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Kavuri A, Das M. Examining the Influence of Digital Phantom Models in Virtual Imaging Trials for Tomographic Breast Imaging. ARXIV 2024:arXiv:2402.00812v1. [PMID: 38351932 PMCID: PMC10862940] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Figures] [Subscribe] [Scholar Register] [Indexed: 02/19/2024]
Abstract
Purpose Digital phantoms are one of the key components of virtual imaging trials (VITs) that aims to assess and optimize new medical imaging systems and algorithms. However, these phantoms vary in their voxel resolution, appearance and structural details. This study aims to examine whether and how variations between digital phantoms influence system optimization with digital breast tomosynthesis (DBT) as a chosen modality. Methods We selected widely used and open access digital breast phantoms generated with different methods. For each phantom type, we created an ensemble of DBT images to test acquisition strategies. Human observer localization ROC (LROC) was used to assess observer performance studies for each case. Noise power spectrum (NPS) was estimated to compare the phantom structural components. Further, we computed several gaze metrics to quantify the gaze pattern when viewing images generated from different phantom types. Results Our LROC results show that the arc samplings for peak performance were approximately 2.5° and 6° in Bakic and XCAT breast phantoms respectively for 3-mm lesion detection task and indicate that system optimization outcomes from VITs can vary with phantom types and structural frequency components. Additionally, a significant correlation (p¡0.01) between gaze metrics and diagnostic performance suggests that gaze analysis can be used to understand and evaluate task difficulty in VITs. Conclusion Our results point to the critical need to evaluate realism in digital phantoms as well as ensuring sufficient structural variations at spatial frequencies relevant to the signal size for an intended task. In addition, standardizing phantom generation and validation tools might aid in lower discrepancies among independently conducted VITs for system or algorithmic optimizations.
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Affiliation(s)
- Amar Kavuri
- Department of Biomedical Engineering, University of Houston, Houston, TX-77204, USA
| | - Mini Das
- Department of Biomedical Engineering, University of Houston, Houston, TX-77204, USA
- Department of Physics, University of Houston, Houston, TX-77204, USA
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Huang H, Scaduto D, Plaunova A, Rinaldi K, Fisher PR, Zhao W. Comparison of lesion detection and conspicuity between narrow-angle and wide-angle digital breast tomosynthesis for dense and non-dense breasts. J Med Imaging (Bellingham) 2023; 10:S22407. [PMID: 37197744 PMCID: PMC10185103 DOI: 10.1117/1.jmi.10.s2.s22407] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2022] [Revised: 04/11/2023] [Accepted: 04/19/2023] [Indexed: 05/19/2023] Open
Abstract
Digital breast tomosynthesis (DBT) has been shown to improve both sensitivity and specificity for breast cancer detection compared to full-field digital mammography. However, its performance could be limited for patients with dense breasts. Clinical DBT systems vary in their system designs, one of which is the acquisition angular range (AR), which leads to varied performance for different imaging tasks. In this study, we aim to compare DBT systems with different AR. We used a previously validated cascaded linear system model to investigate the dependence of in-plane breast structural noise (BSN) and detectability of masses on AR. We conducted a pilot clinical study to compare the lesion conspicuity between clinical DBT systems with the narrowest and the widest AR. Patients called back for diagnostic imaging on suspicious findings were imaged with both narrow-angle (NA) and wide-angle (WA) DBT. We analyzed the BSN for clinical images using noise power spectrum (NPS) analysis. A 5-point Likert scale was used in the reader study to compare the lesion conspicuity. Our theoretical calculation results show that increasing AR leads to reduced BSN and improved mass detectability. The NPS analysis on clinical images shows the lowest BSN for WA DBT. The WA DBT provides better lesion conspicuity for masses and asymmetries and shows a greater advantage for non-microcalcification lesions in dense breasts. The NA DBT provides better characterizations for microcalcifications. The WA DBT can downgrade false-positive findings seen on NA DBT. In conclusion, WA DBT could improve the detection of masses and asymmetries for patients with dense breasts.
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Affiliation(s)
- Hailiang Huang
- Stony Brook Medicine, Department of Radiology, Stony Brook, New York, United States
| | - David Scaduto
- Stony Brook Medicine, Department of Radiology, Stony Brook, New York, United States
| | - Anastasia Plaunova
- Stony Brook Medicine, Department of Radiology, Stony Brook, New York, United States
| | - Kim Rinaldi
- Stony Brook Medicine, Department of Radiology, Stony Brook, New York, United States
| | - Paul R. Fisher
- Stony Brook Medicine, Department of Radiology, Stony Brook, New York, United States
| | - Wei Zhao
- Stony Brook Medicine, Department of Radiology, Stony Brook, New York, United States
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Lee C, Baek J. Effect of optical blurring of X-ray source on breast tomosynthesis image quality: Modulation transfer function, anatomical noise power spectrum, and signal detectability perspectives. PLoS One 2022; 17:e0267850. [PMID: 35587494 PMCID: PMC9119460 DOI: 10.1371/journal.pone.0267850] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2021] [Accepted: 03/24/2022] [Indexed: 11/19/2022] Open
Abstract
We investigated the effect of the optical blurring of X-ray source on digital breast tomosynthesis (DBT) image quality using well-designed DBT simulator and table-top experimental systems. To measure the in-plane modulation transfer function (MTF), we used simulated sphere phantom and Teflon sphere phantom and generated their projection data using two acquisition modes (i.e., step-and-shoot mode and continuous mode). After reconstruction, we measured the in-plane MTF using reconstructed sphere phantom images. In addition, we measured the anatomical noise power spectrum (aNPS) and signal detectability. We constructed simulated breast phantoms with a 50% volume glandular fraction (VGF) of breast anatomy using the power law spectrum and inserted spherical objects with 1 mm, 2 mm, and 5 mm diameters as breast masses. Projection data were acquired using two acquisition modes, and in-plane breast images were reconstructed using the Feldkamp-Davis-Kress (FDK) algorithm. For the experimental study, we used BR3D breast phantom with 50% VGF and obtained projection data using a table-top experimental system. To compare the detection performance of the two acquisition modes, we calculated the signal detectability using the channelized Hotelling observer (CHO) with Laguerre-Gauss (LG) channels. Our results show that spatial resolution of in-plane image in continuous mode was degraded due to the optical blurring of X-ray source. This blurring effect was reflected in aNPS, resulting in large β values. From a signal detectability perspective, the signal detectability in step-and-shoot mode is higher than that in continuous mode for small spherical signals but not large spherical signals. Although the step-and-shoot mode has disadvantage in terms of scan time compared to the continuous mode, scanning in step-and-shoot mode is better for detecting small signals, indicating that there is a tradeoff between scan time and image quality.
