Evaluation of Spatial Resolution of Virtual Monochromatic Imaging In Vitro: Effect of Energy Level and Contrast

OBJECTIVE Our aim was to evaluate effects of the energy level and contrast on the spatial resolution of virtual monochromatic imaging (VMI). METHODS With 2 types of computed tomographic (CT) scanners (Discovery CT750 HD and Revolution CT), we scanned an elliptical cylinder acrylic phantom with 20- or 40-fold dilutions of contrast medium and obtained VMI data sets at 40, 50, 60, and 70 keV. We evaluated the effects of energy levels and contrast on modulation transfer function (MTF) and the effect of energy levels on noise power spectra (NPS). RESULTS With both CT scanners, MTF decreased significantly as the energy level decreased. The effect of the dilution of contrast media on MTF varied with CT scanners. With both scanners, NPS curves demonstrate uniform increase in NPS across the entire spatial frequency as the energy levels decreased. CONCLUSIONS The energy level and contrast can affect the spatial resolution of VMIs.