PLANET: a new approach for quantitative MRI

Abstract

Recent years have witnessed a considerable interest in quantitative Magnetic Resonance Imaging (qMRI), which aims to map quantitative imaging biomarkers (QIBs) representing underlying biological and physiological tissue characteristics. The magnetic relaxation times (T1, T2, T2*) are intrinsic tissue parameters, which are relevant QIBs. Measuring relaxation times has been a goal of research for a long time and many techniques and approaches have been developed to measure these parameters. However, reproducibly obtaining precise and accurate maps of relaxation times within an acceptable time frame remains challenging. Measurement results are known to depend on the methods used for quantification, on the implementation of the pulse sequences used, on MR protocol parameter settings, and even on the type and brand of the MR scanner on which a patient was scanned. In this thesis, research with respect to a new method for quantitative MRI is presented. A method named PLANET: an elliPse fitting approach for simuLtaneous T1 and T2 mApping using phase-cycled balaNced stEady-sTate free precession was developed, which is capable of volumetric reconstruction of five parameter maps: the relaxation times T1 and T2, the local off-resonance, the RF phase (related to the combination of RF transmit and receive phases), and the banding free bSSFP signal magnitude. The methodology is based on prior knowledge of the elliptical trajectory of the complex-valued bSSFP signal acquired over different RF phase increments, and is described in detail in the thesis. The performance of the method was investigated, and the method was optimized for different applications.