A comparative study of limitedâ angle coneâ beam reconstruction methods for breast tomosynthesis

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134781/1/mp7543.pd

Modeling the Anisotropic Resolution and Noise Properties of Digital Breast Tomosynthesis

Digital breast tomosynthesis (DBT) is a 3D imaging modality in which a reconstruction of the breast is generated from various x-ray projections. Due to the newness of this technology, the development of an analytical model of image quality has been on-going. In this thesis, a more complete model is developed by addressing the limitations found in the previous linear systems (LS) model [Zhao, Med. Phys. 2008, 35(12): 5219-32]. A central assumption of the LS model is that the angle of x-ray incidence is approximately normal to the detector in each projection. To model the effect of oblique x-ray incidence, this thesis generalizes Swank\u27s calculations of the transfer functions of x-ray fluorescent screens to arbitrary incident angles. In the LS model, it is also assumed that the pixelation in the reconstruction grid is the same as the detector; hence, the highest frequency that can be resolved is the detector alias frequency. This thesis considers reconstruction grids with smaller pixelation to investigate super-resolution, or visibility of higher frequencies. A sine plate is introduced as a conceptual test object to analyze super-resolution. By orienting the long axis of the sine plate at various angles, the feasibility of oblique reconstruction planes is also investigated. This formulation differs from the LS model in which reconstruction planes are parallel to the breast support. It is shown that the transfer functions for arbitrary angles of x-ray incidence can be modeled in closed form. The high frequency modulation transfer function (MTF) and detective quantum efficiency (DQE) are degraded due to oblique x-ray incidence. In addition, using the sine plate, it is demonstrated that a reconstruction can resolve frequencies exceeding the detector alias frequency. Experimental images of bar patterns verified the existence of super-resolution. Anecdotal clinical examples showed that super-resolution improves the visibility of microcalcifications. The feasibility of oblique reconstructions was established theoretically with the sine plate and was validated experimentally with bar patterns. This thesis develops a more complete model of image quality in DBT by addressing the limitations of the LS model. In future studies, this model can be used as a tool for optimizing DBT

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

Optimization of a High-Energy X-Ray Inline Phase Sensitive Imaging System for Diagnosis of Breast Cancer

Breast cancer screening modalities have received constant research attention that are mainly focused on their abilities to detect cancer at an early stage while reducing the risks of harmful radiation dose delivered to the patient. As a result, numerous advancements have been made over the last two decades which include the introduction of digital mammography (DM) and digital breast tomosynthesis (DBT). Numerous clinical trials have demonstrated the decrease in mortality rates by employing these modalities. Significant research attention remains focused on investigating methods for further improving the detection capabilities and reducing the radiation dose. The conventional x-ray imaging technique relies on the attenuation characteristics of a tissue to produce imaging contrast. However, the similar attenuation characteristics of normal and malignant breast tissue present a challenge in differentiating between them using conventional x-ray imaging. The current technique for providing higher image quality involves the introduction of anti-scatter grids and operating the x-ray tubes at much lower x-ray energies as compared to the other radiography fields, both of which results in an increased radiation dose. The current method for providing higher image quality involves utilizing anti-scatter grids and operating at much lower x-ray energies than other radiography fields, both of which result in an increased radiation dose. Phase sensitive imaging is an emerging technique, which relies not only on attenuation coefficients but also the effects produced by x-ray phase shift coefficients. Within the diagnostic energy range, it has been estimated that the phase shift coefficients of a breast tissue are at least 2-3 orders of magnitude larger than their attenuation coefficients. Thus, this technique holds the potential to increase the x-ray energy and remove the grid without compromising the image quality, which could potentially reduce the patient dose. The inline phase sensitive approach involves the simplest implementation—provided that the imaging system is spatially coherent — as it does not involve the introduction of any optical element between the object and detector. Preclinical studies with the inline phase sensitive imaging technique at the same energy as conventional imaging have indicated the ability to reduce the radiation dose without negatively impacting the diagnostic capabilities. However, there are some existing challenges that have prevented this technique in its clinical implementation. Responding to the challenges, an inline phase sensitive imaging prototype has been developed in the advanced biomedical imaging laboratory. The goal of the research presented in this dissertation comprises a thorough investigation in optimizing a high energy phase sensitive imaging prototype efficiently in terms of its geometric and operating parameters. Once optimized, the imaging performance of this phase sensitive x-ray imaging prototype is going to be compared with the commercial digital mammography and digital breast tomosynthesis (DBT) imaging systems using modular breast phantoms at similar and reduced mean glandular dose (Dg) dose levels. This dissertation includes numerous original contributions, perhaps the most significant of which were the demonstration of the ability of inline phase sensitive imaging prototype to deliver higher image quality required for tumor detection and diagnosis at higher x-ray energies in comparison with low energy commercial imaging systems at similar or less radiation dose levels. These results clearly demonstrate the ability of the high energy inline phase sensitive imaging system to maintain the image quality improvement that is necessary for diagnosis at high x-ray energies without an increase in the radiation dose

