Pilot tone–based motion correction for prospective respiratory compensated cardiac cine MRI

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Abstract
Purpose: To evaluate prospective motion correction using the pilot tone (PT) as a quantitative respiratory motion signal with high temporal resolution for cardiac cine images during free breathing.Methods: Before cine data acquisition, a short prescan was performed, calibrating the PT to the respiratory‐induced heart motion using respiratory‐resolved real‐time images. The calibrated PT was then applied for nearly real‐time prospective motion correction of cine MRI through slice tracking (ie, updating the slice position before every readout). Additionally, in‐plane motion correction was performed retrospectively also based on the calibrated PT data. The proposed method was evaluated in a moving phantom and 10 healthy volunteers.Results: The PT showed very good correlation to the phantom motion. In volunteer studies using a long‐term scan over 7.96 ± 1.40 min, the mean absolute error between registered and predicted motion from the PT was 1.44 ± 0.46 mm in head‐feet and 0.46 ± 0.07 mm in anterior‐posterior direction. Irregular breathing could also be corrected well with the PT. The PT motion correction leads to a significant improvement of contrast‐to‐noise ratio by 68% (P ≤ .01) between blood pool and myocardium and sharpness of endocardium by 24% (P = .04) in comparison to uncorrected data. The image score, which refers to the cine image quality, has improved with the utilization of the proposed PT motion correction.Conclusion: The proposed approach provides respiratory motion‐corrected cine images of the heart with improved image quality and a high scan efficiency using the PT. The PT is independent of the MR acquisition, making this a very flexible motion‐correction approach.

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