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Optimization of image process parameters through factorial experiments using a flat panel detector
Örebro University, Department of Natural Sciences.
Örebro University, School of Health and Medical Sciences.
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. Vol. 52, no 17, p. 5263-5276
Keywords [en]
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: urn:nbn:se:oru:diva-2866DOI: 10.1088/0031-9155/52/17/011OAI: oai:DiVA.org:oru-2866DiVA, id: diva2:135377
Available from: 2007-12-28 Created: 2007-12-28 Last updated: 2018-01-13Bibliographically approved
In thesis
1. Optimisation of radiographic imaging by means of factorial experiments
Open this publication in new window or tab >>Optimisation of radiographic imaging by means of factorial experiments
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:nbn:se:oru:diva-1731 (URN)978-91-7668-568-6 (ISBN)
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

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Norrman, EvaPersliden, Jan

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