Investigation of the Effect of kV Combinations on Image Quality for Virtual Monochromatic Imaging Using Dual-Energy CT: A Phantom Study

Abstract

Background: In this study, we investigate the image quality of virtual monochromatic images synthesized from dual-energy computed tomography (DECT) at voltages of 80/140 kV and 100/140 kV. Materials and Methods: Virtual monochromatic images of a phantom are synthesized from DECT scans from 40 to 70 keV in steps of 1 keV under the two combinations of tube voltages. The dose allocation of dual-energy (DE) scan is 50% for both low-and high-energy tubes. The virtual monochromatic images are compared to single-energy (SE) images at the same radiation dose. In the DE images, noise is reduced using the 100/140 kV scan at the optimal monochromatic energy. Virtual monochromatic images are reconstructed from 40 to 70 keV in 1-keV increments and analyzed using two quality indexes: noise and contrast-to-noise ratio (CNR). Results and Discussion: The DE scan mode with the 100/140 kV protocol achieved a better maximum CNR compared to the 80/140 kV protocol for various materials, except for adipose and brain. Image noise is reduced with the 100/140 kV protocol. The CNR values of DE with the 100/140 kV protocol is similar to or higher than that of SE at 120 kV at the same radiation dose. Furthermore, the maximum CNR with the 100/140 kV protocol is similar to or higher than that of the SE scan at 120 kV. Conclusion: It was found that the CNR achieved with the 100/140 kV protocol was better than that with the 80/140 kV protocol at optimal monochromatic energies. Virtual monochromatic imaging using the 100/140 kV protocol could be considered for application in breast, brain, lung, liver, and bone CT in accordance with the CNR results.

Study on Dual-Energy Signal and Noise of Double-Exposure X-Ray Imaging for High Conspicuity

“…(4) (5) where μj imply the linear-attenuation coefficient of the specific material, wf is the weighting factor for suppression of the non-interest tissue in DE image, and wf for bone suppression is defined as follows: (6) The doses delivered to the patient by LE and HE are 0.01 to 0.09 mGy, respectively, and the total doses are 0.1 mGy. Therefore, the dose allocation (ξ, values between 0 and 1) is defined as: (7)…”

“…Richard [3] provided a valuable guide for the optimization of a clinical prototype for high-performance dual-energy (DE) chest imaging, Bowman et al [4] evaluated the feasibility of DEI techniques, and optimized parameters of the Exac-Trac stereoscopic imaging system, to enhance soft-tissue imaging for application to lung stereotactic body radiation therapy. Jeon et al [5] investigated the image quality of virtual monochromatic images synthesized from DE computed tomography, and found that the DE scan mode with the 100/140 kV protocol achieved a better maximum contrastto-noise ratio (CNR), compared to the 80/140 kV protocol for various materials, except for adipose and brain. We noted that a basis material-decomposition using a calibration phantom had been applied for DE radiography [6].…”