| 1. |
- Niemi, MEK, et al.
(författare)
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- 2021
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swepub:Mat__t
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| 2. |
- Kanai, M, et al.
(författare)
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- 2023
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swepub:Mat__t
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| 3. |
- Fredenberg, Erik, et al.
(författare)
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Measurement of breast-tissue x-ray attenuation by spectral mammography : solid lesions
- 2016
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Ingår i: Physics in Medicine and Biology. - : Institute of Physics Publishing (IOPP). - 0031-9155 .- 1361-6560. ; 61:7, s. 2595-2612
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge of x-ray attenuation is essential for developing and evaluating x-ray imaging technologies. For instance, techniques to distinguish between cysts and solid tumours at mammography screening would be highly desirable to reduce recalls, but the development requires knowledge of the x-ray attenuation for cysts and tumours. We have previously measured the attenuation of cyst fluid using photon-counting spectral mammography. Data on x-ray attenuation for solid breast lesions are available in the literature, but cover a relatively wide range, likely caused by natural spread between samples, random measurement errors, and different experimental conditions. In this study, we have adapted a previously developed spectral method to measure the linear attenuation of solid breast lesions. A total of 56 malignant and 5 benign lesions were included in the study. The samples were placed in a holder that allowed for thickness measurement. Spectral (energy-resolved) images of the samples were acquired and the image signal was mapped to equivalent thicknesses of two known reference materials, which can be used to derive the x-ray attenuation as a function of energy. The spread in equivalent material thicknesses was relatively large between samples, which is likely to be caused mainly by natural variation and only to a minor extent by random measurement errors and sample inhomogeneity. No significant difference in attenuation was found between benign and malignant solid lesions. The separation between cyst-fluid and tumour attenuation was, however, significant, which suggests it may be possible to distinguish cystic from solid breast lesions, and the results lay the groundwork for a clinical trial. In addition, the study adds a relatively large sample set to the published data and may contribute to a reduction in the overall uncertainty in the literature.
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| 4. |
- Fredenberg, Erik, et al.
(författare)
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X-ray attenuation of adipose breast tissue : In-vitro and in-vivo measurements using spectral imaging
- 2015
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Ingår i: MEDICAL IMAGING 2015: PHYSICS OF MEDICAL IMAGING. - : SPIE. - 9781628415025
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Konferensbidrag (refereegranskat)abstract
- The development of new x-ray imaging techniques often requires prior knowledge of tissue attenuation, but the sources of such information are sparse. We have measured the attenuation of adipose breast tissue using spectral imaging, in vitro and in vivo. For the in-vitro measurement, fixed samples of adipose breast tissue were imaged on a spectral mammography system, and the energy-dependent x-ray attenuation was measured in terms of equivalent thicknesses of aluminum and poly-methyl methacrylate (PMMA). For the in-vivo measurement, a similar procedure was applied on a number of spectral screening mammograms. The results of the two measurements agreed well and were consistent with published attenuation data and with measurements on tissue-equivalent material.
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| 5. |
- Sandborg, Michael, et al.
(författare)
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Calculation of contrast and signal-to-noise degradation factors for digital detectors in chest and breast imaging
- 2003
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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.
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| 6. |
- Sandborg, Michael, et al.
(författare)
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Collection and analysis of patient and image data for calibration of a voxelphantombased Monte Carlo code and for the modelling of important structures
- 1997
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The contribution of the Medical Physics Departments at Linköping University (LKP) and The Royal Marsden NHS Trust (RMH) to the joint project ‘Predictivity and Optimisation in Medical Radiation Protection’ is in modelling of the chest and lumbar spine radiographic examinations. This involves:the development of quantitative imaging requirements;an investigation of the effect of imaging technique on image quality and patientdose, andan optimisation of system design.One of the objectives for this first reporting period (0-12 months) was to collect a set of chest and lumbar spine radiographs of patients for subsequent analysis in order to establish patient doses and important features in the images. The set of radiographs and the outcome of the image feature analysis will during this project’s second year be used to calibrate our Monte Carlo computational model of the conventional chest and lumbar spine screen-film X-ray imaging systems.
