Heule Rahel, Bär Peter, Mirkes Christian, Scheffler Klaus, Trattnig Siegfried, Bieri Oliver
Division of Radiological Physics, Department of Radiology, University of Basel Hospital, Basel, Switzerland.
NMR Biomed. 2014 Sep;27(9):1037-45. doi: 10.1002/nbm.3152. Epub 2014 Jul 1.
Quantitative MRI techniques, such as T2 relaxometry, have demonstrated the potential to detect changes in the tissue microstructure of the human brain with higher specificity to the underlying pathology than in conventional morphological imaging. At high to ultra-high field strengths, quantitative MR-based tissue characterization benefits from the higher signal-to-noise ratio traded for either improved resolution or reduced scan time, but is impaired by severe static (B0 ) and transmit (B1 ) field heterogeneities. The objective of this study was to derive a robust relaxometry technique for fast T2 mapping of the human brain at high to ultra-high fields, which is highly insensitive to B0 and B1 field variations. The proposed method relies on a recently presented three-dimensional (3D) triple-echo steady-state (TESS) imaging approach that has proven to be suitable for fast intrinsically B1 -insensitive T2 relaxometry of rigid targets. In this work, 3D TESS imaging is adapted for rapid high- to ultra-high-field two-dimensional (2D) acquisitions. The achieved short scan times of 2D TESS measurements reduce motion sensitivity and make TESS-based T2 quantification feasible in the brain. After validation in vitro and in vivo at 3 T, T2 maps of the human brain were obtained at 7 and 9.4 T. Excellent agreement between TESS-based T2 measurements and reference single-echo spin-echo data was found in vitro and in vivo at 3 T, and T2 relaxometry based on TESS imaging was proven to be feasible and reliable in the human brain at 7 and 9.4 T. Although prominent B0 and B1 field variations occur at ultra-high fields, the T2 maps obtained show no B0 - or B1 -related degradations. In conclusion, as a result of the observed robustness, TESS T2 may emerge as a valuable measure for the early diagnosis and progression monitoring of brain diseases in high-resolution 2D acquisitions at high to ultra-high fields.
定量磁共振成像技术，如T2弛豫测量法，已证明其在检测人类脑组织微观结构变化方面具有潜力，相较于传统形态学成像，它对潜在病理变化具有更高的特异性。在高场强至超高场强下，基于定量磁共振的组织表征受益于更高的信噪比，可用于提高分辨率或缩短扫描时间，但会受到严重的静磁场（B0）和发射磁场（B1）不均匀性的影响。本研究的目的是推导出一种稳健的弛豫测量技术，用于在高场强至超高场强下对人类大脑进行快速T2映射，该技术对B0和B1场变化高度不敏感。所提出的方法依赖于最近提出的三维（3D）三回波稳态（TESS）成像方法，该方法已被证明适用于对刚性目标进行快速的本质上对B1不敏感的T2弛豫测量。在这项工作中，3D TESS成像被改编用于快速的高场强至超高场强二维（2D）采集。2D TESS测量实现的短扫描时间降低了运动敏感性，并使基于TESS的T2定量在大脑中变得可行。在3 T场强下进行体外和体内验证后，在7 T和9.4 T场强下获得了人类大脑的T2图谱。在3 T场强下的体外和体内实验中，基于TESS的T2测量与参考单回波自旋回波数据之间发现了极好的一致性，并且基于TESS成像的T2弛豫测量在7 T和9.4 T场强下的人类大脑中被证明是可行且可靠的。尽管在超高场强下会出现明显的B0和B1场变化，但所获得的T2图谱未显示出与B0或B1相关的退化。总之，由于观察到的稳健性，TESS T2可能成为在高场强至超高场强下进行高分辨率2D采集时用于脑部疾病早期诊断和进展监测的有价值的测量方法。
