A unique anisotropic R₂ of collagen degeneration (ARCADE) mapping as an efficient alternative to composite relaxation...

Anisotropic transverse R₂ (1/T₂ ) 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.

Anisotropic R₂ can be measured inefficiently by standard R₂ mapping after removing an isotropic contribution obtained from R_1ρ mapping. In the proposed method, named as a unique anisotropic R₂ of collagen degeneration (ARCADE) mapping, an assumed uniform isotropic R₂ was estimated at magic angle locations in the deep cartilage, and an anisotropic R₂ was thus isolated in a single T2W sagittal image. Five human knees from 4 volunteers were studied with standard R₂ and R_1ρ mappings at 3T, and anisotropic R₂ derived from ARCADE on the T2W (TE = 48.8 ms) image from R₂ mapping was compared with the composite relaxation (R₂ - R_1ρ ) using statistical analysis including Student's t-test and Pearson's correlation coefficient.

Anisotropic R₂ (1/s) from ARCADE was highly positively correlated with but not significantly different from standard R₂ - R_1ρ (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 R₂ was significantly higher (60.2 ± 18.5% vs. 38.4 ± 16.6%, P < .01) than R₂ - R_1ρ as predicted.

The proposed anisotropic R₂ 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.