MR Imaging of the Knee: Three-Dimensional Fourier Transform GRASS Technique

ABSTRACT

PURPOSE: To evaluate the usefulness of three-dimensional(3D) Fourier transform(FT) gradient refocused acquisition in steady state(GRASS) technique for MR imaging of the knee. MATERIALS AND METHODS: Sixty-three kneesin 61 patients were imaged on the 1.5T MR system. We compared 3DFT GRASS technique with 2D spin echo(SE) techniquein terms of conspicuousness of the lesions of internal knee structures based on the results of arthroscopy or open surgery. As a SE technique, sagittal T1-and T2-weighted, and coronal fat-suppressed T2-weighted sequences were performed. Sixty contiguous axial scans with 0.7 or 1mm section thickness were performed using 3D GRASS technique, and we also evaluated arbitrarily reformatted images produced from the original axial voxel images. RESULTS: For the depiction of the tear, 3DFT GRASS was superior to 2D SE in three cases of medial meniscus, one of later almeniscus, and two of anterior cruciate ligament. Specificity of 3D GRASS was also higher than that af 2D SE inevaluation of lateral meniscus and anterior cruiciate ligament. There was no significant difference in MR diagnosis for tears of the posterior cruciate, medial collateral, and lateral collateral ligaments. 3D GRASS was superior in evaluating the extent and morphology of the torn menisci. CONCLUSION: The 3DFT GRASS technique was comparable or even superior to the 2D SE technique in the evaluation of the internal structure of the knee, andcan be expected to supplement standard MR knee techniques, especially in complicated cases of meniscal orligamentous tears.