Development of a transmit gain calibration method using the Bloch-Siegert shift for nonproton hyperpolarized MRI on a preclinical 7T scanner

Motivation: Transmit gain calibration is necessary for nonproton hyperpolarized MRI to accurately calibrate excitation angles. Goal(s): To implement a phase-based TG calibration method using the Bloch-Siegert shift for nonproton HP MRI on a preclinical 7T scanner. Approach: An off-resonance Fermi-shaped Bloch-Siegert pulse follows directly an excitation pulse. Percent difference between our measured Bloch-Siegert TG calibration factors and the validation TG calibration factors for 1H and 13C were calculated. Results: Our method allows for fast, accurate, and robust TG calibration of preclinical nonproton HP MRI studies with minimal error (<5%) for 1H and 13C. Impact: This method will facilitate efficient transmit calibration for 13C and HP 129Xe MRI on a preclinical 7T scanner, where limited bore size and the inability to easily implement a thermal calibration phantom can make 129Xe TG calibration a challenge.