Imaging of nanoparticles with dual-energy computed tomography

A simulation study was performed to determine the feasibility and performance of imaging nanoparticles as contrast agents in dual-energy computed tomography. An analytical simulation model was used to model the relevant signal-to-noise ratio (SNR) in dual-energy imaging for the specific case of a three-material patient phantom consisting of water, calcium hydroxyapatite and contrast agent. Elemental gold and iodine were both considered as contrast agents. Simulations were performed for a range of monoenergetic (20-150 keV) and polyenergetic (20-150 kVp) beam spectra. A reference configuration was defined with beam energies of 80 and 140 kVp to match current clinical practice. The effect of adding a silver filter to the high-energy beam was also studied. A figure of merit (FOM), which normalized the dual-energy SNR to the square root of the patient integral dose, was calculated for all cases. The units of the FOM were keV-1/2. A simple Rose model of detectability was used to estimate the minimum concentration of either elements needed to be detected (SNR > 5). For monoenergetic beams, the peak FOM of gold was 6.4 x 10-6 keV-1/2, while the peak FOM of iodine was 3.1 x 10-6 keV-1/2, a factor of approximately 2 greater for gold. For polyenergetic spectra, at the reference energies of 80 and 140 kVp, the FOM for gold and iodine was 1.65 x 10-6 and 5.0 x 10-7 keV-1/2, respectively, a factor of approximately 3.3 greater. Also at these energies, the minimum detectable concentration of gold was estimated to be 58.5 mg mL-1, while iodine was estimated to be 117.5 mg mL-1. The results suggest that the imaging of a gold nanoparticle contrast agent is well suited to current conditions used in clinical imaging. The addition of a silver filter of 800 μm further increased the image quality of the gold signal by approximately 50% for the same absorbed dose to the patient.