title: Quantitative T1and T2MRI signal characteristics in the human brain: different patterns of MR contrasts in normal ageing.
abstract: OBJECTIVE
  The objective of this study was to examine age-dependent changes in both T1-weighted and T2-weighted image contrasts and spin-echo T2relaxation 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 T1-weighted, T2weighted and quantitative spin-echo T2imaging. Contrast between image intensities and T2values was calculated for various regions, including between individual hippocampal subfields.
  
  
  RESULTS
  The T1contrast-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, T2CNR and GWR declined in both brain regions. T2relaxation 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 T1and T2MR 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 T2through reduced diffusion effects in later life.
authors.affiliation: School of Experimental Psychology, University of Bristol, 12a Priory Road, Bristol, BS8 1TU, UK. mk13005@bristol.ac.uk.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Knight
authors.affiliation: School of Experimental Psychology, University of Bristol, 12a Priory Road, Bristol, BS8 1TU, UK.
authors.forename: Bryony
authors.initials: B
authors.lastname: McCann
authors.affiliation: Institute of Clinical Neuroscience, University of Bristol, Level 1 Learning and Research Building, Bristol, BS10 5NB, UK.
authors.forename: Demitra
authors.initials: D
authors.lastname: Tsivos
authors.affiliation: Institute of Clinical Neuroscience, University of Bristol, Level 1 Learning and Research Building, Bristol, BS10 5NB, UK.|North Bristol NHS Trust, Southmead Road, Westbury-on-Trym, Bristol, BS10 5NB, UK.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Couthard
authors.affiliation: School of Experimental Psychology, University of Bristol, 12a Priory Road, Bristol, BS8 1TU, UK.|Clinical Research and Imaging Centre, University of Bristol, 60 St Michael's Hill, Bristol, BS2 8DX, UK.
authors.forename: Risto A
authors.initials: RA
authors.lastname: Kauppinen
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging; D001921:Brain / Q000000981:diagnostic imaging*; D015331:Cohort Studies; D003287:Contrast Media; D005260:Female; D006624:Hippocampus / Q000000981:diagnostic imaging; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D059629:Signal-To-Noise Ratio; D066127:White Matter / Q000000981:diagnostic imaging
chemical_list: D003287:Contrast Media
keywords: Brain; Contrast-to-noise ratio; Dephasing; Gray matter; T2 relaxation; White matter