Gilani Irtiza Ali, Sepponen Raimo
Brain Research Unit, Department of Neuroscience and Biomedical Engineering, Aalto University, Aalto, Finland.
Advanced Magnetic Imaging Center, Aalto University, Aalto, Finland.
NMR Biomed. 2016 Jun;29(6):841-61. doi: 10.1002/nbm.3518. Epub 2016 Apr 21.
Macromolecular degeneration and biochemical changes in tissue can be quantified using rotating frame relaxometry in MRI. It has been shown in several studies that the rotating frame longitudinal relaxation rate constant (R1ρ ) and the rotating frame transverse relaxation rate constant (R2ρ ) are sensitive biomarkers of phenomena at the cellular level. In this comprehensive review, existing MRI methods for probing the biophysical mechanisms that affect the rotating frame relaxation rates of the tissue (i.e. R1ρ and R2ρ ) are presented. Long acquisition times and high radiofrequency (RF) energy deposition into tissue during the process of spin-locking in rotating frame relaxometry are the major barriers to the establishment of these relaxation contrasts at high magnetic fields. Therefore, clinical applications of R1ρ and R2ρ MRI using on- or off-resonance RF excitation methods remain challenging. Accordingly, this review describes the theoretical and experimental approaches to the design of hard RF pulse cluster- and adiabatic RF pulse-based excitation schemes for accurate and precise measurements of R1ρ and R2ρ . The merits and drawbacks of different MRI acquisition strategies for quantitative relaxation rate measurement in the rotating frame regime are reviewed. In addition, this review summarizes current clinical applications of rotating frame MRI sequences. Copyright © 2016 John Wiley & Sons, Ltd.
组织中的大分子变性和生化变化可通过磁共振成像（MRI）中的旋转框架弛豫测量法进行量化。多项研究表明，旋转框架纵向弛豫速率常数（R1ρ）和旋转框架横向弛豫速率常数（R2ρ）是细胞水平现象的敏感生物标志物。在这篇综述中，介绍了用于探究影响组织旋转框架弛豫速率（即R1ρ和R2ρ）的生物物理机制的现有MRI方法。在旋转框架弛豫测量法的自旋锁定过程中，长采集时间和高射频（RF）能量沉积到组织中是在高磁场下建立这些弛豫对比的主要障碍。因此，使用共振或非共振RF激发方法进行R1ρ和R2ρ MRI的临床应用仍然具有挑战性。相应地，本综述描述了基于硬RF脉冲簇和绝热RF脉冲的激发方案设计的理论和实验方法，用于准确精确地测量R1ρ和R2ρ。综述了旋转框架模式下不同MRI采集策略用于定量弛豫速率测量的优缺点。此外，本综述总结了旋转框架MRI序列的当前临床应用。版权所有© 2016约翰威立父子有限公司。
