p = 0.005). The PBV scores were lower in the cognitively impaired subjects than in the normal subjects (p = 0.02). The T2LV scores were significantly higher in the cognitively impaired subjects (p = 0.01). An inverse correlation was found between the PHMTR and T2LV (r = -0.747, p < 0.001), and also between the PBV and T2LV (r = -0.823, p < 0.001). A positive correlation was observed between the PHMTR and the PBV (r = 0.846, p < 0.001). Scores on the various neurocognitive tests were positively correlated with the PHMTR (6 of 7 items) and the PBV (5 of 7 items), and they were negatively correlated with the T2LV (5 of 7 items).

Conclusion: Our findings of a correlation among the PBV, the T2LV, and the PHMTR suggest that MTR histograms and the PBV and T2LV can be used as a reliable method and valid statistical tool, respectively, for quantifying the total lesion burden in an aging brain.

Fig. 1

Segmented volume image of the intracranium (A), cerebrospinal fluid (B), and brain parenchyma (C) from proton density-weighted and T2-weighted images.

Fig. 2

Magnetization transfer ratio (MTR) histograms from normal subjects (dotted line) and cognitive impaired subjects (solid line). Normalized peak height of the MTR Histogram is lower for the cognitive impairment group compared with that of the normal groups.