Improving Image Reconstruction for Digital Breast Tomosynthesis

Digital breast tomosynthesis (DBT) has been developed to reduce the issue of overlapping tissue in conventional 2-D mammography for breast cancer screening and diagnosis. In the DBT procedure, the patient’s breast is compressed with a paddle and a sequence of x-ray projections is taken within a small angular range. Tomographic reconstruction algorithms are then applied to these projections, generating tomosynthesized image slices of the breast, such that radiologists can read the breast slice by slice. Studies have shown that DBT can reduce both false-negative diagnoses of breast cancer and false-positive recalls compared to mammography alone. This dissertation focuses on improving image quality for DBT reconstruction. Chapter I briefly introduces the concept of DBT and the inspiration of my study. Chapter II covers the background of my research including the concept of image reconstruction, the geometry of our experimental DBT system and figures of merit for image quality. Chapter III introduces our study of the segmented separable footprint (SG) projector. By taking into account the finite size of detector element, the SG projector improves the accuracy of forward projections in iterative image reconstruction. Due to the more efficient access to memory, the SG projector is also faster than the traditional ray-tracing (RT) projector. We applied the SG projector to regular and subpixel reconstructions and demonstrated its effectiveness. Chapter IV introduces a new DBT reconstruction method with detector blur and correlated noise modeling, called the SQS-DBCN algorithm. The SQS-DBCN algorithm is able to significantly enhance microcalcifications (MC) in DBT while preserving the appearance of the soft tissue and mass margin. Comparisons between the SQS-DBCN algorithm and several modified versions of the SQS-DBCN algorithm indicate the importance of modeling different components of the system physics at the same time. Chapter V investigates truncated projection artifact (TPA) removal algorithms. Among the three algorithms we proposed, the pre-reconstruction-based projection view (PV) extrapolation method provides the best performance. Possible improvements of the other two TPA removal algorithms have been discussed. Chapter VI of this dissertation examines the effect of source blur on DBT reconstruction. Our analytical calculation demonstrates that the point spread function (PSF) of source blur is highly shift-variant. We used CatSim to simulate digital phantoms. Analysis on the reconstructed images demonstrates that a typical finite-sized focal spot (~ 0.3 mm) will not affect the image quality if the x-ray tube is stationary during the data acquisition. For DBT systems with continuous-motion data acquisition, the motion of the x-ray tube is the main cause of the effective source blur and will cause loss in the contrast of objects. Therefore modeling the source blur for these DBT systems could potentially improve the reconstructed image quality. The final chapter of this dissertation discusses a few future studies that are inspired by my PhD research.PHDElectrical Engineering: SystemsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/144059/1/jiabei_1.pd

Comparison of different image reconstruction algorithms for Digital Breast Tomosynthesis and assessment of their potential to reduce radiation dose

