title: The accuracy of signal intensity measurements in magnetic resonance imaging as evaluated within the knee.
abstract: Quantitative signal intensity measurements are being utilized in both clinical and research magnetic resonance imaging protocols. This paper addresses three questions in quantitative MRI measurements as evaluated within the knee: 1) the accuracy of quantitative measurements; 2) improvement of accuracy by phantom normalization; and 3) the amount of signal change that is clinically significant. Seven normal subjects were imaged on three different days within a 1-wk period. Test-tube phantoms of manganous chloride (MnCl2) were imaged posterior to the knee and were used to normalize each image. The variation in signal intensity within the same subject averaged 20% for both the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL). The phantom variation was approximately 18%. Signal intensity normalization by background subtraction, background division, phantom division, or a combination of subtraction and division did not significantly improve either the phantom variation or the ligament variation. Given that an individual ligament intensity will be measured with standard errors of +/- 20% of its value, we calculated the minimum increase in signal intensity to be considered abnormal relative to a normal ligament. A relative signal increase of 46% can be considered pathologic with 95% confidence. These findings emphasize that quantitative measurements must be carefully assessed when being applied in clinical settings.
authors.affiliation: School of Medicine, University of California, San Diego, La Jolla 92093.
authors.forename: G S
authors.initials: GS
authors.lastname: Berns
authors.forename: S M
authors.initials: SM
authors.lastname: Howell
authors.forename: T E
authors.initials: TE
authors.lastname: Farley
mesh_terms: D005069:Evaluation Studies as Topic; D005260:Female; D006801:Humans; D007717:Knee / Q000033:anatomy & histology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008961:Models, Structural