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