umu.sePublications
Change search
Link to record
Permanent link

Direct link
BETA
Andersson, Jonas
Alternative names
Publications (10 of 25) Show all publications
Andersson, J., Granberg, C. & Riklund, K. (2018). A novel system for quality assurance of radiology equipment. In: Eurosafe Imaging 2018: . Paper presented at European Congress of Radiology (ECR).
Open this publication in new window or tab >>A novel system for quality assurance of radiology equipment
2018 (English)In: Eurosafe Imaging 2018, 2018Conference paper, Poster (with or without abstract) (Refereed)
National Category
Other Physics Topics
Research subject
radiofysik
Identifiers
urn:nbn:se:umu:diva-145490 (URN)10.1594/esi2018/ESI-0064 (DOI)
Conference
European Congress of Radiology (ECR)
Available from: 2018-03-07 Created: 2018-03-07 Last updated: 2018-06-09
Bujila, R., Kull, L., Danielsson, M. & Andersson, J. (2018). Applying three different methods of measuring CTDIfree air to the extended CTDI formalism for wide-beam scanners (IEC 60601-2-44): a comparative study. Journal of Applied Clinical Medical Physics, 19(4), 281-289
Open this publication in new window or tab >>Applying three different methods of measuring CTDIfree air to the extended CTDI formalism for wide-beam scanners (IEC 60601-2-44): a comparative study
2018 (English)In: Journal of Applied Clinical Medical Physics, ISSN 1526-9914, E-ISSN 1526-9914, Vol. 19, no 4, p. 281-289Article in journal (Refereed) Published
Abstract [en]

Purpose: The weighted CT dose index (CTDIw) has been extended for a nominal total collimation width (nT) greater than 40 mm and relies on measurements of CTDfree air. The purpose of this work was to compare three methods of measuring CTDIfree air and subsequent calculations of CTDIw to investigate their clinical appropriateness.

Methods: The CTDIfree air, for multiple nTs up to 160 mm, was calculated from (1) high-resolution air kerma profiles from a step-and-shoot translation of a liquid ionization chamber (LIC) (considered to be a dosimetric reference), (2) pencil ionization chamber (PIC) measurements at multiple contiguous positions, and (3) air kerma profiles obtained through the continuous translation of a solid-state detector. The resulting CTDIfree air was used to calculate the CTDIw, per the extended formalism, and compared.

Results: The LIC indicated that a 40 mm nT should not be excluded from the extension of the CTDIw formalism. The solid-state detector differed by as much as 8% compared to the LIC. The PIC was the most straightforward method and gave equivalent results to the LIC.

Conclusions: The CTDIw calculated with the latest CTDI formalism will differ most for 160 mm nTs (e.g., whole-organ perfusion or coronary CT angiography) compared to the previous CTDI formalism. Inaccuracies in the measurement of CTDIfree air will subsequently manifest themselves as erroneous calculations of the CTDIw, for nTs greater than 40 mm, with the latest CTDI formalism. The PIC was found to be the most clinically feasible method and was validated against the LIC.

Place, publisher, year, edition, pages
John Wiley & Sons, 2018
Keywords
computed tomography, computed tomography dose index, dosimetry
National Category
Medical Image Processing
Research subject
radiofysik
Identifiers
urn:nbn:se:umu:diva-149338 (URN)10.1002/acm2.12363 (DOI)000437835600034 ()29900670 (PubMedID)
Available from: 2018-06-19 Created: 2018-06-19 Last updated: 2018-10-01Bibliographically approved
Rottke, D., Andersson, J., Ejima, K.-I., Sawada, K. & Schulze, D. (2017). Influence of lead apron shielding on absorbed doses from cone-beam computed tomography. Radiation Protection Dosimetry, 175(1), 110-117
Open this publication in new window or tab >>Influence of lead apron shielding on absorbed doses from cone-beam computed tomography
Show others...
2017 (English)In: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 175, no 1, p. 110-117Article in journal (Refereed) Published
Abstract [en]

The aim of the present work was to investigate absorbed and to calculate effective doses (EDs) in cone-beam computed tomography (CBCT). The study was conducted using examination protocols with and without lead apron shielding. A full-body male RANDO® phantom was loaded with 110 GR200A thermoluminescence dosemeter chips at 55 different sites and set up in two different CBCT systems (CS 9500®, ProMax® 3D). Two different protocols were performed: the phantom was set up (1) with and (2) without a lead apron. No statistically significant differences in organ and absorbed doses from regions outside the primary beam could be found when comparing results from exposures with and without lead apron shielding. Consequently, calculating the ED showed no significant differences between the examination protocols with and without lead apron shielding. For the ProMax® 3D with shielding, the ED was 149 µSv, and for the examination protocol without shielding 148 µSv (SD = 0.31 µSv). For the CS 9500®, the ED was 88 and 86 µSv (SD = 0.95 µSv), respectively, with and without lead apron shielding. The results revealed no statistically significant differences in the absorbed doses between examination with and without lead apron shielding, especially in organs outside the primary beam.

