LIPID SUPPRESSION USING SELECTIVE INVERSION RECOVERY FOR 3D SPECTROSCOPIC IMG

该子项目是利用NIH/NCRR资助的中心赠款提供的资源的许多研究子项目之一。子项目和研究者（PI）可能从另一个NIH来源获得主要资金，因此可以在其他CRISP条目中表示。所列机构为中心机构，不一定为研究者机构。引言H脑化学位移成像（CSI）中减少脂质信号的最常见方法是通过PRESS技术使用体积预选。[1]该技术在有限的脑体积内产生高质量的代谢物谱。为了实现全脑覆盖，通常应用非选择性反转恢复（IR）技术。[2][3]在1.5T下，IR的代谢物信号损失约为30- 40%。然而，在更高的场，例如3 T，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IR CSI脉冲序列的设计，实施和结果，执行选择性反转脂质抑制。方法脂质与最接近的代谢物（NAA）之间的化学位移为0.7ppm。在3 T下，这两个自旋间隔89 Hz。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，并且脉冲宽度足够短以忽略激发期间的弛豫效应。在设计中，我们选择了一个最小相位的RF脉冲的一个尖锐的过渡带与500 Hz的反转带宽和20毫秒的脉冲宽度。使用Shinnar-Le Roux算法[4]完成射频脉冲合成。选择涟漪幅度，使得过渡带宽小于89 Hz。为了测试选择性IR的效果，采用具有以下特征的3 T CSI成像序列：用于代谢物激发和水抑制的频谱-空间自旋回波脉冲，TR/TI/TE=2000/170/144 ms，螺旋读出梯度，单层，2.5 cc体素和2分钟采集。[5]结论设计并实现了3 T选频红外螺旋CSI脉冲序列。选择性反转恢复的有效性在体内扫描上得到证明，该扫描显示出在10的量级上的脂质抑制因子，同时保持优良的质量代谢物光谱。感谢Lucas基金会，NIH赠款RR 09748，CA 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. Pauly等人，IEEE Trans. Med. Imaging 10，53-65，1991 [5] E. Adalsteinsson等人，MRM，39，889-898，1998年

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