Quantitative T1 and T2 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 T1-weighted and T2-weighted image contrasts and spin-echo T2 relaxation time in the human brain during healthy ageing.

Methods: 37 participants between the ages of 49 and 87 were scanned with a 3 T system, using T1-weighted, T2 weighted and quantitative spin-echo T2 imaging. Contrast between image intensities and T2 values was calculated for various regions, including between individual hippocampal subfields.

Results: The T1 contrast-to-noise (CNR) and gray:white signal intensity ratio (GWR) did not change in hippocampus, but it declined in cingulate cortex with age. In contrast, T2 CNR and GWR declined in both brain regions. T2 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 T1 and T2 MR characteristics influence appearance of brain images at later life and should be considered in image analyses of aged subjects. It is speculated that alterations at the cell biology level, causing alterations to ordered field perturbers, reduce dephasing and as such prolong spin-echo T2 through reduced diffusion effects in later life.