LIPID SUPPRESSION USING SELECTIVE INVERSION RECOVERY FOR 3D SPECTROSCOPIC IMG

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 引言 在H脑化学位移成像(CSI)中，最常见的减少脂质信号的方法是通过按压技术使用体积预选。[1]这项技术在有限的大脑体积内产生高质量的代谢物光谱。为了实现全脑覆盖，通常采用非选择性反转恢复(IR)技术。[2][3]在1.5T时，来自IR的代谢物信号损失约为30%-40%。然而，在更高的磁场中，例如3T，脂质和代谢物之间光谱分离的增加允许频率选择性反转。本文讨论了一种用于选择性反转的红外CSI脉冲序列的设计、实现和结果。 方法 脂类与最接近的代谢物(NAA)之间的化学位移为0.7ppm。在3T时，这两个自旋之间的距离为赫兹。反转脉冲的设计目标是转换带小于89赫兹，反转带足够宽，足以覆盖所有的脂肪信号，以及足够短的脉冲宽度，以忽略激发过程中的松弛效应。在设计中，我们选择了一个最小相位的射频脉冲作为陡峭的过渡带，具有500赫兹的反转带宽和20ms的脉冲宽度。射频脉冲合成是使用Shinnar-Le Roux算法完成的[4]。波纹幅度的选择使过渡带宽小于89赫兹。为了检验选择性IR的效果，实现了一种3T CSI成像序列，其特征如下：用于代谢物激发和水抑制的光谱-空间自旋回波脉冲，tr/ti/te=2000/170/144ms，螺旋读出梯度，单层，2.5cc体素，2min采集。[5] 结论 设计并实现了3T频率选择性红外螺旋CSI脉冲序列。体内扫描证明了选择性反转恢复的有效性，在保持良好质量代谢物光谱的同时，显示出约10个数量级的脂肪抑制因子。 确认 美国国立卫生研究院卢卡斯基金会拨款RR 09748，加利福尼亚州48269 参考文献 [1]P.A.Bottomley，Ann N Y Acad Sci，508,333,333-348,1987 [2]A.Ebel等人，MRM，49,903-908,2003 [3]D.M.Spielman等人，JMRM 2：253-262,1992 [4]J·保利等人，IEEE Trans.地中海医院。影像10，53-65,1991 [5]E.Adalsteinsson等人，MRM，39,889-898,1998

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. INTRODUCTION The most common approach for reducing lipid signals in H brain chemical shift imaging (CSI) is the use of volume preselection via the PRESS technique. [1] This technique produces high quality metabolite spectra within a restricted brain volume. To achieve whole brain coverage, non-selective inversion recovery (IR) techniques are generally applied. [2] [3] At 1.5T, metabolite signal loss from IR is on the order of 30-40%. However, at higher fields, e.g. 3T, the increase in spectral separation between lipids and metabolites allows a frequency selective inversion. This paper discusses the design, implementation and results of an IR CSI pulse sequence that performs selective inversion for lipid suppression. METHOD The chemical shift between lipids and the closest metabolite (NAA) is 0.7 ppm. At 3T, these two spins are separated by 89 Hz. The design goals of the inversion pulse were a transition band less than 89 Hz, an inversion band wide enough to cover all of the lipid signals and a short enough pulse width to neglect relaxation effects during excitation. In the design, we chose a minimum phase RF pulse for a sharp transition band with 500 Hz inversion bandwidth and 20ms pulse width. The RF pulse synthesis was done using the Shinnar-Le Roux algorithm [4]. The ripple amplitudes were chosen such that the transition bandwidth was less than 89Hz. To test the effects of the selective IR, a 3T CSI imaging sequence was implemented with the following characteristics: spectral-spatial spin echo pulse for metabolite excitation and water suppression, TR/TI/TE=2000/170/144 ms, spiral readout gradients, single slice, 2.5 cc voxels and 2 minute acquisition. [5] CONCLUSION We have designed and implemented a 3T frequency selective IR spiral CSI pulse sequence. The effectiveness of the selective inversion recovery is demonstrated on an in vivo scan showing a lipid suppression factor on the order of 10 while maintaining excellent quality metabolite spectra. ACKNOWLEDGEMENTS Lucas foundation, NIH grants RR 09748, CA 48269 REFERENCES [1] P.A. Bottomley, Ann N Y Acad Sci, 508, 333, 333-348, 1987 [2] A. Ebel, et al, MRM, 49, 903-908, 2003 [3] D. M. Spielman, et al., JMRM 2:253-262, 1992 [4] J. Pauly, et al., IEEE Trans. Med. Imaging 10, 53-65, 1991 [5] E. Adalsteinsson, et al., MRM, 39, 889-898, 1998