1 H‐MRS internal thermometry in test‐objects (phantoms) to within 0.1 K for quality assurance in long‐term quantitative MR studies

Many magnetic resonance test‐object properties are temperature‐dependent, with typical temperature coefficients of ∼2–3% K −1 . Therefore, to achieve consistent quality assurance measurements to within 1%, test object temperatures should ideally be known to within 0.3 K. Proton magnetic resonance spectroscopy has previously been used to estimate accurately absolute tissue temperature in vivo , based on the linear temperature dependence of the chemical shift difference between water and temperature‐stable reference metabolites such as N ‐acetylaspartate. In this study, this method of ‘internal thermometry’ in quality assurance test‐objects was investigated, and in particular the value of sodium 3‐(trimethylsilyl)propane‐1‐sulfonate (DSS) as a chemical shift reference was demonstrated. The relationship between the DSS–water chemical shift difference ( σ , expressed in ppm) and temperature τ (in K) was shown to be τ  = 764.55 (±5.05) − 97.72 (±1.05) σ (286 ≤  τ  ≤ 309 K). Internal thermometry in MRI test‐objects is feasible and straightforward, using readily available 1 H‐MRS pulse sequences and standard spectroscopy evaluation packages, with a minimum detectable temperature difference of 100 (±20) mK. Copyright © 2006 John Wiley & Sons, Ltd.