Evaluation of virtual monochromatic imaging with dual-energy computed tomography of small liver metastases from malignant abdominal tumours: Quantitative and qualitative analyses

Background The assessment of small metastatic liver tumours using dual-energy computed tomography (DECT) has not been fully established. Purpose To assess the effect of low-keV virtual monochromatic imaging (VMI) with non-contrast and contrast-enhanced DECT on the qualitative and quantitative image parameters of small liver metastases. Material and methods Two radiologists retrospectively evaluated 92 metastatic liver tumours (5–20 mm) in 32 patients. Non-contrast and contrast-enhanced VMI were reconstructed at seven energy levels (40–100 keV) with 10-keV intervals. Lesion boundary, lesion delineation, image noise, and overall image quality were evaluated using the visual analogue scale. A high subjective score indicates good overall image quality, clear nodal boundaries and delineation, and less noticeable image noise. Subjective scores were compared using the Kruskal–Wallis test. A quantitative analysis involving the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) was performed. Results The lesion boundary was highest at 40 keV and significantly improved during the non-contrast portal venous phase compared to that at higher keV (p < .005). The lesion delineation score was significantly higher at 40 keV and tended to decrease at higher keV. Image noise and overall image quality were rated low at low keV; however, those at 80, 90, and 100 keV were rated the highest (p < .005). The CNR and SNR were highest for non-contrast CT at 100 keV. During the portal venous phase, no significant differences were observed in CNR and SNR at each keV. Conclusion Low-keV imaging using non-contrast and contrast-enhanced DECT is useful for delineating small hepatic metastatic tumours.