Metabolic changes in the normal ageing brain: Consistent findings from short and long echo time proton spectroscopy

Abstract

Objectives Sixty three healthy subjects were measured to assess dependence of brain metabolites on age using short- and long echo time spectroscopy in different brain regions. Material and methods Younger and elderly humans were measured with long echo time (TE = 135 ms) 3D-MR-spectroscopic imaging (MRSI) (10 subjects) and with ultra-short echo (TE = 11 ms) time 2D-MRSI (7 subjects). In addition, results from single voxel 1H-spectroscopy (TE = 20 ms) of two cohorts of 46 healthy subjects were retrospectively correlated with age. Results 3D-MR SI revealed reduced NAA/Cr in the older group in the frontal lobe (−22%; p < 0.01), parietal lobe (−28%; p < 0.01) and semiovale (−9%; p < 0.01) compared to the younger group. Cho/Cr was elevated in the semiovale (+35%; p < 0.01) and in the n. lentiformis (+42%; p < 0.01) in the older group. NAA/Cho was reduced in all regions measured, except the thalamus, in the older group compared to the younger group (from −21 to −49%; p < 0.01). 2D-MRSI revealed decreased total NAA (−3.1% per decade; p < 0.01) and NAA/Cr (−3.8% per decade; p < 0.01), increased total Cho (+3.6% per decade; p < 0.01) and Cho/Cr (+4.6% per decade; p < 0.01) and increased total myo-Inositol (mI, +4.7% per decade; p < 0.01) and mI/Cr (+5.4% per decade; p < 0.01) and decreased NAA/Cho (−8% per decade; p < 0.01) in semiovale WM. Results from single voxel spectroscopy revealed a significantly negative correlation of NAA/Cho in frontal (−13% per decade; p < 0.01) and in temporal lobe (−7.4% per decade; p < 0.01) as well as increased total Cr (10% per decade; p < 0.01) in frontal lobe. Other results from single voxel measurements were not significant, but trends were comparable to that from multivoxel spectroscopy. Conclusion Age-related changes measured with long echo time and short echo time 1H-MRS were comparable and cannot, therefore, be caused by different T2 relaxation times in young and old subjects, as suggested previously.