Contrast agents relaxivity

Keywords Metallofullerene, endohedral, gadolinium, magnetic resonance imaging, contrast agent, relaxivity, cellular imaging, molecular imaging... 

PAMAM dendrimers of generation 5 have also been functionalized with DOTA metal-binding domains and dysprosium complexes investigated as T2 contrast agents. Relaxivity measurements on the dysprosium complexes were interpreted in terms of an inner sphere Curie spin relaxation model with the large temperature dependence suggesting relaxation by a contact interaction effect, with the proton residence time as the primary time constant. The authors beheve that it will be possible to create a new class of T2-selective contrast agents with systems of this type. ... 

Toth E, Hehn L, Merbach AE (2002) Relaxivity of MRI Contrast Agents. 221 61-101 Tovar GEM, Krauter I, Gruber C (2003) Molecularly Imprinted Polymer Nanospheres as Fully Affinity Receptors. 227 125-144... 

Figure 3 Effect of the water exchange rate, kex, and the rotational correlation time, rR, on inner-sphere proton relaxivity. The plot was simulated for a particular value of the longitudinal electron spin relaxation rate, 1/Tie — 5.28xlOss 1. The marketed contrast agents all have relaxivities around 4—5mM 1s 1 in contrast to the theoretically attainable values over lOOrnM-1 s 1, and this is mainly due to their fast rotation...

Figure 7 Receptor-induced magnetization enhancement mechanism. The contrast agent consists of two parts the Gdm chelate and the protein-binding moiety. Within the bloodstream, the agent binds to the protein. The bound form is in equilibrium with the small amount of free form, which can be renally excreted steadily over time. The bound form has high relaxivity by virtue of its slow rotation (reproduced by permission of the American Chemical Society from Chem. Rev., 1999, 99, 2293).

The efficiency of a paramagnetic chelate to act as a contrast agent is expressed by its proton relaxivity, ri or r2, referring to the paramagnetic enhancement of the longitudinal or transverse water proton relaxation rate, 1/T1 and 1/T2, respectively, by a unity concentration of the agent (ImM) ... 

The observed proton relaxation rate, l/Ti ohs is the sum of a diamagnetic contribution, ITi d, and the paramagnetic relaxation rate enhancement, 1 Tip, which is linearly proportional to the concentration of the paramagnetic species, [Gd]. This relation is valid in dilute solutions and in the absence of intermolecular interactions between the contrast agent molecules. Given the... 

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