Low-field MRI of the knee joint: results of a prospective, arthroscopically controlled study.

Purpose: To define the diagnostic accuracy of an open low-field MR unit (Ma gnetom Open(R), Siemens, Erlangen) in traumatic knee lesions. Materials and Methods: The MRIs of 150 patients were prospectively evaluated by two inde pendent readers with different experience levels. The study protocol includ ed a proton-density weighted SE-sequence in the sagittal, a T-2*-weighted F lash-2D-sequence in the coronal, and a 3D-acquisition (DESS) in the axial p lane. 75 patients were treated either conservatively or operatively. Result s: Based on arthroscopy as the gold standard, the sensitivities, specificit ies, and diagnostic accuracies for lesions of the medial and lateral menisc us, the anterior cruciate ligament (ACL), the hyaline cartilage, and the po sterior cruciate ligament (PCL) were 92%, 92% and 92%, 83%, 93% and 92%, 95 %, 96% and 96%, 74%, 93% and 85%, and 100%, respectively, for reader 1. The values for reader 2 were 81%, 74% and 77% (medial meniscus), 61%, 86% and 80% (lateral meniscus), 79%, 95% and 91% (ACL), 48%, 91% and 73% (hyaline c artilage), and 100% each (PCL), respectively. There were no statistical dif ferences between the two readers (Fisher's Exact Test, 95%-confidence inter val). Conclusions: Using a time-consuming examination protocol, the diagnos tic accuracies of the:open low-field MR unit are well comparable to those o btained with mid- or high-field units. Although not statistically significa nt in this study, the experience level of the examiner seems to be of consi derable clinical relevance.