Macromolecular Gd labeled albumins are a new class of contrast agents with a wide range of use e.g., MR angiography, breast MRI, perfusion MRI, Lung perfusion, etc.
Marketed gadolinium-based albumin-bound contrast media are e.g., MultiHance®, and Vasovist™; other prototypes are in development. Malignant tumors often show an increased uptake and metabolism of plasma proteins, especially albumin. Contrast agents with large molecules are delivered to all tissues, but only accumulate in those with leaky vessels by tumor capillaries (tumor neovessels). MRI tumor perfusion studies with Gd labeled albumin can show the success of tumor therapy by quantitative decrease in MR signal of the malignant tissue after therapy compared to before. In addition, the study of tumor sensitivity to a therapy with drug-labeled albumins seems possible.
After renal transplantation, MRI may diagnose albuminuria caused by glomerular disease with an albumin-bound blood pool contrast agent

See also Blood Pool Agents, Intravascular Contrast Agents, Contrast Enhanced MRI.

Short name: PLLGd-DTPA, generic name: (Gd-DTPA)n-polylysine, chemical compound: Gd-DTPA poly(L-lysine-Gd-diethylenetriamine-N,N,N',N'',N''-pentaacetic acid), central moiety: Gd2+, relaxivity: r1=13.1, B0=0.23T
A polymeric MRI contrast agent under development (preclin., Bayer Schering Pharma AG, Berlin, Germany) with advantages in both MRA and in the differential diagnosis of tumors, particularly in perfusion studies of the myocardium and potential in MR lung perfusion. Dozens of the relatively small molecule Gd-DTPA is bound covalently to polylysine, a large molecular weight backbone. The stable, highly water-soluble agent does not diffuse through the endothelium of the vascular system; it is subject to renal elimination.

The concentration of Hydrogen atoms in water molecules or in some groups of fat molecules within tissue. Initial MR signal amplitudes are directly related to H+ density in the tissue being imaged.

Intravenous contrast agents used in MRI are distributed in the extracellular spaces of the body before being excreted. In this sense they are similar to iodinated X-ray contrast media. However, contrast agents used for MRI are quite different from conventional radiographic contrast media in structure and function and there is no known cross sensitivity between these types of contrast agents. Common MRI contrast agents use metal ions (e.g., gadolinium or manganese) complexed with organic molecules.
Gd-DTPA, an ionic linear molecule complex (gadopentetate dimeglumine) was the first marketed MRI contrast agent. Although the osmolality of this substances can be relatively high (up to 1940 mOsm/kg H2O) compared with plasma, adverse reactions and side effects are very rare. The used doses are smaller compared with radiographic contrast media.

See also Nonionic Intravenous Contrast Agents, Dotarem®, and Magnevist®.

Molecular imaging agents may be useful in bimodal imaging - fluorescence and MRI. Bimodal imaging of PBR expressing cells has been possible with Ln-PK-11195, a new imaging agent for the further study of mitochondrial function and its relationship to cancer cell proliferation. By preparing cocktails of both the Gd3+ and Eu3+ or Tb3+ complexes, it will be possible to obtain non-invasive anatomic-scale images by MRI and perform microscopic-scale imaging by fluorescence on the same cell or tissue.
New agents will be created, these include a long circulating bimetallic with enhanced relaxivity for MRI. In-vitro and in-vivo studies will show the safety and efficacy of these molecular imaging agents.