A Unique Anisotropic R-2 Of Collagen Degeneration (Arcade) Mapping As An Efficient Alternative To Composite Relaxation Metric (R-2-R-1 Rho) In Human Knee Cartilage Study

Purpose: Anisotropic transverse R-2 (1/T-2) relaxation of water proton is sensitive to cartilage degenerative changes. The purpose is to develop an efficient method to extract this relaxation metric in clinical studies.Methods: Anisotropic R-2 can be measured inefficiently by standard R-2 mapping after removing an isotropic contribution obtained from R-1 rho mapping. In the proposed method, named as a unique anisotropic R-2 of collagen degeneration (ARCADE) mapping, an assumed uniform isotropic R-2 was estimated at magic angle locations in the deep cartilage, and an anisotropic R-2 was thus isolated in a single T2W sagittal image. Five human knees from 4 volunteers were studied with standard R-2 and R-1 rho mappings at 3T, and anisotropic R-2 derived from ARCADE on the T2W (TE = 48.8 ms) image from R-2 mapping was compared with the composite relaxation (R-2 - R-1 rho) using statistical analysis including Student's t-test and Pearson's correlation coefficient.Results: Anisotropic R-2 (1/s) from ARCADE was highly positively correlated with but not significantly different from standard R-2 - R-1 rho (1/s) in the segmented deep (r = 0.83 +/- 0.06; 8.3 +/- 2.9 vs. 7.3 +/- 1.9, P = .50) and the superficial (r = 0.82 +/- 0.05; 3.5 +/- 2.4 vs. 4.5 +/- 1.6, P = .39) zones. However, after eliminating systematic errors by the normalization in terms of zonal contrast, anisotropic R-2 was significantly higher (60.2 +/- 18.5% vs. 38.4 +/- 16.6%, P < .01) than R-2 - R-1 rho as predicted.Conclusion: The proposed anisotropic R-2 mapping could be an efficient alternative to the conventional approach, holding great promise in providing both high-resolution morphological and more sensitive transverse relaxation imaging from a single T2W scan in a clinical setting.