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Accuracy of stone size measurement using dual-energy virtual non-contrast enhanced CT images: a phantom study
Department of Radiology, Örebro University Hospital, 701 85 Örebro, Sweden.
Department of Radiology, Örebro University Hospital, 701 85 Örebro, Sweden.
Department of Radiology, Örebro University Hospital, 701 85 Örebro, Sweden.
Linköping University, Department of Medical and Health Sciences, Radiology. Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Faculty of Health Sciences.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Background: Accurate estimation of calculus size is an important prediction factor for spontaneous passage. The method used for calculus-size estimation needs to be as precise as possible. Previous studies have shown that the image quality of virtual non-contrast (VNC) images obtained with the new generation of dual-energy CT (DECT) is still inferior compared to native images. However, the difference in assessed image quality compared to native series is smaler with the new than with the older system.

Purpose: The aim of this study is to evaluate the accuracy of measurements of renal calculi in a VNC image series obtained with the new generation of dual-energy CT, compared to actual stone size and single-energy image series in a phantom study.

Material and Methods: For the purpose of this study a ureter phantom was created. The phantom was scanned with DECT (Somatom Definition Flash) at three different radiation-dose settings with single and dual energy, first with water in the ureters then with i.v. contrast medium solution. At each energy level CDTI were set equal for single and dual-energy. VNC series were created. All image series were assessed for stone visibility and size.

Results: All calculi were visible in single- and dual-energy images with water in phantom tubes. With the VNC calculi in the size range 1.42 – 2.02 mm were missed. Results of intraobserver variability in investigated dose levels shows very good agreement between assessments of stone size by both evaluators, with correlation coefficient (CC) variying from 0.97 (95% CI 0.91–0.99) to 1.0 (95% CI 0.99–1.0). Results of correlation tests between the mean of maximal stone size and maximal stone size measured with electronic callipers show good agreement, with a CC variability from 0.93 (95% CI 0.76-0.98) to 0.99 (95% CI 0.96-0.99), a limit of agreement of "1.65 to 1.38 and bias "0.14. With one of the observers, the results of correlation tests in assessments made by the same reader of stone-size in dual-energy and VNC image series for corresponding dose levels show lower ICC for the low dose level, 0.77 (CI 0.36–0.93), with limits of agreement of -2.23–0.57 and bias "0.33.

Conclusions: This study shows that detection of small stones is not reliable despite better image quality with the new DECT and that small stones will be missed with VNC imaging. In larger stones, the inherent measurement error with CT is magnified with VNC imaging.

National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-76722OAI: oai:DiVA.org:liu-76722DiVA: diva2:516383
Available from: 2012-04-18 Created: 2012-04-18 Last updated: 2013-10-21Bibliographically approved
In thesis
1. Aspects on Image Quality in Radiologic Evaluation of the Urinary Tract
Open this publication in new window or tab >>Aspects on Image Quality in Radiologic Evaluation of the Urinary Tract
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The focus of this document is on image quality as one of the factors fundamental for the diagnostic process. With the rising number of procedures and the trend towards more complicated examinations, urinary tract investigations was chosen in this work as a good clinical model for evaluation of the factors influencing image quality and of the ways of evaluating image quality.

In paper I, a method is described for optimisation during the introduction of a new imaging system, with a focus on the maintenance of image quality relative to the older already optimised system. Image quality was assessed using the image criteria of the European guidelines for IVU with visual grading analysis. Equivalent image quality in image pairs was achieved at 30% of the dose. The CDRAD contrast-detail phantom makes it possible to find dose levels that give equal image quality using different imaging systems.

In paper II, the influence of bowel purgation on image quality in urography is questioned. The aim of this study was to compare bowel purgation and two other preparation methods; dietary restrictions and no preparation at all. Image quality was assessed according to European Commission criteria for excretory urography. The effectiveness of bowel purgation and the amount of residual gas were scored separately. The results of our study show that the preparation methods are of equal value and further use of bowel purgation before excretory urography cannot be justified.

In paper III, the image quality of the non-enhanced series is compared to a virtual noncontrast series obtained using two generations of dual-energy CT scanners and taking CT of the urinary tract as a model. The image quality of the VNC images was rated inferior to the single-energy variant for both scanners, the OR range being 11.5–67.3 for the Definition and 2.1–2.8 for the Definition Flash. Visual noise and overall quality were regarded as better with Flash than with Definition. Image quality of VNC images obtained with the new generation of DECT is still slightly inferior compared to native images.

In paper IV, the accuracy of measurement of renal calculi in a dual-energy, virtual, nonenhanced-image series is compared to actual stone size and a single-energy image series in the phantom study. This study shows that detection of small stones is not reliable, despite better image quality, with the new DECT and that small stones will be missed with VNC imaging. With larger stones, the inherent measurement error with CT is magnified with VNC imaging.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. 69 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1298
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:liu:diva-76723 (URN)978-91-7519-943-6 (ISBN)
Public defence
2012-05-18, Bohmansonssalen, Universitetssjukhuset, Örebro, 09:00 (Swedish)
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Available from: 2012-04-18 Created: 2012-04-18 Last updated: 2013-10-21Bibliographically approved

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