Quantitative T 1 and T 2 MRI signal characteristics in the human brain: different patterns of MR contrasts in normal ageing

Objective The objective of this study was to examine age-dependent changes in both T 1 -weighted and T 2 -weighted image contrasts and spin-echo T 2 relaxation time in the human brain during healthy ageing. Methods A total of 37 participants between the ages of 49 and 87 years old were scanned with a 3 Tesla system, using T 1 -weighted, T 2 weighted and quantitative spin-echo T 2 imaging. Contrast between image intensities and T 2 values was calculated for various regions, including between individual hippocampal subfields. Results The T 1 contrast-to-noise (CNR) and gray:white signal intensity ratio (GWR) did not change in the hippocampus, but it declined in the cingulate cortex with age. In contrast, T 2 CNR and GWR declined in both brain regions. T 2 relaxation time was almost constant in gray matter and most (but not all) hippocampal subfields, but increased substantially in white matter, pointing to an age effect on water relaxation in white matter. Conclusions Changes in T 1 and T 2 MR characteristics influence the appearance of brain images in later life and should be considered in image analyses of aged subjects. It is speculated that alterations at the cell biology level, with concomitant alterations to the local magnetic environment, reduce dephasing and subsequently prolong spin-echo T 2 through reduced diffusion effects in later life.