Flexible, high spatial and temporal resolution absolute thermometry of MRI phantoms using ethylene glycol

Quantitative MRI (qMRI) parameters such as relaxation rates and diffusion parameters are typically temperature dependent. Therefore, using phantoms to evaluate the accuracy of qMRI pulse sequences requires accurate knowledge of the absolute temperature throughout the phantom. This work aims to evaluate the use of ethylene glycol (EG) together with a multi-echo gradient recalled echo (ME-GRE) pulse sequence for MR spectroscopic-based measurement of absolute temperature in phantoms.

We develop and test a simple MR spectroscopic imaging approach to rapidly, automatically, accurately, and precisely measure absolute temperature at multiple locations throughout a qMRI phantom. A series of EG cubes are located throughout the phantom and imaged with a ME-GRE pulse sequence over a wide range of temperatures (˜7°C-37°C) and on multiple scanners. The resulting images were automatically processed to isolate the EG. The measured spectral peak spacing was calibrated to temperature using fiber optic probes. The accuracy and precision of the measurements were evaluated between scanners over a range of temperatures.

The spectral peak spacing of EG can be used to predict temperature with an error of 0.6°C ± 0.3°C with an increase of 0.1°C when evaluated on different scanners. An automatic reconstruction approach without manual input is described, highlighting the feasibility of online implementation on a clinical MRI scanner.

The described MR spectroscopic imaging approach is easy to implement and provides robust, automatic, and accurate measurement of absolute temperature throughout a phantom.