Depth-dependent proton magnetization transfer in articular cartilage.
OBJECTIVE
To measure the proton magnetization transfer ratio (MTR) maps in control and collagen-depleted bovine patellar cartilage specimens as a function of cartilage depth during mechanical compression.


METHODS
One-dimensional proton projection MR images employing a spin-echo imaging sequence were obtained on a custom-built NMR spectrometer interfaced to an Oxford magnet operating at 2T. The mechanical compressions were performed with a custom-built MR-compatible pressure cell and evaluated dynamically via one-dimensional projection. High-spatial-resolution two-dimensional MT images were obtained using a fast spin-echo (FSE) sequence on a 4T whole-body GE Signa scanner (GEMS, Milwaukee, WI, USA) to quantify the MTR maps of normal and collagen-depleted bovine patellae.


RESULTS
All of the cartilage plugs from the bovine patellae showed that the MTR value increases continuously as a function of cartilage depth. Although the overall MTR trend as a function of depth is the same in both control and collagen-depleted cartilage, the magnitude of the MTR value differs between the two. The MTR value is decreased with collagen depletion and increased with mechanical compression. The increase in MTR value during compression may be due to a decrease in free water content and volume, resulting in an increase in collagen concentration.


CONCLUSIONS
We demonstrated that the MTR in bovine patellar cartilage is depth-dependent and is relatively higher in the radial zone compared to the superficial zone. The high MTR in the radial zone not only depends on collagen content, it may also reflect a number of other parameters, such as the arrangement of macromolecules, high solid content, bound water fraction attached to macromolecules, radial orientation, etc.
Regatte
Ravinder R
RR
Department of Radiology, Centre for Biomedical Imaging, New York University School of Medicine, 301 East 17th Street, New York, NY 10003, USA. Ravinder.regatte@med.nyu.edu
Akella
Sarma V S
SV
Reddy
Ravinder
R
D000818:Animals; D002358:Cartilage, Articular / Q000033:anatomy & histology* / Q000473:pathology; D002417:Cattle; D004195:Disease Models, Animal; D006025:Glycosaminoglycans / Q000378:metabolism*; D008279:Magnetic Resonance Imaging; D010329:Patella; D012016:Reference Values; D012307:Risk Factors; D012680:Sensitivity and Specificity; D013314:Stress, Mechanical; D046509:Tissue Culture Techniques
D006025:Glycosaminoglycans