Abstract:
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Purpose: To demonstrate that the T2 of articular cartilage can not be predicted unless one accounts for cartilage structure and orientation relative to the static field (B0) in three dimensions.
Methods and Materials: A tendon, straight in the proximal half and curved through a 90° arc distally, served as a phantom representing the curved structure of cartilage extracellular matrix as displayed on electron microscopy studies. T2 maps (TR/TE 1s/10,15,20,25,30 ms) were acquired at 7 Tesla with the straight half parallel to B0 (position a), and then in two different 55° positions. The phantom was tilted 55° away from B0, first in the plane of curvature (position b) and then perpendicular to the direction of the curve (position c). On the T2 map acquired in position a, regions of interest were drawn in the straight region and in the curved region at the level of maximal T2. T2 measurements in these same tendon locations on all three maps were compared. Three T2 maps were then acquired in the same plane through an osteochondral fragment held in three different orientations relative to B0. The sample was first positioned with the articular surface perpendicular to B0 (0°) and then parallel to B0 (90°) with the image plane parallel to and then perpendicular to B0. T2 within a region of interest at the level of longest T2 (the transitional layer) of the sample imaged at 0° was compared to T2 measurements in the same location on the two 90°images.
Results: Tendon T2 in the straight region measured 8.9 ms in position a and increased to 24.8 ms and 28.8 ms in positions b and c respectively when tilted 55° away from B0. T2 in the curved region measured 31.9 ms in position a. After tilting 55°, T2 measured 7.9 ms and 24.8 ms in positions b and c respectively. T2 in the transitional layer of the femoral condyle fragment measured 61.7 ms in the 0° position and 29.2 ms and 34.5 ms in the 90° position with the image plane parallel to and perpendicular to B0 respectively.
Conclusion: If a curved tissue with T2 anisotropy, like articular cartilage is tilted away from B0 the tissue orientation and resulting T2 will vary significantly depending on what direction the tissue is tilted. Predictions of cartilage T2 must account for both the structure of the matrix and the orientation in three dimensions.
Goodwin MD, D,
Predictions of Cartilage T2 Must Account for the Three-dimensional Structure of the Extracellular Matrix. Radiological Society of North America 2003 Scientific Assembly and Annual Meeting, November 30 - December 5, 2003 ,Chicago IL.
http://archive.rsna.org/2003/3105517.html