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| 7. |
- Sandborg, Michael, et al.
(författare)
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Comparison of clinical and physical measures of image quality in chest and pelvis computed radiography at different tube voltages
- 2006
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Ingår i: Medical Physics. - : Wiley. - 0094-2405. ; 33:11, s. 4169-4175
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Sandborg, Michael, et al.
(författare)
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Implementation of unsharpness and noise into the model of the imaging system : Applications to chest and lumbar spine screen-film radiography
- 1999
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A model of the complete x-ray imaging system including the patient is a powerful tool for imaging system analysis and the optimisation of image quality and patient dose. It allows flexible variation of the system components (i.e. x-ray source, antiscatter device and image detector) and study of their effect on image quality and patient risk. Our group has developed, validated and calibrated a Monte Carlo model of the complete imaging system for chest and lumbar spine examination including voxalised human male anatomy. The Monte Carlo program calculates the contrast and signal-to-noise ratio (SNR) of various contrasting details within the voxel phantom. Important details in the images have been selected by consulting radiologist and the EU document of image quality criteria. The entrance surface dose without back-scatter and the effective dose are used as measures of patient radiation risk. The contrasts of the details are derived initially from Monte Carlo estimates of the energy imparted per unit area to the image detector beside and behind the detail. However, this ignores the effects of unsharpness in the imaging chain (such as screen-film, geometric and motion unsharpness) and the influence on contrast of the film characteristic curve. In the Monte Carlo program, SNR is calculated assuming that the noise arises from the random fluctuations in the energy imparted per unit area to the image detector only. However, other noise sources also contribute to the total noise, such as screen and film noise. Hence the model of the imaging system needs to be further developed to take these effects into account. The methods used to extend the model are described below together with illustrations of their effect on the difference in optical density, DOD, and SNR in chest and lumbar spine imaging.
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| 9. |
- Sandborg, Michael, et al.
(författare)
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Report on the study and optimisation of chestand lumbar spine X-ray imaging
- 2000
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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.
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| 10. |
- Sandborg, Michael, et al.
(författare)
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The choice of anti-scatter grids in diagnostic radiology : the optimization of image quality and absorbed dose
- 1993
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A Monte Carlo model is developed to study and optimise the design of antiscatter grids in diagnostic radiology. The imaging chain including X-ray energy spectra, phantom (representing the patient), grid and image receptor is simulated. Image quality is quantified in terms of contrast (conventionai screen-film imaging) and signal-to-noise ratio, SNR (digital imaging) and the radiation detriment to the patient (risk) by the mean absorbed dose in the phantom. The advantages of using fibre instead of aluminium for grid interspaces and covers are quantified. Compared to aluminium grids, the absorbed dose is reduced by 10-50%, contrast is improved by 0-10% and SNR by 10-40% (digital radiography). The advantages are larger at low tube potentials and for grids with high ratio and low strip density. Commercial grids, with different interspace materials, strip density, strip width and grid ratio, are compared in paediatric, lumbar spine and chest examinations. The differences in dose increase and contrast improvement factors obtained with these grids are mainly due to the use of different materials in the grid interspaces, but the strip design is also important. In a global optimisation of grid design and tube potential at fixed contrast, it is found that grids of different strip density and ratio all can have good performances provided that they are used with appropriate strip width and tube potential. In the paediatric examination, low ratio grids need thinner strips than used today to be optimal. A small air gap could alternatively be used. In examinations with more scatter (adult AP), present commercial grids are optimal (r=12-16, d=30-50µm). In the lateral view (even more scatter), grids with ratios larger than 16 are optimal provided the grid can be accurately aligned in the beam. The optimization is performed with grids with fibre interspaces and covers since low atomic number materials should preferably be used for materials between the patient and the receptor. Optimal grids with aluminium for these components have lower grid ratio and higher strip densities than optimal fibre grids.
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