Boer Vincent O, van de Lindt Tessa, Luijten Peter R, Klomp Dennis W J
Department of Radiology, University Medical Center Utrecht, The Netherlands.
Magn Reson Med. 2015 Jun;73(6):2062-8. doi: 10.1002/mrm.25331. Epub 2014 Jun 19.
Lipid suppression in MR brain imaging and spectroscopy has been a long-standing problem for which various techniques have been developed. Most methods are based on inversion recovery or spatially or spectrally selective excitation of the lipid signal followed by dephasing. All techniques require additional RF pulses, gradient crushers and delays, which increase the duration and complexity of sequences. In addition, the lipid signal is poorly shimmed, and is composed of different resonance frequencies that have different relaxation properties.
In this work, a novel approach for suppression of extra cranial lipids is presented, by means of an outer volume crusher coil. It is based on the principle of surface spoiling gradients, which generate a very local and inhomogeneous magnetic field in the outer layer of the head, and thereby destroys the phase coherence of the extra cranial signals.
Dephasing of the signal can be incorporated in almost any sequence because it requires only a short pulse of the coil, and does not require additional RF pulses or delays. Examples of lipid suppression are shown in both gradient echo imaging and spectroscopic imaging.
Outer volume crushing allows for simple fat suppression and boosts scanning efficiency, which is particularly beneficial at ultra-high field strengths.
磁共振脑成像和波谱分析中的脂质抑制一直是个长期存在的问题，针对此已开发出多种技术。大多数方法基于反转恢复或对脂质信号进行空间或频谱选择性激发，随后进行去相位处理。所有技术都需要额外的射频脉冲、梯度破坏器和延迟，这增加了序列的时长和复杂性。此外，脂质信号的匀场效果不佳，且由具有不同弛豫特性的不同共振频率组成。
在这项工作中，提出了一种通过外部容积破坏线圈抑制颅外脂质的新方法。它基于表面扰相梯度原理，在头部外层产生非常局部且不均匀的磁场，从而破坏颅外信号的相位相干性。
信号去相位可纳入几乎任何序列，因为它仅需要线圈的短脉冲，且不需要额外的射频脉冲或延迟。在梯度回波成像和波谱成像中均展示了脂质抑制的示例。
外部容积破坏实现了简单的脂肪抑制并提高了扫描效率，这在超高场强下尤为有益。
