Quantifying precision in cardiac diffusion tensor imaging with second-order motion-compensated convex optimized diffusion encoding

Purpose: To quantify the precision of in vivo cardiac DTI (cDTI) acquired with a spin echo, first-andsecond-order motion-compensated (M1M2), convex optimized diffusion encoding (CODE) sequence. Methods: Free-breathing CODE- M1M2 cDTI were acquired in healthy volunteers (N = 10) at midsystole and diastole with 10 repeated acquisitions per phase. 95% confidence intervals of uncertainty in reconstructed diffusion tensor eigenvectors ((E) over right arrow (1), (E) over right arrow (2), (E) over right arrow (3)), mean diffusivity (MD), fractional anisotropy (FA), and tensor Mode were measured using a bootstrapping approach. Trends in observed tensor metric uncertainty were evaluated as a function of scan duration, image SNR, cardiac phase, and bulk motion artifacts. Results: For midsystolic scans including 5 signal averages (scan time: similar to 5 min), the median myocardial 95% confidence intervals of uncertainties were: (E) over right arrow (1): 15.5 +/- 1.28, ($) over right arrow (2): 31.2 +/- 3.58, (E) over right arrow (3): 21.863.18, MD: 0.38 +/- 0.02 x 10(-3)mm(2)/s, FA: 0.20 +/- 0.01, and Mode: 1.10 +/- 0.08. Uncertainty in all parameters increased for diastolic scans: (E) over right arrow (1): 31.9 +/- 7.18, (E) over right arrow (2): 59.6 +/- 6.88, (E) over right arrow (3) : 40.5 +/- 6.48, MD: 0.52 +/- 0.09 x 10(-3) mm(2)/s, FA: 0.23 +/- 0.01, and Mode: 1.57 +/- 0.11. Diastolic cDTI also reported higher MD (MDDIA = 1.91 +/- 0.34 x 10(-3) mm(2)/s vs. MDSYS = 1.58 +/- 0.09 x 10(-3) mm(2)/s, P = 831023) and lower FA values (FA(DIA) = 0.32 +/- 0.06 vs. FA(SYS) = 0.37 +/- 0.03, P = 0.03). Conclusion: cDTI precision improved with increasing nondiffusion-weighted (b = 0) image SNR, but gains were minimal for SNR >= 25 (similar to 10 averages). cDTI precision was also sensitive to intershot bulk motion artifacts, which led to better precision for midsystolic imaging.