(McAb) Monoclonal antibodies are used for tumor detection and localization in nuclear medicine. In MRI, monoclonal antibodies labeled with paramagnetic or superparamagnetic particles are being studied for targeting tumors, for example contrast agent containing gadolinium attached to a targeting antibody. The antibody would bind to a specific target (e.g., a metastatic melanoma cell) while the gadolinium would increase the MRI signal. Further developments are MRI contrast agents that specifically target glucose receptors on tumor cells; coupled with the high spatial resolution of high field MRI devices, these agents have potentials to detect small tumor foci.
The monoclonal antibody manufacturers produce a wide variety of ligands, which can be directed against a multiplicity of pathologic molecular targets. MRI enhanced with targeted contrast agents can be used for molecular imaging.

(LE) Myocardial late enhancement in contrast enhanced cardiac MRI has the ability to precisely delineate myocardial scar associated with coronary artery disease. Viability imaging implies evaluating infarcted myocardium to see whether there is enough viable tissue available for revascularization. The reversal of myocardial dysfunction is particularly relevant in patients with depressed ventricular function because revascularization improves long-term survival. In comparison to SPECT and PET imaging, myocardial late enhancement MRI demonstrates areas of delayed enhancement exactly in correlation with the infarcted region.
Viability on cardiac MRI (CMR) is based on the fact that all infarcts enhance vividly 10-15 minutes after the administration of intravenous paramagnetic contrast agents. This enhancement represents the accumulation of gadolinium in the extracellular space, due to the loss of membrane integrity in the infarcted tissue. This phenomenon of delayed hyperenhancement has been proven to correlate with the actual extent of the infarct.
MRI myocardial late enhancement can quantify the size, location and transmural extent of the infarct. If the transmural extent of the infarct (region of enhancement on MRI) is less than 50% of the wall thickness, there will be improved contractility in that segment following revascularization. In areas of hypokinesia, if there is a rim of "black" or non-infarcted myocardium that is not contracting well, it indicates the presence of hibernating myocardium, which is likely to improve after revascularization of the artery supplying that particular territory.
The total duration of a myocardial late enhancement MR imaging protocol for viability is approximately 30 minutes, including scout images, first-pass images, cine images in two planes, and delayed myocardial enhancement images. In order to assess viable myocardium, the gadolinium contrast agent is injected at a dose of 0.15 to 0.2 mmol/kg. After about 10 minutes, short axis and long axis views (see cardiac axes) of the heart are obtained using an inversion prepared ECG gated gradient echo sequence. The inversion pulse is adjusted to suppress normal myocardium. Areas of nonviable myocardium retain extremely high signal intensity, black areas show normal tissue.

For Ultrasound Imaging (USI) see Myocardial Contrast Echocardiography at Medical-Ultrasound-Imaging.com.

OptiMARK® is a formulation of a nonionic gadolinium chelate of diethylenetriamine pentaacetic acid bismethoxyethylamide (gadoversetamide), for use as a paramagnetic MRI contrast agent. OptiMARK® (gadoversetamide injection) is to be administered by intravenous injection. OptiMARK® is indicated for MRI diagnostic procedures to provide increased enhancement and visualization of lesions of the brain, spine and liver, including tumors.

WARNING: NEPHROGENIC SYSTEMIC FIBROSIS Gadolinium-based contrast agents increase the risk for nephrogenic systemic fibrosis (NSF) in patients with acute or chronic severe renal insufficiency (glomerular filtration rate less than 30 mL/min/1.73m²), or acute renal insufficiency of any severity due to the hepato-renal syndrome or in the perioperative liver transplantation period.

Paramagnetic materials attract and repel like normal magnets when subject to a magnetic field. This alignment of the atomic dipoles with the magnetic field tends to strengthen it, and is described by a relative magnetic permeability greater than unity. Paramagnetism requires that the atoms individually have permanent dipole moments even without an applied field, which typically implies a partially filled electron shell. In pure Paramagnetism (without an external magnetic field), these atomic dipoles do not interact with one another and are randomly oriented in the absence of an external field, resulting in zero net moment.
Paramagnetic materials in magnetic fields will act like magnets but when the field is removed, thermal motion will quickly disrupt the magnetic alignment. In general, paramagnetic effects are small (magnetic susceptibility of the order of 10^-3 to 10^-5).
In MRI, gadolinium (Gd) one of these paramagnetic materials is used as a contrast agent. Through interactions between the electron spins of the paramagnetic gadolinium and the water nuclei nearby, the relaxation rates (T1 and T2) of the water protons are increased (T1 and T2 times are decreased), causing an increase in signal on T1 weighted images.

See also contrast agents, magnetism, ferromagnetism, superparamagnetism, and diamagnetism.

Pharmacyclics is a pharmaceutical company developing novel agents to improve current therapeutic approaches to cancer, cardiovascular diseases, and inflammation. The company's proprietary products are derived from its core technology in biometallic chemistry. These products under development are based upon small molecules, which bind metals in a unique way and are capable of capturing and focusing forms of energy used in a variety of medical applications. The company has one product in registration with the FDA, Gadolite® Oral Suspension, a contrast agent for imaging the gastrointestinal tract; two products in clinical development, Gd-Tex (Motexafin gadolinium), a radiation sensitizer, Lu-Tex, a photosensitizer; and several compounds in preclinical development.

MRI Contrast Agents: