Carbon-13 Spectroscopy of Human Brain

A proton decoupled ¹³C spectroscopy method using intravenous infusion of [2-¹³C]glucose is being developed on a GE 3.0T clinical scanner. Using this approach we detected the ¹³C signal of glutamate, glutamine, γ-aminobutyric acid (GABA), aspartate, and N-acetylaspartate (NAA) from the carboxylic/amide spectral region. The method allows investigators to measure glucose, glutamate and glutamine kinetics associated with glucose metabolism and glutamatergic neurotransmission in human subjects.

The ¹³C signal is detected by using a surface coil placed against either the occipital lobe or the frontal lobe to achieve optimum signal-to-noise ratio. A proton coil is also utilized to provide head positioning and magnetic field shimming and to perform NOE and proton decoupling during ¹³C data acquisition. Both half-volume proton surface coil and volume proton birdcage coil are available depending on the application requirements.

Two antecubital veins were cannulated, one for administering [2-¹³C]glucose solution and the other for withdrawing blood to monitor glucose. A MR-compatible infusion pump was used to infuse [2-¹³C]glucose solution (99% enrichment, 20% w/w). During glucose infusion, blood samples were withdrawn approximately every 10 minutes to measure blood glucose levels.

Figure 8 in below shows an accumulated ¹³C spectrum acquired from the occipital lobe with proton decoupling (A) and without proton decoupling (B). A half-volume surface proton coil was used to perform NOE and proton decoupling. Signal-to-noise ratio and spectral resolution are significantly improved with proton decoupling and NOE.

¹³C spectra acquired using birdcage coil for proton decoupling are shown in Fig. 9 in below where the upper spectrum (Fig. 9a) was obtained from the occipital lobe and the lower spectrum (Fig. 9b) from the frontal lobe of a healthy human volunteer. Because the strong magnetic field inhomogeneity in the frontal lobe region, the ¹³C linewidth is broader and SNR is lower for the frontal lobe spectrum as compared with the occipital lobe spectrum.

Reference: : Li S, Zhang Y, Wang S, Ferraris Araneta M, Johnson CS, Xiang Y, Innis R, Shen J: “13C MRS of Occipital and Frontal Lobes at 3 Tesla Using a Volume Coil for Stochastic Proton Decoupling.” NMR in Biomedicine, 23, 977-985 (2010).