Carbon radiography (400 MeV/n) yielded best spatial resolution, with MTF10% = 2.7 and 2.8 lp/mm, respectively, at the lung-water and bone-water interfaces. The spatial resolution of the 330 MeV proton beam was better than the 230 MeV proton, because higher incident proton energy suffer smaller deflections within the patient and thus yields better proton radiographic images. The authors also observed that submillimeter resolution can be obtained with both proton and carbon beams.

IntroductionGold nanoparticles (AuNPs) are visualized and quantified in a human‐sized phantom with a clinical MDCT scanner.MethodsExperiments were conducted with AuNPs between 0.00171 and 200 mgAu/mL. CT images were acquired at 80, 100, 120, and 140 kVp in a 33‐cm phantom. Image contrast due to AuNPs was experimentally determined from regions of interest (ROIs) and effective linear attenuation coefficients were calculated from CT x‐ray spectra with consideration of tissue attenuation.ResultsThe typical 12‐bit dynamic range of CT images was exceeded for AuNPs at 150 mgAu/mL. A threshold concentration of 0.3–1.4 mgAu/mL was determined for human visualization in 1‐mm images at a typical diagnostic CTDIvol of 23.6 mGy. Optimal image contrast was also achieved at 120 kVp and verified by calculation.ConclusionsWe have shown that scanners capable of reconstructing images with extended Hounsfield scales are required for distinguishing any contrast differences above 150 mgAu/mL. We have also shown that AuNPs result in optimal image contrast at 120 kVp in a human‐sized phantom due to gold’s 80.7 keV k‐edge and the attenuation of x‐rays by tissue. Typical CT contrast agents, like iodine, require the use of lower kVps for optimal visualization, but lower kVps are more difficult to implement in the clinic because of elevated noise levels, elongated scan times, and/or beam‐hardening artifacts. This indicates another significant advantage of AuNPs over iodine not yet discussed in the literature.