—We would like to thank Goodkin for his very interesting comments concerning our recent article entitled "Gadolinium-Pentetic Acid Magnetic Resonance Imaging in Patients With Relapsing Remitting Multiple Sclerosis."1 He clearly demonstrated that in serial magnetic resonance imaging studies of patients with multiple sclerosis, repositioning errors can be responsible in the apparent development of new enhancing plaques and, in general, of an overestimation of the total number of plaques.We agree with his observations and conclusions that even small repositioning errors could affect the overall evaluation of the brain disease activity, since the appearance, disappearance, enlargement, or reduction in size of a single lesion could be erroneously attributed to a biologic phenomenon rather than to a technical problem. In our study, head repositioning, made with the help of a laser light marker, was based on a direct confrontation of the current reference T1-weighted midline sagittal image,
Capra R, Marciano N, Gasparotti R. The Effect of Repositioning Error on Serial Magnetic Resonance Imaging Scans-Reply. Arch Neurol. 1993;50(6):570–571. doi:10.1001/archneur.1993.00540060011008
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