11 research outputs found

    Digital radiography: image acquisition and scattering reduction in x-ray imaging.

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    Since the discovery of the X-rays in 1895, their use in both medical and industrial imaging applications has gained increasing importance. As a consequence, X-ray imaging devices have evolved and adapted to the needs of individual applications, leading to the appearance of digital image capture devices. Digital technologies introduced the possibility of separating the image acquisition and image processing steps, allowing their individual optimization. This thesis explores both areas, by seeking the improvement in the design of the new family of Varex Imaging CMOS X-ray detectors and by developing a method to reduce the scatter contribution in mammography examinations using image post-processing techniques. During the CMOS X-ray detector product design phase, it is crucial to detect any short- comings that the detector might present. Image characterization techniques are a very efficient method for finding these possible detector features. This first part of the thesis focused in taking these well-known test methods and adapt and optimize them, so they could act as a red flag indicating when something needed to be investigated. The methods chosen in this study have proven to be very effective in finding detector short- comings and the designs have been optimised in accordance with the results obtained. With the aid of the developed imaging characterization tests, new sensor designs have been successfully integrated into a detector, resulting in the recent release into the market of a new family of Varex Imaging CMOS X-ray detectors. The second part of the thesis focuses in X-ray mammography applications, the gold standard technique in breast cancer screening programmes. Scattered radiation degrades the quality of the image and complicates the diagnosis process. Anti-scatter grids, the main scattering reduction technique, are not a perfect solution. This study is concerned with the use of image post-processing to reduce the scatter contribution in the image, by convolving the output image with kernels obtained from simplified Monte Carlo simulations. The proposed semi-empirical approach uses three thickness-dependant symmetric kernels to accurately estimate the environment contribution to the breast, which has been found to be of key importance in the correction of the breast-edge area. When using a single breast thickness-dependant kernel to convolve the image, the post-processing technique can over-estimate the scattering up to 60%. The method presented in this study reduces the uncertainty to a 4-10% range for a 35 to 70 mm breast thickness range, making it a very efficient scatter modelling technique. The method has been successfully proven against full Monte Carlo simulations and mammography phantoms, where it shows clear improvements in terms of the contrast to noise ratio and variance ratio when the performance is compared against images acquired with anti-scatter grids

    Correlation of clinical and physical-technical image quality in chest CT : a human cadaver study applied on iterative reconstruction

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    Background: The first aim of this study was to evaluate the correlation between clinical and physical-technical image quality applied to different strengths of iterative reconstruction in chest CT images using Thiel cadaver acquisitions and Catphan images. The second aim was to determine the potential dose reduction of iterative reconstruction compared to conventional filtered back projection based on different clinical and physical-technical image quality parameters. Methods: Clinical image quality was assessed using three Thiel embalmed human cadavers. A Catphan phantom was used to assess physical-technical image quality parameters such as noise, contrast-detail and contrast-to-noise ratio (CNR). Both Catphan and chest Thiel CT images were acquired on a multislice CT scanner at 120 kVp and 0.9 pitch. Six different refmAs settings were applied (12, 30, 60, 90, 120 and 150refmAs) and each scan was reconstructed using filtered back projection (FBP) and iterative reconstruction (SAFIRE) algorithms (1,3 and 5 strengths) using a sharp kernel, resulting in 24 image series. Four radiologists assessed the clinical image quality, using a visual grading analysis (VGA) technique based on the European Quality Criteria for Chest CT. Results: Correlation coefficients between clinical and physical-technical image quality varied from 0.88 to 0.92, depending on the selected physical-technical parameter. Depending on the strength of SAFIRE, the potential dose reduction based on noise, CNR and the inverse image quality figure (IQF(inv)) varied from 14.0 to 67.8 %, 16.0 to 71.5 % and 22.7 to 50.6 % respectively. Potential dose reduction based on clinical image quality varied from 27 to 37.4 %, depending on the strength of SAFIRE. Conclusion: Our results demonstrate that noise assessments in a uniform phantom overestimate the potential dose reduction for the SAFIRE IR algorithm. Since the IQF(inv) based dose reduction is quite consistent with the clinical based dose reduction, an optimised contrast-detail phantom could improve the use of contrast-detail analysis for image quality assessment in chest CT imaging. In conclusion, one should be cautious to evaluate the performance of CT equipment taking into account only physical-technical parameters as noise and CNR, as this might give an incomplete representation of the actual clinical image quality performance

    Image quality evaluation in X-ray medical imaging based on Thiel embalmed human cadavers

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    Mammography

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    In this volume, the topics are constructed from a variety of contents: the bases of mammography systems, optimization of screening mammography with reference to evidence-based research, new technologies of image acquisition and its surrounding systems, and case reports with reference to up-to-date multimodality images of breast cancer. Mammography has been lagged in the transition to digital imaging systems because of the necessity of high resolution for diagnosis. However, in the past ten years, technical improvement has resolved the difficulties and boosted new diagnostic systems. We hope that the reader will learn the essentials of mammography and will be forward-looking for the new technologies. We want to express our sincere gratitude and appreciation?to all the co-authors who have contributed their work to this volume

    Imaging of the Breast

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    Early detection of breast cancer combined with targeted therapy offers the best outcome for breast cancer patients. This volume deal with a wide range of new technical innovations for improving breast cancer detection, diagnosis and therapy. There is a special focus on improvements in mammographic image quality, image analysis, magnetic resonance imaging of the breast and molecular imaging. A chapter on targeted therapy explores the option of less radical postoperative therapy for women with early, screen-detected breast cancers

    Risk of radiation-induced cancer from screening mammography

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    Background and Objectives: When the benefits and risks of mammography are considered, the risk of radiation-induced cancer is calculated only for the breast using the mean glandular dose (MGD). Whilst MGD is a useful concept, it has many limitations. This thesis aims to establish a novel method to determine and convey radiation risk from full field digital mammography (FFDM) screening using lifetime effective risk. Method: For effective risk calculations, organ doses as well as examined breast MGD are required. Screening mammography was simulated by exposing a breast phantom for cranio-caudal and medio-lateral oblique for each breast using 16 FFDM machines. An anthropomorphic dosimetry phantom loaded with thermo-luminescent detectors (TLDs) was positioned in contact with the breast phantom to simulate the client’s body. Once the risk per individual was calculated, total effective lifetime risk across 48 worldwide screening programmes was calculated. The total effective risk data sets were analysed to establish a regression model to predict the effective risk of any screening programme. Graphs were generated to extrapolate the total effective risk of any screening programme of specific screening commencement age and frequency considering the MGD differences of different FFDM machines. Since the highest radiation dose after examined breast was received by contralateral breast, the effect of a contralateral breast lead shield on effective risk was also investigated. Results: Large differences in the effective lifetime risk exist between worldwide screening programmes. The effective lifetime risk varied from approximately 50 cases/106 to more than 1000 cases/106. These differences were mainly attributed to the commencement age and frequency of screening. Since tissue radio-sensitivity reduces with age, the cessation age of screening mammography does not result in a noteworthy effect on the total effective risk. The use of contralateral breast shield reduces the total effective risk by about 1.5% for most worldwide screening programmes.Conclusion: A novel method has been proposed to assess radiation-induced cancer risk from FFDM screening which considers the radiation dose received by all body tissues in addition to the examined breast. Using effective risk, the data is more likely to be understandable by screening clients and referring clinicians, unlike MGD which is not readily available or understandable by the general populace. This novel method and the data are compatible with the incoming European Commission legislation about giving the patient information on radiation risk

    Infective/inflammatory disorders

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    The radiological investigation of musculoskeletal tumours : chairperson's introduction

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