Feasibility study of virtual monochromatic imaging for metal artifact reduction in spectral CT

摘要

Polychromatic X-ray in computed tomography (CT) can cause metal artifacts and beam hardening artifacts, which arelimiting factors in the detection and diagnosis of lesions. Several groups have introduced virtual monochromatic imaging(VMI) techniques using dual-source CT to reduce these artifacts. However, the dual-source system with two exposures canincrease the patient dose. The photon-counting detector with one exposure can replace a dual-source system. In this study,we investigated the feasibility of VMI in a photon-counting system. A prototype of the photon-counting CT system, whichhas 64 line-pixels Cadmium Zinc Telluride (CZT)-based photon-counting detector, was used. The source-to-detectordistance and the source-to-center of rotation distance were 1,400 and 1,200 mm, respectively. Energy bins were set at 23– 32, 33 – 42, 43 – 52, 53 – 62, and 63 – 90 keV. For comparison, the integrating mode was obtained by sum of five energybins, which is assumed to polychromatic X-ray. Two copper (Cu) rods were inserted into PMMA cylinder phantom. Asresults, the VMI effectively removed metal artifacts. Noise and Signal-to-noise ratio (SNR) were evaluated and the optimalVMI was measured at 77 keV. Our results indicated that VMI in the prototype of the photon-counting system effectivelyeliminates the metal artifact and provides better image quality than integrating mode at 23 – 90 keV.