A New Stationary Digital Breast Tomosynthesis System: Implementation and Characterization

Digital breast tomosynthesis systems (DBT) use a single thermionic x-ray source that moves around the breast in a fixed angular span. As a result, all current DBT system requires the mechanical motion of the x-ray source during the scan, limiting image quality either due to the focal spot blurring or a long scan time. This causes an unfavorable reduction in the in-plane resolution compared to 2D mammography. Our research group developed and demonstrated a first generation stationary digital breast tomosynthesis (s-DBT) system that uses a linear carbon nanotube (CNT) x-ray source array. Since the stationary sources are not subject to focal spot blurring, and images can be acquired rapidly, the in-plane system resolution is improved. Additionally, image acquisition time is independent of angular span since there is no motion, allowing for large angular spans, and increased depth resolution. The improved resolution of the first generation s-DBT system over continuous motion (CM) DBT has been demonstrated with image evaluation phantoms and a human specimen study. The first generation s-DBT is currently undergoing clinical trials at the University of North Carolina Cancer Hospital. Limitations associated with the first generation system, such as limited tube flux, and limited x-ray energy, placed limitations on our clinical trials and future clinical implementation. Also, the limited angular span could be improved for increased depth resolution, as there is no cost on patient imaging time. The goal of this thesis work was to design construct and characterize a second generation s-DBT system, capable of faster image acquisition times, and higher depth resolution than our first generation system. The second generation s-DBT system was built using a newly designed distributed CNT x-ray source array. The system was then characterized and compared to the first generation system and two commercially available DBT systems. Using physical measurements that are used in medical imaging, the system showed significant improvement in resolution over the first generation system and both commercially available systems, coupled with equal or faster image acquisition times. A separate study investigating the feasibility of contrast enhanced (CE) imaging was conducted, where the system showed capability in both temporal subtraction (TS) and dual energy (DE) imaging.Doctor of Philosoph

Quality control in digital breast tomosynthesis: compliance of two phantoms with the EUREF protocol

Ever since the integration of Digital Breast Tomosynthesis (DBT) into breast cancer screening programmes, it has been a European endeavour to draw up standard guidelines for the assessment of the imaging performance of DBT systems. The quantitative evaluation of the quality of reconstructed tomosynthesis images is still an active area of research. In fact, the current version of the EUREF DBT QC protocol represents a preliminary set of guidelines to be used at acceptance, and to establish baseline values for constancy testing. New phantoms for QC in DBT have also been developed. Together, Sun Nuclear's Mammo 3D Performance Kits and CIRS DBT QC Phantom, model 021, have been shown to provide adequate test objects and background material for the assessment of the Automatic Exposure Control system performance, image receptor response function and noise analysis, system sharpness measured in projection images, and in-plane and out-of-plane spatial resolution in the reconstructed tomosynthesis image. From the comparison with the available literature, the use of the two phantoms with the Hologic Selenia Dimensions and Fujifilm AMULET Innovality systems has been validated

The TOMMY trial: a comparison of TOMosynthesis with digital MammographY in the UK NHS Breast Screening Programme--a multicentre retrospective reading study comparing the diagnostic performance of digital breast tomosynthesis and digital mammography with digital mammography alone.

