Value of Axial 3-D Fourier Transformation GRASS MR Images in Diagnosis of Meniscal Tears of the Knee

PURPOSE: The purpose of this study is to compare the sensitivity and specificity of axial 3-D imaging with those of conventional 2-D imaging in the diagnosis of meniscal injuries. MATERIALS AND METHODS: Twenty-nine kneesof 27 patients with clinically suspected meniscal tears were imaged at a 1.5 T MR system. Conventional 2-D imagesand axial 3-D GRASS images were obtained in all cases. Arthroscopic or surgical confirmation was available in allcases and was used as the gold standard. RESULTS: Among the 29 knee-joints evaluated, 21 of 23 meniscal tears and 33 of 35 normal menisci were correctly identified with axial 3-D imaging, yielding a sensitivity of 91.3% and specificity of 94.3%. Conversely, the sensitivity was 82.6% and the specificity was 97.1% for the conventional 2-Dtechnique. A combination of both techniques yielded 95.7% sensitivity and 100% specificity in the diagnosis of meniscal tears. Of the 23 meniscal tears proven at arthroscopy or surgery, there were four discrepancies between the two techniques ; three of the four represented false-negative 2-D images and one was a false-negative axial3-D image. Of 35 normal menisci, two false-positives occurred with axial 3-D imaging and one with 2-D imaging. CONCLUSION: Despite the lack of a statistically significant difference between the efficacy of the two techniques, these results suggest that the sensitivity in the diagnosis of meniscal tears can be improved by adding thin-sliced axial 3-D GRASS imaging to conventional 2-D imaging in the limited cases with clinically suspected meniscal tears.

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

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.