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. 2021 Apr;11(4):1144-1155.
doi: 10.21037/qims-20-854.

Dual-energy computed tomography of the neck-optimizing tube current settings and radiation dose using a 3D-printed patient phantom

Torsten Diekhoff  1 , Michael Scheel  1 , Wiebke Kress  1 , Bernd Hamm  1 , Paul Jahnke  1   2
Affiliations

Dual-energy computed tomography of the neck-optimizing tube current settings and radiation dose using a 3D-printed patient phantom

Torsten Diekhoff et al. Quant Imaging Med Surg. 2021 Apr.

Abstract

Background: Dual-energy computed tomography (DECT) is increasingly used in studies and clinical practice. However, the best protocol is controversially discussed and whether it exhibits more radiation exposure compared to conventional protocols. Thus, the purpose of the study was to determine optimal tube current settings for DECT in a 3D-printed anthropomorphic phantom of the neck.

Methods: A 3D-printed iodinated ink based phantom of a contrast enhanced CT of the neck was imaged. Six dual-energy multi-detector computed tomography scans were performed with six different tube currents (80 kVp: 30-400 mAs; 135 kVp: 5-160 mAs). 120 virtual blended images (VBIs) and 66 virtual monochromatic images (VMIs) were reconstructed and 12 regions of interest (bilaterally: common carotid arteries, subcutaneous soft tissue, mandibular bone, sternocleidomastoid muscle, submandibular gland, and mid-image: vertebral body of C2 and pharyngeal space) in six consecutive slices resulting in 96 measurements per scan were performed. Hounsfield units and signal- and contrast-to-noise ratio were compared to single-energy computed tomography as standard of reference.

Results: VBIs overestimated the Hounsfield units (P<0.0001). Optimal dual-energy scanning parameters resulted in 120% (100 kVe: 51.2 vs. 61.7 and 65.2, for signal and contrast-to-noise ratio, respectively; 120 kVe: 60.8 vs. 72.1 vs. 128.3) of the radiation exposure with about 80% of the signal/contrast-to-noise ratio of the corresponding single-energy images. However, optimal weighting of tube currents for both voltages depended on the desired reconstruction.

Conclusions: Dual-energy protocols apply an estimated 120% of the single-energy radiation exposure and result in approximately 80% of the image quality. Tube current settings should be adapted to the desired information.

Keywords: Phantoms; X-ray computed; imaging; printing; radiation exposure; three-dimensional; tomography.

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Conflict of interest statement

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at http://dx.doi.org/10.21037/qims-20-854). TD held talks for Canon Medical System. However, the company did not influence nor authorize the results of this study. MS reports grants from Bundesministerium für Wirtschaft und Energie (DE), during the conduct of the study; other from PhantomX GmbH, outside the submitted work; in addition, MS has a patent DE202015104282U1 issued, a patent US9924919B2 issued, a patent US10182786B2 issued, and a patent EP3135199A1 pending. BH reports grants to the Department of Radiology outside the submitted work from Abbott, Actelion Pharma, Bayer Schering Pharma, Bayer Vital, BRACCO Group, Bristol-Myers Squibb, Charité Research organisation GmbH, Deutsche Krebshilfe, Dt. Stiftung für Herzforschung, Essex Pharma, EU Programmes, Fibrex Medical Inc., Focused ultrasound Surgery Foundation, Fraunhofer Gesellschaft, Gurbet, INC Research, InSightec Ltd., IPSEN Pharma, Kendle/MorphoSys AG, Lilly GmbH, Lundbeck GmbH, MeVis Medical Solutions AG, Nexus Oncology, Novartis, Parexel CRO Service, Perceptive, Pfizer GmbH, Philipps, sonofis-aventis S.A., Siemens, Spectranetics GmbH, Terumo Medical Corporation, TNS Healthcare GmbH, Canon Medical, UCB Pharma, Wyeth Pharma, Zukunftsfond Berlin (TSB), outside the submitted work. Dr. PJ reports grants from Bundesministerium für Wirtschaft und Energie (DE), during the conduct of the study; other from PhantomX GmbH, outside the submitted work; in addition, PJ has a patent DE202015104282U1 issued, a patent US9924919B2 issued, a patent US10182786B2 issued, and a patent EP3135199A1 pending. The other author has no conflicts of interest to declare.

Figures

Figure 1
Figure 1
Photography of the phantom.
Figure 2
Figure 2
Flow chart of single energy computed tomography (SECT) and dual energy computed tomography (DECT) scans and image reconstructions. Four SECT images were reconstructed and served as standard of reference. In total 186 DECT images were reconstructed: for virtual blended images (VBIs) all possible pairings of tube current for high and low tube voltage of the six different DECT scans were used (n=30), for virtual monochromatic images only the recommended pairings were used (n=6).
Figure 3
Figure 3
Example images of single energy computed tomography (SECT) scans and dual energy computed tomography (DECT) reconstructions. The DECT reconstructions were derived from the 20/115 mAs (high/low energy) dataset. Images are presented with window level 240 and window width 730. The given HU value represents the mean of all ROI measurements in from this scan. VBI, virtual blended images; VMI, virtual monochromatic images.
Figure 4
Figure 4
Hounsfield units (HU) of virtual blended images (VBI) and virtual monochromatic images (VMI) compared to single energy computed tomography (SECT). (A) Virtual blended images in 80, 100, 120 and 135 kVe compared to the corresponding SECT images. (B) Differences in HU between SECT and VBI. Numbers of statistically significant deviations from Dunnett’s multiple comparison test are shown on top (see also Appendix 1A-D). (C) Comparison of HU between VMI and SECT. The horizontal lines indicate the corresponding values of the SECT datasets. There was no difference between the 75 keV VMI and 120 kVp SECT. All plotted values are the mean values of all ROI measurements of the respective reconstruction.
Figure 5
Figure 5
Comparison of image quality and radiation dose of dual-energy computed tomography (DECT) reconstructions to single-energy computed tomography (SECT) images that served as standard of reference. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) values (y-axis) compared to the radiation exposure as measured by the dose length product (DLP; x-axis) of virtual blended images in 100 and 120 kVe reconstructions and selected virtual monochromatic images (35 to 85 keV) compared to SECT datasets. The left upper corner on the graph represents high image quality and low radiation exposure (thus, optimal balance) whereas the right lower corner represents low image quality and high exposure. The figure shows that neither actual measured DECT reconstructions nor extrapolations between the datapoints were able to achieve a similar or superior ratio of radiation exposure and image quality as SECT images (with the exception of 65 keV VMI images that may meet the SNR/DLP of 135 kVp SECT).
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