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Optimisation of radiographic imaging by means of factorial experiments
Örebro University, Department of Natural Sciences.
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the optimisation process of radiographic imaging, factorial designed experiments can be applied. The parameters (factors) are varied together instead of one at a time, making it possible to discover interactions between the factors as well as main influences of them on the result variable. A 2k design implies having k number of factors each one set to two different levels (low and high).

A computer program, CoCIQ, designed to automatically analyse and evaluate test images of a contrast-detail phantom, was evaluated and adjusted to clinical situations using a flat panel detector. The program gives a quantified measurement of image quality by calculating an Image Quality Figure (IQF) for the X-ray image. It was shown that the program produces IQF with small variations. It was also found that there was a strong linear statistical relation between the computerised evaluation and the evaluation performed by human observers.

2k factorial experiments were evaluated by investigating the influence of tube potential, tube loading, focus size and filtration on the result variables IQF, Kerma Area Product (KAP) and effective dose using a flat panel detector. It was found that the result variables were mainly influenced by tube loading, tube potential and filtration. Interactions between tube potential and filtration as well as between tube loading and filtration were observed, too. This work demonstrates that accepted knowledge was reproduced and that the effects of interactions between parameters were revealed.

Extended 2k experiments were then applied at three different optimisation procedures. Two studies were performed using a flat panel detector for lumbar spine radiography. The aim was to find optimal settings for tube potential, system sensitivity and filtration for different sized patients and, in a separate study, to investigate the effect of the image post processing parameters and the possibility for dose reduction by adjusting these. The parameters are ROI (Region Of Interest) density, gamma, detail contrast enhancement, unsharp masking, kernel size and noise compensation.

After determining the optimal settings from these experiments, X-ray images of the lumbar spine of an Alderson phantom were acquired and evaluated in a visual grading analysis (VGA).

The results illustrated that the image quality was maintained at a lower effective dose by operating with a reduced tube potential and increased sensitivity of the X-ray system.

The experiments on image post process parameters revealed their influence on image quality and indicated that image quality could be improved by changing the settings of the process parameters.

Factorial experiments were also performed, using a multislice CT scanner to investigate the possibility for dose reduction at paediatric head examinations. An anthropomorphic phantom simulating a one-year-old child was scanned using different settings of tube potential, tube loading and reconstruction filter.

The study showed that a 25 % reduction of dose was possible with maintained image quality by reducing the tube loading.

Factorial designed experiments provide an effective method to simultaneously predict the influence of various parameters on image quality and radiation dose in the optimisation in diagnostic radiology.

Place, publisher, year, edition, pages
Örebro: Örebro universitetsbibliotek , 2007. , p. 87
Series
Örebro Studies in Physics, ISSN 1652-148X ; 3
National Category
Physical Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:oru:diva-1731ISBN: 978-91-7668-568-6 (print)OAI: oai:DiVA.org:oru-1731DiVA, id: diva2:135379
Public defence
2008-01-18, HSP 1, Prismahuset, Örebro universitet, Örebro, 10:00
Opponent
Supervisors
Available from: 2007-12-28 Created: 2007-12-18 Last updated: 2017-10-18Bibliographically approved
List of papers
1. A clinical evaluation of the image quality computer program, CoCIQ
Open this publication in new window or tab >>A clinical evaluation of the image quality computer program, CoCIQ
2005 (English)In: Journal of digital imaging, ISSN 0897-1889, E-ISSN 1618-727X, Vol. 18, no 2, p. 138-144Article in journal (Refereed) Published
Abstract [en]

To provide an objective way of measuring image quality, a computer program was designed that automatically analyzes the test images of a contrast-detail (CD) phantom. The program gives a quantified measurement of image quality by calculating an Image Quality Figure (IQF). The aim of this work was to evaluate the program and adjust it to clinical situations in order to find the detectable level where the program gives a reliable figure of the contrast resolution. The program was applied on a large variety of images with lumbar spine and urographic parameters, from very low to very high image qualities. It was shown that the computer program produces IQFs with small variations and there were a strong linear statistical relation between the computerized evaluation and the evaluation performed by human observers (R2 = 0.98). This method offers a fast and easy way of conducting image quality evaluations.

