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Photon counting detector based on semiconductor materials is a promising imaging modality and provides many benefits
for x-ray imaging compared with conventional detectors. This detector is able to measure the x-ray photon energy
deposited by each event and provide the x-ray spectrum formed by detected photon. Recently, photon counting detectors
have been developed for x-ray imaging. However, there has not been done many works for developing the novel x-ray
imaging techniques and evaluating the image quality in x-ray system based on photon counting detectors. In this study,
we simulated computed tomography (CT) images using projection-based and image-based energy weighting techniques
and evaluate the effect of energy weighting in CT images. We designed the x-ray CT system equipped with cadmium
telluride (CdTe) detector operating in the photon counting mode using Geant4 Application for Tomographic Emission
(GATE) simulation. A micro focus X-ray source was modeled to reduce the flux of photons and minimize the spectral
distortion. The phantom had a cylindrical shape of 30 mm diameter and consisted of ploymethylmethacrylate (PMMA)
which includes the blood (1.06 g/cm3), iodine, and gadolinium (50 mg/cm3). The reconstructed images of phantom were
acquired with projection-based and image-based energy weighting techniques. To evaluate the image quality, the
contrast-to-noise ratio (CNR) is calculated as a function of the number of energy-bins. The CNR of both images acquired
with energy weighting techniques were improved compared with those of integrating and counting images and increased
as a function of the number of energy-bins. When the number of energy-bins was increased, the CNR in the image-based
energy weighting image is higher than the projection-based energy weighting image. The results of this study show that
the energy weighting techniques based on the photon counting detector can improve the image quality and the number of
energy-bins used for generating the image is important.
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