Virtual unenhanced second generation dual-source CT of the liver: Is it time to discard the conventional unenhanced phase?  T. Barrett, D.J. Bowden, N. Shaida, E.M. Godfrey, A. Taylor, D.J. Lomas, A.S. Shaw  European Journal of Radiology  Volume 81, Issue 7, Pages 1438-1445 (July 2012) DOI: 10.1016/j.ejrad.2011.03.042 Copyright © 2011 Elsevier Ireland Ltd Terms and Conditions

Fig. 1 Box and whisker's plot comparing the average liver Hounsfield unit (HU) values for all patients, for the conventional unenhanced (CU), virtual unenhanced (VU) portal and VU arterial series. Note the trend towards higher HU in the portal unenhanced series. Outliers are from a patient with marked hepatic steatosis. European Journal of Radiology 2012 81, 1438-1445DOI: (10.1016/j.ejrad.2011.03.042) Copyright © 2011 Elsevier Ireland Ltd Terms and Conditions

Fig. 2 Bland–Altman difference plot comparing the distribution of arterial virtual unenhanced (A) and portal virtual unenhanced (B) regions-of-interest to conventional unenhanced regions-of-interest, shows good agreement between the two datasets, the majority of points lie within the two error bars (±1.96 standard deviations). European Journal of Radiology 2012 81, 1438-1445DOI: (10.1016/j.ejrad.2011.03.042) Copyright © 2011 Elsevier Ireland Ltd Terms and Conditions

Fig. 3 Conventional unenhanced (A) and virtual unenhanced axial CT images derived from the dual-energy portal series (B). Series acquired in the same patient, performed in the same session. The images were scored subjectively as being of equivalent, excellent quality. Note the red field-of-view circle present on the VU image, the iodine subtraction calculation is only performed within this circle. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.) European Journal of Radiology 2012 81, 1438-1445DOI: (10.1016/j.ejrad.2011.03.042) Copyright © 2011 Elsevier Ireland Ltd Terms and Conditions

Fig. 4 Virtual unenhanced field of view artefact. The red circle relates to the smaller (33.2cm) field of view of the B detector. Iodine maps and subsequent iodine subtraction to create the virtual unenhanced images can only be performed within the circle. In larger patients (>40cm actual body diameter) important anatomy may be omitted from the subtraction. In this example the lateral aspect of the right lobe of the liver fails to ‘become unenhanced’ (arrows). Such artefact can be avoided by off-centre positioning of the patient, with the organ of interest being central, but this increases the radiation dose. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.) European Journal of Radiology 2012 81, 1438-1445DOI: (10.1016/j.ejrad.2011.03.042) Copyright © 2011 Elsevier Ireland Ltd Terms and Conditions

Fig. 5 Virtual unenhanced motion-induced artefact. The VU series are susceptible to motion artefact if rapid motion occurs for a very short time interval perpendicular to the X-ray beam. (A and B): Respiratory motion artefact leads to apparent high density around the dome of the liver (arrows). (C and D) pulsation artefact in the ascending thoracic aorta leads to apparent high density in aortic wall, which may be mistaken for calcium or intra-mural haematoma (arrows). Note also the corresponding dark band where over-subtraction has occurred (open arrows). (E and F) Cardiac motion artefact leads to apparent high density in the left pericardium which may be confused with pericardial calcification or haemopericardium (arrows), contrast medium is also seen unsubtracted’ within the left ventricle for the same reason. European Journal of Radiology 2012 81, 1438-1445DOI: (10.1016/j.ejrad.2011.03.042) Copyright © 2011 Elsevier Ireland Ltd Terms and Conditions

Fig. 6 Virtual unenhanced subtraction of pre-existing iodinated contrast may lead to misinterpretation. Conventional unenhanced (A) and virtual unenhanced (B) images in a patient who previously underwent transcatheter arterial chemoembolization for the treatment of hepatocellular carcinoma. Lipiodol is subtracted from the VU series (B) due to the presence of Iodine, on a subsequent post-contrast series, which may be confused with residual or recurrent tumour. European Journal of Radiology 2012 81, 1438-1445DOI: (10.1016/j.ejrad.2011.03.042) Copyright © 2011 Elsevier Ireland Ltd Terms and Conditions

Fig. 7 Virtual unenhanced potential benefits. (A and B) Increased conspicuity of a lesion within the right lobe of the liver is noted on the VU series (B) compared to the CU series (A). (C and D) Conventional unenhanced image (C) demonstrates oral contrast medium in the stomach, this Iodinated agent is subtracted from the VU series in the same patient (D). Note also the increased conspicuity of the lesion within the dome of the liver noted on the VU image (D) as compared to the CU image (C). European Journal of Radiology 2012 81, 1438-1445DOI: (10.1016/j.ejrad.2011.03.042) Copyright © 2011 Elsevier Ireland Ltd Terms and Conditions