MRI linear accelerator hybrid systems use balanced steady state free precession sequences (bSSFP) during radiotherapy due to the sequence’s high signal to noise ratio and rapid acquisition times. However, bSSFP sequences are highly sensitive to off-resonance effects.1 As a result, the position and velocity of the radiotherapy gantry can cause imaging artifacts that can impact tumor tracking and cause fluctuations in the main magnetic field that can result in radiotherapy/MRI isocenter misalignments. Sequence parameters were adjusted during the sequence run time to reduce these issues by integrating a navigator into the bSSFP sequence and measuring B0 variations in real-time.
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