Improved interobserver agreement for visual detection of active T2 lesionson serial MR scans in multiple sclerosis using image registration

The aim of this study was to analyse the effect of image registration on in terobserver agreement in the visual detection of active multiple sclerosis (MS) lesions from serial magnetic resonance (MR) scans. TZW spin-echo MR sc ans (3-mm slices) of 16 MS patients participating in a treatment trial were selected. For each patient, two pairs of scans were used: an original (i.e ., non-registered) and a registered pair. For the original pair, baseline a nd month 6 were used, and for the registered pair month 3 and 9. For regist ration an automatic matching algorithm based on Mutual Information was used . Six observers identified active lesions on both original and registered s cans. Kappa values were calculated to assess interobserver agreement. Resli cing caused a slight blurring of the images, but near perfect registration. The kappa value of 0.35 +/- 0.07 for new lesions on original images improv ed to 0.62 (+/- 0.06) by registration (p = 0.004). For enlarging lesions on original images it was extremely poor (kappa 0.11 +/- 0.05), and did not b enefit much by registration (kappa 0.20 +/- 0.11). Thus, image registration improved interobserver agreement for visual detection of new lesions. For enlarging lesions, registration improved agreement but still not to a satis factory level.