Virtual monoenergetic images from spectral detector CT as a surrogate for conventional CT images: Unaltered attenuation characteristics with reduced image noise

Nils Große Hokamp; R Gilkeson; M K Jordan; K R Laukamp; Victor-Frederick Neuhaus; S Haneder; S S Halliburton; A Gupta

doi:10.1016/j.ejrad.2019.05.019

Virtual monoenergetic images from spectral detector CT as a surrogate for conventional CT images: Unaltered attenuation characteristics with reduced image noise

Eur J Radiol. 2019 Aug:117:49-55. doi: 10.1016/j.ejrad.2019.05.019. Epub 2019 May 29.

Authors

Nils Große Hokamp¹, R Gilkeson², M K Jordan³, K R Laukamp², Victor-Frederick Neuhaus⁴, S Haneder⁴, S S Halliburton⁵, A Gupta²

Affiliations

¹ IUniversity of Cologne, Faculty of Medicine and University Hospital Cologne, Institute for Diagnostic and Interventional Radiology, Cologne, Germany; Department of Radiology, Case Western Reserve University, Cleveland, OH, USA; Department of Radiology, University Hospitals Medical Center, Cleveland, OH, USA. Electronic address: nils.grosse-hokamp@uk-koeln.de.
² Department of Radiology, Case Western Reserve University, Cleveland, OH, USA; Department of Radiology, University Hospitals Medical Center, Cleveland, OH, USA.
³ Department of Radiology, Case Western Reserve University, Cleveland, OH, USA.
⁴ IUniversity of Cologne, Faculty of Medicine and University Hospital Cologne, Institute for Diagnostic and Interventional Radiology, Cologne, Germany.
⁵ Philips Healthcare, Clinical Science CT, Cleveland OH, USA.

PMID: 31307652
DOI: 10.1016/j.ejrad.2019.05.019

Abstract

Objective: This study aimed to identify the energy level of virtual monoenergetic images (VMI) that closest represents conventional images (CI) in order to demonstrate that these images provide improved image quality in terms of noise and Signal-to-noise ratio (SD/SNR) while attenuation values (HU) remain unaltered as compared to CI.

Methods: 60 and 30 patients with contrast-enhanced (CE) and non-enhanced (NCE) spectral detector CT (SDCT) of the abdomen were included in this retrospective, IRB-approved study. CI and VMI of 66-74 keV as well as quantitative iodine maps were reconstructed (Q-IodMap). Two regions of interest were placed in each: pulmonary trunk, abdominal aorta, portal vein, liver, pancreas, renal cortex left/right, psoas muscle, (filled) bladder and subcutaneous fat. For each reconstruction, HU and SD were averaged. ΔHU and SNR (SNR = HU/SD) were calculated. Q-IodMap were considered as confounder for ΔHU. In addition, two radiologists compared VMI of 72 keV and CI in a forced-choice approach regarding image quality.

Results: In NCE studies, no significant differences for any region was found. In CE studies, VMI_72keV images showed lowest ΔHU (HU_liver CI/VMI_72keV: 104 ± 18/103 ± 17, p ≥ 0.05). Iodine containing voxels as indicated by Q-IodMap resulted in an over- and underestimation of attenuation in lower and higher VMI energies, respectively. Image noise was lower in VMI images (e.g. muscle: CI/ VMI_72keV: 15.3 ± 3.3/12.3 ± 2.9 HU, p ≤ 0.05). Hence, SNR was significantly higher in VMI_72keV compared to CI (e.g. liver 3.8 ± 0.6 vs 3.0 ± 0.8, p ≤ 0.05). In visual analysis, VMI_72keV were preferred over CI at all times.

Conclusions: VMI_72keV show improved SD/SNR characteristics while the attenuation remains unaltered as compared to CI.

Keywords: Dual energy computed tomography; Image reconstruction; Spectral detector computed tomography; Virtual monoenergetic images.

MeSH terms

Adult
Aged
Aged, 80 and over
Female
Humans
Male
Middle Aged
Multidetector Computed Tomography
Radiographic Image Interpretation, Computer-Assisted
Radiography, Abdominal*
Reproducibility of Results
Retrospective Studies
Signal-To-Noise Ratio*
Tomography, X-Ray Computed* / methods
Virtual Reality*