# Improved Navigator-Gated Motion Compensation in Cardiac MR Using Additional Constraint of Magnitude of Motion-Corrupted Data

 Title: Improved Navigator-Gated Motion Compensation in Cardiac MR Using Additional Constraint of Magnitude of Motion-Corrupted Data Author: Shaw, Jaime L; Moghari, Mehdi H.; Akcakaya, Mehmet; Chan, Raymond Ho Ming; Manning, Warren J.; Nezafat, Reza Note: Order does not necessarily reflect citation order of authors. Citation: Shaw, Jaime L., Mehdi H. Moghari, Mehmet Akcakaya, Raymond H. Chan, Warren J. Manning, and Reza Nezafat. 2012. Improved navigator-gated motion compensation in cardiac MR using additional constraint of magnitude of motion-corrupted data. Journal of Cardiovascular Magnetic Resonance 14(Suppl 1): P245. Full Text & Related Files: 3304776.pdf (1.270Mb; PDF) Abstract: Background. In conventional prospective respiratory navigator (NAV) acquisitions, 40-60% of the acquired data are discarded resulting in low efficiency and long scan times [1,2].Compressed-sensing Motion Compensation (CosMo) has a shorter fixed scan time by acquiring the full inner k-space and estimating the NAV-rejected outer k-space lines [3]. Respiratory motion will mainly manifest itself as phase variation in the acquired k-space data. We sought to determine if the addition of the magnitude of the rejected k-space lines as a constraint in image reconstruction will improve the performance of CosMo. Methods. To investigate the variability of the magnitude of kspace lines at different respiratory phases, free-breathing, ECG-triggered, targeted right coronary images with multiple averages were acquired from 10 healthy adult subjects. Magnitude variability was investigated quantitatively by calculating the cross-correlation between accepted and rejected k-space lines. CosMo was implemented retrospectively on one acquisition from each subject. The inner k-space (31 ky by 7 kz lines) was filled with lines acquired within the 5mm gating window from all acquisitions. The outer kspace was then filled only with lines from the first average acquired within the 5 mm gating window, resulting in an undersampled k-space with a fully sampled center. For reliable image reconstruction with CosMo, 10-20% of the inner k-space must be fully-sampled. The missing outer k-space lines were then estimated using LOST with an additional magnitude constraint within each estimation iteration or in the final iteration for each coil [4]. The results were compared with prospective NAVgating with a gating window of 5 mm and CosMo reconstruction without the magnitude constraint. Results. Figure 1 shows the cross-correlation between the accepted and worst rejected k-space lines for each position. The correlation is close to 1 at the center of kspace where the majority of image information is contained, indicating low variability in magnitude information at different respiratory phases. Figure 2 shows right coronary images acquired using a) fully-sampled, 5-mm gated data, b) the original CosMo, and CosMo with the additional magnitude constraint c) inside each iteration and d) in the final iteration. The relative signal-to-noise in the left ventricle blood pool is: $$30.71 \pm 6.5; 40.32 \pm 14.2; 53.9 \pm 26.8; 56.8 \pm 25.9$$ for each reconstruction, respectively. Significant differences (p<0.05) are present for all measurements except between the original CosMo and the CosMo image with the magnitude constraint in each iteration (p=0.09). Conclusions. The addition of the magnitude of rejected lines, readily available in all navigator-gated scans, as a constraint in CosMo results in improved image quality as measured by relative SNR. Funding. NIH R01EB008743-01A2. Published Version: doi:10.1186/1532-429X-14-S1-P245 Other Sources: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3304776/pdf/ Terms of Use: This article is made available under the terms and conditions applicable to Other Posted Material, as set forth at http://nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of-use#LAA Citable link to this page: http://nrs.harvard.edu/urn-3:HUL.InstRepos:10246885 Downloads of this work: