MR Spectroscopy (MRS), Chemical Exchange Saturation Transfer (CEST), and Magnetization Transfer (MT)

Abstract

The development of motion correction methods for magnetic resonance spectroscopy (MRS) is emerging yet in an early stage with limited clinical applications to date. The critical needs of motion correction arise from the fact that subject motion during scans affects not only the quality of data but also the reliability of measurements due to changes in the voxel locations of MRS. Thus, the ultimate detrimental effects of motion on MRS could be quantification errors. The particular demands for motion correction in MRS include factors such as the sensitivity to B0 field changes, low signal-to-noise ratio, and longer scan time than conventional MRI. The same is true for chemical exchange saturation transfer (CEST) and magnetization transfer (MT) because of their long scan times as well as susceptibility to B0 inhomogeneity. In this chapter, we will first describe the direct and indirect effects of motion on MRS and CEST/MT measurements, and then the requirements of motion correction, and various motion correction approaches with their respective applications. Currently, the prospective motion correction approach with internal navigators has been recommended as an important strategy due to the capabilities to update both localization and B0 field information in real time during scans, thus significantly improving the data quality without requiring extra hardware. Recently a hybrid motion correction approach using both internal navigators and external tracking devices has also emerged with promising results, but faces challenges due to increased technical complexities. Overall, the field of motion correction in MRS and CEST/MT is actively evolving to meet the great needs and challenges of achieving robust and reliable measurements.