(Gd) Gadolinium is a Lanthanide element that is paramagnetic in its trivalent state.
This paramagnetic substance is used for MR imaging because of the effect of strongly decreasing the T1 relaxation times of the tissues to which gadolinium has access. When injected during magnetic resonance imaging, gadolinium will tend to change signal intensities by shortening the T1 time in its surroundings.
The relaxivity of gadolinium is an important measure of its efficacy, which is dependent on the chemical properties of the complex. The gadolinium ion cannot be used in its chloride, sulfate, or acetate forms because of poor tolerance and low solubility in water in the neutral pH range. Although toxic by itself, gadolinium can be given safely in a chelated form such as DTPA, that still retains much of its strong effect on relaxation times (relaxivity).

See also Dotarem®, Gadovist®, MultiHance®, Omniscan®, OptiMARK®, and Contrast Agents, the info sheet gives an overview and more in-dept information about different types of MRI contrast agents.

Gadolinium oxide (Gd2O3) is a prototype paramagnetic agent for contrast enhanced MRI. Gd2O3 particles have very high relaxivity. With its high magnetic moment, gadolinium reduces the relaxation time and enhance MR signal intensity. All gadolinium compounds are highly toxic. Very stable complexes are developed to eliminate the toxicity. See also Paramagnetic Substance, Paramagnetism, Paramagnetic Contrast Agents and Contrast Agents, the info sheet gives an overview and more in-dept information about different types of MRI Contrast media.

(Gadolite® oral Suspension) An oral paramagnetic MRI contrast agent to enhance delineation of the bowel. Zeolites are hydrated aluminosilicates with large holes that can provide a temporary home for guest molecules like gadolinium. Zeolites modified with Gd (III) are effective positive MRI contrast agents for gastrointestinal application.

An oral suspension of synthetic crystalline aqueous orange-flavored MRI contrast agent to enhance delineation of the bowel. Gadolite contains gadolinium, a lanthanide metal with paramagnetic characteristics. The toxic Gd is bound to become inert, along with water, inside a zeolite crystalline lattice structure. Gadolite gives a bright signal, and provides improved definition of the gastrointestinal tract from adjacent tissues.
Pharmacyclics receives an approvable letter from the FDA for Gadolite® Oral Suspension and in the United Kingdom an European marketing agreement signed with E-Z-Em, Ltd. in Dec. 1996.

Short name: (Gd-DTPA)-17, 24 cascade polymer, generic name: Gadomer-17, 24, central moiety: Gd2+, relaxivity: r1=11.9, B0=1.0 T, r2=16.5, Dose: 0.05 mmol/kg
An intravascular macromolecular MRI contrast agent with positive enhancement under development (Bayer Schering Pharma AG) for MR angiography and tumor differentiation. The synthetic dendrimer with large molecular weight (17kD - limits agent to vascular space) is linked to Gadolinium. The renal excretion is slowed to intermediate molecular size. In MRA a longer lasting venous and arterial enhancement was seen with Gadomer-17 due to the particular pharmacokinetics of this agent.

See also Tumor Specific Agents, and Intravascular Contrast Agents.