Tese de mestrado, Engenharia Física, 2022, Universidade de Lisboa, Faculdade de CiênciasDigital Breast Tomosynthesis is a three-dimensional medical imaging technique that allows the view of sectional parts of the breast. Obtaining multiple slices of the breast constitutes an advantage in contrast to conventional mammography examination in view of the increased potential in breast cancer detectability. Conventional mammography, despite being a screening success, has undesirable specificity, sensitivity, and high recall rates owing to the overlapping of tissues. Although this new technique promises better diagnostic results, the acquisition methods and image reconstruction algorithms are still under research. Several articles suggest the use of analytic algorithms. However, more recent articles highlight the iterative algorithm’s potential for increasing image quality when compared to the former. The scope of this dissertation was to test the hypothesis of achieving higher quality images using iterative algorithms acquired with lower doses than those using analytic algorithms. In a first stage, the open-source Tomographic Iterative GPU-based Reconstruction (TIGRE) Toolbox for fast and accurate 3D x-ray image reconstruction was used to reconstruct the images acquired using an acrylic phantom. The algorithms used from the toolbox were the Feldkamp, Davis, and Kress, the Simultaneous Algebraic Reconstruction Technique, and the Maximum Likelihood Expectation Maximization algorithm. In a second and final state, the possibility of further reducing the radiation dose using image postprocessing tools was evaluated. A Total Variation Minimization filter was applied to the images reconstructed with the TIGRE toolbox algorithm that provided the best image quality. These were then compared to the images of the commercial unit used for the image acquisitions. With the use of image quality parameters, it was found that the Maximum Likelihood Expectation Maximization algorithm performance was the best of the three for lower radiation doses, especially with the filter. In sum, the result showed the potential of the algorithm in obtaining images with quality for low doses

A dual modality, DCE-MRI and x-ray, physical phantom for quantitative evaluation of breast imaging protocols

The current clinical standard for breast cancer screening is mammography. However, this technique has a low sensitivity which results in missed cancers. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) has recently emerged as a promising technique for breast cancer diagnosis and has been reported as being superior to mammography for screening of high-risk women and evaluation of extent of disease. At the same time, low and variable specificity has been documented in the literature as well as a rising number of mastectomies possibly due to the increasing use of DCE-MRI. In this study, we developed and characterized a dual-modality, x-ray and DCE-MRI, anthropomorphic breast phantom for the quantitative assessment of breast imaging protocols. X-ray properties of the phantom were quantitatively compared with patient data, including attenuation coefficients, which matched human values to within the measurement error, and tissue structure using spatial covariance matrices of image data, which were found to be similar in size to patient data. Simulations of the phantom scatter-to-primary ratio (SPR) were produced and experimentally validated then compared with published SPR predictions for homogeneous phantoms. SPR values were as high as 85% in some areas and were heavily influenced by the heterogeneous tissue structure. MRI properties of the phantom, T1 and T2 relaxation values and tissue structure, were also quantitatively compared with patient data and found to match within two error bars. Finally, a dynamic lesion that mimics lesion border shape and washout curve shape was included in the phantom. High spatial and temporal resolution x-ray measurements of the washout curve shape were performed to determine the true contrast agent concentration as a function of time. DCE-MRI phantom measurements using a clinical imaging protocol were compared against the x-ray truth measurements. MRI signal intensity curves were shown to be less specific to lesion type than the x-ray derived contrast agent concentration curves. This phantom allows, for the first time, for quantitative evaluation of and direct comparisons between x-ray and MRI breast imaging modalities in the context of lesion detection and characterization

Advancing the Clinical Potential of Carbon Nanotube-enabled stationary 3D Mammography

Scope and purpose. 3D imaging has revolutionized medicine. Digital breast tomosynthesis (DBT), also recognized as 3D mammography, is a relatively recent example. stationary DBT (sDBT) is an experimental technology in which the single moving x-ray source of conventional DBT has been replaced by a fixed array of carbon nanotube (CNT)-enabled sources. Given the potential for a higher spatial and temporal resolution compared to commercially-available, moving-source DBT devices, it was hypothesized that sDBT would provide a valuable tool for breast imaging. As such, the purpose of this work was to explore the clinical potential of sDBT. To accomplish this purpose, three broad Aims were set forth: (1) study the challenges of scatter and artifact with sDBT, (2) assess the performance of sDBT relative to standard mammographic screening approaches, and (3) develop a synthetic mammography capability for sDBT. Throughout the work, developing image processing approaches to maximize the diagnostic value of the information presented to readers remained a specific goal. Data sources and methodology. Sitting at the intersection of development and clinical application, this work involved both basic experimentation and human study. Quantitative measures of image quality as well as reader preference and accuracy were used to assess the performance of sDBT. These studies imaged breast-mimicking phantoms, lumpectomy specimens, and human subjects on IRB-approved study protocols, often using standard 2D and conventional 3D mammography for reference. Key findings. Characterizing scatter and artifact allowed the development of new processing approaches to improve image quality. Additionally, comparing the performance of sDBT to standard breast imaging technologies helped identify opportunities for improvement through processing. This line of research culminated in the incorporation of a synthetic mammography capability into sDBT, yielding images that have the potential to improve the diagnostic value of sDBT. Implications. This work advanced the evolution of CNT-enabled sDBT toward a viable clinical tool by incorporating key image processing functionality and characterizing the performance of sDBT relative to standard breast imaging techniques. The findings confirmed the clinical utility of sDBT while also suggesting promising paths for future research and development with this unique approach to breast imaging.Doctor of Philosoph

DEVELOPMENT AND CHARACTERIZATION OF A HIGH-ENERGY IN-LINE PHASE CONTRAST TOMOSYNTHESIS PROTOTYPE

Phase sensitive 3D imaging techniques have been an emerging field in x-ray imaging for two decades. Among them, in-line phase contrast tomosynthesis has been investigated with great potential for translation into clinical applications in the near future, due to combining the advantages of configuration simplicity, structural noise elimination and potentially low radiation dose delivery. The high-energy in-line phase contrast tomosynthesis technique developed and presented in this dissertation initiates this translational procedure by optimizing the imaging conditions, performing phase retrieval, offering opportunities to further reduce radiation dose delivery, improving detectability and specificity with the employment of auxiliary phase contrast agents, and potentially performing quantitative imaging. First, the high-energy in-line phase contrast tomosynthesis prototype was developed and characterized in this dissertation as the first of its kind following a number of engineering trade-off considerations. The quantitative results as well as the imaging results of tissue-simulating phantoms and biology-related phantoms demonstrate the extensive capability of this imaging prototype in improving tumor detectability. In addition, the optimization of the x-ray prime beam toward the PAD phase retrieval method proved the potential of high-energy imaging and predicated the solution toward imaging time reduction by employing photon counting based imaging techniques. In the past several years, applications of microbubbles as a phase contrast agent have shown the capability for image quality improvement in quantitative imaging. In this dissertation, a preliminary study of quantitative imaging of microbubbles using the in-line phase contrast projection mode imaging prototype, which is a system without tomosynthesis capability, provided a discussion on how the materials of the bubble shells and gas infills could impact the imaging capabilities and resulting image detectability. In addition, the results of the study provided a guideline for microbubble selections for in-line phase contrast mode imaging modalities. Based on this criterion discussed in the study, the albumin-shell microbubbles were selected as the phase contrast agent for the imaging prototype presented in this dissertation. The imaging results showed the feasibility of performing quantitative imaging by employing microbubbles as the auxiliary phase contrast agent. Clinical conditions were simulated by distributing microbubbles on the interface between two tissue-like phantom structures. The quantitative imaging results provided clinical motivation for translating phantom studies into more biology-related investigations providing radiation dose reductions in the future