Fig 2. Mismatch of contrast agents uptake in an ultra-small-particle iron oxide (USPIO)-enhanced acute multiple sclerosis (MS) plaque. MR imaging 1 T2-weighted (A) and T1-weighted postgadolinium images (B) shows a large MS lesion that was not enhanced by gadolinium. MR imaging 2 shows the USPIO uptake at the periphery of the lesion (arrows), seen as a decreased signal intensity on T2-weighted images (C) and a high signal intensity on T1-weighted images (D). According to histologic observations (Lucchinetti et al, 2000), the number of macrophages at the center of acute MS lesions is usually minor.