An indirect method for in vivo T-2 mapping of [1-C-13] pyruvate using hyperpolarized C-13 CSI

An indirect method for in vivo T-2 mapping of C-13-labeled metabolites using T-2 and T-2* information of water protons obtained a priori is proposed. The T-2 values of C-13 metabolites are inferred using the relationship to T-2 of coexisting H-1 and the T-2* of C-13 metabolites, which is measured using routine hyperpolarized C-13 CSI data. The concept is verified with phantom studies. Simulations were performed to evaluate the extent of T-2 estimation accuracy due to errors in the other measurements. Also, bias in the C-13 T-2* estimation from the C-13 CSI data was studied. In vivo experiments were performed from the brains of normal rats and a rat with C6 glioma. Simulation results indicate that the proposed method provides accurate and unbiased C-13 T-2 values within typical experimental settings. The in vivo studies found that the estimated T-2 of [1-C-13] pyruvate using the indirect method was longer in tumor than in normal tissues and gave values similar to previous reports. This method can estimate localized T-2 relaxation times from multiple voxels using conventional hyperpolarized C-13 CSI and can potentially be used with time resolved fast CSI. Copyright © 2017 John Wiley & Sons, Ltd.1

Metabolite-selective hyperpolarized C-13 imaging using extended chemical shift displacement at 9.4 T

Purpose: To develop a technique for frequency-selective hyperpolarized C-13 metabolic imaging in ultra-high field strength which exploits the broad spatial chemical shift displacement in providing spectral and spatial selectivity. Methods: The spatial chemical shift displacement caused by the slice-selection gradient was utilized in acquiring metabolite-selective images. Interleaved images of different metabolites were acquired by reversing the polarity of the slice-selection gradient at every repetition time, while using a low-bandwidth radio-frequency excitation pulse to altematingly shift the displaced excitation bands outside the imaging subject Demonstration of this technique is presented using H-1 phantom and in vivo mouse renal hyperpolarized C-13 imaging experiments with conventional chemical shift imaging and fast low-angle shot sequences. Results: From phantom and in vivo mouse studies, the spectral selectivity of the proposed method is readily demonstrated using results of chemical shift spectroscopic imaging, which displayed clearly delineated images of different metabolites. Imaging results using the proposed method without spectral encoding also showed effective separation while also providing high spatial resolution. Conclusion: This method provides a way to acquire spectrally selective hyperpolarized C-13 metabolic images in a simple implementation, and with potential ability to support combination with more elaborate readout methods for faster imaging. (C) 2015 Elsevier Inc. All rights reserved1661sciescopu

Flow-suppressed hyperpolarized 13C chemical shift imaging using velocity-optimized bipolar gradient in mouse liver tumors at 9.4 T

Purpose: To optimize and investigate the influence of bipolar gradients for flow suppression in metabolic quantification of hyperpolarized 13C chemical shift imaging (CSI) of mouse liver at 9.4 T. Methods: The trade-off between the amount of flow suppression using bipolar gradients and T2 * effect from static spins was simulated. A free induction decay CSI sequence with alternations between the flow-suppressed and non–flow-suppressed acquisitions for each repetition time was developed and was applied to liver tumor–bearing mice via injection of hyperpolarized [1-13C] pyruvate. Results: The in vivo results from flow suppression using the velocity-optimized bipolar gradient were comparable with the simulation results. The vascular signal was adequately suppressed and signal loss in stationary tissue was minimized. Application of the velocity-optimized bipolar gradient to tumor-bearing mice showed reduction in the vessel-derived pyruvate signal contamination, and the average lactate/pyruvate ratio increased by 0.095 (P < 0.05) in the tumor region after flow suppression. Conclusion: Optimization of the bipolar gradient is essential because of the short 13C T2 * and high signal in venous flow in the mouse liver. The proposed velocity-optimized bipolar gradient can suppress the vascular signal, minimizing T2 *-related signal loss in stationary tissues at 9.4 T. Magn Reson Med 78:1674–1682, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicin1