Elena Vescovo1, Andrew Levick2,
Sha Zhao1, Graham Machin2, Charmaine Childs3,
Timothy Rainey3, Steve Williams1
1Imaging Science and Biomedical
Engineering, The University of Manchester, Manchester, Greater Manchester,
United Kingdom; 2Temperature Group, National Physical Laboratory,
Teddington, Middlesex, United Kingdom; 3Brain Injury Research
Group, The University of Manchester, Manchester, Greater Manchester, United
Kingdom
Estimation
of temperature by MRS from the chemical shift of water relative to
N-acetylaspartate (NAA) relies on a calibration curve. To date these have
never been related back to primary standards. We describe extremely stable
temperature control of an MRS phantom at 1.5T using a circulating water bath
and organic fixed-point materials, with measurements related back to the
International Temperature Scale 1990 (ITS-90) at the UK National Physical
Laboratory. Frequency differences (water-NAA) were highly reproducible
(SD<10-4 ppm) at fixed temperature and R2 for the fit was 0.9996. Ionic
strength affected the intercept but not slope of the temperature calibration.