Fig 3. Positive, negative, and net changes from pairs of subtraction images: the discriminatory power of SSEG. Change measurements obtained from pairs of dual-echo images using CSEG and SSEG methods are depicted. A, Patient-by-patient representation of lesion volume changes measured with SSEG and CSEG in pairs of dual-echo MR images from 21 patients with MS. The CSEG method can only measure the net change in lesion volume (black bar in each patient). In contrast, the SSEG method provides information about the volume change in new (red bars), enlarging (yellow bars), and resolving lesions (blue bars), as well as yielding a net lesion volume change (sum of new and enlarging lesion volumes minus resolving lesion volume; green bars). B, The average lesion volume changes measured with the CSEG and SSEG methods are shown. Greater average net lesion volume change is measured with the SSEG method, although no statistically significant difference is found in the net lesion volume change measured with both methods (P = 0.14, Wilcoxon test).