利用体内局部二维恒时COSY光谱对谷氨酸、γ-氨基丁酸和谷氨酰胺进行绝对定量分析。

Watanabe Hidehiro, Takaya Nobuyuki, Mitsumori Fumiyuki

Center for Environmental Measurement and Analysis, National Institutes for Environmental Studies.

Magn Reson Med Sci. 2014;13(1):25-32. doi: 10.2463/mrms.2013-0025. Epub 2014 Jan 31.

PURPOSE

We propose an absolute quantitation method for metabolites with strongly coupled spin systems using localized 2-dimensional (2D) constant-time correlation spectroscopy (CT-COSY). We also develop two methods for improving the quality of in vivo CT-COSY spectra.

METHODS

We substituted an image selected in vivo spectroscopy (ISIS) pulse for a 180° slice pulse in the CT-COSY module to decrease the slice displacement error caused by the chemical shift difference. We measured the slice displacement error due to the differences in the carrier frequency of slice pulse in a phantom experiment to demonstrate this feature. We also developed an asymmetric sampling scheme along the t1 direction to resolve diagonal peaks even in the magnitude mode of 2D spectra. We collected CT-COSY signals of a human brain for a 14% asymmetric sampling scheme. After reconstruction, we obtained a 2D CT-COSY spectrum in magnitude mode and compared a peak of glutamate (Glu) C4H on that spectrum to a peak displayed in absorption mode. In our proposed absolute quantitation method, we developed T2 correction, curve-fitting for computing peak volume and calibration by an internal water reference. We used the method to measure the Glu concentration in 10-mM glutamate phantom experiments. We also attempted to measure concentrations of Glu, γ-aminobutyric acid (GABA) and glutamine (Gln) in a human brain.

RESULTS

Slice displacement error was decreased by a factor of 2.5 using the proposed sequence. Spectra with narrow linewidths could be obtained using the asymmetric sampling scheme in the magnitude mode. Measured Glu concentration in the solution phantom was 9.4 mM. Concentrations of Glu (9.5 mM), GABA (0.61 mM) and Gln (3.6 mM) in a human brain measured by our method agreed well with previously reported values.

CONCLUSION

Concentrations of metabolites with strongly coupled spin systems can be measured using our proposed absolute quantitation method on 2D CT-COSY spectra.

目的

我们提出一种使用局部二维（2D）恒时相关光谱法（CT-COSY）对具有强耦合自旋系统的代谢物进行绝对定量的方法。我们还开发了两种提高体内CT-COSY谱质量的方法。

方法

我们在CT-COSY模块中用图像选择体内光谱法（ISIS）脉冲替代180°切片脉冲，以减少由化学位移差异引起的切片位移误差。我们在体模实验中测量了由于切片脉冲载波频率差异导致的切片位移误差，以证明此特性。我们还开发了一种沿t1方向的不对称采样方案，即使在二维谱的幅度模式下也能解析对角线峰。我们针对14%的不对称采样方案采集了人脑的CT-COSY信号。重建后，我们获得了幅度模式下的二维CT-COSY谱，并将该谱上谷氨酸（Glu）C4H的峰与吸收模式下显示的峰进行比较。在我们提出的绝对定量方法中，我们开发了T2校正、用于计算峰体积的曲线拟合以及通过内部水参考进行校准。我们使用该方法在10 mM谷氨酸体模实验中测量Glu浓度。我们还尝试测量人脑内Glu、γ-氨基丁酸（GABA）和谷氨酰胺（Gln）的浓度。