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Metal artifacts in computed tomography: impact of reduction methods on image quality and radiotherapy treatment planning
Örebro University, School of Medical Sciences.
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Degradation of image quality by metal artifacts is a common problem in computed tomography (CT) imaging, which can limit the diagnostic value of a CT examination and also introduce inaccuracies in radiotherapy (RT) treatment planning. In recent years, commercial metal artifact reduction (MAR) methods have been launched by several CT vendors. The overall aim of this thesis was to evaluate MAR methods in diagnostic imaging and RT treatment planning.

Evaluations of hip prosthesis phantom CT images showed that MAR algorithms in general improved image quality, based on both visual grading analysis and quantitative measures, while the application of virtual monoenergetic reconstructions insufficiently reduced metal artifacts. In some cases additional artifacts were introduced by the MAR algorithms. MAR algorithms were also evaluated in hip prosthesis phantom CT imaging used for proton therapy treatment planning, where improvements in dose calculation accuracy were observed.

Studies of Head & Neck (H&N) implant CT images in RT treatment planning were also performed. By visual grading of anatomy visualization with respect to target delineation in dental implant patient images, MAR algorithms were shown to significantly improve image quality. However, only minor effects of H&N implant artifacts on proton dose distributions were seen. The impact might be greater for more severe artifacts than those studied here, and thus further investigations of such cases are needed.

In conclusion, MAR algorithms have been shown to enhance image quality for diagnostic applications and to improve anatomy visualization in RT treatment planning. The MAR algorithms led to increased proton dose calculation accuracy in some cases, while in other situations only minor changes were seen.

Place, publisher, year, edition, pages
Örebro: Örebro University , 2018. , p. 81
Series
Örebro Studies in Medicine, ISSN 1652-4063 ; 172
Keywords [en]
computed tomography, metal artifacts, image quality, visual grading analysis, radiotherapy, proton therapy, hip prosthesis, dental implants
National Category
Surgery
Identifiers
URN: urn:nbn:se:oru:diva-63420ISBN: 978-91-7529-228-1 (print)OAI: oai:DiVA.org:oru-63420DiVA, id: diva2:1167540
Public defence
2018-03-09, Örebro universitet, Campus USÖ, hörsal C3, Södra Grev Rosengatan 32, Örebro, 09:30 (Swedish)
Opponent
Supervisors
Available from: 2017-12-19 Created: 2017-12-19 Last updated: 2018-02-15Bibliographically approved
List of papers
1. Evaluation of a metal artifact reduction algorithm in CT studies used for proton radiotherapy treatment planning
Open this publication in new window or tab >>Evaluation of a metal artifact reduction algorithm in CT studies used for proton radiotherapy treatment planning
2014 (English)In: Journal of Applied Clinical Medical Physics, ISSN 1526-9914, E-ISSN 1526-9914, Vol. 15, no 5, p. 112-119Article in journal (Refereed) Published
Abstract [en]

Metal objects in the body such as hip prostheses cause artifacts in CT images. When CT images degraded by artifacts are used for treatment planning of radiotherapy, the artifacts can yield inaccurate dose calculations and, for particle beams, erroneous penetration depths. A metal artifact reduction software (O-MAR) installed on a Philips Brilliance Big Bore CT has been tested for applications in treatment planning of proton radiotherapy. Hip prostheses mounted in a water phantom were used as test objects. Images without metal objects were acquired and used as reference data for the analysis of artifact-affected regions outside of the metal objects in both the O-MAR corrected and the uncorrected images. Water equivalent thicknesses (WET) based on proton stopping power data were calculated to quantify differences in the calculated proton beam penetration for the different image sets. The WET to a selected point of interest between the hip prostheses was calculated for several beam directions of clinical relevance. The results show that the calculated differences in WET relative to the reference case were decreased when the O-MAR algorithm was applied. WET differences up to 2.0 cm were seen in the uncorrected case while, for the O-MAR corrected case, the maximum difference was decreased to 0.4 cm. The O-MAR algorithm can significantly improve the accuracy in proton range calculations. However, there are some residual effects, and the use of proton beam directions along artifact streaks should only be used with caution and appropriate margins.

Place, publisher, year, edition, pages
John Wiley & Sons, 2014
Keywords
metal artifact reduction, radiation therapy, water equivalent thickness, proton range
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:oru:diva-65011 (URN)10.1120/jacmp.v15i5.4857 (DOI)000345121900010 ()28297224 (PubMedID)2-s2.0-84929502869 (Scopus ID)
Available from: 2018-02-15 Created: 2018-02-15 Last updated: 2018-02-15Bibliographically approved
2. Metal artefact reduction in CT imaging of hip prostheses-an evaluation of commercial techniques provided by four vendors
Open this publication in new window or tab >>Metal artefact reduction in CT imaging of hip prostheses-an evaluation of commercial techniques provided by four vendors
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2015 (English)In: British Journal of Radiology, ISSN 0007-1285, E-ISSN 1748-880X, Vol. 88, no 1052, article id 20140473Article in journal (Refereed) Published
Abstract [en]

Objective: The aim of this study was to evaluate commercial metal artefact reduction (MAR) techniques in X-ray CT imaging of hip prostheses.

