 We are excited to share this technical note entitled CT Imaging of Gold Nanoparticles in a Human-Sized Phantom which has just been accepted for publication in the Journal of Applied Clinical Medical Physics. Iodine is the most commonly administered intravenous contrast agent used today for highlighting specific organs, blood vessels, and tissue types. Iodine-based contrast agents can greatly improve diagnostic accuracy in CT and they allow for producing beautiful images like those shown here. The image on the left shows a stent placed around an abdominal aortic aneurysm. The image on the right shows contrast in various blood vessels and organs throughout the chest and abdomen. These images would simply not have been possible without iodine-based contrast agents. A major problem, however, with iodine-based contrast agents is that they've been associated with the development of acute kidney injury known as contrast-induced nephropathy, as well as thyroid dysfunction, particularly among individuals with pre-existing renal conditions. So alternative contrast agents must be considered and since the initial reports of Hainfield et al. intense interest has steadily grown in gold nanoparticles. Many studies have already thus been published regarding gold nanoparticles as CT contrast agents. But they have all thus far been limited to Monte Carlo simulations, small phantom studies, or mouse studies. The goals of our study are to 1. Image AUNPs in a human-sized phantom with a clinical MDCT scanner. 2. Determine the KVP setting which yields the maximum contrast and contrast to noise ratio. And 3. Determine the AUNP concentration required for visualization in an average-sized patient under typical diagnostic imaging conditions. Gold nanoparticles were imaged in the GAM-X RMI-467 electron density phantom which has a diameter of 33 centimeters and a Siemens somatom definition AS+. The observed image contrast was generally so extreme in the high concentration regime that the typical 12-bit dynamic range of 4096 was exceeded at 150 milligrams AU per ml. Typical contrast agents usually require lower KVP settings for optimal image contrast. Iodine's effective linear attenuation coefficient, for example, is always higher at lower KVPs. Because of Iodine's 33 KEVK edge, this relationship is true despite whether imaging in air or in tissue. Gold's 80.7 KEVK edge, on the other hand, causes the relationship between the effective linear attenuation coefficient and KVP to switch at a given depth in tissue. A very interesting phenomenon. All dose normalized CNRs for concentrations less than about 0.2 milligrams AU per ml were below 0.5. Since the rose criterion states that a CNR of 3 to 5 is required for a concentration to be visually detectable to an observer, these experiments were successful in establishing a lower limit for visible AUNP concentrations. By interpolating between the high and low concentration regime experiments, we provide a range of 0.3 to 1.4 milligrams AU per ml as the required minimum concentration for imaging in humans. Our first conclusion is that 0.3 to 1.4 milligrams AU per ml is required for human visualization in 1 millimeter images at a typical diagnostic CTDI vol of 23.6 mG. Our second conclusion is that scanners capable of reconstructing images with extended Houndsfield scales are required for distinguishing any contrast differences above 150 milligrams AU per ml. And our third conclusion is that AU and P's result in optimal image contrast at 120 KVP and a human size phantom due to Gold's 80.7 KEVK edge and the attenuation of X-rays by tissue.