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Affiliation(s)
- Changwoo Lee
- Medical Metrology Team, Safety Measurement Institute, Korea Research Institute of Standards and Science (KRISS), Daejeon, South Korea
| | - Jongduk Baek
- School of Integrated Technology, Yonsei University, Incheon, South Korea
- * E-mail:
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Winter AM, Moy L, Gao Y, Bennett DL. Comparison of Narrow-angle and Wide-angle Digital Breast Tomosynthesis Systems in Clinical Practice. JOURNAL OF BREAST IMAGING 2021; 3:240-255. [PMID: 38424829 DOI: 10.1093/jbi/wbaa114] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2020] [Indexed: 03/02/2024]
Abstract
Digital breast tomosynthesis (DBT) is a pseudo 3D mammography imaging technique that has become widespread since gaining Food and Drug Administration approval in 2011. With this technology, a variable number of tomosynthesis projection images are obtained over an angular range between 15° and 50° for currently available clinical DBT systems. The angular range impacts various aspects of clinical imaging, such as radiation dose, scan time, and image quality, including visualization of calcifications, masses, and architectural distortion. This review presents an overview of the differences between narrow- and wide-angle DBT systems, with an emphasis on their applications in clinical practice. Comparison examples of patients imaged on both narrow- and wide-angle DBT systems illustrate these differences. Understanding the potential variable appearance of imaging findings with narrow- and wide-angle DBT systems is important for radiologists, particularly when comparison images have been obtained on a different DBT system. Furthermore, knowledge about the comparative strengths and limitations of DBT systems is needed for appropriate equipment selection.
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Affiliation(s)
- Andrea M Winter
- Saint Louis University, Department of Radiology, St. Louis, MO, USA
| | - Linda Moy
- NYU Langone Health, NYU School of Medicine, Department of Radiology, New York, NY, USA
| | - Yiming Gao
- NYU Langone Health, NYU School of Medicine, Department of Radiology, New York, NY, USA
| | - Debbie L Bennett
- Saint Louis University, Department of Radiology, St. Louis, MO, USA
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Weir A, Schofield KA, McCurrach A. Setting Scottish diagnostic reference levels for mammography incorporating both craniocaudal and oblique projections between 30 and 80 mm. JOURNAL OF RADIOLOGICAL PROTECTION : OFFICIAL JOURNAL OF THE SOCIETY FOR RADIOLOGICAL PROTECTION 2021; 41:97-117. [PMID: 33684070 DOI: 10.1088/1361-6498/abcf8b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/14/2020] [Accepted: 12/01/2020] [Indexed: 06/12/2023]
Abstract
Optimisation must be carried out on all medical radiological units to ensure doses are as low as reasonably practicable, consistent with the intended purpose. To achieve this, population doses must be estimated and diagnostic reference levels (DRLs) set. For mammography examinations, mean glandular doses (MGDs) are calculated for this purpose. The average MGD per unit is compared to the national mammography DRL, which is applicable to compressed breast thicknesses (CBTs) of 50-60 mm for oblique (OB) views only and set using data from screening units. It is the purpose of this work to assess planar MGDs across Scotland and set DRLs based on data collected from all screening and symptomatic units across Scotland, considering craniocaudal (CC) and OB views and a wider range of CBTs. Data from the most recent dose audit (spanning 2015-2017) for 67 mammography x-ray units were collated and analysed (26 195 images). No large differences between MGD of CC and OB views were found when considering specific CBT ranges (median difference 2.6%). There was, however, a significant difference between screening and symptomatic data (19%). As expected, MGD increased with CBT and there were significant differences in MGD between manufacturers. From the data analysed, Scottish DRLs were set based on 95th percentile values for digital mammography units for three CBT ranges (30-49, 50-60 and 61-80 mm): 1.3, 1.8 and 2.6 mGy respectively. These values consider OB and CC views collectively. Fifth percentile values are quoted to highlight units at greater risk of insufficient image quality. These MGD values, together with image quality assessments, will facilitate optimisation across Scotland. Results show that use of different CBT ranges and inclusion of CC views increases the number of images included in dose audit data analysis from approximately 12%-92%, which is substantially more representative of the population.
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Affiliation(s)
- A Weir
- Health Physics, NHS Greater Glasgow and Clyde, West House, 1055 Great Western Road, G12 0XH Glasgow, United Kingdom
| | - K A Schofield
- Health Facilities Scotland, NHS National Services Scotland, Gyle Square, 1 South Gyle Crescent, EH12 9EB Edinburgh, United Kingdom
| | - A McCurrach
- Health Facilities Scotland, NHS National Services Scotland, Gyle Square, 1 South Gyle Crescent, EH12 9EB Edinburgh, United Kingdom
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Kavuri A, Das M. Relative Contributions of Anatomical and Quantum Noise in Signal Detection and Perception of Tomographic Digital Breast Images. IEEE TRANSACTIONS ON MEDICAL IMAGING 2020; 39:3321-3330. [PMID: 32356742 DOI: 10.1109/tmi.2020.2991295] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Anatomical and quantum noise inhibits detection of malignancies in clinical images such as in digital mammography (DM), digital breast tomosynthesis (DBT) and breast CT (bCT). In this work, we examine the relative influence and interactions of these two types of noise on the task of low contrast mass detectability in DBT. We show how the changing levels of quantum noise contributes to the estimated power-law slope β by changing DBT acquisition parameters as well as with spatial filtering like an adaptive Weiner filtering. Finally, we examine via human observer LROC studies whether power spectral parameters obtained from DBT images correlate with mass detectability in those images. Our results show that lower values of power-law slope β can result from heightened quantum noise or image artifacts and do not necessarily imply reduced anatomical noise or improved signal detectability for the given imaging system. These results strengthen the argument that when power-law magnitude K is varying, β is less relevant to lesion detectability. Our preliminary results also point to K values having strong correlation to human observer performance, at least for the task shown in this paper. As a byproduct of these main results, we also show that while changes in acquisition geometry can improve mass detectability, the use of efficient filters like an adaptive Weiner filtering can significantly improve the detection of low contrast masses in DBT.
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Abadi E, Segars WP, Tsui BMW, Kinahan PE, Bottenus N, Frangi AF, Maidment A, Lo J, Samei E. Virtual clinical trials in medical imaging: a review. J Med Imaging (Bellingham) 2020; 7:042805. [PMID: 32313817 PMCID: PMC7148435 DOI: 10.1117/1.jmi.7.4.042805] [Citation(s) in RCA: 73] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2019] [Accepted: 03/23/2020] [Indexed: 12/13/2022] Open
Abstract
The accelerating complexity and variety of medical imaging devices and methods have outpaced the ability to evaluate and optimize their design and clinical use. This is a significant and increasing challenge for both scientific investigations and clinical applications. Evaluations would ideally be done using clinical imaging trials. These experiments, however, are often not practical due to ethical limitations, expense, time requirements, or lack of ground truth. Virtual clinical trials (VCTs) (also known as in silico imaging trials or virtual imaging trials) offer an alternative means to efficiently evaluate medical imaging technologies virtually. They do so by simulating the patients, imaging systems, and interpreters. The field of VCTs has been constantly advanced over the past decades in multiple areas. We summarize the major developments and current status of the field of VCTs in medical imaging. We review the core components of a VCT: computational phantoms, simulators of different imaging modalities, and interpretation models. We also highlight some of the applications of VCTs across various imaging modalities.
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Affiliation(s)
- Ehsan Abadi
- Duke University, Department of Radiology, Durham, North Carolina, United States
| | - William P. Segars
- Duke University, Department of Radiology, Durham, North Carolina, United States
| | - Benjamin M. W. Tsui
- Johns Hopkins University, Department of Radiology, Baltimore, Maryland, United States
| | - Paul E. Kinahan
- University of Washington, Department of Radiology, Seattle, Washington, United States
| | - Nick Bottenus
- Duke University, Department of Biomedical Engineering, Durham, North Carolina, United States
- University of Colorado Boulder, Department of Mechanical Engineering, Boulder, Colorado, United States
| | - Alejandro F. Frangi
- University of Leeds, School of Computing, Leeds, United Kingdom
- University of Leeds, School of Medicine, Leeds, United Kingdom
| | - Andrew Maidment
- University of Pennsylvania, Department of Radiology, Philadelphia, Pennsylvania, United States
| | - Joseph Lo
- Duke University, Department of Radiology, Durham, North Carolina, United States
| | - Ehsan Samei
- Duke University, Department of Radiology, Durham, North Carolina, United States
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8
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Lee C, Han M, Baek J. Human observer performance on in-plane digital breast tomosynthesis images: Effects of reconstruction filters and data acquisition angles on signal detection. PLoS One 2020; 15:e0229915. [PMID: 32163472 PMCID: PMC7067468 DOI: 10.1371/journal.pone.0229915] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2019] [Accepted: 02/17/2020] [Indexed: 11/29/2022] Open
Abstract
For digital breast tomosynthesis (DBT) systems, we investigate the effects of the reconstruction filters for different data acquisition angles on signal detection. We simulated a breast phantom with a 30% volume glandular fraction (VGF) of breast anatomy using the power law spectrum and modeled the breast mass as a spherical object with a 1 mm diameter. Projection data were acquired using two different data acquisition angles and numbers of projection view pairs, and in-plane breast images were reconstructed using the Feldkamp-Davis-Kress (FDK) algorithm with three different reconstruction filter schemes. To measure the ability to detect a signal, we conducted the human observer study with a binary detection task and compared the signal detectability of human to that of channelized Hotelling observer (CHO) with Laguerre-Gauss (LG) channels and dense difference-of-Gaussian (D-DOG) channels. We also measured the contrast-to-noise ratio (CNR), signal power spectrum (SPS), and β values of the anatomical noise power spectrum (NPS) to show the association between human observer performance and these traditional metrics. Our results show that using a slice thickness (ST) filter degraded the signal detection performance of human observers at the same data acquisition angle. This could be predicted by D-DOG CHO with internal noise, but the correlation between the traditional metrics and signal detectability was not observed in this work.
