Research On Dual Energy CT Imaging Standards And Evaluation Methods

Objective: Recently,there have been few domestic and foreign studies on the criteria for evaluating dual-energy CT imaging.This study established a complete set of evaluation methods based on the imaging characteristics of dual-energy CT.At the same time,a group of plans is obtained that can effectively evaluate dual-energy CT by analyzing and summarizing the results of the tests.The evaluation method acquired in this study can ensure the safety of dual-energy CT.It can also serve as a methodological reference for clinicians in mode selection and parameter adjustment.Methods: This study analyzed the conventional and spectral performance of imaging,traditional performance experiments is studied by using a dual-energy CT from Canon and spectral performance experiments is studied by using a dual-energy CT from Neusoft.When assessing the density resolution of dual-energy CT imaging,the size of the smallest object is measured at a given contrast,a given tube current and a given dose.The MTF method is used to measured phantoms when assessing the spatial resolution of dual-energy CT imaging.Then the differences caused by the different environments are analyzed.When evaluating the noise of dual-energy CT imaging,the noise varies from layer to layer.It is measured in this paper by the CT value of the image and the standard deviation of its mean CT value.The next step is to assess the imaging’s homogeneity,accuracy and linearity.The uniformity of CT values was first obtained by measuring edge-to-center CT values.The accuracy of the CT values is then obtained by switching between repeated scans with different settings.Then,the linearity of the CT values is received by measuring the CT values of other substances,where the linear attenuation coefficient is used as the horizontal coordinate and the CT values as the vertical coordinate,and then fitting a straight line to the software to find the contrast.Finally,the energy spectral performance of imaging is evaluated,including the assessment of substance separation and substance quantification performance.The former is measured by testing the contrast between the base and separated materials.The latter is calculated by comparing the difference between the estimated and expected values,which can be a CT value or substance concentration value.The latter is measured according to the spectroscopy application’s different quantitative information.All of these assays require repeated measurements recorded and analyzed through many experiments.Results: 1.The density resolution,spatial resolution and noise evaluation methods for dual-energy CT imaging were obtained by conducting many experiments in different environments.In the density resolution test,the average smallest identifiable diameter was 3.6mm at a contrast ratio of 0.3% or 0.86%,and the average smallest identifiable object diameter was 1.07 mm using the MTF method.This method is commonly used to evaluate the performance of conventional CT imaging,and based on the experimental results,it is demonstrated that it is concluded that this method is still applicable to dualenergy CT imaging evaluation.2.Regarding evaluating CT value uniformity,accuracy and linearity of dual-energy CT imaging,experiments yielded deviations in the range of ±4 HU for the uniformity of CT values for water and within ±4 HU for accuracy under different external environmental tests.The accuracy deviation for air was within±10HU,and the linearity deviation of CT values for the four different materials was between ±20HU to ± 100 HU.This method is commonly used to evaluate the performance of conventional CT imaging.Based on the experimental results,it has been demonstrated that this method still applies to evaluating dual-energy CT imaging.3.In the evaluation of the spectral performance of dual-energy CT imaging,for separation performance,water and iodine are experimentally separated to obtain the corresponding contrast values,which are judged by the difference between the measured CT values and the standard CT values.For quantitative performance,specific CT and substance concentration values are calculated using specific information about the measured substance and then analyzed for differences with the standard values.In the quantitative performance of the substance concentration distribution image,the difference is minimized to 0 for water measurements.Conclusion: Conventional and energy spectrum imaging evaluation methods established a system for evaluating dual-energy CT.It provides a better assessment of dual-energy CT imaging and better quality control of dual-energy CT.