Objectives: The aim of this study was to perform an objective and subjective image analysis of traditional and advanced noise-optimized virtual monoenergetic imaging (VMI) algorithms and standard linearly blended images in third-generation dual-source dual-energy computed tomography angiography (DE-CTA) of the thorax and abdomen.
Materials and methods: Thoracoabdominal DE-CTA examinations of 55 patients (36 male; mean age, 64.2 ± 12.7 years) were included in this retrospective institutional review board-approved study. Dual-energy computed tomography angiography data were reconstructed using standard linearly blended M_0.6 (merging 60% low kiloelectron volt [90 kV] with 40% high kiloelectron volt [150 kV] spectrum), traditional (VMI), and advanced VMI (VMI+) algorithms. Monoenergetic series were calculated ranging from 40 to 120 keV with 10 keV increments. Attenuation and standard deviation of 8 arteries and various anatomical landmarks of the thorax and abdomen were measured to calculate contrast-to-noise ratio values. Two radiologists subjectively assessed image quality, contrast conditions, noise, and visualization of small arterial branches using 5-point Likert scales.
Results: Vascular attenuation of VMI and VMI+ series showed a gradual increase from high to low kiloelectron volt levels without significant differences between both algorithms (P < 0.894). VMI+ 40-keV series showed the highest contrast-to-noise ratio for both thoracic and abdominal DE-CTA (P < 0.001), albeit revealing higher noise than M_0.6 images (objectively and subjectively, P < 0.001) and were rated best for visualization of small arterial branches in the subjective analysis (P < 0.109). Substantially increased noise was found for VMI 40 and 50 keV series compared with all other reconstructions (objectively and subjectively, P < 0.001). VMI+ images at 100 keV+ were rated best regarding image noise (P < 0.843), whereas VMI+ reconstructions at 70 keV were found to have superior subjective image quality (P < 0.031) compared with other series except for 60 and 80 keV VMI+ series (P < 0.587). Contrast conditions at 50 keV VMI+ were rated superior compared with 60 to 100 keV VMI and VMI+ reconstructions (P < 0.012).
Conclusions: General image quality of DE-CTA examinations can be substantially improved using the VMI+ algorithm with observer preference of 70 keV, while 40 to 50 keV series provide superior contrast and improved visualization of small arterial branches compared with traditional VMI and standard linearly blended series.