Dual-Energy Multi-Detector Row CT with Virtual Monochromatic Imaging for Improving Patient-to-Patient Uniformity of Aortic Enhancement during CT Angiography: An in Vitro and in Vivo Study

Purpose: To determine whether virtual monochromatic imaging from a dual-energy acquisition can improve patient-to-patient uniformity of aortic enhancement during multi-detector row computed tomographic (CT) angiography. Materials and Methods: This retrospective single-center HIPAA-compliant study was approved by the institutional review board, with a waiver of informed consent. A proprietary tapered hollow phantom that contained a bone-mimicking insert and a hollow tube insert that mimicked the aorta was used. The aortic insert was filled with different iodine dilutions to mimic various degrees of enhancement. The phantom was imaged with both dual-energy and single-energy multi-detector row CT at four energy levels (80, 100, 120, and 140 kVp). Dual-energy multi-detector row CT was also performed in 62 patients (38 men; mean age, 60 years +/- 12.7 [standard deviation]). For both the phantom and the patients, virtual monochromatic images were reconstructed from 40 to 140 keV, at 20-keV increments. The relationship between aortic attenuation and effective diameter was assessed by using a statistical model. Results: For all polychromatic data sets, the mean aortic attenuation decreased proportionally to the effective diameter of the phantom (slope, >= 3.0 HU/cm). For virtual monochromatic data sets ranging from 80 to 140 keV, the regression slopes of aortic attenuation as a function of the phantom's effective diameter were negligible (slope, <1.0 HU/cm) for all iodine-to-water dilutions. In patients, the slope of the regression lines was also negligible (-0.69 < slope < 0.16) for virtual monochromatic data sets ranging from 100 to 140 keV. Conclusion: Within an energy range of 100-140 keV, virtual monochromatic images improve patient-to-patient uniformity of aortic enhancement compared with conventional polychromatic acquisitions. (C) RSNA, 2014