Increasing interest in in vivo preclinical imaging has made micro-computed tomography (micro-CT) a powerful research tool for studying tissue morphology and monitoring disease status in rodents. Although, micro-CT images have high contrast for bone, the contrast between various soft tissues is typically low. To overcome this inherent issue, attenuating exogenous contrast agents are used which allows contrast enhancement in vascular and abdominal organs. The aim of this study is to determine the time course of computed tomography (CT) contrast enhancement of a gold nanoparticle bloodpool contrast agent. Six healthy female C57BL/6 mice were anesthetized and imaged after receiving an injected dose of MVivo™ gold nanoparticle blood-pool contrast agent. Micro-CT scans were acquired at 0, 0.25, 0.5, 0.75, 1, 2, 4, 8, 24, 48 and 72 hours after injection. The mean CT number was determined in a region of interest in 7 organs. No contrast enhancement was noticed in the bladder, kidneys or muscle. However, it clearly appears that the contrast enhancement is high in both right ventricle and vena cava, even with a low dose of contrast agent. A single injection of the blood-pool contrast agent can be used for investigations of cardiac or vascular disease. An optimal cardiac imaging window during the first hour after injection has been determined. Furthermore, the long-lasting contrast enhancement can be very useful when using protocols that require long acquisition times.