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Calculation of images from an anthropomorphic chest phantom using Monte Carlo methods
Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
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.ORCID-id: 0000-0003-3352-8330
The Royal Marsden NHS Trust, United Kingdom.
Vise andre og tillknytning
2006 (engelsk)Inngår i: Proceedings of SPIE, 2006, Vol. 6142Konferansepaper, Publicerat paper (Fagfellevurdert)
Abstract [en]

Monte Carlo (MC) computer simulation of chest x-ray imaging systems has hitherto been performed using anthropomorphic phantoms with too large (3 mm) voxel sizes. The aim for this work was to develop and use a Monte Carlo computer program to compute projection x-ray images of a high-resolution anthropomorphic voxel phantom for visual clinical image quality evaluation and dose-optimization. An Alderson anthropomorphic chest phantom was imaged in a CT-scanner and reconstructed with isotropic voxels of 0.7 mm. The phantom was segmented and included in a Monte Carlo computer program using the collision density estimator to derive the energies imparted to the detector per unit area of each pixel by scattered photons. The image due to primary photons was calculated analytically including a pre-calculated detector response function. Attenuation and scatter of x-rays in the phantom, grid and image detector was considered. Imaging conditions (tube voltage, anti-scatter device) were varied and the images compared to a real computed radiography (Fuji FCR 9501) image. Four imaging systems were simulated (two tube voltages 81 kV and 141 kV using either a grid with ratio 10 or a 30 cm air gap). The effect of scattered radiation on the visibility of thoracic vertebrae against the heart and lungs is demonstrated. The simplicity in changing the imaging conditions will allow us not only to produce images of existing imaging systems, but also of hypothetical, future imaging systems. We conclude that the calculated images of the high-resolution voxel phantom are suitable for human detection experiments of low-contrast lesions.

sted, utgiver, år, opplag, sider
2006. Vol. 6142
Serie
; 6142
HSV kategori
Identifikatorer
URN: urn:nbn:se:liu:diva-13221DOI: 10.1117/12.644119OAI: oai:DiVA.org:liu-13221DiVA, id: diva2:18074
Tilgjengelig fra: 2008-04-28 Laget: 2008-04-28 Sist oppdatert: 2015-03-20
Inngår i avhandling
1. Quantifying image quality in diagnostic radiology using simulation of the imaging system and model observers
Åpne denne publikasjonen i ny fane eller vindu >>Quantifying image quality in diagnostic radiology using simulation of the imaging system and model observers
2008 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Accurate measures of both clinical image quality and patient radiation risk are needed for successful optimisation of medical imaging with ionising radiation. Optimisation in diagnostic radiology means finding the image acquisition technique that maximises the perceived information content and minimises the radiation risk or keeps it at a reasonably low level. The assessment of image quality depends on the diagnostic task and may in addition to system and quantum noise also be hampered by overlying projected anatomy.

The main objective of this thesis is to develop methods for assessment of image quality in simulations of projection radiography. In this thesis, image quality is quantified by modelling the whole x‐ray imaging system including the x‐ray tube, patient, anti‐scatter device, image detector and the observer. This is accomplished by using Monte Carlo (MC) simulation methods that allow simultaneous estimates of measures of image quality and patient dose. Measures of image quality include the signal‐to‐noise‐ratio, SNR, of pathologic lesions and radiation risk is estimated by using organ doses to calculate the effective dose. Based on high‐resolution anthropomorphic phantoms, synthetic radiographs were calculated and used for assessing image quality with model‐observers (Laguerre‐Gauss (LG) Hotelling observer) that mimic real, human observers. Breast and particularly chest imaging were selected as study cases as these are particularly challenging for the radiologists.

In chest imaging the optimal tube voltage in detecting lung lesions was investigated in terms of their SNR and the contrast of the lesions relative to the ribs. It was found that the choice of tube voltage depends on whether SNR of the lesion or the interfering projected anatomy (i.e. the ribs) is most important for detection. The Laguerre‐Gauss (LG) Hotelling observer is influenced by the projected anatomical background and includes this into its figure‐of‐merit, SNRhot,LG. The LG‐observer was found to be a better model of the radiologist than the ideal observer that only includes the quantum noise in its analysis. The measures of image quality derived from our model are found to correlate relatively well with the radiologist’s assessment of image quality. Therefore MC simulations can be a valuable and an efficient tool in the search for dose‐efficient imaging systems and image acquisition schemes.

sted, utgiver, år, opplag, sider
Institutionen för medicin och hälsa, 2008
Serie
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1050
Emneord
radiology, radiation physics, image quality, optimisation, effective dose, chest radiography
HSV kategori
Identifikatorer
urn:nbn:se:liu:diva-11662 (URN)9789173939522 (ISBN)
Disputas
2008-05-09, Eken, Campus US, Linköpings universitet, Linköping, 09:00 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2008-04-28 Laget: 2008-04-28 Sist oppdatert: 2017-12-15

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