Three-point Dixon chemical-shift imaging for evaluating articular cartilage defects in the knee joint on a low-field-strength open magnet

OBJECTIVE. The purpose of our study was to assess the value of a modified three-point Dixon MR technique for evaluating articular cartilage defects in the knee joint on a low-field-strength open magnet, correlated with arthroscopy. SUBJECTS AND METHODS: Twenty consecutive patients who underwent both MR imaging and arthroscopy of the knee joint for suspected internal derangement were examined. A modified three-point Dixon MR sequence with a single radiofrequency echo single-scan method for water and fat separation with correction of the static field inhomogeneities was performed on a 0.35-T open magnet to obtain fat suppression. The MR images were prospectively evaluated for the presence and grade of articular cartilage defects. RESULTS. Uniform fat suppression was obtained in all patients using the modified three-point Dixon technique. Fifty-nine cartilage abnormalities were identified in 19 patients on the basis of arthroscopy. Forty-seven of 59 arthroscopically proven abnormalities were prospectively detected on MR imaging. Compared with arthroscopy, the overall sensitivity of the modified three-point Dixon technique in detecting cartilage lesions was 80% and the specificity was 73%. Sixty-five percent of the cartilage abnormalities were graded identically on MR imaging and arthroscopy. CONCLUSION. The modified three-point Dixon sequence is a useful technique for achieving fat suppression in the knee joint on a 0.35-T open magnet. It is a sensitive and specific technique :for the assessment of cartilage abnormalities in the knee.