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 t hree-point Dixon MR technique for evaluating articular cartilage defects in the knee joint on a low-field-strength open magnet, correlated with arthro scopy. SUBJECTS AND METHODS: Twenty consecutive patients who underwent both MR ima ging and arthroscopy of the knee joint for suspected internal derangement w ere examined. A modified three-point Dixon MR sequence with a single radiof requency echo single-scan method for water and fat separation with correcti on of the static field inhomogeneities was performed on a 0.35-T open magne t 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 mod ified three-point Dixon technique. Fifty-nine cartilage abnormalities were identified in 19 patients on the basis of arthroscopy. Forty-seven of 59 ar throscopically proven abnormalities were prospectively detected on MR imagi ng. Compared with arthroscopy, the overall sensitivity of the modified thre e-point Dixon technique in detecting cartilage lesions was 80% and the spec ificity was 73%. Sixty-five percent of the cartilage abnormalities were gra ded identically on MR imaging and arthroscopy. CONCLUSION. The modified three-point Dixon sequence is a useful technique f or 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 abno rmalities in the knee.