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短回波时间和重复时间的人脑高磁场谱磁共振波谱学

High-field MRS of the human brain at short TE and TR.

机构信息

Department of Radiology, Radiotherapy and Nuclear Medicine, UMC Utrecht, Utrecht, The Netherlands.

出版信息

NMR Biomed. 2011 Nov;24(9):1081-8. doi: 10.1002/nbm.1660. Epub 2011 Feb 10.

Abstract

In vivo MRS of the human brain at 7 tesla allows identification of a large number of metabolites at higher spatial resolutions than currently possible at lower field strengths. However, several challenges complicate in vivo localization and artifact suppression in MRS at high spatial resolution within a clinically feasible scan time at 7 tesla. Published MRS sequences at 7 tesla suffer from long echo times, inherent signal-to-noise ratio (SNR) loss, large chemical shift displacement artifacts or long repetition times because of excessive radiofrequency (RF) power deposition. In the present study a pulse-acquire sequence was used that does not suffer from these high field drawbacks. A slice selective excitation combined with high resolution chemical shift imaging for in-plane localization was used to limit chemical shift displacement artifacts. The pulse-acquire approach resulted in a very short echo time of 1.4 ms. A cost function guided shimming algorithm was developed to constrain frequency offsets in the excited slice, therefore adiabatic frequency selective suppression could be employed to minimize artifacts from high intensity lipids and water signals in the excited slice. The high sensitivity at a TR of 1 s was demonstrated both on a supraventricular slice as well as in an area very close to the skull in the frontal cortex at a nominal spatial resolution of 0.25 cc within a feasible scan time.

摘要

在 7 特斯拉的人体大脑中进行体内 MRS 可以比在较低场强下更高的空间分辨率识别大量代谢物。然而,在 7 特斯拉的临床可行扫描时间内,高空间分辨率的体内定位和伪影抑制存在几个挑战,使其复杂化。发表的 7 特斯拉 MRS 序列由于射频(RF)功率沉积过多而具有长回波时间、固有信噪比(SNR)损失、大的化学位移位移伪影或长重复时间。在本研究中,使用了一种不会受到这些高场缺点影响的脉冲采集序列。使用片选激发和高分辨率化学位移成像进行平面内定位,以限制化学位移位移伪影。脉冲采集方法导致非常短的回波时间为 1.4ms。开发了一种基于成本函数的调谐算法来约束激发片内的频率偏移,因此可以采用绝热频率选择抑制来最小化激发片内高强度脂质和水信号的伪影。在 1s 的 TR 下,无论是在上矢状窦切片还是在前额皮质非常靠近颅骨的区域,都在名义空间分辨率为 0.25cc 的可行扫描时间内展示了高灵敏度。

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