INTERSCANNER VARIATION IN BRAIN MRI LESION LOAD MEASUREMENTS IN MS - IMPLICATIONS FOR CLINICAL-TRIALS

We evaluated the effect of interscanner variation on brain MRI-measure d lesion volumes and measurement reproducibility in MS. Twenty clinica lly definite MS patients were each scanned on two or three scanners (a total of 14 scanners were used). In addition, a formalin-fixed MS bra in was studied on eight scanners from different manufacturers and with different field strengths. For the formalin-fixed MS brain, on each m achine we obtained two scans with slice thicknesses of 5 and 3 mm. Onl y 5-mm-thick slices were obtained from patients. The lesion volume pre sent on each scan was evaluated three times by a single observer in ra ndom order, using a local thresholding technique. In two groups of eig ht patients scanned on machines with different field strengths, the me an lesion volumes present on scans obtained at 1.5 T were significantl y higher than those measured on scans obtained with machines operating at 0.5 and 1.0 T (p < 0.01). When a single observer repeatedly evalua ted the same scan, a median intraobserver agreement of 98.7% (95% CI, 97.9 to 99.1) was achieved. However, when the observer evaluated the s cans from different MRI scanners, the agreement (an interscanner agree ment) fell to 91.1% (CI, 90.2 to 94.1). When only scanners operating a t 1.5 T were considered, the median interscanner agreement was 96.7% ( CI, 95 to 97.5). Also, for the formalin-fixed MS brain, the intraobser ver agreements obtained with both slice thicknesses were significantly higher than the corresponding interscanner agreements. The interscann er agreement, but not the intraobserver agreement, obtained with a sli ce thickness of 3 mm was higher than that obtained with a slice thickn ess of 5 mm. Our results indicate that lesion volume measurements in M S are influenced significantly by the use of different MR scanners and that a patient included in a serial study should be always scanned wi th the same MR machine using 3-mm thick slices.