UCSF

PURPOSE: Acquisition timing and B₁ calibration are two key factors that affect the quality and accuracy of hyperpolarized ¹³ C MRI. The goal of this project was to develop a new approach using regional bolus tracking to trigger Bloch-Siegert B₁ mapping and real-time B₁ calibration based on regional B₁ measurements, followed by dynamic imaging of hyperpolarized ¹³ C metabolites in vivo. METHODS: The proposed approach was implemented on a system which allows real-time data processing and real-time control on the sequence. Real-time center frequency calibration upon the bolus arrival was also added. The feasibility of applying the proposed framework for in vivo hyperpolarized ¹³ C imaging was tested on healthy rats, tumor-bearing mice and a healthy volunteer on a clinical 3T scanner following hyperpolarized [1-¹³ C]pyruvate injection. Multichannel receive coils were used in the human study. RESULTS: Automatic acquisition timing based on either regional bolus peak or bolus arrival was achieved with the proposed framework. Reduced blurring artifacts in real-time reconstructed images were observed with real-time center frequency calibration. Real-time computed B₁ scaling factors agreed with real-time acquired B₁ maps. Flip angle correction using B₁ maps results in a more consistent quantification of metabolic activity (i.e, pyruvate-to-lactate conversion, k_PL ). Experiment recordings are provided to demonstrate the real-time actions during the experiment. CONCLUSIONS: The proposed method was successfully demonstrated on animals and a human volunteer, and is anticipated to improve the efficient use of the hyperpolarized signal as well as the accuracy and robustness of hyperpolarized ¹³ C imaging.