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Affiliation(s)
- Changwoo Lee
- Center for Medical Convergence Metrology, Korea Research Institute of Standards and Science (KRISS), Daejeon, South Korea
| | - Minah Han
- School of Integrated Technology and Yonsei Institute of Convergence Technology, Yonsei University, Incheon, South Korea
| | - Jongduk Baek
- School of Integrated Technology and Yonsei Institute of Convergence Technology, Yonsei University, Incheon, South Korea
- * E-mail:
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9
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Gunnell ET, Franceschi DK, Inscoe CR, Hartman A, Goralski JL, Ceppe A, Handly B, Sams C, Fordham LA, Lu J, Zhou O, Lee YZ. Initial clinical evaluation of stationary digital chest tomosynthesis in adult patients with cystic fibrosis. Eur Radiol 2019; 29:1665-1673. [PMID: 30255248 PMCID: PMC6896210 DOI: 10.1007/s00330-018-5703-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2018] [Revised: 07/19/2018] [Accepted: 07/31/2018] [Indexed: 01/26/2023]
Abstract
OBJECTIVE The imaging evaluation of cystic fibrosis currently relies on chest radiography or computed tomography. Recently, digital chest tomosynthesis has been proposed as an alternative. We have developed a stationary digital chest tomosynthesis (s-DCT) system based on a carbon nanotube (CNT) linear x-ray source array. This system enables tomographic imaging without movement of the x-ray tube and allows for physiological gating. The goal of this study was to evaluate the feasibility of clinical CF imaging with the s-DCT system. MATERIALS AND METHODS CF patients undergoing clinically indicated chest radiography were recruited for the study and imaged on the s-DCT system. Three board-certified radiologists reviewed both the CXR and s-DCT images for image quality relevant to CF. CF disease severity was assessed by Brasfield score on CXR and chest tomosynthesis score on s-DCT. Disease severity measures were also evaluated against subject pulmonary function tests. RESULTS Fourteen patients underwent s-DCT imaging within 72 h of their chest radiograph imaging. Readers scored the visualization of proximal bronchi, small airways and vascular pattern higher on s-DCT than CXR. Correlation between the averaged Brasfield score and averaged tomosynthesis disease severity score for CF was -0.73, p = 0.0033. The CF disease severity score system for tomosynthesis had high correlation with FEV1 (r = -0.685) and FEF 25-75% (r = -0.719) as well as good correlation with FVC (r = -0.582). CONCLUSION We demonstrate the potential of CNT x-ray-based s-DCT for use in the evaluation of cystic fibrosis disease status in the first clinical study of s-DCT. KEY POINTS • Carbon nanotube-based linear array x-ray tomosynthesis systems have the potential to provide diagnostically relevant information for patients with cystic fibrosis without the need for a moving gantry. • Despite the short angular span in this prototype system, lung features such as the proximal bronchi, small airways and pulmonary vasculature have improved visualization on s-DCT compared with CXR. Further improvements are anticipated with longer linear x-ray array tubes. • Evaluation of disease severity in CF patients is possible with s-DCT, yielding improved visualization of important lung features and high correlation with pulmonary function tests at a relatively low dose.
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Affiliation(s)
- Elias Taylor Gunnell
- School of Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA.
| | - Dora K Franceschi
- School of Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA
| | - Christina R Inscoe
- Department of Physics and Astronomy, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA
| | - Allison Hartman
- Department of Physics and Astronomy, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA
| | - Jennifer L Goralski
- Marsico Lung Institute, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA
- Division of Pulmonary and Critical Care Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA
- Division of Pediatric Pulmonology, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA
| | - Agathe Ceppe
- Marsico Lung Institute, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA
| | - Brian Handly
- Department of Radiology, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA
| | - Cassandra Sams
- Department of Radiology, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA
| | - Lynn Ansley Fordham
- Department of Radiology, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA
| | - Jianping Lu
- Department of Physics and Astronomy, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA
| | - Otto Zhou
- Department of Physics and Astronomy, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA
| | - Yueh Z Lee
- Department of Physics and Astronomy, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA
- Marsico Lung Institute, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA
- Department of Radiology, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA
- Lineberger Comprehensive Cancer Center, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA
- Biomedical Research Imaging Center, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA
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Rose SD, Sidky EY, Reiser I, Pan X. Imaging of fiber-like structures in digital breast tomosynthesis. J Med Imaging (Bellingham) 2019; 6:031404. [PMID: 30662927 DOI: 10.1117/1.jmi.6.3.031404] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2018] [Accepted: 12/10/2018] [Indexed: 11/14/2022] Open
Abstract
Fiber-like features are an important aspect of breast imaging. Vessels and ducts are present in all breast images, and spiculations radiating from a mass can indicate malignancy. Accordingly, fiber objects are one of the three types of signals used in the American College of Radiology digital mammography (ACR-DM) accreditation phantom. Our work focuses on the image properties of fiber-like structures in digital breast tomosynthesis (DBT) and how image reconstruction can affect their appearance. The impact of DBT image reconstruction algorithm and regularization strength on the conspicuity of fiber-like signals of various orientations is investigated in simulation. A metric is developed to characterize this orientation dependence and allow for quantitative comparison of algorithms and associated parameters in the context of imaging fiber signals. The imaging properties of fibers, characterized in simulation, are then demonstrated in detail with physical DBT data of the ACR-DM phantom. The characterization of imaging of fiber signals is used to explain features of an actual clinical DBT case. For the algorithms investigated, at low regularization setting, the results show a striking variation in conspicuity as a function of orientation in the viewing plane. In particular, the conspicuity of fibers nearly aligned with the plane of the x-ray source trajectory is decreased relative to more obliquely oriented fibers. Increasing regularization strength mitigates this orientation dependence at the cost of increasing depth blur of these structures.
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Affiliation(s)
- Sean D Rose
- University of Wisconsin, Department of Medical Physics, Madison, Wisconsin, United States
| | - Emil Y Sidky
- University of Chicago, Department of Radiology, Chicago, Illinois, United States
| | - Ingrid Reiser
- University of Chicago, Department of Radiology, Chicago, Illinois, United States
| | - Xiaochuan Pan
- University of Chicago, Department of Radiology, Chicago, Illinois, United States
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11
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Sujlana PS, Mahesh M, Vedantham S, Harvey SC, Mullen LA, Woods RW. Digital breast tomosynthesis: Image acquisition principles and artifacts. Clin Imaging 2018; 55:188-195. [PMID: 30236642 DOI: 10.1016/j.clinimag.2018.07.013] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2018] [Revised: 06/26/2018] [Accepted: 07/16/2018] [Indexed: 11/16/2022]
Abstract
Digital breast tomosynthesis (DBT) is a new technology that is being used more frequently for both breast cancer screening and diagnostic purposes and its utilization is likely to continue to increase over time. The major benefit of tomosynthesis over 2D-mammography is that it allows radiologists to view breast tissue using a three-dimensional dataset and improves diagnostic accuracy by facilitating differentiation of potentially malignant lesions from overlap of normal tissue. In addition, image processing techniques allow reconstruction of two dimensional synthesized mammograms (SM) from DBT data, which eliminates the need for acquiring two dimensional full field digital mammography (FFDM) in addition to tomosynthesis and thereby reduces the radiation dose. DBT systems incorporate a moveable x-ray tube, which moves in a prescribed way over a limited angular range to obtain three-dimensional data of patients' breasts, and utilize reconstruction algorithms. The limited angular range for DBT leads to incomplete sampling of the object, and a movable x-ray tube prolongs the imaging time, both of which make DBT and SM susceptible to artifacts. Understanding the etiology of these artifacts should help radiologists in reducing the number of artifacts and in differentiating a true finding from one related to an artifact, thus potentially decreasing recall rates and false positive rates. This is becoming especially important with increased incorporation of DBT in practices around the world. The goal of this article is to review the physics principles behind DBT systems and use these principles to explain the origin of artifacts that can limit diagnostic evaluation.
