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  • 1.
    Andersson, Karin
    Örebro University, School of Medical Sciences.
    Metal artifacts in computed tomography: impact of reduction methods on image quality and radiotherapy treatment planning2018Doctoral 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.

    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
    Show others...
    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
    Show others...
    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
  • 2.
    Andersson, Karin M.
    et al.
    Department of Medical Physics, Örebro University Hospital, Örebro, Sweden.
    Ahnesjo, Anders
    Uppsala University, Uppsala, Sweden.
    Vallhagen Dahlgren, Christina
    Skandionkliniken, Uppsala, Sweden..
    Evaluation of a metal artifact reduction algorithm in CT studies used for proton radiotherapy treatment planning2014In: Journal of Applied Clinical Medical Physics, ISSN 1526-9914, E-ISSN 1526-9914, Vol. 15, no 5, p. 112-119Article in journal (Refereed)
    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.

  • 3.
    Andersson, Karin M.
    et al.
    Örebro University, School of Medical Sciences.
    Norrman, Eva
    Örebro University, School of Medical Sciences. Örebro University Hospital.
    Thunberg, Per
    Örebro University, School of Medical Sciences. Örebro University Hospital.
    Metal Artifacts in CT Imaging of Hip Prostheses: Evaluation of Metal Artifact Reduction Techniques Provided by Four Vendors2015Conference paper (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.

  • 4.
    Andersson, Karin M.
    et al.
    Örebro University, School of Medical Sciences.
    Nowik, P.
    Department of Medical Physics, Karolinska University Hospital, Stockholm, Sweden.
    Persliden, Jan
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden. Department of Medical Physics, Faculty of Health and Medical Sciences, Örebro University, Örebro, Sweden.
    Thunberg, Per
    Department of Medical Physics, Örebro University Hospital, Örebro, Sweden.
    Norrman, Eva
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden. Department of Medical Physics, Faculty of Health and Medical Sciences, Örebro University, Örebro, Sweden.
    Metal artefact reduction in CT imaging of hip prostheses-an evaluation of commercial techniques provided by four vendors2015In: British Journal of Radiology, ISSN 0007-1285, E-ISSN 1748-880X, Vol. 88, no 1052, article id 20140473Article in journal (Refereed)
    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.

  • 5.
    Andersson, Karin M.
    et al.
    Örebro University, School of Medical Sciences. Department of Medical Physics, Faculty of Health and Medical Sciences, Örebro University, Örebro, Sweden.
    Vallhagen Dahlgren, C.
    The Skandion clinic, Uppsala, Sweden.
    Reizenstein, J.
    Department of Oncology, Örebro University Hospital, Örebro, Sweden; , Faculty of Health and Medical Sciences, Örebro University, Örebro, Sweden.
    Ahnesjö, A.
    Medical Radiation Sciences, Department of Immunology-Genetics and Pathology, Uppsala University, Uppsala, Sweden.
    Thunberg, Per
    Örebro University, School of Medical Sciences. Department of Medical Physics , Faculty of Health and Medical Sciences, Örebro University, Örebro, Sweden.
    Impact of Metal Artifacts on Proton Therapy Treatment Planning Accuracy2017In: 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 (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

  • 6.
    Andersson, Karin M.
    et al.
    Örebro University, School of Medical Sciences.
    Vallhagen Dahlgren, Christina
    The Skandion Clinic, Uppsala, Sweden.
    Reizenstein, Johan
    Department of Oncology, Faculty of Medicine and Health, Örebro University, Sweden.
    Cao, Yang
    Örebro University, School of Medical Sciences. Örebro University Hospital. Unit of Biostatistics, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
    Ahnesjö, Anders
    Medical Radiation Sciences, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden.
    Thunberg, Per
    Örebro University, School of Medical Sciences.
    CT image metal artifacts in proton radiotherapy treatment planning: evaluation of two commercial correction algorithmsManuscript (preprint) (Other academic)
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