The characteristic time between significant fluctuations in the local magnetic field experienced by a spin due to molecular motions. For values of the correlation time such that the magnetic field as a function of time has large Fourier components near the resonance frequency, the T1 relaxation time will be shortened.

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Cytogen Corporation of Princeton, NJ is a product-driven, oncology-focused biopharmaceutical company. Cytogen markets several products through its in- house oncology sales force: ProstaScint® (a monoclonal antibody-based imaging agent used to image the extent and spread of prostate cancer); BrachySeed™ I-125 and BrachySeed™ Pd-103 (two uniquely designed, next generation radioactive seed implants for the treatment of localized prostate cancer), and NMP22® BladderChek™ (a highly accurate and convenient antibody-based point-of-care staging test for bladder cancer detection). Cytogen has also developed Quadramet®, a skeletal targeting therapeutic radiopharmaceutical for the relief of bone pain in prostate and other types of cancer. Cytogen's pipeline comprises product candidates at various stages of clinical development, including fully human monoclonal antibodies and cancer vaccines based on PSMA (prostate specific membrane antigen) technology, which was exclusively licensed from Memorial Sloan-Kettering Cancer Center.
A license and marketing agreement with AMAG Pharmaceuticals Inc' (formerly Advanced Magnetics), to market the functional molecular imaging agent Combidex®, was terminated in 2007.

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).

The diethylenetriaminepentaacetic acid-chelate contains five acetate moieties linked by a molecular backbone, which bind a metallic ion complex. This chemical bonding solves the problem of toxicity of, e.g. Gadolinium, because DTPA complexes are very stable.
DTPA is used together with technetium-99m as a nuclear imaging radiopharmaceutical and with gadolinium as a MR contrast medium. DTPA chelates undergo renal glomerular filtration and can be used to quantify it. DTPA is also used as a decontamination agent in individuals who have ingested radioactive materials.

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.