Is There an Optimal Respiratory Reference Position for Self-Navigated Whole-Heart Coronary MR Angiography?

Purpose: To test the direct influence of the reference respiratory position on image quality for self-navigated whole-heart coronary MRI. Methods: Self-navigated whole-heart coronary MRI was performed in 11 healthy adult subjects. Respiratory motion was compensated for by using three different respiratory reference positions of the heart: end-inspiratory, end-expiratory, and the mean of the entire respiratory excursion. All datasets were reconstructed without motion compensation for comparison. Image quality was assessed in all reconstructions using signal-to-noise ratio (SNR) and contrst-to-noise ratio (CNR) measurements, as well as percentage vessel sharpness and visible length of the coronary arteries. Results: While SNR and CNR remained close to constant in all reconstructions, a clear and significant improvement in vessel sharpness was identified in all motion corrected datasets with respect to their uncorrected counterpart (e.g., percentage sharpness of the proximal right coronary artery (RCA): 61.6+/-8.2% for end-inspiration, 64.1+/-10.7% for end-expiration, and 63.3+/-7.0% for the mean respiratory position versus 55.0+/-10.4 for the uncorrected datasets; P<0.05). Among all motion corrected reconstructions, the use of an end-expiratory reference position most consistently provided the highest image quality. In particular, some of the improvements in vessel sharpness and length measured for end-expiration were statistically significant with respect to the reconstructions performed at end-inspiration (e.g., percentage sharpness of the proximal left anterior descending coronary: 58.2+/-7.4% versus 55.8+/-8.4%; P<0.05; and visible length of the RCA: 125.7+/-25.9 mm versus 114.4+/-27.4 mm; P<0.05). Conclusion: The use of end-expiration as a reference position for respiratory motion correction in free-breathing self-navigated whole heart coronary MRA significantly improves image quality.