BACKGROUND: Digital breast tomosynthesis (DBT) is a three-dimensional mammography technique with the potential to improve accuracy by improving differentiation between malignant and non-malignant lesions. OBJECTIVES: The objectives of the study were to compare the diagnostic accuracy of DBT in conjunction with two-dimensional (2D) mammography or synthetic 2D mammography, against standard 2D mammography and to determine if DBT improves the accuracy of detection of different types of lesions. STUDY POPULATION: Women (aged 47-73 years) recalled for further assessment after routine breast screening and women (aged 40-49 years) with moderate/high of risk of developing breast cancer attending annual mammography screening were recruited after giving written informed consent. INTERVENTION: All participants underwent a two-view 2D mammography of both breasts and two-view DBT imaging. Image-processing software generated a synthetic 2D mammogram from the DBT data sets. RETROSPECTIVE READING STUDY: In an independent blinded retrospective study, readers reviewed (1) 2D or (2) 2D + DBT or (3) synthetic 2D + DBT images for each case without access to original screening mammograms or prior examinations. Sensitivities and specificities were calculated for each reading arm and by subgroup analyses. RESULTS: Data were available for 7060 subjects comprising 6020 (1158 cancers) assessment cases and 1040 (two cancers) family history screening cases. Overall sensitivity was 87% [95% confidence interval (CI) 85% to 89%] for 2D only, 89% (95% CI 87% to 91%) for 2D + DBT and 88% (95% CI 86% to 90%) for synthetic 2D + DBT. The difference in sensitivity between 2D and 2D + DBT was of borderline significance (p = 0.07) and for synthetic 2D + DBT there was no significant difference (p = 0.6). Specificity was 58% (95% CI 56% to 60%) for 2D, 69% (95% CI 67% to 71%) for 2D + DBT and 71% (95% CI 69% to 73%) for synthetic 2D + DBT. Specificity was significantly higher in both DBT reading arms for all subgroups of age, density and dominant radiological feature (p < 0.001 all cases). In all reading arms, specificity tended to be lower for microcalcifications and higher for distortion/asymmetry. Comparing 2D + DBT to 2D alone, sensitivity was significantly higher: 93% versus 86% (p < 0.001) for invasive tumours of size 11-20 mm. Similarly, for breast density 50% or more, sensitivities were 93% versus 86% (p = 0.03); for grade 2 invasive tumours, sensitivities were 91% versus 87% (p = 0.01); where the dominant radiological feature was a mass, sensitivities were 92% and 89% (p = 0.04) For synthetic 2D + DBT, there was significantly (p = 0.006) higher sensitivity than 2D alone in invasive cancers of size 11-20 mm, with a sensitivity of 91%. CONCLUSIONS: The specificity of DBT and 2D was better than 2D alone but there was only marginal improvement in sensitivity. The performance of synthetic 2D appeared to be comparable to standard 2D. If these results were observed with screening cases, DBT and 2D mammography could benefit to the screening programme by reducing the number of women recalled unnecessarily, especially if a synthetic 2D mammogram were used to minimise radiation exposure. Further research is required into the feasibility of implementing DBT in a screening setting, prognostic modelling on outcomes and mortality, and comparison of 2D and synthetic 2D for different lesion types. STUDY REGISTRATION: Current Controlled Trials ISRCTN73467396. FUNDING: This project was funded by the NIHR Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 19, No. 4. See the HTA programme website for further project information.This project was funded by the NIHR Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 19, No. 4. See the HTA programme website for further project information.Gilbert FJ, Tucker L, Gillan MGC, Willsher P, Cooke J, Duncan KA, et al. The TOMMY trial: a comparison of TOMosynthesis with digital MammographY in the UK NHS Breast Screening Programme – a multicentre retrospective reading study comparing the diagnostic performance of digital breast tomosynthesis and digital mammography with digital mammography alone. Health Technol Assess 2015;19(4). © Queen’s Printer and Controller of HMSO 2015. This work was produced by Gilbert et al. under the terms of a commissioning contract issued by the Secretary of State for Health. This issue may be freely reproduced for the purposes of private research and study and extracts (or indeed, the full report) may be included in professional journals provided that suitable acknowledgement is made and the reproduction is not associated with any form of advertising. Applications for commercial reproduction should be addressed to: NIHR Journals Library, National Institute for Health Research, Evaluation, Trials and Studies Coordinating Centre, Alpha House, University of Southampton Science Park, Southampton SO16 7NS, UK