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Affiliation(s)
- Parvinder S Sujlana
- Johns Hopkins Medical Institutions, The Russell H. Morgan Department of Radiology and Radiological Science, 601 N. Wolfe Street, Baltimore, MD 21287, United States of America
| | - Mahadevappa Mahesh
- Johns Hopkins Medical Institutions, The Russell H. Morgan Department of Radiology and Radiological Science, 601 N. Wolfe Street, Baltimore, MD 21287, United States of America
| | - Srinivasan Vedantham
- University of Arizona - Banner University Medical Center, 1609 N. Warren Ave, Tucson, AZ 85719, United States of America
| | - Susan C Harvey
- Johns Hopkins Medical Institutions, The Russell H. Morgan Department of Radiology and Radiological Science, 601 N. Wolfe Street, Baltimore, MD 21287, United States of America
| | - Lisa A Mullen
- Johns Hopkins Medical Institutions, The Russell H. Morgan Department of Radiology and Radiological Science, 601 N. Wolfe Street, Baltimore, MD 21287, United States of America
| | - Ryan W Woods
- University of Wisconsin School of Medicine and Public Health, Department of Radiology, 600 Highland Avenue, Madison, WI 53792, United States of America.
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12
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Karbaschi Z, Gifford HC. Assessing CT acquisition parameters with visual-search model observers. J Med Imaging (Bellingham) 2018; 5:025501. [PMID: 29662920 DOI: 10.1117/1.jmi.5.2.025501] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2017] [Accepted: 03/12/2018] [Indexed: 11/14/2022] Open
Abstract
A principal difference between the channelized Hotelling (CH) and visual-search (VS) model observers is how they respond to noise texture in images. We compared the two observers in lesion-detection studies to evaluate linear and angular sampling parameters for CT. Simulated lung images were generated from a single two-dimensional mathematical torso phantom containing circular lesions of fixed radius and relative contrast. Projection datasets were produced for two detector pixel sizes and from 15 to 128 projections at 15 and 65 M counts per set. Filtered backprojection reconstructions were obtained with dimensions of [Formula: see text] and [Formula: see text]. A localization receiver operating characteristic study was conducted with two human observers, three single-feature VS observers, and a feature-adaptive VS observer. The effects of the sampling parameters on performance were similar for all of these observers. The CH observer, applied in location-known studies with and without background variability, was not affected by the variations in angular sampling. The two-stage VS framework was an effective modification of the CH observer for assessing the effects of noise texture on human-observer performance in this study.
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Affiliation(s)
- Zohreh Karbaschi
- University of Houston, Department of Biomedical Engineering, Houston, Texas, United States
| | - Howard C Gifford
- University of Houston, Department of Biomedical Engineering, Houston, Texas, United States
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Wen G, Chang HC, Reinhold J, Lo JY, Markey MK. Virtual assessment of stereoscopic viewing of digital breast tomosynthesis projection images. J Med Imaging (Bellingham) 2018; 5:015501. [PMID: 29376103 DOI: 10.1117/1.jmi.5.1.015501] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Accepted: 12/12/2017] [Indexed: 11/14/2022] Open
Abstract
Digital breast tomosynthesis (DBT) acquires a series of projection images from different angles as an x-ray source rotates around the breast. Such imaging geometry lends DBT naturally to stereoscopic viewing as two projection images with a reasonable separation angle can easily form a stereo pair. This simulation study assessed the efficacy of stereo viewing of DBT projection images. Three-dimensional computational breast phantoms with realistically shaped synthetic lesions were scanned by three simulated DBT systems. The projection images were combined into a sequence of stereo pairs and presented to a stereomatching-based model observer for deciding lesion presence. Signal-to-noise ratio was estimated, and the detection performance with stack viewing of reconstructed slices was the benchmark. We have shown that: (1) stereo viewing of projection images may underperform stack viewing of reconstructed slices for current DBT geometries; (2) DBT geometries may impact the efficacy of the two viewing modes differently: narrow-arc and wide-arc geometries may be better for stereo viewing and stack viewing, respectively; (3) the efficacy of stereo viewing may be more robust than stack viewing to reductions in dose. While in principle stereo viewing is potentially effective for visualizing DBT data, effective stereo viewing may require specifically optimized DBT image acquisition.
