![]() When conjugated to certain diagnostic or therapeutic proteins, low molecular weight Gd( III) chelates could cross the blood–brain barrier (BBB) by means of a receptor-mediated transport system or receptor-mediated transcytosis. Through conjugation to biomacromolecules such as polymers, dendrimers or non-covalent binding to plasma proteins, contrast agents could increase the blood half-life and can be used for contrast-enhanced MRI. Nowadays, 2540 of all clinical MRIs employ contrast. MRI contrast agents can be used to determine tumor oxygenation, vascular volume, blood flow, permeability, vessel size and density, leakiness, and grade ( 27 ). The higher relaxivity and efficacy of the contrast agent can be improved by designing pH-, metal ion-, enzyme- or small biomolecule-dependent “smart” contrast agents. The first reported use of contrast agents in human MRI studies employed oral ferric chloride to monitor bowel metabolic processes 1. The physico-chemical parameters and structure-related relaxation mechanisms provide the strategies for chelate design. The relaxivity and stability of Gd( III) chelates are the primary requisites for the development of contrast agents as both small doses and low release of free Gd( III) ions will reduce the toxicity. The intravascular agents are confined to the blood pool and to specific tumors. The particulates are isolated in the liver, spleen and lymph nodes. In clinical magnetic resonance imaging, gadolinium-based contrast agents are commonly used for detecting brain tumors and evaluating the extent of malignancy. ![]() The use of Gd( III) chelate contrast agents is projected to increase as new agents and applications arise, thanks to the favorable combination of a large magnetic moment and long electron spin relaxation time of the Gd( III) ion. Intravenous MRI contrast agents are comprised of chelates of paramagnetic ions, both ionic and nonionic. Currently it is estimated that nearly half of all MR studies performed are contrast-enhanced. MnO As MR Contrast Agents In Imaging-Guided Tumor Therapy Nanomedicine has the ability to greatly increase the dose and accuracy of targeted drug delivery to reduce toxic side effects, meaning it can treat tumors more effectively under non-invasive conditions. Paramagnetic Gd( III) chelate contrast agents have been extensively used to enhance the signal of MRI scans for the last three decades. Since approval of the first magnetic resonance (MR) contrast agent was granted in 1988, there has been remarkable growth in the utilization of intravenous gadolinium (Gd)-based agents. ![]()
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