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MRS thermometry calibration at 3T: effects of protein, ionic concentration and magnetic field strength.

Babourina-Brooks, B*; Simpson, R; Arvanitis, T N*; Machin, G; Peet, A C*; Davies, N P* (2015) MRS thermometry calibration at 3T: effects of protein, ionic concentration and magnetic field strength. MNR in Biomed., 28 (7). pp. 792-800.

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MRS thermometry has been utilized to measure temperature changes in the brain, which may aid in the diagnosis of brain trauma and tumours. However, the temperature calibration of the technique has been shown to be sensitive to non-temperature based factors, which may provide unique information on the tissue microenvironment if the mechanisms can be further understood. The focus of this study was to investigate the effects of varied protein content on the calibration of the MRS thermometry at 3T, which has not been thoroughly explored in the literature. The effect of ionic concentration and magnetic field strength were also considered. Temperature reference materials were controlled by water circulation and freezing organic fixed-point compounds (diphenyl ether and ethylene carbonate) stable to within 0.2°C. The temperature was measured throughout the scan time with a fluoro-optic probe, uncertainty of 0.16°C. The probe was calibrated at the National Physical Laboratory (NPL) with traceability to the International Temperature Scale 1990 (ITS-90). MRS thermometry measures were based on single voxel spectroscopy chemical shift differences between water and N-acetylaspartate (NAA), (H20-NAA), using a Philips Achieva 3T scanner. Six different phantom solutions with varying protein or ionic concentration, simulating potential tissue differences, were investigated within a temperature range of 21-42°C. Results were compared to a similar study performed at 1.5T to observe the effect of field strengths. Temperature calibration curves were plotted to convert (H20-NAA) to apparent temperature. The apparent temperature changed by -0.2°C /% of bovine serum albumin (BSA) and a trend of 0.5°C/50mM ionic concentration was observed. Differences in the calibration coefficients for the 10% BSA solution were seen in this study at 3 T compared with a study at 1.5 T. MRS thermometry may be utilized to measure temperature and the tissue microenvironment, which could provide unique unexplored information for brain abnormalities and other pathologies.

Item Type: Article
Keywords: MRS thermometry, brain temperature, proton resonance frequency, chemical shift, MRI, calibration
Subjects: Engineering Measurements
Engineering Measurements > Thermal
Identification number/DOI: 10.1002/nbm.3303
Last Modified: 02 Feb 2018 13:13
URI: http://eprintspublications.npl.co.uk/id/eprint/6713

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