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Affiliation(s)
- Gezheng Wen
- University of Texas at Austin, Electrical and Computer Engineering, Austin, Texas, United States
| | - Ho-Chang Chang
- University of Texas at Austin, Electrical and Computer Engineering, Austin, Texas, United States
| | - Jacob Reinhold
- University of Texas at Austin, Applied Research Laboratories, Austin, Texas, United States
| | - Joseph Y Lo
- Duke University School of Medicine, Diagnostic Radiology, Durham, North Carolina, United States
| | - Mia K Markey
- University of Texas at Austin, Biomedical Engineering, Austin, Texas, United States.,University of Texas MD Anderson Cancer Center, Imaging Physics, Houston, Texas, United States
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14
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Zhao C, Kanicki J. Task-Based Modeling of a 5k Ultra-High-Resolution Medical Imaging System for Digital Breast Tomosynthesis. IEEE TRANSACTIONS ON MEDICAL IMAGING 2017; 36:1820-1831. [PMID: 28436856 DOI: 10.1109/tmi.2017.2695982] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
High-resolution, low-noise X-ray detectors based on CMOS active pixel sensor (APS) technology have demonstrated superior imaging performance for digital breast tomosynthesis (DBT). This paper presents a task-based model for a high-resolution medical imaging system to evaluate its ability to detect simulated microcalcifications and masses as lesions for breast cancer. A 3-D cascaded system analysis for a 50- [Formula: see text] pixel pitch CMOS APS X-ray detector was integrated with an object task function, a medical imaging display model, and the human eye contrast sensitivity function to calculate the detectability index and area under the ROC curve (AUC). It was demonstrated that the display pixel pitch and zoom factor should be optimized to improve the AUC for detecting small microcalcifications. In addition, detector electronic noise of smaller than 300 e- and a high display maximum luminance (>1000 cd/cm 2) are desirable to distinguish microcalcifications of [Formula: see text] in size. For low contrast mass detection, a medical imaging display with a minimum of 12-bit gray levels is recommended to realize accurate luminance levels. A wide projection angle range of greater than ±30° in combination with the image gray level magnification could improve the mass detectability especially when the anatomical background noise is high. On the other hand, a narrower projection angle range below ±20° can improve the small, high contrast object detection. Due to the low mass contrast and luminance, the ambient luminance should be controlled below 5 cd/ [Formula: see text]. Task-based modeling provides important firsthand imaging performance of the high-resolution CMOS-based medical imaging system that is still at early stage development for DBT. The modeling results could guide the prototype design and clinical studies in the future.
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Calliste J, Wu G, Laganis PE, Spronk D, Jafari H, Olson K, Gao B, Lee YZ, Zhou O, Lu J. Second generation stationary digital breast tomosynthesis system with faster scan time and wider angular span. Med Phys 2017; 44:4482-4495. [PMID: 28569999 DOI: 10.1002/mp.12393] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2016] [Revised: 04/18/2017] [Accepted: 04/21/2017] [Indexed: 01/04/2023] Open
Abstract
PURPOSE The aim of this study was to characterize a new generation stationary digital breast tomosynthesis system with higher tube flux and increased angular span over a first generation system. METHODS The linear CNT x-ray source was designed, built, and evaluated to determine its performance parameters. The second generation system was then constructed using the CNT x-ray source and a Hologic gantry. Upon construction, test objects and phantoms were used to characterize system resolution as measured by the modulation transfer function (MTF), and artifact spread function (ASF). RESULTS The results indicated that the linear CNT x-ray source was capable of stable operation at a tube potential of 49 kVp, and measured focal spot sizes showed source-to-source consistency with a nominal focal spot size of 1.1 mm. After construction, the second generation (Gen 2) system exhibited entrance surface air kerma rates two times greater the previous s-DBT system. System in-plane resolution as measured by the MTF is 7.7 cycles/mm, compared to 6.7 cycles/mm for the Gen 1 system. As expected, an increase in the z-axis depth resolution was observed, with a decrease in the ASF from 4.30 mm to 2.35 mm moving from the Gen 1 system to the Gen 2 system as result of an increased angular span. CONCLUSIONS The results indicate that the Gen 2 stationary digital breast tomosynthesis system, which has a larger angular span, increased entrance surface air kerma, and faster image acquisition time over the Gen 1 s-DBT system, results in higher resolution images. With the detector operating at full resolution, the Gen 2 s-DBT system can achieve an in-plane resolution of 7.7 cycles per mm, which is better than the current commercial DBT systems today, and may potentially result in better patient diagnosis.
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Affiliation(s)
- Jabari Calliste
- Department of Applied Physical Sciences, University of North Carolina at Chapel Hill, 120 E. Cameron Avenue, Chapel Hill, 27599, USA
| | - Gongting Wu
- Department of Physics and Astronomy, University of North Carolina at Chapel Hill, 120 E. Cameron Avenue, Chapel Hill, 27599, USA
| | - Philip E Laganis
- XinRay Systems, Inc., Research Triangle Park, Morrisville, NC, 27709, USA
| | - Derrek Spronk
- XinRay Systems, Inc., Research Triangle Park, Morrisville, NC, 27709, USA
| | - Houman Jafari
- XinRay Systems, Inc., Research Triangle Park, Morrisville, NC, 27709, USA
| | - Kyle Olson
- XinRay Systems, Inc., Research Triangle Park, Morrisville, NC, 27709, USA
| | - Bo Gao
- XinRay Systems, Inc., Research Triangle Park, Morrisville, NC, 27709, USA
| | - Yueh Z Lee
- Department of Radiology, University of North Carolina at Chapel Hill, 101 Manning Drive, Chapel Hill, 27514, USA
| | - Otto Zhou
- Department of Applied Physical Sciences, University of North Carolina at Chapel Hill, 120 E. Cameron Avenue, Chapel Hill, 27599, USA.,Department of Physics and Astronomy, University of North Carolina at Chapel Hill, 120 E. Cameron Avenue, Chapel Hill, 27599, USA.,University of North Carolina at Chapel Hill, Lineberger Cancer Center, 101 Manning Drive, Chapel Hill, 27514, USA
| | - Jianping Lu
- Department of Physics and Astronomy, University of North Carolina at Chapel Hill, 120 E. Cameron Avenue, Chapel Hill, 27599, USA
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Zeng R, Badano A, Myers KJ. Optimization of digital breast tomosynthesis (DBT) acquisition parameters for human observers: effect of reconstruction algorithms. Phys Med Biol 2017; 62:2598-2611. [PMID: 28151728 DOI: 10.1088/1361-6560/aa5ddc] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
We showed in our earlier work that the choice of reconstruction methods does not affect the optimization of DBT acquisition parameters (angular span and number of views) using simulated breast phantom images in detecting lesions with a channelized Hotelling observer (CHO). In this work we investigate whether the model-observer based conclusion is valid when using humans to interpret images. We used previously generated DBT breast phantom images and recruited human readers to find the optimal geometry settings associated with two reconstruction algorithms, filtered back projection (FBP) and simultaneous algebraic reconstruction technique (SART). The human reader results show that image quality trends as a function of the acquisition parameters are consistent between FBP and SART reconstructions. The consistent trends confirm that the optimization of DBT system geometry is insensitive to the choice of reconstruction algorithm. The results also show that humans perform better in SART reconstructed images than in FBP reconstructed images. In addition, we applied CHOs with three commonly used channel models, Laguerre-Gauss (LG) channels, square (SQR) channels and sparse difference-of-Gaussian (sDOG) channels. We found that LG channels predict human performance trends better than SQR and sDOG channel models for the task of detecting lesions in tomosynthesis backgrounds. Overall, this work confirms that the choice of reconstruction algorithm is not critical for optimizing DBT system acquisition parameters.
