The purpose of this study was to determine the MR image resolution and signal-to-noise ratio (SNR) required to reveal morphologic abnormalities in degenerative cartilage.
In vitro MR microscopy of healthy bovine and degenerative human patellar cartilage was performed and image resolution degraded to simulate resolution achievable in routine and optimized clinical MR images. Noise was then added to images as in-plane resolution was increased to simulate the MR imaging appearance of cartilage with improved resolution, which is possible using a standard magnetic field strength. MR images of patellar cartilage from a healthy volunteer were also obtained to determine optimal SNR and image resolution achievable at 1.5 T; these images were compared with in vitro images to determine those features of abnormal cartilage that can be identified using available clinical MR imaging techniques.
In-plane resolution of 39 microns exquisitely defines degenerative changes in articular cartilage. As in-plane resolution decreases to 600 microns, only gross cartilage thinning and signal intensity alterations are seen. MR images simulating progressively improved resolution using higher field strength gradients with conventional field strengths and RF coils provided suboptimal information because of low SNR.
Routine clinical MR images do not accurately reveal early degenerative changes in articular cartilage; only large defects and distorted changes in the signal intensity of cartilage are seen.