LIPID SUPPRESSION USING SELECTIVE INVERSION RECOVERY FOR 3D SPECTROSCOPIC IMG

本子项目是利用由NIH/NCRR资助的中心赠款提供的资源的众多研究子项目之一。子项目和研究者（PI）可能已经从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。列出的机构是中心的，不一定是研究者的机构。在脑化学位移成像（CSI）中减少脂质信号最常见的方法是通过PRESS技术使用体积预选。该技术在有限的脑容量内产生高质量的代谢物光谱。为了实现全脑覆盖，一般采用非选择性反演恢复（IR）技术。在1.5T时，IR的代谢物信号损失约为30-40%。然而，在更高的场，例如3T，脂质和代谢物之间的光谱分离的增加允许频率选择性反转。本文讨论了一种红外CSI脉冲序列的设计、实现和结果，该序列对脂质抑制进行选择性反转。方法脂质与最接近的代谢物（NAA）之间的化学位移为0.7 ppm。在3T时，这两个自旋相隔89赫兹。反转脉冲的设计目标是过渡带小于89 Hz，反转带足够宽以覆盖所有脂质信号，脉冲宽度足够短以忽略激发时的松弛效应。在设计中，我们选择了一个最小相位射频脉冲，用于反转带宽为500 Hz，脉冲宽度为20ms的急剧过渡带。射频脉冲合成采用Shinnar-Le Roux算法。纹波幅值的选择使过渡带宽小于89Hz。为了测试选择性红外的效果，采用3T CSI成像序列，具有以下特征：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=2000/170/144 ms，螺旋读数梯度，单片，2.5 cc体素和2分钟采集。结论我们设计并实现了3T频率选择性红外螺旋CSI脉冲序列。选择性反转恢复的有效性在体内扫描中得到了证明，在保持优质代谢物光谱的同时，显示了10的脂质抑制因子。致谢：Lucas foundation， NIH grants RR 09748, CA 48269 REFERENCES [2] P.A. Bottomley， Ann N Y学术科学，508,333,333- 348,1987 [2]A. Ebel等，MRM, 49, 903- 908,2003 [2] D. M. Spielman等，JMRM, 2:253-262, 1992 bbb J. Pauly等，IEEE Trans。[3]张建军，张建军，张建军，等。中国医学影像杂志，1998,13 (3):557 - 557

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