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

Abstract

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. Recently, the advancement of CT technology, such as dual-source technology or fast peak kilovoltage switching technology, has enabled the routine clinical application of dual-energy spectral CT for the abdomen [4]. The results of preliminary investigations suggest that dual-energy techniques may be used to provide information about tissue composition and how tissues behave at different energies in the abdomen [5][6][7][8][9]. New parameters, such as the iodine concentration and the spectral curve, can be acquired using spectral CT. However, because the ability of spectral CT to characterise lesions is still uncertain, no diagnosis is possible, only reference to the pattern of spectral curves or other spectral CT parameters. Therefore the morphological characteristics and enhancement features of lesions in cross-sectional images still remain the basis of diagnosis of abdominal spectral CT images. In addition, the reconstruction of cross-sectional images remains a routine procedure for spectral CT imaging of the abdomen. In the present spectral CT system based on fast peak kilovoltage switching technology, there are two cross-sectional image reconstruction modes available: monochromatic and polychromatic modes. To our knowledge, there has not been a study designed to demonstrate which routine reconstruction mode should be used after spectral CT imaging. To answer this question, our study seeks to compare the quality of CT images of the abdomen reconstructed in monochromatic mode with those from a polychromatic mode, and therefore provide evidence for the selection of the optimal reconstruction mode.

Low kV versus dual-energy virtual monoenergetic CT imaging for proven liver lesions: what are the advantages and trade-offs in conspicuity and image quality? A pilot study

“…However, previous studies using early DE-VM algorithms have shown that high-contrast, low-monoenergetic-energy images that contain increased iodine signal also contain higher levels of image noise [4, 5]. This significant noise burden at lower energies has been a limiting factor in the clinical application of virtual monoenergetic imaging.…”

Assessment of the Hepatic Veins in Poor Contrast Conditions using Dual Energy CT: Evaluation of a Novel Monoenergetic Extrapolation Software Algorithm

“…6). Previous studies showed that liver imaging was able to benefit by monochromatic extrapolation of CT images [16,17] in terms of increased sensitivity for the detection of lesions and greater diagnostic confidence [17]. Nevertheless, 70 keV was recommended due to increased noise levels to achieve the best overall image quality [15,17].…”

Improving Image Quality of Bronchial Arteries with Virtual Monochromatic Spectral CT Images

“…On the other hand, dual energy spectral CT imaging generates a set of virtual monochromatic images through the material decomposition process enabled by the use of the information from the two energy spectra of high and low kVp projections. The use of a monochromatic X-ray beam in CT would greatly reduce the averaging attenuation effect and increases contrast resolution[ 13 ]. The generation of virtual monochromatic image sets of various energy levels, especially low photon energy images in spectral CT imaging also allows us to select the optimal energy level to maximize the contrast-to-noise ratio for bronchial arteries in contrast-enhanced CT scans.…”