Classification and basic properties of contrast agents for magnetic resonance imaging

Abstract

A comprehensive classification of contrast agents currently used or under development for magnetic resonance imaging (MRI) is presented. Agents based on small chelates, macromolecular systems, iron oxides and other nanosystems, as well as responsive, chemical exchange saturation transfer (CEST) and hyperpolarization agents are covered in order to discuss the various possibilities of using MRI as a molecular imaging technique. The classification includes composition, magnetic properties, biodistribution and imaging applications. Chemical compositions of various classes of MRI contrast agents are tabulated, and their magnetic status including diamagnetic, paramagnetic and superparamagnetic are outlined. Classification according to biodistribution covers all types of MRI contrast agents including, among others, extracellular, blood pool, polymeric, particulate, responsive, oral, and organ specific (hepatobiliary, RES, lymph nodes, bone marrow and brain). Various targeting strategies of molecular, macromolecular and particulate carriers are also illustrated.

PET/MRI and the revolution of the third eye

“…MRI contrast agents shorten the T1 relaxation time of protons [8]. Gadolinium as a complexed ligand is most commonly used in MR angiography and for brain tumour enhancement associated with alterations in the blood-brain barrier.…”

Solid MRI contrast agents for long-term, quantitative in vivo oxygen sensing

“…The concentration of contrast agents decreases over time owing to systemic clearance (3); some magnetic resonance (MR) methods, such as dynamic contrast-enhanced imaging, exploit this clearance of contrast agent to make inferences about the underlying physiology. Some applications, however, require a consistent concentration of contrast agent for repeatable, accurate, and quantitative measurements (4), and an internal control must be added to account for the time-changing concentration. Repeat measurements to track the progression of disease or the response to treatment also require a new bolus injection of contrast agent.…”

Dendrimer-based magnetic resonance imaging agents for brain cancer

“…MRI contrast agents can be classified as paramagnetic and superparamagnetic [21,22], and the most important feature of a contrast agent is its relaxivity (r), which relates to its capacity to generate imaging signal contrast. Paramagnetic agents such as gadolinium (Gd 3+ ) and manganese (Mn 2+ ) increase both the longitudinal relaxation rate (R 1 ) and the transverse relaxation rate (R 2 ) to a similar extent, and they exhibit "positive" (bright) contrast.…”