National Category
Other Physics Topics
Research subject
radiofysik
Identifiers
urn:nbn:se:umu:diva-126833 (URN)10.1093/rpd/ncw275 (DOI)000404476500014 ()27664428 (PubMedID)
Available from: 2016-10-16 Created: 2016-10-16 Last updated: 2018-06-09Bibliographically approved
Andersson, J. & Tölli, H. (2017). Modeling ion recombination in liquid ionization chambers: Improvement and analysis of the two-dose-rate method. Medical physics (Lancaster), 44(11), 5977-5987
Open this publication in new window or tab >>Modeling ion recombination in liquid ionization chambers: Improvement and analysis of the two-dose-rate method
2017 (English)In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 44, no 11, p. 5977-5987Article in journal (Refereed) Published
Abstract [en]

Purpose: The use of liquid ionization chambers can provide useful information to endeavors with radiation dosimetry for highly modulated beams. Liquid ionization chambers may be particularly suitable for computed tomography applications where conventional ionization chambers do not present a high enough sensitivity for the spatial resolution required to characterize common X-ray beams. Due to the sensitivity, which leads to high charge densities, liquid ionization chambers can suffer from large recombination losses leading to degradation in signal to dose rate linearity. To solve this problem, a two-dose-rate method for general recombination correction has been proposed for liquid ionization chambers. However, the valid range of recombination losses that the method can accurately account for has been found to vary depending on radiation quality. The present work provides an in-depth analysis of the performance of the two-dose-rate method. Furthermore, the soundness of applying gas theory to liquids is investigated by using the two-dose-rate method.

Methods: In the present work, the two-dose-rate method for general recombination correction of liquid ionization chambers used in continuous beams is studied by employing theory for gas-filled ionization chambers. An approximate relation for the general collection efficiency containing a material-specific parameter that is traceable to liquids has been derived for theoretical and experimental investigation alongside existing theory. Furthermore, the disassociation between initial and general recombination in the method is analyzed both theoretically and experimentally.

Results: The results indicate that liquids and gases share general recombination characteristics, where the liquids investigated (isooctane and tetramethylsilane) to a large extent mimic the behavior theoretically expected in gases. Furthermore, it is shown that the disassociation between initial and general recombination in the two-dose-rate method is an approximation that depends on the relation between initial recombination and the collecting electric field strength at the dose rates used.

Conclusions: Due to the approximation used to separate initial and general recombination the valid range of collection efficiencies for the two-dose-rate method will not only depend on the model used to describe general recombination but also on the type of liquid and radiation beam quality. As there is no robust theory for initial recombination in liquids to apply, the valid range of general collection efficiencies for the two-dose-rate method should be experimentally evaluated for each radiation dosimetry application.

Place, publisher, year, edition, pages
John Wiley & Sons, 2017
Keywords
general recombination, initial recombination, isooctane, liquid ionization chamber, radiation dosimetry, tetramethylsilane
National Category
Other Physics Topics Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:umu:diva-68941 (URN)10.1002/mp.12515 (DOI)000414970800040 ()28801951 (PubMedID)
Note

Originally included in thesis in manuscript form with title "A study of recombination losses in liquid ionization chambers".

Available from: 2013-04-30 Created: 2013-04-30 Last updated: 2018-06-08Bibliographically approved
Åhlström Riklund, K., Andersson, J., Granberg, C. & Lundman, J. (2017). Patient centering effects on Size-Specific Dose Estimates (SSDE). In: EuroSafe Imaging 2017: . Paper presented at European Congress of Radiology 2017.
Open this publication in new window or tab >>Patient centering effects on Size-Specific Dose Estimates (SSDE)
2017 (English)In: EuroSafe Imaging 2017, 2017Conference paper, Poster (with or without abstract) (Refereed)
Abstract [en]

The concept of Size-Specific Dose Estimates (SSDE) for refining computed tomography (CT) dosimetry has been proposed in the Report of the American Association of Physicists in Medicine (AAPM) Task Group 204.[1] The present conventional metrics for patient exposure in CT applications are the Computed Tomography Dose Index (CTDI) and Dose Length Product (DLP), which do not take patient size into account. Due to Tube Current Modulation (TCM) functionality being used in most CT examinations to achieve consistent clinical image quality independent of patient size, follow-up of radiation exposure and optimization is not straightforward with the CTDI and DLP metrics.

