THE VARIABILITY OF MANUAL AND COMPUTER-ASSISTED QUANTIFICATION OF MULTIPLE-SCLEROSIS LESION VOLUMES

The high resolution and excellent soft tissue contrast of Magnetic Res onance Imaging (MRI) have enabled direct, noninvasive visualization of Multiple Sclerosis (MS) lesions in vivo. This has allowed the quantif ication of changes in the appearance of lesions in MR exams to be used as a measure of disease state. Nevertheless, accurate quantification techniques are subject to inter- and intra-operator variability, which may hinder monitoring of disease progression. We have developed a com puter program to assist an experienced operator in the quantification of MS lesions in standard spin-echo MR exams. The accuracy of assisted and manual quantification under known conditions was studied using ex ams of a test phantom, while inter- and intra-operator reliability and variability were studied using exams of a MS patient. Results from th e phantom study show that accuracy is improved by assisted quantificat ion. The patient exam results indicate that assisted quantification re duced inter-operator variability from 0.34 to 0.17 cm(3), and reduced intra-operator variability from 0.23 to 0.15 cm(3). In addition, the m inimum significant change between two successive measurements of lesio n volume by the same operator was 0.64 cm(3) for manual quantification and 0.42 cm(3) for assisted quantification. For two different operato rs making successive measurements, the minimum significant change was 0.94 cm(3) for manual quantification, but only 0.47 cm(3) for assisted quantification. Finally, the number of lesions to be monitored for an average change in volume at a given power and significance level was reduced by a factor of 2-4 by assisted quantification. These results s uggest that assisted quantification may have practical applications in clinical trials, especially those that are large, multicenter, or ext ended over time; and therefore require lesion measurements by one or m ore operators. (C) 1996 American Association of Physicists in Medicine .