Free‐breathing 2D radial cine MRI with respiratory auto‐calibrated motion correction (RAMCO)

PURPOSE: To develop a free‐breathing (FB) 2D radial balanced steady‐state free precession cine cardiac MRI method with 100% respiratory gating efficiency using respiratory auto‐calibrated motion correction (RAMCO) based on a motion‐sensing camera. METHODS: The signal from a respiratory motion‐sensing camera was recorded during a FB retrospectively electrocardiogram triggered 2D radial balanced steady‐state free precession acquisition using pseudo–tiny‐golden‐angle ordering. With RAMCO, for each acquisition the respiratory signal was retrospectively auto‐calibrated by applying different linear translations, using the resulting in‐plane image sharpness as a criterium. The auto‐calibration determines the optimal magnitude of the linear translations for each of the in‐plane directions to minimize motion blurring caused by bulk respiratory motion. Additionally, motion‐weighted density compensation was applied during radial gridding to minimize through‐plane and non‐bulk motion blurring. Left ventricular functional parameters and sharpness scores of FB radial cine were compared with and without RAMCO, and additionally with conventional breath‐hold Cartesian cine on 9 volunteers. RESULTS: FB radial cine with RAMCO had similar sharpness scores as conventional breath‐hold Cartesian cine and the left ventricular functional parameters agreed. For FB radial cine, RAMCO reduced respiratory motion artifacts with a statistically significant difference in sharpness scores (P < 0.05) compared to reconstructions without motion correction. CONCLUSION: 2D radial cine imaging with RAMCO allows evaluation of left ventricular functional parameters in FB with 100% respiratory efficiency. It eliminates the need for breath‐holds, which is especially valuable for patients with no or impaired breath‐holding capacity. Validation of the proposed method on patients is warranted.