Purpose: Detailed examination of cartilage with short T2 relaxation times near the cartilage/bone interface may provide accurate measurements of cartilage thickness and information about collagen fiber organization. This information could be important in assessment of normal cartilage structure, injury and chondrocyte transplants. We have developed a method for high resolution short echo time spectroscopic imaging of cartilage. Materials and Methods: The short echo time spectroscopic imaging sequence uses either a half-pulse (TE 0.2 ms) or conventional excitation (TE 1.6 ms). Excitation is followed immediately by projection reconstruction readout gradients. Minimum FOV is 6 cm, with an in-plane resolution of 117 micrometers. Slice thickness is 2-3 mm, and scan time is from 4.5 to 9 minutes. Spectral resolution is 1.0 ppm, and spectral bandwidth is 6.7 ppm. Reconstruction of the 33 megabyte data set takes 4 minutes on a Sun Ultrasparc. All imaging was done on a 1.5T GE Signa with Echospeed gradients. Results: Ten normal volunteers and four patients with cartilage transplants have been studied. Normal cartilage shows increasing line width and decreasing peak area when moving from the articular surface towards the bone. Spectroscopic imaging resolves chemical shift artifact, and the short echo time allows evaluation of the cartilage in the calcified zone near the bony cortex. Conclusion: High resolution spectroscopic imaging of articular cartilage can be performed on a whole-body scanner. This technique may yield new information about the organization and type of collagen fibers present. It may be possible to follow the development and integration of chondrocyte transplants, and distinguish fibrocartilage from hyaline cartilage at the transplant site.
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