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Wen G, Markey MK, Park S. Model observer design for multi-signal detection in the presence of anatomical noise. Phys Med Biol 2017; 62:1396-1415. [DOI: 10.1088/1361-6560/aa51e9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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18
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Cockmartin L, Marshall NW, Zhang G, Lemmens K, Shaheen E, Van Ongeval C, Fredenberg E, Dance DR, Salvagnini E, Michielsen K, Bosmans H. Design and application of a structured phantom for detection performance comparison between breast tomosynthesis and digital mammography. Phys Med Biol 2017; 62:758-780. [PMID: 28072573 DOI: 10.1088/1361-6560/aa5407] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
This paper introduces and applies a structured phantom with inserted target objects for the comparison of detection performance of digital breast tomosynthesis (DBT) against 2D full field digital mammography (FFDM). The phantom consists of a 48 mm thick breast-shaped polymethyl methacrylate (PMMA) container filled with water and PMMA spheres of different diameters. Three-dimensionally (3D) printed spiculated masses (diameter range: 3.8-9.7 mm) and non-spiculated masses (1.6-6.2 mm) along with microcalcifications (90-250 µm) were inserted as targets. Reproducibility of the phantom application was studied on a single system using 30 acquisitions. Next, the phantom was evaluated on five different combined FFDM & DBT systems and target detection was compared for FFDM and DBT modes. Ten phantom images in both FFDM and DBT modes were acquired on these 5 systems using automatic exposure control. Five readers evaluated target detectability. Images were read with the four-alternative forced-choice (4-AFC) paradigm, with always one segment including a target and 3 normal background segments. The percentage of correct responses (PC) was assessed based on 10 trials of each reader for each object type, size and imaging modality. Additionally, detection threshold diameters at 62.5 PC were assessed via non-linear regression fitting of the psychometric curve. The reproducibility study showed no significant differences in PC values. Evaluation of target detection in FFDM showed that microcalcification detection thresholds ranged between 110 and 118 µm and were similar compared to the detection in DBT (range of 106-158 µm). In DBT, detection of both mass types increased significantly (p = 0.0001 and p = 0.0002 for non-spiculated and spiculated masses respectively) compared to FFDM, achieving almost 100% detection for all spiculated mass diameters. In conclusion, a structured phantom with inserted targets was able to show evidence for detectability differences between FFDM and DBT modes for five commercial systems. This phantom has potential for application in task-based assessment at acceptance and commissioning testing of DBT systems.
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Affiliation(s)
- L Cockmartin
- Department of Radiology, UZ Leuven, Herestraat 49, B-3000 Leuven, Belgium. Department of Imaging and Pathology, Division of Medical Physics and Quality Assessment, KU Leuven, Herestraat 49, B-3000 Leuven, Belgium
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Gifford HC, Liang Z, Das M. Visual-search observers for assessing tomographic x-ray image quality. Med Phys 2016; 43:1563-75. [PMID: 26936739 DOI: 10.1118/1.4942485] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
PURPOSE Mathematical model observers commonly used for diagnostic image-quality assessments in x-ray imaging research are generally constrained to relatively simple detection tasks due to their need for statistical prior information. Visual-search (VS) model observers that employ morphological features in sequential search and analysis stages have less need for such information and fewer task constraints. The authors compared four VS observers against human observers and an existing scanning model observer in a pilot study that quantified how mass detection and localization in simulated digital breast tomosynthesis (DBT) can be affected by the number P of acquired projections. METHODS Digital breast phantoms with embedded spherical masses provided single-target cases for a localization receiver operating characteristic (LROC) study. DBT projection sets based on an acquisition arc of 60° were generated for values of P between 3 and 51. DBT volumes were reconstructed using filtered backprojection with a constant 3D Butterworth postfilter; extracted 2D slices were used as test images. Three imaging physicists participated as observers. A scanning channelized nonprewhitening (CNPW) observer had knowledge of the mean lesion-absent images. The VS observers computed an initial single-feature search statistic that identified candidate locations as local maxima of either a template matched-filter (MF) image or a gradient-template MF (GMF) image. Search inefficiencies that modified the statistic were also considered. Subsequent VS candidate analyses were carried out with (i) the CNPW statistical discriminant and (ii) the discriminant computed from GMF training images. These location-invariant discriminants did not utilize covariance information. All observers read 36 training images and 108 study images per P value. Performance was scored in terms of area under the LROC curve. RESULTS Average human-observer performance was stable for P between 7 and 35. In the absence of search inefficiencies, the VS models based on the GMF analysis provided the best correlation (Pearson ρ ≥ 0.62) with the human results. The CNPW-based VS observers deviated from the humans primarily at lower values of P. In this limited study, search inefficiencies allowed for good quantitative agreement with the humans for most of the VS observers. CONCLUSIONS The computationally efficient training requirements for the VS observer are suitable for high-resolution imaging, indicating that the observer framework has the potential to overcome important task limitations of current model observers for x-ray applications.
