Novel non‑metal‑based contrast agents for MR imaging: Emerging approaches and clinical perspectives (Review)

Magnetic Resonance Imaging (MRI) relies on contrast agents to enhance image quality and diagnostic accuracy. Traditional metal‑based agents, such as gadolinium compounds, raise safety concerns due to potential toxicity and long‑term retention in the body. The present review examines recent advancements in non‑metal‑based MRI contrast agents, focusing on fluorine‑19 (19F) compounds, chemical exchange saturation transfer (CEST) agents, nitroxide radicals, and hyperpolarized carbon agents. It discussed the mechanisms by which these agents improve contrast, including their biocompatibility and ability to provide molecular and metabolic information. Key findings highlight the high specificity of19F agents due to negligible background signals, the capacity of CEST agents for molecular imaging without metals, nitroxide radicals' utility in redox‑sensitive imaging, and hyperpolarized ¹³C compounds' role in real‑time metabolic assessment. Despite challenges such as low sensitivity and technical complexities, these non‑metal‑based agents offer promising, safer alternatives with enhanced diagnostic capabilities, paving the way for more precise and personalized medical imaging.