Article Figures & Data
Figures
- Fig 1.
Gd-DOTA (Dotarem; Guerbet, Aulnay-sous-Bois, France) and Gd-DTPA (Magnevist; Schering, Berlin, Germany). Two examples of clinically used Gd3+ poly(amino carboxylate) complexes. All other approved Gd3+-based contrast agents are derivatives of Gd-DOTA or Gd-DTPA.
- Fig 2.
In Gd3+-based contrast agents, the paramagnetic Gd3+ ion is coordinated by an organic ligand. The water molecules directly linked to the metal exchange with bulk water, and this exchange transmits the paramagnetic effect of Gd3+ to the surrounding environment. The efficacy of the agent is mainly related to the number of water molecules bound to Gd3+ (the hydration number), q (the exchange rate of the coordinated water molecule[s] with the surrounding water), kex, and the rotational correction time τR.
- Fig 3.
Schematic representation of a PARACEST agent with exchangeable protons on the ligand (amine, amide, alcohol…) (gray) or on the coordinated water (white).
- Fig 4.
Illustration of 2 different strategies to modulate relaxivity of Gd3+ complexes by cation recognition. A and B, Change in the q (A) and change in the size, hence the τR (B). The binding site for the sensed metal ion has to be highly selective with respect to other endogenous cations.
- Fig 5.
An example of an enzyme-activated PARACEST contrast agent: The enzyme specifically reacts with the substrate leading to the spontaneous elimination of the self-immolative linker. This gives rise to a change in the PARACEST properties.
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