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. Author manuscript; available in PMC: 2014 May 6.
Published in final edited form as: Wiley Interdiscip Rev Nanomed Nanobiotechnol. 2013 Jan 17;5(2):163–179. doi: 10.1002/wnan.1205

FIGURE 1.

FIGURE 1

(a) Schematic representation of a Gd3+ chelate surrounded by bulk water with one inner sphere and three second sphere water molecules and several outer sphere water molecules. Modification of contrast agents by PEG could change the water properties which could further influence relaxivity. (b) Simulated magnetic field-dependent relaxivity r1 of clinical MRI contrast agents and ProCA based on the given τR, τm, τv, and Δ2 and Solomon-Bloembergen-Morgan (SBM) theory using combinations of τR (100 ps for clinical MRI contrast agents and 10 ns for ProCA), τm (0.1, 1, 10, and 100 ns), τv (10 ps), and Δ2 (5 × 1019 s–2) under a magnetic field strength from 0.01 MHz to 10,000 MHz. (c) Model structure of ProCA1 with PEG modification. (Reprinted with permission from Ref 32. Copyright 2012 Elsevier)