1.
Sandborg, Michael
(författare)
Bildkvalitet vid projektionsradiografi
2004
Rapport (övrigt vetenskapligt/konstnärligt) abstract
En bild av god klinisk kvalitet har egenskaper som möjliggör att diagnostiskt viktiga detaljer och strukturer kan observeras av radiologen med tillräckligt stor säkerhet. Kvalitetsbegreppet bör relateras till hur väl (dvs. med vilken säkerhet) bilden ger svar på frågeställningen i remissen, eller hur väl bilden tillsammans med radiologens kunskap och erfarenhet löser uppgiften. Målet är att att åstadkomma tillräckligt bra bilder för säker diagnostik, att bildkvaliteten är reproducerbar och att patienten utsätts för ett minimum av stråldos och andra undersökningsrelaterade biverkningar. För att säkerställa detta krävs mätningar av bildkvaliteten. Mätning av klinisk bildkvalitet kan omfatta en studie av en eller flera radiologers observationer eller bedömningar av bilderna som ett diagnostiskt redskap. Med fysikalisk bildkvalitet menas här objektiva mätningar av olika egenskaper i bilderna eller i bilddata som är relaterade till den kliniska bildkvaliteten.
2.
Sandborg, Michael, et al.
(författare)
Calculation of contrast and signal-to-noise degradation factors for digital detectors in chest and breast imaging
2003
Rapport (övrigt vetenskapligt/konstnärligt) abstract
The Monte Carlo model of an x-ray imaging system, used in the EU 5th framework project by the Linköping and London partner to study chest and breast imaging, was developed jointly by the London and Linköping partners. It incorporates a model of the x-ray imaging system (x-ray tube, filtration, anti-scatter device and image receptor etc.) and the patient by using a voxel phantom of an adult male. Validation and calibration experiments have been performed for both the chest (Ullman et al 2003b) and the breast model. The model allows inclusion of anatomical or pathological details at particular positions in the anatomy and is able to calculate measures of image quality such as contrast and signal-to-noise ratio and measures of radiation risk for example entrance air kerma and effective dose. It allows alteration of imaging system settings such as tube voltage, filtration, beam size and position, choice of anti-scatter device and choice of image detector etc. The model is a useful tool for optimisations since it has been shown that in chest and lumbar spine radiography is able to predict clinical image quality as assessed by a group of radiologists. In the Monte Carlo model (MC-model) the image quality measures are calculated assuming a perfectly sharp imaging system and correction factors need to be applied to the computed data in order to make the image quality measures agree on an absolute scale. The calculation of correction factors for contrast and signal-tonoises are described in this report. A similar report focusing on analogue screen-film chest and lumbar spine radiography was completed some years ago and some of the concepts and methods are similar.
3.
Sandborg, Michael, et al.
(författare)
Comparison of human observer efficiency in pelvis radiographs in two different anatomical regions
2004
Rapport (övrigt vetenskapligt/konstnärligt) abstract
The performance of an x-ray imaging system is often evaluated in terms of how well low-contrast details are visualised in the images. It is however difficult to obtain reliable results because a threshold for human visibility does not strictly exist. The degree of how well a low-contrast detail is ‘seen’ varies from ‘not seen’ to ‘clearly seen’ related to the certainty (or level of confidence) of detection. The visibility criterion is difficult to define, communicate and maintain which results in comparably large inter- and intraobserver variability. The detection probability depends not only on the imaging task, the technical performance of the imaging system and the observer´s skill and training but also on the projected anatomy in the region where the detail (i.e. lung nodule) is situated. This has been explored by Kundel et al (1985), Samei et al (1999), Håkansson et al (2004), and in Båth et al (2004) by ROC studies mainly in chest radiography. In this work, human observer detection efficiency was measured in a pelvis anthropomorphic phantom. Low-contrast lesions were constructed and positioned in two different regions, one region with a fairly homogeneous, the other region with a heterogeneous anatomical background. A group of human observers were asked to identify the lesion in a set of two-alternative forced choice (2-AFC) experiments.
4.
Sandborg, Michael, 1961-, et al.
(författare)
Demonstration of correlation between physical and clinical image quality measures in chest and lumbar spine imaging.
2000
Ingår i: Digest of papers of the 2000 world congress on medical physics. CD-Rom Chicago July 23-28,2000. - : IEEE. - 0780364651 ; , s. 3078-3081 vol.4
Konferensbidrag (refereegranskat) abstract
Clinical and physical assessments of image quality are compared and the correlation between the two derived. Clinical assessment has been made by a group of expert radiologists who evaluated the fulfillment of the European Image Criteria for chest and lumbar spine radiography; yielding the so-called Image Criteria Score, ICS. Physical measures of image quality were calculated using a Monte Carlo model of the complete imaging system. This model includes a voxelised male anatomy and calculates contrast and signal-to-noise ratio of various anatomical details and a measure of useful dynamic range. Correlations between the ICS and the physical image quality measures were sought. Four lumbar spine and 16 chest imaging systems were evaluated and simulated with the model. The most useful physical quantities for chest radiography were the dynamic range and contrast of blood vessels in the retro-cardiac area. In lumbar spine, it was the signal-to-noise ratio of trabecular structures. The significant correlation is encouraging and shows that clinical image quality can be predicted provided the imaging conditions are well known and that relevant measures of physical image quality are used to assess the quality of the image
5.
Sandborg, Michael, 1961-, et al.
