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CTmod: a toolkit for Monte Carlo simulation of projections including scatter in computed tomography
Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.ORCID-id: 0000-0003-1257-2383
Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.ORCID-id: 0000-0003-3352-8330
Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.ORCID-id: 0000-0003-0209-498X
2008 (engelsk)Inngår i: Computer Methods and Programs in Biomedicine, ISSN 0169-2607, E-ISSN 1872-7565, Vol. 90, nr 2, s. 167-178Artikkel i tidsskrift (Fagfellevurdert) 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.

sted, utgiver, år, opplag, sider
Elsevier , 2008. Vol. 90, nr 2, s. 167-178
Emneord [en]
Monte Carlo, Computed tomography, Cone beam, Scatter
HSV kategori
Identifikatorer
URN: urn:nbn:se:liu:diva-13035DOI: 10.1016/j.cmpb.2007.12.005OAI: oai:DiVA.org:liu-13035DiVA, id: diva2:17699
Merknad
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/ Tilgjengelig fra: 2008-03-13 Laget: 2008-03-13 Sist oppdatert: 2017-12-13
Inngår i avhandling
1. Calculation of scatter in cone beam CT: Steps towards a virtual tomograph
Åpne denne publikasjonen i ny fane eller vindu >>Calculation of scatter in cone beam CT: Steps towards a virtual tomograph
2008 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Institutionen för medicin och hälsa, 2008. s. 67
Serie
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1051
HSV kategori
Identifikatorer
urn:nbn:se:liu:diva-11275 (URN)978-91-7393-951-5 (ISBN)
Disputas
2008-04-09, Elsa Brändströmsalen, Campus US, Linköpings universitet, Linköping, 09:00 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2008-03-13 Laget: 2008-03-13 Sist oppdatert: 2015-03-20

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