Reversed Laminar Appearance of Articular Cartilage by T1-Weighting in 3D Fat-Suppressed Spoiled Gradient Recalled Echo (SPGR) Imaging

Purpose: To investigate the reversed intensity pattern in the laminar appearance of articular cartilage by 3D fat-suppressed spoiled gradient recalled echo (FS-SPGR) imaging in magnetic resonance imaging (MRI). Materials and Methods: The 3D SPGR experiments were carried out on canine articular cartilage with an echo time (TE) of 2.12 msec, a repetition time (TR) of 60 msec, and various flip angles (5 to 800). In addition, T1, T2, and T2* in cartilage were imaged and used to explain the laminar appearance in SPGR imaging. Results: The profiles of T2 and T2* in cartilage were similar in shape. However, the T2 values from the multigradient-echo imaging sequence were about 1/3 of those from single spin-echo sequences at a pixel resolution of 26 mu m. While the laminar appearance of cartilage in spin-echo imaging is caused mostly by T2-weighting, the laminar appearance of cartilage in fast imaging (ie. short TR) at the magic angle can have a reversed intensity pattern, which is caused mostly by T1-weighting. Conclusion: The laminar appearance of articular cartilage can have opposite intensity patterns in the deep part of the tissue, depending on whether the image is T1 weighted or T2-weighted. The underlying molecular structure and experimental protocols should both be considered when one examines cartilage images in MRI.