The Influence of Effective Energy on Computed Tomography Number Depends on Tissue Characteristics in Monoenergetic Cardiac Imaging

Purpose. To evaluate the influence of effective energy on computed tomography (CT) number in monoenergetic images (MEIs). Methods. Three bottle phantoms filled with water, oil, and a contrast agent were scanned at 100 and 140 kVp tube energy with a dual-source CT scanner. Cardiac dual-energy CT data was collected from 17 patients. CT numbers were measured in the 3 phantom materials and in the left ventricular cavity, myocardium, pericardial fat, and vertebral bone in MEIs from 40 to 190 keV. Results. In the phantoms, the mean CT number increased in oil whereas it decreased in the contrast agent as the energy level increased (P < 0.001). In clinical subjects, the mean CT numbers for the left ventricular cavity, myocardium, and vertebral bone were highest in the 40 keV images (P < 0.001) and decreased as the energy level increased. In contrast, the CT number for pericardial fat was lowest in the 40 keV images (P < 0.001) and increased with increasing energy. Conclusions. The influence of effective energy on CT number varies with material and tissue type in monoenergetic cardiac imaging, which could evaluate tissue characteristics through assessment of the changes in CT number associated with effective energies.