Risk of radiation-induced cancer from screening mammography

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

STATIONARY DIGITAL TOMOSYNTHESIS: IMPLEMENTATION, CHARACTERIZATION, AND IMAGE PROCESSING TECHNIQUES

The use of carbon nanotube cathodes for x-ray generation was pioneered and perfected by our team in the Applied Nanotechnology Laboratory at the University of North Carolina at Chapel Hill. Over the past decade, carbon nanotube (CNT) field emission x-ray source technology has matured and translated into multiple pre-clinical and clinical devices. One of the most prominent implementations of CNT x-ray technology is a limited angle tomography method called tomosynthesis, which is rapidly emerging in clinical radiography. The purpose of this project is two-fold, to develop and characterize to the latest iteration, stationary intraoral tomosynthesis, and develop a low-dose, effective scatter reduction technique for breast and chest tomosynthesis. The first portion of this project was to develop and evaluate a new quasi-3D imaging modality for dental imaging. My work consists of experiments which dictated the design parameters and subsequent system evaluation of the dedicated s-IOT clinical prototype system currently installed in the UNC Department of Oral and Maxillofacial Radiology clinic in the School of Dentistry. Experiments were performed in our lab to determine optimal source array geometry and system configuration. The system was fabricated by our commercial partner then housed in our research lab where I performed initial characterization and assisted with software development. After installation in the SOD, I performed additional system characterization, including source output validation, dosimetry, and quantification of resolution. The system components and software were refined through a rapid feedback loop with the engineers involved. Four pre-clinical imaging studies have been performed in collaboration with several dentists using phantoms, extracted teeth, and cadaveric dentition. I have generated an operating manual and trained four dental radiologists in the use of the s-IOT device. The system has now been vetted and is ready for patient use. The second portion of this project consists of hardware development and implementation of an image processing technique for scatter correction. The primary sampling scatter correction (PSSC) is a beam pass technique to measure the primary transmission through the patient and calculate the scatter profile for subtraction. Though developed for breast and chest tomosynthesis, utilization in mammography and chest radiography are also demonstrated in this project. This dissertation is composed of five chapters. Chapters one and two provide the basics of x-ray generation and a brief history of the evolution of carbon nanotube x-ray source technology in our lab at UNC. Chapter three focuses on stationary intraoral tomosynthesis. The first section provides background information on dental radiology and project motivation. Sections 3.2 and 3.3 detail my work in benchtop feasibility and optimization studies, as well as characterization and evaluation of the clinical prototype. Chapter four introduces scatter in imaging, providing motivation for my work on primary sampling scatter correction (PSSC) image processing method, detailed in chapter five.Doctor of Philosoph

Mammography

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

Performance of a carbon nanotube field emission X-ray source array for stationary digital breast tomosynthesis

This work describes the performance of a stationary digital breast tomosynthesis (s-DBT) X-ray tube based on carbon nanotube (CNT) cathodes, and the imaging system developed around it. The s-DBT system has the potential to improve the detection and diagnosis of breast cancer over commercially available digital breast tomosynthesis (DBT) systems. DBT is growing in popularity in the United States, and around the world, as a potential replacement for traditional 2D mammography. The main advantage of DBT over 2D mammography lies in the pseudo-3D nature of the technique allowing the removal of overlapping breast tissue within the image. s-DBT builds on this advantage by removing blur from focal spot motion. Introductions to breast imaging techniques and the DBT modality are given, followed by an introduction to carbon nanotube field emission, the foundation of the s-DBT technology. Details of the s-DBT X-ray tube design and system integration are discussed including specific design parameters, system requirements, and the development process. Also included are summaries of the X-ray tube and system performance over time, and results from characterization measurements. Specific focus is given to the development and completion of a fabrication procedure for tungsten gate mesh, characterization of the CNT cathodes, and improving the system's spatial resolution with use of the focusing electrodes. The tungsten gate mesh is an essential component for extracting electrons from CNTs. A successful deep reactive ion etching fabrication procedure was developed, and the improved gate mesh allowed for higher cathode current and longer pulse widths to be employed in the s-DBT system. Characterization of the CNT cathodes revealed their high-current capacity and the ability to produce relatively long pulse widths, mimicking a 2D imaging modality. This work confirmed that the cathodes are well suited for the task of breast imaging, and explored possible improvements. Lastly, it was shown that by employing and optimizing the focusing electrodes, spatial resolution of the s-DBT system improved, with a tradeoff in loss of transmission rate. This work has contributed to the development and evaluation of the s-DBT technology from the laboratory research stage through clinical trials on human tissue and patients.Doctor of Philosoph