FAT SUPPRESSION FOR 1H MRSI AT 7T USING SPECTRALLY SELECTIVE ADIABATIC IR

这个子项目是许多利用 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 1H磁共振波谱成像（1H MRSI）是一种用于测量体内脑中代谢物水平的有用技术。 在更高的场（例如7 T）下的1H MRSI提供了增加的SNR和光谱分离的优点。短τ反转恢复（STIR）[1，2]是一种常用的脂肪抑制方法，其在PRESS序列中的90 <$激励脉冲之前采用180 <$反转脉冲，反转时间（TI）经过调整，使得当主激励发生时，短T1物质（例如脂肪）的纵向磁化通过零值。 虽然大多数代谢产物都有T1虽然它们的长度明显长于脂肪，但它们在7 T下仍遭受约50%的部分信号损失。 幸运的是，在7 T下增加的光谱分离使得有可能设计一种光谱选择性绝热反转脉冲，其仅反转脂质共振，而不影响大多数代谢物。 这种脉冲的两个版本已经被设计并插入到标准PRESS序列中。 第一种是高度选择性的绝热光谱脉冲，其反转整个体积中的脂肪以用于板选择性PRESS。 第二个是绝热空间光谱（SPSP）脉冲，允许同时在空间和频率的选择性，同时保持对B1不均匀性的不敏感性。 该脉冲具有选择性反转脂肪的光谱轮廓，并且是切片选择性的，适合于多切片MRSI。在7 T下，与容积方法相比，多层MRSI特别有吸引力，因为它能够使用动态匀场单独优化每个切片的B 0均匀性[3，4]。 体内7 T数据表明，光谱和空间光谱绝热脂肪选择性反转脉冲都成功抑制脂肪，同时不会降低大脑中大多数感兴趣代谢物的信号。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. 1H Magnetic resonance spectroscopic imaging (1H MRSI) is a useful technique for measuring metabolite levels in the brain in vivo. 1H MRSI at higher fields, such as 7T, offers the advantages of increased SNR and spectral separation. Short Tau Inversion Recovery (STIR) [1,2] is a commonly used fat suppression method which employs a 180¿ inversion pulse prior to the 90¿ excitation pulse in a PRESS sequence with inversion time (TI) adjusted such that the longitudinal magnetization of short T1 species (e.g. fat) passes through a null when primary excitation occurs. Although most metabolites have T1s significantly longer than fat, they nonetheless suffer from a partial signal loss on the order of 50% at 7T. Fortunately, the increased spectral separation at 7T makes it possible to design a spectrally selective adiabatic inversion pulse that only inverts lipid resonances, leaving most of the metabolites untouched. Two versions of such a pulse have been designed and inserted into a standard PRESS sequence. The first is a highly selective adiabatic spectral pulse that inverts the fat in the entire volume for slab-selective PRESS. The second is an adiabatic spatial-spectral (SPSP) pulse that allows simultaneous selectivity in both space and frequency while maintaining insensitivity to B1 inhomogeneities. The pulse has a spectral profile that selectively inverts the fat and, being slice-selective, is amenable for multi-slice MRSI. At 7T, multislice MRSI is particularly attractive, as compared to volumetric methods, due to the ability to individually optimize the B0 homogeneity of each slice using dynamic shimming [3,4]. In vivo 7T data demonstrates that both spectral and spatial-spectral adiabatic fat-selective inversion pulses successfully suppress fat while not degrading signal from most of the metabolites of interest in the brain.