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Comparison of clinical and physical measures of image quality in chest and pelvis computed radiography at different tube voltages
Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.ORCID iD: 0000-0003-3352-8330
Department of Radiation Physics, Malmö University Hospital, Malmö, Sweden.
Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
Joint Department of Physics, The Royal Marsden NHS Trust and Institute of Cancer Research, London.
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2006 (English)In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 33, no 11, 4169-4175 p.Article in journal (Refereed) Published
Abstract [en]

The aim of this work was to study the dependence of image quality in digital chest and pelvis radiography on tube voltage, and to explore correlations between clinical and physical measures of image quality. The effect on image quality of tube voltage in these two examinations was assessed using two methods. The first method relies on radiologists' observations of images of an anthropomorphic phantom, and the second method was based on computer modeling of the imaging system using an anthropomorphic voxel phantom. The tube voltage was varied within a broad range (50–150  kV), including those values typically used with screen-film radiography. The tube charge was altered so that the same effective dose was achieved for each projection. Two x-ray units were employed using a computed radiography (CR) image detector with standard tube filtration and antiscatter device. Clinical image quality was assessed by a group of radiologists using a visual grading analysis (VGA) technique based on the revised CEC image criteria. Physical image quality was derived from a Monte Carlo computer model in terms of the signal-to-noise ratio, SNR, of anatomical structures corresponding to the image criteria. Both the VGAS (visual grading analysis score) and SNR decrease with increasing tube voltage in both chest PA and pelvis AP examinations, indicating superior performance if lower tube voltages are employed. Hence, a positive correlation between clinical and physical measures of image quality was found. The pros and cons of using lower tube voltages with CR digital radiography than typically used in analog screen-film radiography are discussed, as well as the relevance of using VGAS and quantum-noise SNR as measures of image quality in pelvis and chest radiography.

Place, publisher, year, edition, pages
2006. Vol. 33, no 11, 4169-4175 p.
Keyword [en]
diagnostic radiography, Monte Carlo methods, image denoising, dosimetry, phantoms, biomedical equipment
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-13220DOI: 10.1118/1.2362871OAI: oai:DiVA.org:liu-13220DiVA: diva2:18073
Available from: 2008-04-28 Created: 2008-04-28 Last updated: 2017-12-13
In thesis
1. Quantifying image quality in diagnostic radiology using simulation of the imaging system and model observers
Open this publication in new window or tab >>Quantifying image quality in diagnostic radiology using simulation of the imaging system and model observers
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
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.

Place, publisher, year, edition, pages
Institutionen för medicin och hälsa, 2008
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1050
Keyword
radiology, radiation physics, image quality, optimisation, effective dose, chest radiography
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:liu:diva-11662 (URN)9789173939522 (ISBN)
Public defence
2008-05-09, Eken, Campus US, Linköpings universitet, Linköping, 09:00 (English)
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Supervisors
Available from: 2008-04-28 Created: 2008-04-28 Last updated: 2017-12-15

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Sandborg, MichaelUllman, GustafAlm Carlsson, Gudrun

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