The effect of Moidal non-linear blending function for dual-energy CT on CT image quality

Abstract

Objective To compare the difference between linear blending and non-linear blending function for dual-energy CT, and to evaluate the effect on CT image quality. Methods The model was made of a piece of fresh pork liver inserted with 5 syringes containing various concentrations of iodine solutions ( 16.3,26.4,48.7,74.6 and 112.3 HU). Linear blending images were automatically reformatted after the model was scanned in the dual-energy mode. Non-linear blending images were reformatted using the software of optimal contrast in Syngo workstation. Images were divided into 3 groups, including linear blending group, non-linear blending group and 120 kV group. Contrast noise ratio (CNR) were measured and calculated respectively in the 3 groups and the different figure of merit (FOM) values between the groups were compared using one-way ANOVA. Twenty patients scanned in the dual-energy mode were randomly selected and the SNR of their liver, renal cortex, spleen, pancreas and abdominal aorta were measured. The independent sample t test was used to compare the difference of signal to noise ratio (SNR) between linear blending group and non linear blending group. Two readers' agreement score and single-blind method were used to investigate the conspicuity difference between linear blending group and non linear blending group.Results With models of different CT values, the FOM values in non-linear blending group were 20. 65 ±8.18,11.40±4.25, 1.60±0.82,2.40±1.13, 45.49±17. 86. In 74. 6 HU and 112. 3 HU models, the differences of the FOM values observed among the three groups were statistically significant ( P＜0.05),which were 0.30±0. 06 and 14. 43 ±4. 59 for linear blending group, and 0. 22 ±0. 05 and 15.31±5.16 for 120 kV group. And non-linear blending group had a better FOM value. The SNR of renal cortex and abdominal aorta were 19.2±5.1 and 36. 5 ± 13.9 for non-linear blending group, while they were 12.4 ±3.8 and 22.6±7.0 for linear blending group. There were statistically significant differences between the two groups. The conspicuity scores of different organs in non linear blending group were far higher than those in the linear bending group. The Kappa value was 0. 64, showing good consistency. Conclusion Compared to the linear blending method, the non-linear blending method was a better option, especially in improving SNR and conspicuity. Key words: Tomography,X-ray computed; Comparative study