Intra- and inter-observer variability in measuring lesion volume changes on serial brain MRI scans in patients with multiple sclerosis

This study evaluated the intra- and inter-observer variabilities when measuring long-term changes of multiple sclerosis (MS) brain lesion volumes on magnetic resonance imaging (MRI) scans with both 5 mm and 3 mm thick slices. We scanned 18 patients on two separate occasions with a mean interval 16.4 months between the two examinations. In each scanning session, a scan with 24 contiguous 5 mm thick and another with 40 contiguous 3 mm thick axial slices were acquired consecutively without moving the patient from the scanner. We assessed MRI lesion loads using a semi-automated local thresholding technique. Lesion volumes were significantly higher on scans with 3 mm thick slices than on those with 5 mm thick slices both at baseline and at follow up (p <0.001). Significant increases in the total lesion volume were observed during the follow up period on scans with 5 mm (median difference=+3.1%, range=53.7%-+49.2%; p=0.003) and on those with 3 mm (median difference=+4.5%, range=-46.2%-+41.9%; p=0.003) thick slices. The intra-observer (p <0.001) and the inter-observer (p-