Table 1.

Types of contract agents used for MRI with their significance

Type of contrast agent	Examples	Significance	References
Gadolinium-Based Contrast Agents (GBCAs)	Gadobutrol, Gadopentetate dimeglumine, Gadoterate meglumine, Gadobenate dimeglumine	Have enhanced contrast between healthy and abnormal tissues in MRI scans. GBCAs are generally safe but expensive and extensive imaging time needed	[23–25] [26]
Iron oxide nanoparticles	Ferumoxytol, Ferucarbotran	Used as a contrast agent for MRI scans of the liver, spleen, lymph nodes, and tumors. They are also used for imaging inflammation and cellular tracking in preclinical and clinical studies. Iron oxide nanoparticles are safe and well-tolerated, but they may cause mild adverse reactions, such as transient hypotension, flushing, or dyspnea	[17, 27]
Ultrasmall superparamagnetic iron oxide (USPIO)	Ferumoxides, Ferumoxtran-10	Used to enhance the contrast in MRI scans of the liver, spleen, lymph nodes, and tumors. They are also used for imaging inflammation, atherosclerosis, and cell trafficking in preclinical and clinical studies. USPIOs are safe and well-tolerated, but they may cause mild adverse reactions, such as transient hypotension, flushing, or dyspnea	[28, 29]
Perfluorocarbon-based Contrast Agents	Perflubron, PFOB	Used to enhance the contrast in MRI scans of the lungs, blood vessels, and tumors. They are also used for imaging inflammation and cellular trafficking in preclinical and clinical studies	[30]
Manganese-based Contrast Agents	MnDPDP, MnCl2, Mn-MOFs	Used to enhance the contrast in MRI scans of the liver, pancreas, heart, and brain. They are also used for imaging cell metabolism, brain function, and neurodegenerative diseases in preclinical and clinical studies. Manganese-based contrast agents are generally safe and well-tolerated, but they may cause mild adverse reactions, such as nausea, dizziness, or flushing	[31, 32]
Hyperpolarized Gases	Hyperpolarized helium-3 (He-3), hyperpolarized xenon-129 (Xe-129)	These gases are used as contrast agents in lung MRI to visualize the airspaces and lung function in real-time. They have high sensitivity and specificity for detecting lung diseases, such as asthma, COPD, and pulmonary fibrosis. However, their production and administration require specialized equipment and expertise	[33, 34]
Metal–Organic Framework-based Contrast Agents	Zirconium-based MOFs, Gadolinium-based MOFs	These MOFs are a new class of contrast agents that have high stability, biocompatibility, and tunable properties. They can be functionalized with various targeting ligands and imaging probes to enhance their specificity and sensitivity. They are also suitable for multi-modal imaging and theranostics	[35, 36]
CEST Contrast Agents	Iopamidol-CEST, creatine-CEST	These contrast agents use chemical exchange saturation transfer (CEST) to detect and quantify specific molecules or metabolic processes in tissues. They have high sensitivity and specificity for imaging tumors, stroke, and neurodegenerative diseases. They also have potential for monitoring drug delivery and response	[37–39]