liu.seSearch for publications in DiVA
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
CTmod: a toolkit for Monte Carlo simulation of projections including scatter in computed tomography
Linköping University, Department of Medical and Health Sciences, Radiation Physics. Linköping University, Faculty of Health Sciences.ORCID iD: 0000-0003-1257-2383
Linköping University, Department of Medical and Health Sciences, Radiation Physics. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre for Surgery, Orthopaedics and Cancer Treatment, Department of Radiation Physics UHL.ORCID iD: 0000-0003-3352-8330
Linköping University, Department of Medical and Health Sciences, Radiation Physics. Linköping University, Faculty of Health Sciences.ORCID iD: 0000-0003-0209-498X
2008 (English)In: Computer Methods and Programs in Biomedicine, ISSN 0169-2607, E-ISSN 1872-7565, Vol. 90, no 2, 167-178 p.Article in journal (Refereed) Published
Abstract [en]

The CTmod toolkit is a set of C++ class libraries based on the CERN’s application development framework ROOT. It uses the Monte Carlo method to simulate energy imparted to a CT-scanner detector array. Photons with a given angle–energy distribution are emitted from the X-ray tube approximated by a point source, transported through a phantom, and their contribution to the energy imparted per unit surface area of each detector element is scored. Alternatively, the scored quantity may be the fluence, energy fluence, plane fluence, plane energy fluence, or kerma to air in the center of each detector element. Phantoms are constructed from homogenous solids or voxel arrays via overlapping. Implemented photon interactions (photoelectric effect, coherent scattering, and incoherent scattering) are restricted to the energy range from 10 to 200 keV. Variance reduction techniques include the collision density estimator and survival biasing combined with the Russian roulette. The toolkit has been used to estimate the amount of scatter in cone beam computed tomography and planar radiography.

Place, publisher, year, edition, pages
Elsevier , 2008. Vol. 90, no 2, 167-178 p.
Keyword [en]
Monte Carlo, Computed tomography, Cone beam, Scatter
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-13035DOI: 10.1016/j.cmpb.2007.12.005OAI: oai:DiVA.org:liu-13035DiVA: diva2:17699
Note
Original Publication: Alexandr Malusek, Michael Sandborg and Gudrun Alm Carlsson, CTmod: a toolkit for Monte Carlo simulation of projections including scatter in computed tomography, 2008, Computer Methods and Programs in Biomedicine, (90), 2, 167-178. http://dx.doi.org/10.1016/j.cmpb.2007.12.005 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/ Available from: 2008-03-13 Created: 2008-03-13 Last updated: 2015-03-20
In thesis
1. Calculation of scatter in cone beam CT: Steps towards a virtual tomograph
Open this publication in new window or tab >>Calculation of scatter in cone beam CT: Steps towards a virtual tomograph
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Scattered photons—shortly scatter—are generated by interaction processes when photon beams interact with matter. In diagnostic radiology, they deteriorate image quality since they add an undesirable signal that lowers the contrast in projection radiography and causes cupping and streak artefacts in computed tomography (CT). Scatter is one of the most detrimental factors in cone beam CT owing to irradiation geometries using wide beams. It cannot be fully eliminated, nevertheless its amount can be lowered via scatter reduction techniques (air gaps, antiscatter grids, collimators) and its effect on medical images can be suppressed via scatter correction algorithms.

Aim: Develop a tool—a virtual tomograph—that simulates projections and performs image reconstructions similarly to a real CT scanner. Use this tool to evaluate the effect of scatter on projections and reconstructed images in cone beam CT. Propose improvements in CT scanner design and image reconstruction algorithms.

Methods: A software toolkit (CTmod) based on the application development framework ROOT was written to simulate primary and scatter projections using analytic and Monte Carlo methods, respectively. It was used to calculate the amount of scatter in cone beam CT for anthropomorphic voxel phantoms and water cylinders. Configurations with and without bowtie filters, antiscatter grids, and beam hardening corrections were investigated. Filtered back-projection was used to reconstruct images. Automatic threshold segmentation of volumetric CT data of anthropomorphic phantoms with known tissue compositions was tested to evaluate its usability in an iterative image reconstruction algorithm capable of performing scatter correction.

Results: It was found that computer speed was the limiting factor for the deployment of this method in clinical CT scanners. It took several hours to calculate a single projection depending on the complexity of the geometry, number of simulated detector elements, and statistical precision. Data calculated using the CTmod code confirmed the already known facts that the amount of scatter is almost linearly proportional to the beam width, the scatter-to-primary ratio (SPR) can be larger than 1 for body-size objects, and bowtie filters can decrease the SPR in certain regions of projections. Ideal antiscatter grids significantly lowered the amount of scatter. The beneficial effect of classical antiscatter grids in cone beam CT with flat panel imagers was not confirmed by other researchers nevertheless new grid designs are still being tested. A simple formula estimating the effect of scatter on the quality of reconstructed images was suggested and tested.

Conclusions: It was shown that computer simulations could calculate the amount of scatter in diagnostic radiology. The Monte Carlo method was too slow for a routine use in contemporary clinical practice nevertheless it could be used to optimize CT scanner design and, with some enhancements, it could become a part of an image reconstruction algorithm that performs scatter correction.

Place, publisher, year, edition, pages
Institutionen för medicin och hälsa, 2008. 67 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1051
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:liu:diva-11275 (URN)978-91-7393-951-5 (ISBN)
Public defence
2008-04-09, Elsa Brändströmsalen, Campus US, Linköpings universitet, Linköping, 09:00 (English)
Opponent
Supervisors
Available from: 2008-03-13 Created: 2008-03-13 Last updated: 2015-03-20

Open Access in DiVA

fulltext(344 kB)1424 downloads
File information
File name FULLTEXT01.pdfFile size 344 kBChecksum SHA-512
c5788f58c0d0511f9d358aed2d08ce03685c6bc47c70b8132e2e71db16000f6a3dccf4d8975a5e61687091d364a2f927d2757b4f30a1a309e785a70609a5a8f9
Type fulltextMimetype application/pdf

Other links

Publisher's full textLink to Ph.D. thesis

Authority records BETA

Malusek, AlexandrSandborg, MichaelAlm Carlsson, Gudrun

Search in DiVA

By author/editor
Malusek, AlexandrSandborg, MichaelAlm Carlsson, Gudrun
By organisation
Radiation PhysicsFaculty of Health SciencesDepartment of Radiation Physics UHL
In the same journal
Computer Methods and Programs in Biomedicine
Medical and Health Sciences

Search outside of DiVA

GoogleGoogle Scholar
Total: 1426 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 1247 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf