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A factorial experiment on image quality and radiation dose
Örebro University, Department of Natural Sciences.
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.

Place, publisher, year, edition, pages
2005. Vol. 114, no 1-3, p. 246-252
National Category
Physical Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:oru:diva-2864DOI: 10.1093/rpd/nch557OAI: oai:DiVA.org:oru-2864DiVA, id: diva2:135375
Available from: 2007-12-28 Created: 2007-12-28 Last updated: 2017-12-14Bibliographically 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, Eva

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