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Aspects on Image Quality in Radiologic Evaluation of the Urinary Tract
Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medical and Health Sciences. Linköping University, Faculty of Health Sciences.
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: urn:nbn:se:liu:diva-76723ISBN: 978-91-7519-943-6 (print)OAI: oai:DiVA.org:liu-76723DiVA: diva2:516406
Public defence
2012-05-18, Bohmansonssalen, Universitetssjukhuset, Örebro, 09:00 (Swedish)
Opponent
Supervisors
Available from: 2012-04-18 Created: 2012-04-18 Last updated: 2013-10-21Bibliographically approved
List of papers
1. Reducing dose in urography while maintaining image quality - A comparison of storage phosphor plates and a flat-panel detector
Open this publication in new window or tab >>Reducing dose in urography while maintaining image quality - A comparison of storage phosphor plates and a flat-panel detector
2006 (English)In: European Radiology, ISSN 0938-7994, E-ISSN 1432-1084, Vol. 16, no 1, 221-226 p.Article in journal (Refereed) Published
Abstract [en]

The introduction of new flat-panel detector technology often forces us to accept too high dose levels as proposed by the manufacturers. We need a tool to compare the image quality of a new system with the accepted standard. The aim of this study was to obtain a comparable image quality for two systems - storage phosphor plates and a flat-panel system using intravenous urography (IVU) as a clinical model. The image quality figure was calculated using a contrast-detail phantom (CDRAD) for the two evaluated systems. This allowed us to set a dose for the flat-panel system that gave equivalent image quality to the storage phosphor plates. This reduced detector dose was used in an evaluation of clinical images to find out if the dose reduction from the phantom study indeed resulted in images of equal clinical image quality. The image quality was assessed using 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. © Springer-Verlag 2005.

Keyword
Digital radiography, Flat-panel detector, Image quality, Phantoms
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-50322 (URN)10.1007/s00330-005-2772-3 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12Bibliographically approved
2. Bowel preparation for excretory urography is not necessary: a randomized trial
Open this publication in new window or tab >>Bowel preparation for excretory urography is not necessary: a randomized trial
2007 (English)In: British Journal of Radiology, ISSN 0007-1285, E-ISSN 1748-880X, Vol. 80, no 956, 617-624 p.Article in journal (Refereed) Published
Abstract [en]

Despite the fact that computed tomography is becoming more commonly used to investigate the genitourinary tract, intravenous urography still plays an important role in uroradiology. The aim of this study was to compare bowel purgation and two other preparation methods — dietary restrictions and no preparations at all — in an attempt to find the optimal procedure for uniform practice. 210 consecutive patients were randomised to three preparation groups with 70 in each group. Group 1 received standard bowel purgation, Group 2 was instructed to fast, while Group 3 had no preparation at all. Irrespective of preparation, all patients underwent the same examination procedure. The examining radiographer and evaluating radiologists were unaware of the type of preparation given. 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. There was no statistically significant difference in the proportions with fulfilled criteria between preparation Groups 1 and 2 and Groups 1 and 3. A criterion was regarded as fulfilled only when all three observers agreed. Assessment of the amount of residual faeces proved the effectiveness of our standard bowel purgation. The results of our study show equality of the evaluated preparation methods and cannot justify further use of bowel purgation before excretory urography.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-76719 (URN)10.1259/bjr/78311002 (DOI)000249951000005 ()
Available from: 2012-04-18 Created: 2012-04-18 Last updated: 2017-12-07Bibliographically approved
3. Virtual non-contrast dual-energy CT compared to single-energy CT of the urinary tract: a prospective study
Open this publication in new window or tab >>Virtual non-contrast dual-energy CT compared to single-energy CT of the urinary tract: a prospective study
Show others...
2012 (English)In: Acta Radiologica, ISSN 0284-1851, E-ISSN 1600-0455, Vol. 53, no 6, 689-694 p.Article in journal (Refereed) Published
Abstract [en]

Background: Dual-energy computed tomography (DECT) has been shown to be useful for subtracting bone or calcium in CT angiography and gives an opportunity to produce a virtual non-contrast-enhanced (VNC) image from a series where contrast agents have been given intravenously. High noise levels and low resolution have previously limited the diagnostic value of the VNC images created with the first generation of DECT. With the recent introduction of a second generation of DECT, there is a possibility of obtaining VNC images with better image quality at hopefully lower radiation dose compared to the previous generation.

Purpose: The aim of this study is to compare the image quality of the single-energy series to a VNC series obtained with a two generations of DECT scanners. CT of the urinary tract was used as a model.

Material and Methods: Thirty patients referred for evaluation of haematuria were examined with an older system (Somatom Definition) and another 30 patients with a new generation (Somatom Definition Flash). One single-energy series was obtained before and one dual-energy series after administration of intravenous contrast media. We created a VNC series from the contrast-enhanced images. Images were assessed concerning image quality with a visual grading scale evaluation of the VNC series with the single-energy series as gold standard.

Results: The image quality of the VNC images was rated inferior to the single-energy variant for both scanners, OR range 11.5-67.3 for the Definition and OR 2.1-2.8 for the Definition Flash. Visual noise and overall quality were regarded as better with Flash than Definition.

Conclusions: Image quality of VNC images obtained with the new generation of DECT is still slightly inferior compared to native images. However the difference is smaller with the new compared to the older system.

Place, publisher, year, edition, pages
Informa Healthcare, 2012
Keyword
Dual-energy computed tomography, image quality, urinary tract imaging, virtual non-enhanced image series, bone-iodine differentiation
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-76721 (URN)10.1258/ar.2012.110661 (DOI)000306984000017 ()
Available from: 2012-04-18 Created: 2012-04-18 Last updated: 2017-12-07Bibliographically approved
4. Accuracy of stone size measurement using dual-energy virtual non-contrast enhanced CT images: a phantom study
Open this publication in new window or tab >>Accuracy of stone size measurement using dual-energy virtual non-contrast enhanced CT images: a phantom study
Show others...
(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:nbn:se:liu:diva-76722 (URN)
Available from: 2012-04-18 Created: 2012-04-18 Last updated: 2013-10-21Bibliographically approved

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