Purpose: Hyperpolarized (HP) 13 C MRI has enabled real-time imaging of specific enzyme-catalyzed metabolic reactions, but advanced pulse sequences are necessary to capture the dynamic, localized metabolic information. Herein we describe the design, implementation, and testing of a rapid and efficient HP 13 C pulse sequence strategy on a cryogen-free simultaneous positron emission tomography/ MR molecular imaging platform with compact footprint. Methods:We developed an echo planar spectroscopic imaging pulse sequence incorporating multi-band spectral-spatial radiofrequency (SSRF) pulses for spatially coregistered excitation of 13 C metabolites with differential individual flip angles. Excitation profiles were measured in phantoms, and the SSRF-echo planar spectroscopic imaging sequence was tested in rats in vivo and compared to conventional echo planar spectroscopic imaging. The new sequence was applied for 2D dynamic metabolic imaging of HP [1-13 C]pyruvate and its molecular analog [1-13 C] -ketobutyrate at a spatial resolution of 5 mm × 5 mm × 20 mm and temporal resolution of 4 s. We also obtained simultaneous 18 F-fluorodeoxyglucose positron emission tomography data for comparison with HP [1-13 C]pyruvate data acquired during the same scan session. Results: Measured SSRF excitation profiles corresponded well to Bloch simulations. Multi-band SSRF excitation facilitated efficient sampling of the multispectral kinetics of [1-13 C]pyruvate and [1-13 C] -ketobutyrate. Whereas high pyruvate to lactate conversion was observed in liver, corresponding reduction of -ketobutyrate to [1-13 C] -hydroxybutyrate ( HB) was largely restricted to the kidneys and heart, consistent with the known expression pattern of lactate dehydrogenase B. Conclusion: Advanced 13 C SSRF imaging approaches are feasible on our compact positron emission tomography/MR platform, maximizing the potential of

Hyperpolarized (HP) 13C MRI requires advanced pulse sequences to capture the dynamic, localized metabolic information. We developed an echo planar spectroscopic imaging (EPSI) pulse sequence incorporating multi-band spectral-spatial radiofrequency (SSRF) pulses for rapid and efficient HP 13C MRI on a new cryogen-free simultaneous PET/MR molecular imaging platform with compact footprint. Excitation profiles were measured in phantoms, and the SSRF-EPSI sequence was tested in rats using two HP 13C probes. We also obtained simultaneous 18F-FDG-PET data for comparison. In conclusion, advanced 13C SSRF imaging approaches are feasible on the new PET/MR platform, facilitating direct comparison with PET.