 

Estimation of the SSDE is done in two steps, first determination of patient size from the actual CT images, either the localizer radiograph(s) or axial images. When patient size is known, the Report of AAPM Task Group 204 supplies conversion factors per patient size to determine a correction factor, f, which is used together with the CTDI to determine the SSDE, i.e. SSDE = f x CTDIvol (mGy).

 

The physical patient size, in cm, is easily determined manually from a patient image, e.g. by a measurement tool in PACS. However, this is not feasible in large-scale optimization and clinical audit projects. Furthermore, as detailed in the Report of AAPM Task Group 220,[2] a more robust metric for estimating patient exposure via the SSDE is the Water Equivalent Diameter (WED), which determines patient size as equivalent thickness of X-ray beam attenuation in water. The WED is particularly suited for the for making the SSDE robust for comparisons of patient exposure between different anatomical regions, e.g. thorax and abdomen, where physical patient size make be very similar but the attenuation properties will vary considerably due to tissue density.

 

The WED cannot be determined manually from patient images, nor is it feasible to use the less robust metric given by patient physical size in large-scale projects. In this work we therefore present results from a software solution, which is part of the REMbox framework (Dicom Port AB, Umeå, Sweden), for determining the SSDE via automated image segmentation. Furthermore, when working in the image domain other quality assurance related metrics can be determined, e.g. evaluation of patient centering in CT examinations. Patient centering is something that has been discussed for a long time in optimization of CT examinations, due to complex relations between bow-tie filter X-ray beam shaping and TCM, which have optimal functionality with regard to both clinical image quality and patient exposure if the patient is perfectly centered in the CT gantry.

National Category
Other Physics Topics
Research subject
radiofysik
Identifiers
urn:nbn:se:umu:diva-140511 (URN)10.1594/esi2017/ESI-0048 (DOI)
Conference
European Congress of Radiology 2017
Available from: 2017-10-12 Created: 2017-10-12 Last updated: 2018-06-09
de Las Heras Gala, H., Torresin, A., Dasu, A., Rampado, O., Delis, H., Hernández Girón, I., . . . Zervides, C. (2017). Quality control in cone-beam computed tomography (CBCT) EFOMP-ESTRO-IAEA protocol (summary report). Physica medica (Testo stampato), 39, 67-72
Open this publication in new window or tab >>Quality control in cone-beam computed tomography (CBCT) EFOMP-ESTRO-IAEA protocol (summary report)
Show others...
2017 (English)In: Physica medica (Testo stampato), ISSN 1120-1797, E-ISSN 1724-191X, Vol. 39, p. 67-72Article in journal (Refereed) Published
Abstract [en]

The aim of the guideline presented in this article is to unify the test parameters for image quality evaluation and radiation output in all types of cone-beam computed tomography (CBCT) systems. The applications of CBCT spread over dental and interventional radiology, guided surgery and radiotherapy. The chosen tests provide the means to objectively evaluate the performance and monitor the constancy of the imaging chain. Experience from all involved associations has been collected to achieve a consensus that is rigorous and helpful for the practice. The guideline recommends to assess image quality in terms of uniformity, geometrical precision, voxel density values (or Hounsfield units where available), noise, low contrast resolution and spatial resolution measurements. These tests usually require the use of a phantom and evaluation software. Radiation output can be determined with a kerma-area product meter attached to the tube case. Alternatively, a solid state dosimeter attached to the flat panel and a simple geometric relationship can be used to calculate the dose to the isocentre. Summary tables including action levels and recommended frequencies for each test, as well as relevant references, are provided. If the radiation output or image quality deviates from expected values, or exceeds documented action levels for a given system, a more in depth system analysis (using conventional tests) and corrective maintenance work may be required.

