Nikita Garnov, Presenter: Nothing to Disclose

Gregor Thörmer, Abstract Co-Author: Nothing to Disclose

Wilfried Gründer, Abstract Co-Author: Nothing to Disclose

Robert Trampel PhD, Abstract Co-Author: Nothing to Disclose

Robert Turner PhD, Abstract Co-Author: Nothing to Disclose

Thomas Kurt Kahn MD, Abstract Co-Author: Nothing to Disclose

Harald F. Busse PhD, Abstract Co-Author: Nothing to Disclose

To evaluate whether T2-weighted (T2w) knee imaging in a whole-body 7T MRI can help to non-invasively assess the collagen network structure and the layer boundaries within the cartilage.

The right knees of ten healthy volunteers (21-30 y) were examined in a 7T whole-body MR scanner. Sagittal images of the lateral condyles were acquired with an 8-ch. phased array coil using a T2w multi-echo SE sequence (TR/TE=2500/12–96 ms; 8 echoes; FOV=130×130 mm2; ST=1 mm; matrix=4482). Small ROIs were defined in the femur and tibia near the joint contact area and T2-maps were calculated. Intensity profiles as a function of cartilage depth were calculated for each echo time. Further analysis was performed for that echo time where the intensity profile best matched that of the T2-map. The data were analyzed with respect to an analytical model that quantitatively describes the dependence of the MR intensity on the ultrastructure of the collagen network (fascicle model). The intensity profiles were fitted to a dose-response curve with variable slope and then normalized assuming the minimum and maximum values to correspond to the theoretical values at an opening (fascicle) angle of α=0° (radial) and of α=90° (isotropic arrangement). The normalized intensity values were then used to convert the intensity profiles to depth-dependent profiles of α. The boundary between radial and transitional zone (R/T boundary) was assumed at α=35°. A paired t test was performed to analyze differences between femoral and tibial cartilage.

At 7T, high resolution images of the knee cartilage (voxel size of 0.3x0.3x1 mm3) had a sufficient SNR for subsequent quantitative analysis. In 13/20 cases, images at TE=60 ms were used. The cartilage thickness was 2.6-3.8 (femur) and 3.2-5.2 mm (tibia). The relative position of the R/T boundary of the femoral cartilage (mean±SD=0.54±0.16) appears to lie deeper than that of the tibial cartilage (0.65±0.16) although the values did not reach statistical significance (P=0.195).  

Using T2w 7T MRI data and assuming a simplified structure model allows to derive quantitative parameters of the collagen fiber arrangement and to estimate the thickness of the radial zone in adult cartilage.

With aging, the radial structure of the cartilage becomes more isotropic. The presented method could therefore be used to non-invasively determine the “biologic age” of the cartilage.  

Garnov, N, Thörmer, G, Gründer, W, Trampel, R, Turner, R, Kahn, T, Busse, H, Analysis of Collagen Fiber Arrangement of the Knee Cartilage of Ten Healthy Volunteers in a 7 T Whole Body MRI.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9003200.html