An order parameter without magic angle effect (OPTIMA) derived from R1ρ dispersion in ordered tissue. Issue 5 (5th November 2019)

• Record Type: Journal Article
• Authors: Pang, Yuxi
• Is Part Of: Magnetic resonance in medicine. Volume 83:Issue 5(2020)
• Page Start: 1783
• Page End: 1795
• Publication Date: 2019-11-05
• Subjects: anisotropic R2 -- collagen -- correlation time -- magic angle effect -- order parameter -- R1ρ dispersion; Nuclear magnetic resonance -- Periodicals; Electron paramagnetic resonance -- Periodicals; 616.07548
• DOI: 10.1002/mrm.28045
• Languages: English
• ISSNs: 0740-3194

Abstract

Abstract : Purpose: MR R 2 imaging of ordered tissue exhibits the magic angle effect, potentially masking subtle pathological changes in cartilage. This work aimed to develop an orientation‐independent order parameter ( S ) exclusively sensitive to collagen degeneration. Methods: A theory was developed based on R 1 ρ dispersion coupled with a simplified molecular motion model in which anisotropic R 2 a ( θ ) became directly proportional to correlation time τ b θ and S could be derived. This new parameter was validated with ex vivo R 1 ρ dispersion reported on orientated (n = 4), enzymatically depleted bovine cartilage (n = 6), and osteoarthritic human knee specimens (n = 14) at 9.4 Tesla, which was further demonstrated on 1 healthy human knee in vivo at 3 Tesla. Results: τ b θ from orientation‐dependent R 1 ρ dispersion revealed a significantly high average correlation ( r = 0.89 ± 0.05, P < 0.05) with R 2 a ( θ ) on cartilage samples and a moderate correlation ( r = 0.48, P < 0.001) for the human knee in vivo. The derived S (10 −3 ) significantly decreased in advanced osteoarthritis (1.64 ± 0.03 vs. 2.30 ± 0.11, P < 0.001) and collagen‐depleted samples (1.30 ± 0.11 vs. 2.12 ± 0.12, P < 0.001) when compared with early osteoarthritis and the control, respectively. Conclusion: The proposed order parameter could be a potentially useful orientation‐independent MR biomarker for collagen alterations in cartilage and other highly structured tissues.