Reliability of MRSI brain temperature mapping at 1.5 and 3 T

Abstract

MRSI permits the non-invasive mapping of brain temperature in vivo, but information regarding its reliability is lacking. We obtained MRSI data from 31 healthy male volunteers [age range, 22–40 years; mean ± standard deviation (SD), 30.5 ± 5.0 years]. Eleven subjects (age range, 23–40 years; mean ± SD, 30.5 ± 5.2 years) were invited to receive four point-resolved spectroscopy MRSI scans on each of 3 days in both 1.5-T (TR/TE = 1000/144 ms) and 3-T (TR/TE = 1700/144 ms) clinical scanners; a further 20 subjects (age range, 22–40 years; mean ± SD, 30.5 ± 4.9 years) were scanned on a single occasion at 3 T. Data were fitted in the time domain to determine the water–N-acetylaspartate chemical shift difference, from which the temperature was estimated. Temperature data were analysed using a linear mixed effects model to determine variance components and systematic temperature changes during the scanning sessions. To characterise the effects of instrumental drift on apparent MRSI brain temperature, a temperature-controlled phantom was constructed and scanned on multiple occasions. Components of apparent in vivo temperature variability at 1.5 T/3 T caused by inter-subject (0.18/0.17 °C), inter-session (0.18/0.15 °C) and within-session (0.36/0.14 °C) effects, as well as voxel-to-voxel variation (0.59/0.54 °C), were determined. There was a brain cooling effect during in vivo MRSI of 0.10 °C [95% confidence interval (CI): –0.110, –0.094 °C; p < 0.001] and 0.051 °C (95% CI: –0.054, –0.048 °C; p < 0.001) per scan at 1.5 T and 3 T, respectively, whereas phantom measurements revealed minimal drift in apparent MRSI temperature relative to fibre-optic temperature measurements. The mean brain temperature at 3 T was weakly associated with aural (R = 0.55, p = 0.002) and oral (R = 0.62, p < 0.001) measurements of head temperature. In conclusion, the variability associated with MRSI brain temperature mapping was quantified. Repeatability was somewhat higher at 3 T than at 1.5 T, although subtle spatial and temporal variations in apparent temperature were demonstrated at both field strengths. Such data should assist in the efficient design of future clinical studies. © 2013 The Authors. NMR in Biomedicine published by John Wiley & Sons, Ltd.

Reproducibility of whole‐brain temperature mapping and metabolite quantification using proton magnetic resonance spectroscopy

“…It is not clear whether these temperature variations are due to physiological (e.g., molecular environment) differences among these brain regions, or other effects related to magnetic susceptibility‐induced frequency shifts (a limitation of 1 H‐MRS for temperature mapping) 10 . However, larger within‐subject variability (0.28°C) was observed for repeated temperature measurements in similar brain regions (i.e., parietal, precuneus) in the present study, compared with Thrippleton et al (0.14°C) 41 . Differences in the brain temperature reproducibility between the two studies could be attributed to differences in study design, acquisition factors and brain parcellation methods.…”

“…Differences in the brain temperature reproducibility between the two studies could be attributed to differences in study design, acquisition factors and brain parcellation methods. For example, in Thrippleton et al, 41 four consecutive scans within the same day were acquired to test the reproducibility of brain temperature measurements within a 10 mm brain slice, while in the present study three repeated scans were acquired with a mean interval of 1 week between the scan sessions. Larger variability for repeated measurements might be expected due to instrument variability, subject alignment and/or biological variability.…”

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

“…The temperature calibration curves for the ionic solutions showed small differences between this study at 3 T and that of Vescovo et al at 1.5 T, although this does not rule out significant effects at higher field strengths or in more complex microenvironments. An MRSI based MR thermometry study investigating field strength effects, 1.5 T versus 3 T, also showed that no magnetic field effects were observed on the temperature calibration curve using an ionic concentration solution of 56 mM . In contrast, the calibration curves with varying protein concentration presented here did show different mean results compared with those of Vescovo et al at 1.5 T (see Fig.…”

Optimization of Single Voxel MR Spectroscopy Sequence Parameters and Data Analysis Methods for Thermometry in Deep Hyperthermia Treatments

“…Small frequency drifts, slow organ motion components, or magnetic field inhomogeneities are no longer a source of uncertainties in the MR thermometry because the peak difference is measured in the same voxel at the same time. Feasibility studies of using SVS for temperature information in animal 27,28,30 or in human brain 31,32 are reported. The difference in fat and water peak yields information about the temperature inside the investigated voxel: measured power spectrum (green) and fitted power spectrum (blue).…”