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Articular Cartilage in the Knee: Mapping of the Physiologic Parameters at MR Imaging with a Local Gradient Coil—Preliminary Results

¹ Department of Radiology, Veterans Administration Medical Center, 9114–RI, 3350 La Jolla Village Dr, San Diego, CA 92161.

View larger version (127K): [in a new window]   Figure 1. The local gradient and RF coil system used in this study.

View larger version (150K): [in a new window]   Figure 2. High-spatial-resolution image (FOV, 16 cm; section thickness, 3 mm; matrix, 256 x 256; two signals acquired) of the normal knee in a volunteer, obtained with the two-dimensional GRE sequence (600/9 with 20° flip angle). The patellar cartilage (arrow) is clearly evident and of normal thickness.

View larger version (58K): [in a new window]   Figure 3. High-spatial-resolution images (FOV, 9.4 cm; matrix, 256 x 256; one signal acquired) of a cadaveric specimen with a region of cartilage abnormality (arrow). Left: Three-dimensional spoiled GRE image (60/5; flip angle, 20°; section thickness, 1.5 mm); the abnormality is apparent as a region of decreased relative signal intensity. Right: T2-weighted, spin-echo image (4,000/80; section thickness, 3 mm); the abnormality is apparent as a region of increased relative signal intensity.

View larger version (63K): [in a new window]   Figure 4. Fat-suppressed, projection-reconstruction images of a cadaveric specimen with a region of cartilage abnormality (short arrows). Images were acquired with 500-µsec (left) or 200-µsec (right) ramp times facilitated by the local gradient coil. The abnormality is again clearly evident, but it appears in the image on the right as a bright region (long arrow) near the subchondral bone that is suggestive of the calcified cartilage region.

View larger version (86K): [in a new window]   Figure 5. T1 (top) and T2 (bottom) maps calculated from the data for a set of high-spatial-resolution (FOV, 9.4 cm; section thickness, 5 mm; matrix, 256 x 256; one signal acquired) long TR, double-echo (4,000/20, 80) and short TR (600/20) images. The maps were obtained in a region of normal cartilage (left) and in a region of cartilage abnormality (right, arrow). The scale indicates milliseconds. The cartilage abnormality is clearly seen on both maps, which suggests that relaxation rate imaging is potentially useful as a method of detecting cartilage abnormalities before gross structural changes occur and may provide a framework for quantification of these changes. The observed changes in relaxation rate are consistent with the theory that structural changes that accompany cartilage degradation are associated with hydration.

View larger version (81K): [in a new window]   Figure 6a. Proton-density maps calculated from the data for a set of high-spatial-resolution long TR, double-echo and short TR images. The maps were obtained in a region of normal cartilage (left) and in a region of cartilage abnormality (right, arrow). The scale indicates arbitrary units. The cartilage abnormality is clearly seen, suggesting that these may also be useful as a method for early detection of cartilage abnormalities. These changes are also consistent with the theory that structural changes that accompany cartilage degradation are associated with hydration.

View larger version (86K): [in a new window]   Figure 6b. Proton-density maps calculated from the data for a set of high-spatial-resolution long TR, double-echo and short TR images. The maps were obtained in a region of normal cartilage (left) and in a region of cartilage abnormality (right, arrow). The scale indicates arbitrary units. The cartilage abnormality is clearly seen, suggesting that these may also be useful as a method for early detection of cartilage abnormalities. These changes are also consistent with the theory that structural changes that accompany cartilage degradation are associated with hydration.

View larger version (44K): [in a new window]   Figure 7a. Maps of apparent diffusion coefficient calculated from the data for spin-echo images (600/40; FOV, 9.4 cm; section thickness, 10 mm; matrix, 256 x 256; one signal acquired; b factor, approximately 373 sec/mm2 along each of the three axes). The maps were obtained at a region of normal cartilage (left) and a region of cartilage abnormality (right, arrow). The scale indicates square microns per millisecond x 1,000. The cartilage abnormality clearly shows an increase in apparent diffusion coefficient, which is again consistent with changes in hydration.

View larger version (44K): [in a new window]   Figure 7b. Maps of apparent diffusion coefficient calculated from the data for spin-echo images (600/40; FOV, 9.4 cm; section thickness, 10 mm; matrix, 256 x 256; one signal acquired; b factor, approximately 373 sec/mm2 along each of the three axes). The maps were obtained at a region of normal cartilage (left) and a region of cartilage abnormality (right, arrow). The scale indicates square microns per millisecond x 1,000. The cartilage abnormality clearly shows an increase in apparent diffusion coefficient, which is again consistent with changes in hydration.