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Andersson, Karin M.
Publications (6 of 6) Show all publications
Andersson, K. (2018). Metal artifacts in computed tomography: impact of reduction methods on image quality and radiotherapy treatment planning. (Doctoral dissertation). Örebro: Örebro University
Open this publication in new window or tab >>Metal artifacts in computed tomography: impact of reduction methods on image quality and radiotherapy treatment planning
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
computed tomography, metal artifacts, image quality, visual grading analysis, radiotherapy, proton therapy, hip prosthesis, dental implants
National Category
Surgery
Identifiers
urn:nbn:se:oru:diva-63420 (URN)978-91-7529-228-1 (ISBN)
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
Andersson, K. M., Vallhagen Dahlgren, C., Reizenstein, J., Ahnesjö, A. & Thunberg, P. (2017). Impact of Metal Artifacts on Proton Therapy Treatment Planning Accuracy. In: 56th Annual Meeting of the Particle Therapy Cooperative Group (PTCOG) 8-13 May 2017: Proceedings. Paper presented at 56th Annual Meeting of the Particle Therapy Cooperative Group (PTCOG 56), Yokohama, Japan, May 8-13, 2017 (pp. 68-68). The Particle Therapy Cooperative Group, 4, Article ID 1.
Open this publication in new window or tab >>Impact of Metal Artifacts on Proton Therapy Treatment Planning Accuracy
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2017 (English)In: 56th Annual Meeting of the Particle Therapy Cooperative Group (PTCOG) 8-13 May 2017: Proceedings, The Particle Therapy Cooperative Group , 2017, Vol. 4, p. 68-68, article id 1Conference paper, Oral presentation with published abstract (Other academic)
Abstract [en]

Purpose: To evaluate for proton therapy treatment planning the feasibility of two commercial metal artifact reduction (MAR) algorithms in CT-imaging.

Materials and Methods: A head phantom with removable dental fillings and a body phantom with a removable hip prosthesis were scanned to evaluate O-MAR (Philips) and iMAR (Siemens). Reference images (scans without metal) were acquired and subtracted from the uncorrected (no MAR) and MAR-images. CT number-differences were mapped to differences in stopping power ratios to water. In addition, proton treatment plans for a parotid, tonsil and prostate-target were optimized based on uncorrected and MAR images and recalculated on reference images. Beams were arranged to not traverse metal, enabling evaluation of metal artifact impact on target coverage.

Results: MAR algorithms reduced the most extreme dental filling artifacts, but residual artifacts still remained. iMAR reduced hip prosthesis artifacts to large extent, while considerable artifacts still were present with O-MAR. For parotid and tonsil-plans, D98%to PTV was nearly intact in the reference recalculations for both uncorrected and MAR-based plans, with maximum-difference,0.3%. For uncorrected prostate plans, D98%decreased more than 4% in the reference recalculation. For the iMAR prostate plan, D98%was almost identical in the reference recalculation (97.5% versus 97.4%). A slight D98%-decrease was seen in the reference for the O-MAR based plan (96.8% versus 97.5%).

Conclusion: Hip prosthesis artifacts reduced target coverage accuracy, but it was substantially improved with MAR algorithms. Dental filling artifacts were moderately reduced with MAR, but did not substantially affect target coverage

Place, publisher, year, edition, pages
The Particle Therapy Cooperative Group, 2017
Series
International Journal of Particle Therapy, E-ISSN 2331-5180 ; Vol. 4 (2017): 1
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:oru:diva-63384 (URN)10.14338/IJPT.17-PTCOG-1.1 (DOI)
Conference
56th Annual Meeting of the Particle Therapy Cooperative Group (PTCOG 56), Yokohama, Japan, May 8-13, 2017
Available from: 2017-12-15 Created: 2017-12-15 Last updated: 2018-08-13Bibliographically approved
Andersson, K. M., Nowik, P., Persliden, J., Thunberg, P. & Norrman, E. (2015). Metal artefact reduction in CT imaging of hip prostheses-an evaluation of commercial techniques provided by four vendors. British Journal of Radiology, 88(1052), Article ID 20140473.
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
Andersson, K. M., Norrman, E. & Thunberg, P. (2015). Metal Artifacts in CT Imaging of Hip Prostheses: Evaluation of Metal Artifact Reduction Techniques Provided by Four Vendors. In: : . Paper presented at Radiological Society of North America (RSNA 2015), Chicago, USA, November 29 - December 4, 2015.
Open this publication in new window or tab >>Metal Artifacts in CT Imaging of Hip Prostheses: Evaluation of Metal Artifact Reduction Techniques Provided by Four Vendors
2015 (English)Conference paper, Poster (with or without abstract) (Other academic)
Abstract [en]

PURPOSE: The aim of this study was to evaluate metal artifact reduction (MAR) techniques, provided by four vendors, in CT imaging of hip prostheses.

METHOD AND MATERIALS: A water phantom containing hip prostheses mounted in calf bones was scanned with four CT scanners; Philips Ingenuity; Toshiba Aquilion ONE Vision edition; GE Discovery 750 HD and Siemens SOMATOM Definition Flash. An uncorrected (reference) image was obtained for every CT and compared with images acquired with the scanner specific MAR technique; either monoenergetic reconstruction of Dual Energy CT (DECT) data (GE and Siemens) or the use of a MAR algorithm software (Philips and Toshiba), or a combination of the two (GE). The MAR techniques were applied for varying tube voltage, kernel and reconstruction technique. The reference images were quantitatively compared to the MAR images by analyzing the noise and the CT number accuracy in region of interests (ROIs). Visual grading was performed by five radiologists based on ten image quality (IQ) criteria.

RESULTS: The MAR algorithms implied a general noise reduction (by up to 77%) and improved IQ based on the majority of the visual grading criteria. The use of monoenergetic reconstructions of DECT data, without any MAR algorithm, did not decrease the noise in the ROIs to the same extent as the MAR algorithms (up to 41%) and did even increase the noise in one ROI. The visual grading evaluation showed that monoenergetic reconstructions in general degraded the IQ for one of the DECT scanners and improved the IQ for only a few of the criteria for the other DECT scanner.

CONCLUSION: The quantitative analysis and the visual grading evaluation showed that the IQ was generally improved when the MAR algorithms were used. However, additional artifacts and degradation of the IQ were noted in some MAR image regions. The use of monoenergetic reconstruction was concluded to not reduce metal artifacts to the same extent as the MAR algorithms and to even degrade the IQ in several image regions.

CLINICAL RELEVANCE/APPLICATION: This study points out advantages and potential risks of using MAR techniques in CT imaging of hip prostheses and will be useful for clinics when optimizing CT scan protocols and purchasing new CT systems.

National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:oru:diva-63495 (URN)
Conference
Radiological Society of North America (RSNA 2015), Chicago, USA, November 29 - December 4, 2015
Available from: 2017-12-20 Created: 2017-12-20 Last updated: 2017-12-20Bibliographically approved
Andersson, K. M., Ahnesjo, A. & Vallhagen Dahlgren, C. (2014). Evaluation of a metal artifact reduction algorithm in CT studies used for proton radiotherapy treatment planning. Journal of Applied Clinical Medical Physics, 15(5), 112-119
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
Andersson, K. M., Vallhagen Dahlgren, C., Reizenstein, J., Cao, Y., Ahnesjö, A. & Thunberg, P.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
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(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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