[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 (Magnetom Open, Siemens, Erlangen) in traumatic knee lesions.

MATERIALS AND METHODS: The MRIs of 150 patients were prospectively evaluated by two independent readers with different experience levels. The study protocol included a proton-density weighted SE-sequence in the sagittal, a T2.-weighted Flash-2D-sequence in the coronal, and a 3D-acquisition (DESS) in the axial plane. 75 patients were treated either conservatively or operatively.

RESULTS: Based on arthroscopy as the gold standard, the sensitivities, specificities, and diagnostic accuracies for lesions of the medial and lateral meniscus, the anterior cruciate ligament (ACL), the hyaline cartilage, and the posterior 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 cartilage), and 100% each (PCL), respectively. There were no statistical differences between the two readers (Fisher's Exact Test, 95%-confidence interval).

CONCLUSIONS: Using a time-consuming examination protocol, the diagnostic accuracies of the open low-field MR unit are well comparable to those obtained with mid- or high-field units. Although not statistically significant in this study, the experience level of the examiner seems to be of considerable clinical relevance.