Highly branched macromolecules, e.g. poly(amidoamine) dendrimers (known as PAMAM dendrimers, or 'starburst polymers') or Gadomer 17, a contrast agent designed for angiography and tumor differentiation.

DAB-Am64-(1B4M-Gd)64 is a new macromolecular MRI contrast agent for the diagnosis of liver micro-metastasis, consisting of a polypropylenimine diaminobutane (DAB) dendrimer conjugated with a bifunctional DTPA derivative complexing Gd(III).

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.

Nitroxide radicals (or nitroxyl spin labels) are stable organic compounds with theoretical potential for use as a paramagnetic MRI contrast agent. Similar to gadolinium they have an unpaired electron, a property that provides enhancement in T1 based MRI, and a comparable pharmacokinetic. Depending on their structure and chemical bonding, different nitroxides formula may have the potential for use as cardiovascular imaging agents, to enhance the MR imaging on joints (e.g., dendrimer-linked nitroxides have a strong affinity for cartilage), to evaluate brain tumors and infarction, and as a contrast enhancement agent of body/abdominal NMR imaging. Nitroxides are rapidly enzymatically reduced in tissues to products that do not enhance the NMR signal, which can be a problem for MR imaging. In animal experiments with EPRI (electron paramagnetic resonance imaging), tissue redox studies show differences between tumors and normal tissues, which reflect their respective redox status consistent with the reduction/clearance of nitroxides.