Polyethylene glycol, due to its “stealth” characteristics and biocompatibility, is frequently used in the administration of drugs and nanomaterials. PEGylation enables biomaterials and particle delivery systems to circumvent the immune system and extend circulation lifetimes. To diagnose various diseases, substantial attempts are being made to create alternative imaging techniques that can improve the signal or produce high positive contrast for effective molecular imaging. The development of PEGylated nanoparticles as contrast agents in imaging technology has made it possible to gain precise cellular and molecular imaging, detect drug delivery, particularly to tumoral areas, and provide information for adequate surgical excision of solid tumors. PEGylated nanocarriers have been identified as potential candidates for the targeted treatment and imaging of malignant tumors. Peptides or antibodies can be conjugated to the surface of PEGylated nanocarriers to directly target tumor cells and potentially impair their active signaling pathways. They improve magnetic resonance imaging contrast, helping physicians to track anatomical, physiological, and molecular changes in a disease as treatment progresses. PEGylated nanocarriers are effective imaging tools for tumor diagnosis, follow-up, and disease monitoring, which help in the overall clinical management of tumors.