▎ 摘　　要

NOVELTY - A contrast agent comprises 13C-containing graphene quantum dot or 13C-containing oxidized graphene quantum dot. USE - The contrast agent is useful for MRI, Raman imaging, positron emission tomography and fluorescence imaging which are useful for imaging spleen, reticuloendothelial system, vessels, lymph nodes, angiogenesis of cancer cells (angiogenesis) or atherosclerotic plaque (all claimed). DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for manufacture of contrast agent.