Gold nanoparticles: a new X-ray contrast agent.

There have been few fundamental improvements in clinical X-ray contrast agents in more than 25 years, and the chemical platform of tri-iodobenzene has not changed. Current agents impose serious limitations on medical imaging: short imaging times, the need for catheterization in many cases, occasional renal toxicity, and poor contrast in large patients. This report is the first demonstration that gold nanoparticles may overcome these limitations. Gold has higher absorption than iodine with less bone and tissue interference achieving better contrast with lower X-ray dose. Nanoparticles clear the blood more slowly than iodine agents, permitting longer imaging times. Gold nanoparticles, 1.9 nm in diameter, were injected intravenously into mice and images recorded over time with a standard mammography unit. Gold biodistribution was measured by atomic absorption. Retention in liver and spleen was low with elimination by the kidneys. Organs such as kidneys and tumours were seen with unusual clarity and high spatial resolution. Blood vessels less than 100 microm in diameter were delineated, thus enabling in vivo vascular casting. Regions of increased vascularization and angiogenesis could be distinguished. With 10 mg Au ml(-1) initially in the blood, mouse behaviour was unremarkable and neither blood plasma analytes nor organ histology revealed any evidence of toxicity 11 days and 30 days after injection. Gold nanoparticles can be used as X-ray contrast agents with properties that overcome some significant limitations of iodine-based agents.