Keywords
Cone-beam CT, Diagnostic radiology, Ionizing radiation, Quality control, Radiation protection
National Category
Other Physics Topics
Research subject
radiofysik
Identifiers
urn:nbn:se:umu:diva-137460 (URN)10.1016/j.ejmp.2017.05.069 (DOI)000405493200009 ()28602688 (PubMedID)
Available from: 2017-07-03 Created: 2017-07-03 Last updated: 2018-06-09Bibliographically approved
Nowik, P., Bujila, R., Kull, L., Andersson, J. & Poludniowski, G. (2017). The dosimetric impact of including the patient table in CT dose estimates. Physics in Medicine and Biology, 62(23), 538-547
Open this publication in new window or tab >>The dosimetric impact of including the patient table in CT dose estimates
Show others...
2017 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 62, no 23, p. 538-547Article in journal (Refereed) Published
Abstract [en]

The purpose of this study was to evaluate the dosimetric impact of including the patient table in Monte Carlo CT dose estimates for both spiral scans and scan projection radiographs (SPR). CT scan acquisitions were simulated for a Siemens SOMATOM Force scanner (Siemens Healthineers, Forchheim, Germany) with and without a patient table present. An adult male, an adult female and a pediatric female voxelized phantom were simulated. The simulated scans included tube voltages of 80 and 120 kVp. Spiral scans simulated without a patient table resulted in effective doses that were overestimated by approximately 5 % compared to the same simulations performed with the patient table present. Doses in selected individual organs (breast, colon, lung, red bone marrow and stomach) were overestimated by up to 8 %. Effective doses from SPR acquired with the X-ray tube stationary at 6 o'clock (posterior-anterior) were overestimated by 14-23 % when the patient table was not included, with individual organ dose discrepancies (breast, colon, lung red bone marrow and stomach) all exceeding 13%. The reference entrance skin dose to the back were in this situation overestimated by 6-15 %. These results highlight the importance of including the patient table in patient dose estimates for such scan situations.

Keywords
Monte Carlo, computed tomography, dosimetry, patient dose, patient table
National Category
Other Physics Topics
Research subject
radiofysik
Identifiers
urn:nbn:se:umu:diva-140510 (URN)10.1088/1361-6560/aa9259 (DOI)000425833200001 ()28994662 (PubMedID)
Available from: 2017-10-12 Created: 2017-10-12 Last updated: 2018-06-09Bibliographically approved
Bujila, R., Kull, L., Nowik, P., Poludniowski, G. & Andersson, J. (2016). Characterization of Beam Shaping Filters and Photon Spectra From HVL Profiles in CT. In: : . Paper presented at 58th AAPM Annual Meeting and Exhibition 2016, Washington, DC, USA, Jul 31 - Aug 4 (2016).
Open this publication in new window or tab >>Characterization of Beam Shaping Filters and Photon Spectra From HVL Profiles in CT
Show others...
2016 (English)Conference paper, Poster (with or without abstract) (Refereed)
Abstract [en]

Purpose: Advanced dosimetry in CT (e.g., the Monte Carlo method) requires an accurate characterization of the shaped filter and radiation quality used during a scan. The purpose of this work was to develop a method where half value layer (HVL) profiles along shaped filters could be made. From the HVL profiles, the beam shaping properties and effective photon spectrum for a particular scan can be inferred.

Methods: A measurement rig was developed to allow determinations of the HVL under a scatter-free narrow-beam geometry and constant focal spot to ionization chamber distance, for different fan angles. For each fan angle, the HVL is obtained by fitting the transmission of radiation through different thicknesses of an Al absorber (type 1100) using an appropriate model. The effective Al thickness of shaped filters and effective photon spectra are estimated using a model of photon emission from a Tungsten anode. This method is used to obtain the effective photon spectra and effective Al thickness of shaped filters for a CT scanner recently introduced to the market.

Results: This study resulted in a set of effective photon spectra (central ray) for each kVp along with effective Al thicknesses of the different shaped filters. The effective photon spectra and effective Al thicknesses of shaped filters were used to obtain numerically approximated HVL profiles and compared to measured HVL profiles (mean absolute percentage error = 0.02). The central axis HVL found in the vendor’s technical documentation were compared to approximated HVL values (mean absolute percentage error = 0.03).

Conclusion: This work has resulted in a unique method of measuring HVL profiles along shaped filters in CT. Further, the effective photon spectra and the effective Al thicknesses of shaped filters that were obtained can be incorporated into Monte Carlo simulations.

