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Molecular origin of a loading‐induced black layer in the deep region of articular cartilage at the magic angle
Author(s) -
Wang Nian,
Kahn David,
Badar Farid,
Xia Yang
Publication year - 2015
Publication title -
journal of magnetic resonance imaging
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.563
H-Index - 160
eISSN - 1522-2586
pISSN - 1053-1807
DOI - 10.1002/jmri.24658
Subject(s) - cartilage , magic angle , magnetic resonance imaging , glycosaminoglycan , chemistry , articular cartilage , materials science , nuclear magnetic resonance , biomedical engineering , anatomy , pathology , osteoarthritis , nuclear magnetic resonance spectroscopy , medicine , biochemistry , physics , alternative medicine , organic chemistry , radiology
Purpose To investigate the molecular origin of an unusual low‐intensity layer in the deep region of articular cartilage as seen in magnetic resonance imaging (MRI) when the tissue is imaged under compression and oriented at the magic angle. Materials and Methods Microscopic MRI (μMRI) T 2 and T 1 ρ experiments were carried out on 18 specimens, both native and degraded (treated with trypsin). The glycosaminoglycan (GAG) concentrations in the specimens were quantified by both sodium ICP‐OES and μMRI Gd(DTPA) 2‐ ‐contrast methods. The mechanical modulus of the specimens was also measured. Results Native tissue shows no load‐induced layer, while the trypsin‐degraded tissue shows clearly the low‐intensity line at the deep part of tissue. The GAG reductions were confirmed by the sodium ICP‐OES (from 81.7 ± 5.4 mg/mL to 9.2 ± 3.4 mg/mL), MRI GAG quantification (from 72.4 ± 6.7 mg/mL to 11.2 ± 2.9 mg/mL). The modulus reduction was confirmed by biomechanics (from 4.3 ± 0.7 MPa to 0.3 ± 0.1 MPa). Conclusion Both T 2 and T 1 ρ profiles in native and degraded cartilage show strongly strain‐, depth‐, and angle‐dependence using high‐resolution MRI. The GAG reduction is responsible for the visualization of a low‐intensity layer in deep cartilage when it is loaded and oriented at 55°. J. Magn. Reson. Imaging 2015;41:1281–1290. © 2014 Wiley Periodicals, Inc.