Mastering Rotating Frames: Challenges and Opportunities for MRI in Neuroscience

Quantitative rotating frame relaxation techniques based on frequency swept (FS) radiofrequency (RF) pulses, including adiabatic T1r and T2r, and the non-adiabatic method entitled Relaxation Along a Fictitious Field (RAFF) in the rotating frame of rank n (RAFFn), offer sensitivity to a broad range of motional regimes. The reduced power deposition of RAFFn with enhanced sensitivity to slow motions in high rotating frames of rank n and to exchange-induced relaxations during the periodic irradiation are distinct advantages of this methodology. The methodologies for detection of fast relaxing spins using asymptotic relaxation mapping with Zero-TE imaging readouts will be described. Applications of adiabatic T1r, T2r and non-adiabatic RAFFn techniques for detection of the pathological abnormalities in Parkinson’s and Alzheimer’s disease, aging, essential tremor, myocardial infarction will be presented. We will discuss how the fictitious magnetic fields generated during non-adiabatic evolution of spin ensemble influence the MRI relaxation contrasts in vivo, and we will evaluate the formation of the geometric phases, i.e., adiabatic (Berry’s phase) and non-adiabatic (Aharonov-Anandan phases) during the FS RF pulses. We will also discuss how the sub-geometric phases (SGP) influence polarization generated during the application of amplitude and frequency modulated RF pulses. Finally, we will describe how the rotating fields are utilized for the orientation selective Deep Brain and Spinal Cord stimulations (DBS and SCS, respectively), combined with the functional MRI in vivo using zero-TE pulses sequences in the single and dual – FOV configurations. 

After completion of his PhD program at the Hebrew University of Jerusalem, Israel, in 1996, Dr. S. Michaeli conducted PostDoctoral research at Argonne National Laboratory, USA, and subsequently relocated to the CMRR, University of Minnesota, where he currently holds the position of Professor at the Department of Radiology, Medical School. Dr. S. Michaeli has broad background and experience in the field of Magnetic Resonance (MR). He serves as PI and Co-I of multiple NIH grants, and successfully leads several projects in applications to humans and animal models. His research is focused on the relaxations during radiofrequency irradiation and development of non-invasive contrast methods for MR imaging and spectroscopy at high magnetic fields (3T and higher). He is actively involved in multimodal applications combined with functional MRI in animals and humans.