Methods: Monoenergetic reconstructions of dual-energy CT (DECT) data and several different MAR algorithms, combined with single-energy CT or DECT, were evaluated by imaging a bilateral hip prosthesis phantom. The MAR images were compared with uncorrected images based on CT number accuracy and noise in different regions of interest.

Results: The three MAR algorithms studied implied a general noise reduction (up to 67%, 74% and 77%) and an improvement in CT number accuracy, both in regions close to the prostheses and between the two prostheses. The application of monoenergetic reconstruction, without any MAR algorithm, did not decrease the noise in the regions close to the prostheses to the same extent as did the MAR algorithms and even increased the noise in the region between the prostheses.

Conclusion: The MAR algorithms evaluated generally improved CT number accuracy and substantially reduced the noise in the hip prostheses phantom images, both close to the prostheses and between the two prostheses. The study showed that the monoenergetic reconstructions evaluated did not sufficiently reduce the severe metal artefact caused by large orthopaedic implants.

Advances in knowledge: This study evaluates several commercially available MAR techniques in CT imaging of large orthopaedic implants.

Place, publisher, year, edition, pages
British Institute of Radiology, 2015
National Category
Radiology, Nuclear Medicine and Medical Imaging
Research subject
Radiology
Identifiers
urn:nbn:se:oru:diva-46510 (URN)10.1259/bjr.20140473 (DOI)000363313000002 ()26110201 (PubMedID)2-s2.0-84938837932 (Scopus ID)
Available from: 2015-11-17 Created: 2015-11-16 Last updated: 2018-09-04Bibliographically approved
3. Visual grading evaluation of commercially available metal artefact reduction techniques in hip prosthesis computed tomography
Open this publication in new window or tab >>Visual grading evaluation of commercially available metal artefact reduction techniques in hip prosthesis computed tomography
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2016 (English)In: British Journal of Radiology, ISSN 0007-1285, E-ISSN 1748-880X, Vol. 89, no 1063, article id 20150993Article in journal (Refereed) Published
Abstract [en]

Objectives: To evaluate metal artefact reduction (MAR) techniques from four computed tomography (CT) vendors in hip prosthesis imaging.

Methods: Bilateral hip prosthesis phantom images, obtained by using MAR algorithms for single energy CT data or dual energy CT (DECT) data and by monoenergetic reconstructions of DECT data, were visually graded by five radiologists using ten image quality criteria. Comparisons between the MAR images and a reference image were performed for each scanner separately. Ordinal probit regression analysis was used.

Results: The MAR algorithms in general improved the image quality based on the majority of the criteria (up to between 8/10 and 10/10) with a statistically improvement in overall image quality (P<0.001). However, degradation of image quality, such as new artefacts, was seen in some cases. A few monoenergetic reconstruction series improved the image quality (P<0.004) for one of the DECT scanners, but it was only improved for some of the criteria (up to 5/10). Monoenergetic reconstructions resulted in worse image quality for the majority of the criteria (up to 7/10) for the other DECT scanner.

Conclusions: The MAR algorithms improved the image quality of the hip prosthesis CT images. However, since additional artefacts and degradation of image quality were seen in some cases, all algorithms should be carefully evaluated for every clinical situation. Monoenergetic reconstructions were in general concluded to be insufficient for reducing metal artifacts. Advances in knowledge: Qualitative evaluation of the usefulness of several MAR techniques from different vendors in CT imaging of hip prosthesis.

Place, publisher, year, edition, pages
London, United Kingdom: British Institute of Radiology, 2016
National Category
Radiology, Nuclear Medicine and Medical Imaging
Research subject
Radiology
Identifiers
urn:nbn:se:oru:diva-50103 (URN)10.1259/bjr.20150993 (DOI)000378096400009 ()27123700 (PubMedID)
Available from: 2016-05-03 Created: 2016-05-03 Last updated: 2019-04-12Bibliographically approved
4. CT image metal artifacts in proton radiotherapy treatment planning: evaluation of two commercial correction algorithms
Open this publication in new window or tab >>CT image metal artifacts in proton radiotherapy treatment planning: evaluation of two commercial correction algorithms
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:oru:diva-65012 (URN)
Available from: 2018-02-15 Created: 2018-02-15 Last updated: 2018-09-18Bibliographically approved

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Andersson, Karin

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