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High-precision calibration of MRS thermometry using validated temperature standards: effects of ionic strength and protein content on the calibration.

Vescovo, E*; Levick, A P; Childs, C*; Machin, G; Zhao, S*; Williams, S R* (2013) High-precision calibration of MRS thermometry using validated temperature standards: effects of ionic strength and protein content on the calibration. NMR Biomed., 26 (2). pp. 213-223.

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Abstract

New calibrations of magnetic resonance spectroscopic (MRS) thermometry are reported that were made with novel temperature-reference phantoms. The phantoms are comprised of two concentric glass spheres: the inner one contains the phantom material to be measured by MRS, while the outer one contains a substance with a known temperature stable to within 0.2 °C. The substances were freezing organic fixed-point compounds (diphenyl ether and ethylene carbonate, freezing at 26.3 °C and 35.8 °C respectively) or temperature-controlled circulating-water. Phantom temperature was continuously monitored with a fluoroptic probe calibrated at the National Physical Laboratory with traceability to the International Temperature Scale 1990 (ITS-90).

The temperature is obtained by measuring the chemical shift of water relative to N-Acetylaspartate (NAA) in a single-voxel using a 1.5 T Philips Intera scanner. Measurements were made for several phantom materials to assess the affect of tissue composition on temperature. The phantom mixtures contained 25 mM NAA buffered to pH 6.5 or 7.5 and several ionic salts or bovine serum albumin (BSA). Spectra were acquired from 25 to 45 °C. The correlation between frequency differences and phantom temperature was very linear with small residuals. However there is variation in linear fit parameters with ionic composition and BSA concentration.

Item Type: Article
Subjects: Engineering Measurements
Engineering Measurements > Thermal
Identification number/DOI: 10.1002/nbm.2840
Last Modified: 02 Feb 2018 13:14
URI: http://eprintspublications.npl.co.uk/id/eprint/5726

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