PRIMO: Precise radiofrequency inference from multiple observations

Purpose This paper presents Precise Radiofrequency Inference from Multiple Observations (PRIMO), a comprehensive reconstruction framework for calibrating MRI systems with parallel transmit and parallel receive radiofrequency capabilities. Theory and Methods To date, the vast majority of radiofrequency (RF) calibration methods have considered transmit and receive calibration separately, without acknowledging that transmit field calibration sequences measure sufficient data for receive calibration. PRIMO provides a method of extracting both transmit and receive fields from transmit calibration data without presuming knowledge of either. The method is tested for accuracy through simulation, comparison to a gold standard dataset, and is demonstrated on in-vivo data acquired at 3T. Results PRIMO is shown to produce RF fields faithful to the gold standard with errors of less than 3% in realistic noise conditions. The in-vivo reconstructions demonstrate the method's ability to produce high quality transmit and receive maps, with an 8 transmit/8 receive channel system being fully calibrated in three dimensions in approximately 2 minutes. Conclusion PRIMO provides a unified framework for estimating all transmit and receive fields in a single calibration step. This is becoming increasingly relevant in an era of MRI systems with highly parallel RF architectures. Magn Reson Med 74:372-383, 2015.