Comparison of Virtual Non-Enhanced DECT Imaging of the Liver with True Non-Enhanced DECT Imaging

Dr Patrick Markey,

Dr Daniel Kirkpatrick,

Mrs Alexa Seal,

Dr Neha Singh (FRANZCR)

Abstract:

In hepatic imaging multiphase protocols are often required to adequately characterize hepatic lesions. Dual Energy CT techniques offer the possibility of subtracting iodine from

contrast-enhanced datasets to reconstruct virtual non-enhanced images of the liver

parenchyma. The estimated radiation dose reduction by omitting a true unenhanced

liver series is reported to range from 19 to 50%. However, reconstruction of a virtual

unenhanced series for diagnostic purposes comes with the risk of incomplete coverage

of the abdomen or the possibility of minor artifacts that may impair diagnostic image

quality, depending on the location of the lesions under scrutiny.1

Previous studies conducted have shown no statistical difference between virtual and

true datasets of the liver, with acceptable image quality being obtained in 95% of 40

cases compared to 97.5% of true nonenhced imaging. It was additionally determined that hepatic lesions showed similar CT density measurements on virtual unenhanced and true unenhanced images in addition to a superior signal to noise ratio on virtual images.2 A similar paper conducted in the UK showed a similar percentage of virtual unenhanced images (97.4%) were of acceptable quality to replace the conventional unenhanced series.3

More recently, studies conducted with second-generation DECT scanners have identified potential limitations to adopting virtual unenhanced images. Increased presence of artifacts impairing image interpretation secondary to DECT scanning technique and patient body habitus was reported on virtual images. Differing density value scores (Hounsfield units) between virtual and true datasets and the subtraction of metallic clips, important to identifying anastomotic sites, were additionally noted.4 The most recently published journal article on this topic concluded virtual and conventional non enhanced images were of comparable diagnostic quality, with an increased detection of small low density lesions at

the cost of missing a larger percentage of calcified nodules in the former.5

Aim of research

Determining if virtual non-enhanced DECT of the liver is diagnostically equivalent to directly acquired non-enhanced CT, such that the pre-contrast series may be omitted.

Significance of research

There have been several international studies conducted since 2009 with differing onclusions comparing virtual and conventional non-contrast DECT images of the liver. To our knowledge no studies of this nature have been conducted in Australia or Riverina Medical and Surgical Symposium | 5 with a GE single source DECT. The results of this study will add to the current literature and may assist in guiding protocols, so that conventional non-enhanced images are confidently not required in selected patients.

References

1 - Heye, T., Nelson, R., Ho, L., Marin, D., & Boll, D. (2012). Dual-Energy CT Applications in the Abdomen. American Journal of Roentgenology, 199(5_supplement), S64–S70. doi:10.2214/AJR.12.9196

2 - DeCecco, C., Buffa, V., Fedeli, S., Luzietti, M., Vallone, A., Ruopoli, R., … David, V. (2010). Dual energy CT (DECT) of the liver: conventional versus virtual unenhanced images. European Radiology, 20(12), 2870–2875. doi:10.1007/s00330-010-1874-

3 - Barrett, T., Bowden, D. J., Shaida, N., Godfrey, E. M., Taylor, A., Lomas, D. J., & Shaw, A. S. (2012). Virtual unenhanced second generation dual-source CT of the liver: Is it time to discard the conventional unenhanced phase? European Journal of Radiology, 81(7), 1438–1445. doi:10.1016/j.ejrad.2011.03.042

4 - DeCecco, C., Darnell, A., Macías, N., Ayuso, J., Rodríguez, S., Rimola, J., … Ayuso, C. (2013). Virtual Unenhanced Images of the Abdomen With Second-Generation Dual-Source Dual-Energy Computed Tomography: Image Quality and Liver Lesion Detection. Investigative Radiology, 48(1), 1. doi:10.1097/RLI.0b013e31826e7902

5 - De Cecco, C. N., Muscogiuri, G., Schoepf, U. J., Caruso, D., Wichmann, J. L., Cannaò, P. M., … Hardie, A. D. (2016). Virtual unenhanced imaging of the liver with third-generation dual-source dual-energy CT and advanced modeled iterative reconstruction. European journal of radiology, 85(7), 1257–64. doi:10.1016/j.ejrad.2016.04.012