(A) Model of PEGylated ProCA1 metalated with GdIII (pink: GdIII; blue: metalation site; green: ProCA1; red and green: PEG; yellow and red: water); (B) Relaxivity values of ProCA1 and PEGylated-ProCA1 (blue at 3 T and red at 9.4 T). Reprinted from the Journal of Inorganic Biochemistry, 107, S. Li, J. Jiang, J. Zou, J. Qiao, S. Xue, L. Wei, R. Long, L. Wang, A. Castiblanco, N. White, J. Ngo, H. Mao, Z.-R. Liu and J. J. Yang, PEGylation of Protein-Based MRI Contrast Agents Improves Relaxivities and Biocompatibilities, 111–118, Copyright 2013, with permission from Elsevier.