Preliminary study on the optimal keV of virtual monoenergetic images in transplanted renal artery on a dual-layer spectral detector CT / 中华放射学杂志

ABSTRACT

Objective:To investigate the optimal monoenergetic level of virtual monoenergetic images (VMI) in transplanted renal artery on a dual-layer spectral detector CT.Methods:A retrospective study was performed on 16 renal transplant patients who underwent transplanted renal angiography on a dual-layer spectral detector CT in Union Hospital, Tongji Medical College, Huazhong University of Science and Technology from June 2020 to April 2021. Conventional 120 kVp polyenergetic images (PI) were reconstructed, and virtual monoenergetic images (VMIs) in range of 40-200 keV with interval of 10 keV were reconstructed, too. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of 120 kVp PI and VMIs were measured. Meanwhile, the subjective scores of the display of transplanted renal artery were performed on volume rendering images of 120 kVp PI and VMIs. Spearman correlation analysis was used to explore the correlation between energy levels and SNR or CNR. Rank sum tests were performed to compare the parameters of image quality between the VMI which had the highest SNR and CNR, and the other VMIs, or 120 kVp PI.Results:Among the VMIs, SNR or CNR was negatively correlated with energy levels ( r =-0.86 and -0.88, all P<0.001). The SNR [22.80(18.57, 34.16)] and CNR [35.38(25.97, 39.01)] of 40 keV VMI were the highest, and significantly higher than that of 120 kVp PI and 50-200 keV VMIs, all the differences were statistically significant (all P<0.05). The subjective scores of 40 keV VMI and 120 kVp PI were 5 (5, 5) and 4 (3, 5), respectively. The score of 40 keV VMI was significantly higher than that of 120 kVp PI ( Z=-2.60, P=0.009). There were no significant differences in subjective scores between 40 keV VMI and 50-70 keV VMIs ( Z=-1.00, -1.41, -1.73, P=0.317, 0.157, 0.083), but the subjective score of 40 keV VMI was higher than that of 80-200 keV VMIs and the differences were statistically significant (all P<0.05). Conclusions:As for the images of transplanted renal angiography on a dual-layer spectral detector CT, the image quality of 40 keV VMI was best, thus 40 keV was the optimal monoenergetic level.