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Comparison of virtual unenhanced CT images of the abdomen under different iodine flow rates

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Abstract

Objective

To assess the effect of varying iodine flow rate (IFR) and iodine concentration on the quality of virtual unenhanced (VUE) images of the abdomen obtained with dual-energy CT.

Methods

94 subjects underwent unenhanced and triphasic contrast-enhanced CT scan of the abdomen, including arterial phase, portal venous phase, and delayed phase using dual-energy CT. Patients were randomized into 4 groups with different IFRs or iodine concentrations. VUE images were generated at 70 keV. The CT values, image noise, SNR and CNR of aorta, portal vein, liver, liver lesion, pancreatic parenchyma, spleen, erector spinae, and retroperitoneal fat were recorded. Dose–length product and effective dose for an examination with and without plain phase scan were calculated to assess the potential dose savings. Two radiologists independently assessed subjective image quality using a five-point scale. The Kolmogorov–Smirnov test was used first to test for normal distribution. Where data conformed to a normal distribution, analysis of variance was used to compare mean HU values, image noise, SNRs and CNRs for the 4 image sets. Where data distribution was not normal, a nonparametric test (Kruskal–Wallis test followed by stepwise step-down comparisons) was used. The significance level for all tests was 0.01 (two-sided) to allow for type 2 errors due to multiple testing.

Results

The CT numbers (HU) of VUE images showed no significant differences between the 4 groups (p > 0.05) or between different phases within the same group (p > 0.05). VUE images had equal or higher SNR and CNR than true unenhanced images. VUE images received equal or lower subjective image quality scores than unenhanced images but were of acceptable quality for diagnostic use. Calculated dose–length product and estimated dose showed that the use of VUE images in place of unenhanced images would be associated with a dose saving of 25%.

Conclusions

VUE images can replace conventional unenhanced images. VUE images are not affected by varying iodine flow rates and iodine concentrations, and diagnostic examinations could be acquired with a potential dose saving of 25%.

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Abbreviations

IFR:

Iodine flow rate

VUE:

Virtual unenhanced

AP:

Arterial phase

VP:

Portal venous phase

DP:

Delayed phase

TUE:

True unenhanced

DLP:

Dose–length product

ED:

Effective dose

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Authors and Affiliations

  1. Department of Radiology, The First Hospital of JiLin University, Changchun, 130000, Jilin, China

    Yongrui Li, Ye Li, Xiaodong Li, Chunjie Guo & Huimao Zhang

  2. Wolfson Molecular Imaging Center, University of Manchester, Withington, Manchester, M20 3LJ, UK

    Alan Jackson

  3. GE Healthcare (Life Science), Beijing, 100176, China

    Ning Huang

Authors
  1. Yongrui Li
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  2. Ye Li
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  3. Alan Jackson
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  4. Xiaodong Li
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  5. Ning Huang
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  6. Chunjie Guo
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  7. Huimao Zhang
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Correspondence to Huimao Zhang.

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Conflict of interest

Huang, Ning is an employee of GE Healthcare, Life Science China. All other authors declare that they have no conflict of interest.

Ethical approval

All procedures in this study were in accordance with the ethical standards of the institutional research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

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Li, Y., Li, Y., Jackson, A. et al. Comparison of virtual unenhanced CT images of the abdomen under different iodine flow rates. Abdom Radiol 42, 312–321 (2017). https://doi.org/10.1007/s00261-016-0842-4

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  • DOI: https://doi.org/10.1007/s00261-016-0842-4

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