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, 2016. © 2016 International Society for Magnetic Resonance in Medicine.