National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:oru:diva-2863 (URN)10.1007/s10278-004-1036-0 (DOI)
Available from: 2007-12-28 Created: 2007-12-28 Last updated: 2017-12-14Bibliographically approved
2. A factorial experiment on image quality and radiation dose
Open this publication in new window or tab >>A factorial experiment on image quality and radiation dose
2005 (English)In: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 114, no 1-3, p. 246-252Article in journal (Refereed) Published
Abstract [en]

To find if factorial experiments can be used in the optimisation of diagnostic imaging, a factorial experiment was performed to investigate some of the factors that influence image quality, kerma area product (KAP) and effective dose (E). In a factorial experiment the factors are varied together instead of one at a time, making it possible to discover interactions between the factors as well as major effects. The factors studied were tube potential, tube loading, focus size and filtration. Each factor was set to two levels (low and high). The influence of the factors on the response variables (image quality, KAP and E) was studied using a direct digital detector. The major effects of each factor on the response variables were estimated as well as the interaction effects between factors. The image quality, KAP and E were mainly influenced by tube loading, tube potential and filtration. There were some active interactions, for example, between tube potential and filtration and between tube loading and filtration. The study shows that factorial experiments can be used to predict the influence of various parameters on image quality and radiation dose.

National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:oru:diva-2864 (URN)10.1093/rpd/nch557 (DOI)
Available from: 2007-12-28 Created: 2007-12-28 Last updated: 2017-12-14Bibliographically approved
3. Optimising the tube potential for lumbar spine radiography using a flat-panel digital detector
Open this publication in new window or tab >>Optimising the tube potential for lumbar spine radiography using a flat-panel digital detector
(English)Manuscript (preprint) (Other academic)
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:oru:diva-2865 (URN)
Available from: 2007-12-28 Created: 2007-12-28 Last updated: 2017-10-18Bibliographically approved
4. Optimization of image process parameters through factorial experiments using a flat panel detector
Open this publication in new window or tab >>Optimization of image process parameters through factorial experiments using a flat panel detector
2007 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 52, no 17, p. 5263-5276Article in journal (Refereed) Published
Abstract [en]

In the optimization process of lumbar spine examinations, factorial experiments were performed addressing the question of whether the effective dose can be reduced and the image quality maintained by adjusting the image processing parameters. A 2(k)-factorial design was used which is a systematic and effective method of investigating the influence of many parameters on a result variable. Radiographic images of a Contrast Detail phantom were exposed using the default settings of the process parameters for lumbar spine examinations. The image was processed using different settings of the process parameters. The parameters studied were ROI density, gamma, detail contrast enhancement (DCE), noise compensation, unsharp masking and unsharp masking kernel (UMK). The images were computer analysed and an image quality figure (IQF) was calculated and used as a measurement of the image quality. The parameters with the largest influence on image quality were noise compensation, unsharp masking, unsharp masking kernel and detail contrast enhancement. There was an interaction between unsharp masking and kernel indicating that increasing the unsharp masking improved the image quality when combined with a large kernel size. Combined with a small kernel size however the unsharp masking had a deteriorating effect. Performing a factorial experiment gave an overview of how the image quality was influenced by image processing. By adjusting the level of noise compensation, unsharp masking and kernel, the IQF was improved to a 30% lower effective dose.

Place, publisher, year, edition, pages
Bristol: IOP publishing, 2007
Keyword
Quality, Coefficients, Radiography, Reduction, Urography
National Category
Natural Sciences Physical Sciences Medical and Health Sciences Physiology Radiology, Nuclear Medicine and Medical Imaging
Research subject
Physics; Medicine; Radio Physics
Identifiers
urn:nbn:se:oru:diva-2866 (URN)10.1088/0031-9155/52/17/011 (DOI)
Available from: 2007-12-28 Created: 2007-12-28 Last updated: 2018-01-13Bibliographically approved
5. Optimisation of paediatric CT head examinations through factorial experiments
Open this publication in new window or tab >>Optimisation of paediatric CT head examinations through factorial experiments
(English)Manuscript (Other academic)
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:oru:diva-2867 (URN)
Available from: 2007-12-28 Created: 2007-12-28 Last updated: 2017-10-18Bibliographically approved

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