Which should be the routine cross-sectional reconstruction mode in spectral CT imaging: monochromatic or polychromatic?

Objective: To provide evidence for the selection of an optimal cross-sectional reconstruction mode in spectral CT imaging of the abdomen, we compared the monochromatic images with polychromatic images. Methods: Three phase-enhanced CT scans of the abdomen were recorded using the spectral imaging technique on 100 patients. Images were reconstructed using two modes: polychromatic and 70 keV monochromatic. The following variables were then compared: contrast-to-noise ratio (CNR) of the liver, spleen, gallbladder, kidney and pancreas, and the noise. Paired t-tests were used to compare differences between the two sets of images. Three experienced doctors graded the quality of the images with a five-point scale. The image quality scores were compared with a non-parametric rank sum test. Results: Compared with polychromatic images, the 70 keV monochromatic mode images yielded significantly greater tissue-to-fat CNR and lower noise (p < 0.001 for all comparisons). The image quality of the 70 keV monochromatic mode showed significantly better results than the polychromatic mode (p < 0.001). Conclusions: In abdominal spectral CT imaging, 70 keV monochromatic mode reconstruction images were better than those reconstructed using the polychromatic mode. The monochromatic mode may become the routine reconstruction mode for cross-sectional images.