MRS thermometry calibration at 3 T: effects of protein, ionic concentration and magnetic field strength.
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 MRS thermometry at 3 T, which has not been thoroughly explored in the literature. The effects 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, with an 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), Δ(H20-NAA), using a Philips Achieva 3 T 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 with a similar study performed at 1.5 T to observe the effect of field strengths. Temperature calibration curves were plotted to convert Δ(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/50 mM 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.
School of Cancer Sciences, University of Birmingham, Birmingham, West Midlands, UK.|Birmingham Children's Hospital NHS Foundation Trust, Birmingham, West Midlands, UK.
Ben
B
Babourina-Brooks
Temperature Group, National Physical Laboratory, Teddington, Middlesex, UK.
Robert
R
Simpson
Birmingham Children's Hospital NHS Foundation Trust, Birmingham, West Midlands, UK.|Institute of Digital Healthcare, WMG, University of Warwick, Coventry, UK.
Theodoros N
TN
Arvanitis
Temperature Group, National Physical Laboratory, Teddington, Middlesex, UK.
Graham
G
Machin
School of Cancer Sciences, University of Birmingham, Birmingham, West Midlands, UK.|Birmingham Children's Hospital NHS Foundation Trust, Birmingham, West Midlands, UK.
Andrew C
AC
Peet
School of Cancer Sciences, University of Birmingham, Birmingham, West Midlands, UK.|Imaging and Medical Physics, University Hospitals Birmingham NHS Foundation Trust, Birmingham, West Midlands, UK.
Nigel P
NP
Davies
D000465:Algorithms; D000818:Animals; D001923:Brain Chemistry; D002138:Calibration; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007477:Ions; D060526:Magnetic Fields; D009682:Magnetic Resonance Spectroscopy / Q000379:methods* / Q000592:standards; D011506:Proteins / Q000737:chemistry*; D011829:Radiation Dosage; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013817:Thermography / Q000379:methods* / Q000592:standards
D007477:Ions; D011506:Proteins
MRI; MRS thermometry; brain temperature; calibration; chemical shift; proton resonance frequency