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Heterogeneity of cartilage laminae in MR imaging
1Department of Physics and Center for Biomedical Research, Oakland University, Rochester, Michigan 48309, USA. xia@oakland.edu
Abstract:
The purpose of this study was to investigate the discrepancy in the number of laminae observed in magnetic resonance (MR) images of articular cartilage (the magic angle effect in MRI of cartilage). Microscopic MR imaging (muMRI) experiments were carried out at 14-micrometer pixel resolution on full-depth cartilage-bone plugs from several locations (central, intermediate, and peripheral) on the humeral heads of two young healthy beagles. When the articular surface of the plug was perpendicular to the direction of the magnetic field, the cartilage appeared to have two layers in the plugs from the central locations of the humeral head, three layers in the plugs from the greater tubercle side of the humeral head, and three or five layers in the plugs from the lesser tubercle side. This heterogeneity of cartilage laminae was observed within a single humeral head and was symmetrical about the median plane of the animal. This result suggests that some structural variations related to cartilage structure in various regions of load bearing may cause some unique laminar patterns seen in MRI of cartilage. This novel and new observation may resolve the controversy about whether cartilage appears as two or three layers in MR images. A comprehensive model for the collagen structure over a curved two-dimensional surface of a joint is suggested as a replacement of the classic three-zone model of fiber orientation in collagen. This heterogeneity of cartilage laminae is speculated to be related to the load-bearing status of the tissue in the joint. The ability to visualize such structural heterogeneity is important because of the direct connection between collagen structure and the mechanical characteristics of cartilage.
Insights
Investigating the magic angle effect in magnetic resonance (MR) imaging of cartilage revealed regional variations in laminar patterns. This heterogeneity in articular cartilage laminae may explain discrepancies in MR imaging observations.
Area of Science:
- Biomedical Engineering
- Orthopedics
- Medical Imaging
Background:
- The appearance of articular cartilage in magnetic resonance (MR) images, specifically the number of observed laminae, has been a subject of debate.
- The magic angle effect in MR imaging of cartilage can influence image interpretation, leading to discrepancies in observed laminar structures.
Purpose of the Study:
- To investigate the discrepancy in the number of laminae observed in magnetic resonance (MR) images of articular cartilage, focusing on the magic angle effect.
- To explore potential structural variations in cartilage that may cause regional differences in laminar patterns seen in MR images.
Main Methods:
- Microscopic MR imaging (muMRI) was performed at 14-micrometer pixel resolution on full-depth cartilage-bone plugs.
- Samples were obtained from various locations (central, intermediate, peripheral) on the humeral heads of two healthy beagles.
- Imaging was conducted with the articular surface perpendicular to the magnetic field to observe the magic angle effect.
Main Results:
- Regional heterogeneity in cartilage laminae was observed within a single humeral head, with varying layer counts (2, 3, or 5) depending on the location.
- Specific laminar patterns were noted: two layers in central locations, three layers on the greater tubercle side, and three to five layers on the lesser tubercle side.
- This heterogeneity was symmetrical about the animal's median plane, suggesting a link to structural variations and load-bearing status.
Conclusions:
- The study suggests that regional structural variations in cartilage, potentially related to load-bearing, cause unique laminar patterns observed in MR imaging.
- This finding may resolve the controversy regarding whether cartilage appears as two or three layers in MR images.
- A comprehensive model for collagen structure over a curved joint surface is proposed, emphasizing the importance of visualizing structural heterogeneity for understanding mechanical properties.