(författare)
Demonstration of correlations between clinical and physical image quality measures in chest and lumbar spine screen-film radiography
2001
Ingår i: British Journal of Radiology. - : British Institute of Radiology. - 0007-1285 .- 1748-880X. ; 74:882, s. 520-528
Tidskriftsartikel (refereegranskat) abstract
The ability to predict clinical image quality from physical measures is useful for optimization in diagnostic radiology. In this work, clinical and physical assessments of image quality are compared and correlations between the two are derived. Clinical assessment has been made by a group of expert radiologists who evaluated fulfilment of the European image criteria for chest and lumbar spine radiography using two scoring methods: image criteria score (ICS) and visual grading analysis score (VGAS). Physical image quality measures were calculated using a Monte Carlo simulation model of the complete imaging system. This model includes a voxelized male anatomy and was used to calculate contrast and signal-to-noise ratio of various important anatomical details and measures of dynamic range. Correlations between the physical image quality measures on the one hand and the ICS and VGAS on the other were sought. 16 chest and 4 lumbar spine imaging system configurations were compared in frontal projection. A statistically significant correlation with clinical image quality was found in chest posteroanterior radiography for the contrast of blood vessels in the retrocardiac area and a measure of useful dynamic range. In lumbar spine anteroposterior radiography, a similar significant correlation with clinical image quality was found between the contrast and signal-to-noise ratio of the trabecular structures in the L1-L5 vertebrae. The significant correlation shows that clinical image quality can, at least in some cases, be predicted from appropriate measures of physical image quality.
6.
Sandborg, Michael, et al.
(författare)
Report on the study and optimisation of chestand lumbar spine X-ray imaging
2000
Rapport (övrigt vetenskapligt/konstnärligt) abstract
The optimisation of radiological equipment and equipment parameters is a key stage in the optimisation of image quality and patient dose in diagnostic radiology. It is essential, however, to underpin such optimisation with theoretical modelling which can provide both the direct quantification of the effect on image quality and dose of changes in system parameters and the opportunity for optimisation of equipment selection and use. Our principal contribution to the joint CEC-project 'Predictivity and Optimisation in Diagnostic Radiology' is in modelling of planar chest and lumbar spine radiographic examinations. The results of this work for the chest PA, lumbar spine AP and lumbar spine lateral examinations are presented in this report. Prior to this, several development stages have been completed which include the calibration and validation of our methods by measurements in the clinical environment on patients and patient images. These important aspects are not dealt with in detail here, but are described in separate reports. This report focuses on three aspects from our results of using our Monte Carlo model of the patient and imaging equipment: (1) Study of the effects on image quality and patient dose when the imaging parameters are varied; Establishment of imaging parameters and systems that result in as least as good image quality as systems with good performance singled out from results of clinical trials (optimisations); Comparison of the results from the model with the results from clinical trials performed by partners in the joint CEC-project. An objective of the report is to present our results at a level of detail not usually possible in the refereed scientific literature. The report should therefore not be read all at once, but preferably used as a ‘reference library’ or documentation of all our efforts. There are many interesting results and findings from this collaborative work and these will be submitted for publication to the appropriate journals.
7.
8.
Tingberg, Anders, et al.
(författare)
Influence of the characteristic curve on the clinical image quality of lumbar spine and chest radiographs.
2004
Ingår i: The British journal of radiology. - : British Institute of Radiology. - 0007-1285 .- 1748-880X. ; 77:915, s. 204-15
Tidskriftsartikel (refereegranskat) abstract
The "European Guidelines on Quality Criteria for Diagnostic Radiographic Images" do not address the choice of the film characteristic (H&D) curve, which is an important parameter for the description of a radiographic screen-film system. The image contrast of clinical lumbar spine and chest radiographs was altered by digital image processing techniques, simulating images with different H&D curves, both steeper and flatter than the original. The manipulated images were printed on film for evaluation. Seven experienced radiologists evaluated the clinical image quality by analysing the fulfilment of the European Image Criteria (ICS) and by visual grading analysis (VGA) of in total 224 lumbar spine and 360 chest images. A parallel study of the effect of the H&D curve has also been made using a theoretical model. The contrast (DeltaOD) of relevant anatomical details was calculated, using a Monte Carlo simulation-model of the complete imaging system including a 3D voxel phantom of a patient. Correlations between the calculated contrast and the radiologists' assessment by VGA were sought. The results of the radiologists' assessment show that the quality in selected regions of lumbar spine and chest images can be significantly improved by the use of films with a steeper H&D curve compared with the standard latitude film. Significant (p<0.05) correlations were found between the VGA results and the calculations of the contrast of transverse processes and trabecular details in the lumbar spine vertebrae, and with the contrast of blood vessels in the retrocardiac area of the chest.
9.
10.
Ullman, Gustav, et al.
(författare)
Comparison of clinical and physical measures of image quality in chest PA and pelvis AP views at varying tube voltages
2004
Rapport (övrigt vetenskapligt/konstnärligt) abstract
Image quality in digital chest PA and pelvis AP was assessed using two different methods; one based on observations of images of an anthropomorphic phantom, one based on computer modelling 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 approximately the same effective dose was achieved in the modelled patient (anthropomorphic phantom). Two x-ray units were employed using a digital image detector (computed radiography, CR, system) with standard tube filtration and anti-scatter 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 the computer model in terms of the signal-to-noise ratio, SNR for fixed effective dose in the voxel phantom. The computer model uses Monte Carlo simulations of the patient and complete imaging system. Both the VGAS (visual grading analysis score) and SNR increase with decreasing tube voltage in both chest PA and pelvis AP examinations, indicating superior performance if lower tube voltages than used today are employed in digital radiology. 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 analogue screen-film radiography are discussed as well as the relevance of using VGAS and quantum noise SNR as measures of image quality.