National Category
Physical Sciences
Research subject
radiofysik
Identifiers
urn:nbn:se:umu:diva-124375 (URN)
Conference
58th AAPM Annual Meeting and Exhibition 2016, Washington, DC, USA, Jul 31 - Aug 4 (2016)
Available from: 2016-08-08 Created: 2016-08-08 Last updated: 2018-06-07
Åhlström Riklund, K., Andersson, J., Lundman, J. & Granberg, C. (2016). Experiences with large-scale radiation exposure monitoring in Västerbotten County, Sweden. In: : . Paper presented at EuroSafe Imaging 2016.
Open this publication in new window or tab >>Experiences with large-scale radiation exposure monitoring in Västerbotten County, Sweden
2016 (English)Conference paper, Poster (with or without abstract) (Refereed)
Abstract [en]

Background/Introduction: In October 2014, Västerbotten County (VLL), Sweden, installed Sectra DoseTrack1 for radiation exposure monitoring in radiology. A versatile and robust IT-solution for exposure monitoring to assist with follow-up of the processes of justification and optimization had been discussed in multidisciplinary X-ray modality specific forums prior to the procurement.

Description of activity and work performed: The installation of Sectra DoseTrack is fairly straightforward from the user end, involving the configuration of sending RDSR and MPPS metadata from an X-ray unit to be connected to the service. During the installation process some assistance from certified service engineers is required due to restrictions in X-ray equipment software.

Conclusion and Recommendations: VLL has used the Sectra DoseTrack radiation exposure monitoring IT-solution since October 2014. Since then, 34 different X-ray units have been connected to the service and DICOM metadata associated with approximately 170 000 examinations and interventional procedures have been recorded. Sectra DoseTrack offers a robust infrastructure for collecting DICOM metadata and presenting macroscopic information on radiation exposure levels, which may be used to improve the processes of justification and optimization for healthcare providers.

National Category
Other Physics Topics
Research subject
radiofysik
Identifiers
urn:nbn:se:umu:diva-118334 (URN)10.1594/esi2016/ESI-0035 (DOI)
Conference
EuroSafe Imaging 2016
Available from: 2016-03-16 Created: 2016-03-16 Last updated: 2018-06-07
Andersson, J. & Pavlicek, W. (2016). Patient organ dose with computed tomography - a review of present methodology and DICOM information: executive summary of the joint report of AAPM task group 246 and EFOMP. In: ECR 2016 Book of Abstracts: . Paper presented at European Congress of Radiology 2016, March 2–6 2016, Vienna, Austria. , 7(1), Article ID B0303.
Open this publication in new window or tab >>Patient organ dose with computed tomography - a review of present methodology and DICOM information: executive summary of the joint report of AAPM task group 246 and EFOMP
2016 (English)In: ECR 2016 Book of Abstracts, 2016, Vol. 7, no 1, article id B0303Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Purpose: The justification and optimisation of medical imaging employing ionizing radiation have been intensely discussed in recent years, particularly for computed tomography (CT). A key point in this discussion is the estimation of patient dose, which commonly employs radiation output metrics developed for quality assurance and no patient specific information. Such patient dose estimates are of limited value, and more refined methods needs to be promoted and provided to the community.

Methods and Materials: AAPM Task Group 246 was formed in 2013, and in a joint venture with EFOMP charged with summarizing present methodology and DICOM information available for estimating patient dose with computed tomography.

Results: The Joint Report of AAPM Task Group 246 and EFOMP is a comprehensive resource for the clinical medical physicist. The possibilities of patient specific dosimetry from the Computed Tomography Dose Index (CTDIvol), to the Size-Specific Dose Estimates (SSDE) and advanced Monte Carlo methods are discussed together with available DICOM information, as well as practical examples on how patient dose estimates can be achieved. The report also summarizes important factors contributing to the uncertainty in patient dose estimates and gives examples of achievable confidence intervals.

Conclusion: The SSDE and Monte Carlo methods can together with detailed scanner, examination and patient specific DICOM information offer refined estimates of patient dose for justification and optimisation of CT examinations. Given the present robustness of available methods AAPM Task Group 246 and EFOMP recommend that all reports of patient dose should be accompanied by estimates of the associated uncertainty.

National Category
Other Physics Topics
Research subject
radiofysik
Identifiers
urn:nbn:se:umu:diva-118330 (URN)10.1007/s13244-016-0475-8 (DOI)
Conference
European Congress of Radiology 2016, March 2–6 2016, Vienna, Austria
Available from: 2016-03-16 Created: 2016-03-16 Last updated: 2018-06-07Bibliographically approved
Organisations

Search in DiVA

Show all publications