MRI is a non-invasive, non-radiation, tomographic imaging modality that offers good resolution of soft tissue such as brain, heart, eyes, ligaments, and cartilage. MRI is a scanning technique based on the nuclear magnetic resonance and provides images of the inside of the body. Moreover, to enhance the therapeutic efficacy, various treatment methods have been developed for various types of disease, such as chemotherapy, radiotherapy, nucleic acid therapy, phototherapy, and hyperthermia treatment. Targeting antibodies, peptides, aptamers, siRNA, pH-sensitive polymers, temperature-sensitive polymers, catalyst-responsive polymers, light sensitive polymers, ultrasound sensitive polymers, and magnetic stimuli polymers have been investigated to enhance contrast effect at target sites. To increase the target specific imaging, various methods have been applied on theranostic agents. In order to increase the efficiency of the theranostic agent, it is necessary to increase the contrast effect at target site or to achieve their desired therapeutic effect. These features of theranostic agents offer synergetic advantages in comparison to traditional CAs that are used only to visualize the inside of the body. Theranostic agents provide imaging as well as therapy at the same time. Theranostic is a new field of medicine which combines diagnosis and targeted therapy as a single agent. Recently, there have been growing interest in the combination of contrast and therapy. For assisting radiologists’ interpretation, contrast agents (CAs) have been developed for enhancing contrast effect of abnormalities such as cancer, edema, stroke, and fracture. After medical images have been obtained by various medical imaging tools, they are interpreted by radiologist for effective treatment and disease management. These applications of magnetic resonance contrast agents demonstrate the usefulness of theranostic agents for diagnosis and treatment.Įach imaging technique has its advantages and disadvantages, and some imaging techniques are more adaptable than others for specific diagnosis. Furthermore, we will discuss the combination of theranostic such as contrast agent and drug, contrast agent and thermal therapy, contrast agent and photodynamic therapy, and neutron capture therapy, which can provide for cancer diagnosis and therapeutics. This review discusses the principles of magnetic resonance imaging and recent efforts focused on specificity of contrast agents on specific organs such as liver, blood, lymph nodes, atherosclerotic plaque, and tumor. In order to develop high relaxivity agents, gadolinium or iron oxide-based contrast agents can be synthesized via conjugation with targeting ligands or functional moiety for specific interaction and achieve accumulation of contrast agents at disease sites. Gadolinium based contrast agents are examples of T1 agents and iron oxide contrast agents are examples of T2 agents. Contrast agents are known to shorten both T1 and T2. Thus, there is a desire to develop contrast agents with higher efficiency. Although magnetic resonance imaging offers great temporal and spatial resolution and rapid in vivo images acquisition, it is less sensitive than other methodologies for small tissue lesions, molecular activity or cellular activities. It is noninvasive methodology which provides excellent spatial resolution. Magnetic resonance imaging is one of the diagnostic tools that uses magnetic particles as contrast agents.
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