Absolute temperature imaging using intermolecular multiple quantum MRI

Purpose: A review of MRI temperature imaging methods based on intermolecular multiple quantum coherences (iMQCs) is presented. Temperature imaging based on iMQCs can provide absolute temperature maps that circumvent the artefacts that other proton frequency shift techniques suffer from such as distortions to the detected temperature due to susceptibility changes and magnetic field inhomogeneities. Thermometry based on iMQCs is promising in high-fat tissues such as the breast, since it relies on the fat signal as an internal reference. This review covers the theoretical background of iMQCs, and the necessary adaptations for temperature imaging using iMQCs. Materials and methods: Data is presented from several papers on iMQC temperature imaging. These studies were done at 7T in both phantoms and in vivo. Results from phantoms of cream (homogeneous mixture of water and fat) are presented as well as in vivo temperature maps in obese mice. Results: Thermometry based on iMQCs offers the potential to provide temperature maps which are free of artefacts due to susceptibility and magnetic field inhomogeneities, and detect temperature on an absolute scale. Conclusions: The data presented in the papers reviewed highlights the promise of iMQC-based temperature imaging in fatty tissues such as the breast. The change in susceptibility of fat with temperature makes standard proton frequency shift methods (even with fat suppression) challenging and iMQC-based imaging offers an alternative approach.