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

Abstract

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.

Multiparametric quantification of thermal heterogeneity within aqueous materials by water 1H NMR spectroscopy: Paradigms and algorithms

“…The use of the water 1 H NMR signal for temperature measurement in a hydrogel-loaded cell perfusion system has been demonstrated more than 20 years ago [27], and was further developed for in vivo applications based on selected cross sections of biological tissue [28–30]. A large number of studies were aimed at clinical applications [31–33]. Conventionally, the chemical shift of the highest point ("the" maximum) of the water 1 H NMR resonance is converted to a temperature value based on a calibration curve, and this value is interpreted to indicate "the" temperature of the measured volume or volume element (voxel) [27, 30].…”

Quantitative magnetic resonance imaging phantoms: A review and the need for a system phantom

“…Biomarkers (1)(2)(3) are objectively measured parameters that indicate the biological state, biological/pathobiological processes, or pharmacologic responses to treatment. Examples of MR biomarkers include tumor volume (4-6), brain volume (7)(8)(9)(10), functional network connectivity (11)(12)(13), isotropic (14,15) or anisotropic (16,17) water diffusion constants (18), local metabolite concentrations (10,15,19,20), blood flow fields (21)(22)(23), fat fraction (24)(25)(26)(27), lung function (28,29), temperature (30)(31)(32), and tissue elasticity (33,34).…”

Magnetic Resonance Spectroscopy Thermometry at 3 Tesla: Importance of Calibration Measurements

“…The scientific rationale for calibration measurements before performing MR thermometry in vivo is explained by the variance due to different hardware and software environments applied in different research groups, scientific institutions, and clinical routine. Implementing our calibration constants into the regression parameters of other studies (Corbett et al, 1995;Samson et al, 2006;Covaciu et al, 2010;Cady et al, 2011;Vescovo et al, 2013;Babourina-Brooks et al, 2015) resulted in varying temperatures further underlining the importance of calibration measurements, particularly when considering MR thermometry for patients with acute brain injury.…”

“…Today, there are several temperature-dependent magnetic resonance imaging (MRI) parameters that can be exploited for thermometry, such as magnetic resonance (MR) spectroscopy to determine the water-chemical shift. This has been demonstrated to be the most feasible method and allows for the estimation of the absolute temperature in combination with high-spatialresolution MRI (Kuroda, 2005;McDannold, 2005;Rieke and Pauly, 2008;Bainbridge et al, 2013;Babourina-Brooks et al, 2015). The water-chemical shift difference is determined by the temperature-dependent variation of the water peak and a temperature-independent reference compound (e.g., DSS) in MR spectra.…”