Contrast agents gadolinium chelates

Gadolinium is a paramagnetic ion and is the most frequently used contrast agent. Gadolinium is chelated with other substances such as dimeglumine and diethylenetriaminepentaacetic add (DTPA) before intravenous use. The usual dose for children is 0.1 mmol/kg. 

Gadolinium(ni) chelates as magnetoresonance imaging (MRI) contrast agents 99CRV2293. 

Briicher E (2002) Kinetic Stabilities of Gadolinium (III) Chelates Used as MRI Contrast Agents. 221 103-122... 

Briicher, E. Kinetic Stabilities of Gadolinium(III) Chelates used as MRI Contrast Agents. In Contrast Agents I. Magnetic Resonance Imaging Krause, W., Ed. Topics in Current Chemistry Springer Berlin, 2002 Vol. 221, p 104. 

Figure 1.17 The texaphyrin-gadolinium chelate structure used as a photosensitizer and MRI contrast agent in the detection and treatment of cancer.

Caravan P, Ellison JJ, McMurry TJ, Lauffer RB (1999) Gadolinium(III) chelates as MRI contrast agents structure, dynamics, and applications. Chem. Rev. 99 2293-2352. 

Bray KL (2001) High Pressure Probes of Electronic Structure and Luminescence Properties of Transition Metal and Lanthanide Systems. 213 1-94 Briicher E (2002) Kinetic Stabilities of Gadolinium(III) Chelates Used as MRI Contrast Agents. 221 103- 122... 

All currently available extracellular contrast agents are gadolinium chelates. This rare earth metal ion exhibits the strongest effect of all elements on the longitudinal relaxation time Tl. The ligands of these chelates belong to two different types of structure Acyclic (open-chain) compounds and macrocyclics. 

Two extracellular contrast agents which contain neutral gadolinium chelates have entered the market gadodiamide (Omniscan) (Fig. 4 a) and gadoverse-tamide (Optimark) (Fig. 4b). 

The development of low osmolar non-ionic X-ray contrast agents has resulted in a distinct reduction in the toxicity and the observed side-effects in patients. However, as already mentioned the osmotic activity of MRI contrast agents is less important in view of the smaller injection volumes which are used. All the formulations of extracellular gadolinium chelates are hypertonic when compared with blood. But the overall increase in osmolality after injection of even 0.3 mmol/kg body weight is insignificant. Osmololatiy-induced adverse reactions have been observed rarely not only because of the relatively small injection volumes but also because of the rapid dilution of the injected agent in the blood. 

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