engleski

Impact of the weighting factors on image quality in polychromatic dual energy computed tomography brain reconstructions - a phantom study

Dual-energy computed tomography (DECT) is a radiological imaging method that uses two X-ray beams of different energies and provides numerous possibilities for post-processing, depending on the indication. The simultaneous use of low-energy and high-energy X-ray beams enables the optimization of the contrast to noise ratio (CNR) and the reduction of artifacts, which is especially important in brain imaging. When imaging with low-energy X-ray beam CNR is higher but also noise and artifact levels are higher, while imaging with high energy X-ray noise and artifactsn level decrease but so does CNR between gray and white matter. Weighted average (WA) images have been proposed for the routine evaluation in DECT imaging. To generate weighted average images, weighting factor (WF) ranging from 0 to 1, which determines the ratio of the data obtained at low and high energies is selected. The aim of this study is to investigate how different WF impact on image quality of the brain. For this study antrophomorphic head phantom (True Phantom Solutions, Windsor, Canada) was used. The phantom is designed based on an average human male head and it is made of realistic tissue mimicking materials. It was scanned with standard DECT protocol and the WA images with different WF were generated. Quantitative image quality was performed calculating CNR ratio between grey and white matter in three different parts of the brain. As the measure of noise, standard deviation (SD) was measured in the area of most prominent posterior fossa and in addition to bone neurocranium. The results of WA brain images of the phantom showed that with higher TF values CNR and, also noise and artifact level were increasing. The idea of selecting different WF is to find the optimal value were CNR and noise are well balanced. To propose the optimal value for clinical use qualitative evaluation of the images by the radiologist is also required. Radiologists’ evaluation is important because publications showed that in most cases radiologist would prefer images with higher CNR even though there is a lot of noise over the images with lower CNR and lower noise. Qualitative evaluation of the phantom images would be the next step in our research.

CT, DECT, weighting factors, brain imaging

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