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Affiliation(s)
- Howard C Gifford
- Department of Biomedical Engineering, University of Houston, Houston, Texas 77204
| | - Zhihua Liang
- Department of Biomedical Engineering, University of Houston, Houston, Texas 77204 and Department of Physics, University of Houston, Houston, Texas 77204
| | - Mini Das
- Department of Biomedical Engineering, University of Houston, Houston, Texas 77204 and Department of Physics, University of Houston, Houston, Texas 77204
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Michielsen K, Nuyts J, Cockmartin L, Marshall N, Bosmans H. Design of a model observer to evaluate calcification detectability in breast tomosynthesis and application to smoothing prior optimization. Med Phys 2016; 43:6577. [DOI: 10.1118/1.4967268] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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21
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Park S, Zhang G, Myers KJ. Comparison of Channel Methods and Observer Models for the Task-Based Assessment of Multi-Projection Imaging in the Presence of Structured Anatomical Noise. IEEE TRANSACTIONS ON MEDICAL IMAGING 2016; 35:1431-1442. [PMID: 26742128 DOI: 10.1109/tmi.2016.2515027] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Although Laguerre-Gauss (LG) channels are often used for the task-based assessment of multi-projection imaging, LG channels may not be the most reliable in providing performance trends as a function of system or object parameters for all situations. Partial least squares (PLS) channels are more flexible in adapting to background and signal data statistics and were shown to be more efficient for detection tasks involving 2D non-Gaussian random backgrounds (Witten , 2010). In this work, we investigate ways of incorporating spatial correlations in the multi-projection data space using 2D LG channels and two implementations of PLS in the channelized version of the 3D projection Hotelling observer (Park , 2010) (3Dp CHO). Our task is to detect spherical and elliptical 3D signals in the angular projections of a structured breast phantom ensemble. The single PLS (sPLS) incorporates the spatial correlation within each projection, whereas the combined PLS (cPLS) incorporates the spatial correlations both within each of and across the projections. The 3Dp CHO-R indirectly incorporates the spatial correlation from the response space (R), whereas the 3Dp CHO-C from the channel space (C). The 3Dp CHO-R-sPLS has potential to be a good surrogate observer when either sample size is small or one training set is used for training both PLS channels and observer. So does the 3Dp CHO-C-cPLS when the sample size is large enough to have a good sized independent set for training PLS channels. Lastly a stack of 2D LG channels used as 3D channels in the CHO-C model showed the capability of incorporating the spatial correlation between the multiple angular projections.
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Dustler M, Petersson H, Timberg P. VOLUMETRIC LOCALISATION OF DENSE BREAST TISSUE USING BREAST TOMOSYNTHESIS DATA. RADIATION PROTECTION DOSIMETRY 2016; 169:392-397. [PMID: 26922782 DOI: 10.1093/rpd/ncw022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
This study attempted to use combined data from reconstructed digital breast tomosynthesis (DBT) volumes and density estimation of projection images to localise dense tissue inside the breast, using the assumption that the breast can be treated as consisting of only two types of tissue: fibroglandular (dense) and adipose (fatty). To be able to verify results, software breast phantoms generated using fractal Perlin noise were employed. Projection images were created using the PENELOPE Monte Carlo package. Dense tissue volume was estimated from the central projection image. The density image was used to determine the number of dense voxels at each pixel location, which were then placed using the DBT image as a template. The method proved capable of accurately determining the composition of 75±5 % of voxels.
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Affiliation(s)
- M Dustler
- Medical Radiation Physics, Department of Translational Medicine, Lund University, SUS, SE-205 02 Malmö, Sweden
| | - H Petersson
- Medical Radiation Physics, Department of Translational Medicine, Lund University, SUS, SE-205 02 Malmö, Sweden
| | - P Timberg
- Medical Radiation Physics, Department of Translational Medicine, Lund University, SUS, SE-205 02 Malmö, Sweden
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Rodríguez-Ruiz A, Castillo M, Garayoa J, Chevalier M. Evaluation of the technical performance of three different commercial digital breast tomosynthesis systems in the clinical environment. Phys Med 2016; 32:767-77. [PMID: 27180118 DOI: 10.1016/j.ejmp.2016.05.001] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/25/2015] [Revised: 04/13/2016] [Accepted: 05/04/2016] [Indexed: 10/21/2022] Open
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Armstrong H, Jones B, Miften M. Characterization of image quality in digital tomosynthesis for radiotherapy applications. Biomed Phys Eng Express 2016. [DOI: 10.1088/2057-1976/2/2/025013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Zhong Y, Lai CJ, Wang T, Shaw CC. A dual-view digital tomosynthesis imaging technique for improved chest imaging. Med Phys 2015; 42:5238-51. [PMID: 26328973 DOI: 10.1118/1.4928214] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
PURPOSE Digital tomosynthesis (DTS) has been shown to be useful for reducing the overlapping of abnormalities with anatomical structures at various depth levels along the posterior-anterior (PA) direction in chest radiography. However, DTS provides crude three-dimensional (3D) images that have poor resolution in the lateral view and can only be displayed with reasonable quality in the PA view. Furthermore, the spillover of high-contrast objects from off-fulcrum planes generates artifacts that may impede the diagnostic use of the DTS images. In this paper, the authors describe and demonstrate the use of a dual-view DTS technique to improve the accuracy of the reconstructed volume image data for more accurate rendition of the anatomy and slice images with improved resolution and reduced artifacts, thus allowing the 3D image data to be viewed in views other than the PA view. METHODS With the dual-view DTS technique, limited angle scans are performed and projection images are acquired in two orthogonal views: PA and lateral. The dual-view projection data are used together to reconstruct 3D images using the maximum likelihood expectation maximization iterative algorithm. In this study, projection images were simulated or experimentally acquired over 360° using the scanning geometry for cone beam computed tomography (CBCT). While all projections were used to reconstruct CBCT images, selected projections were extracted and used to reconstruct single- and dual-view DTS images for comparison with the CBCT images. For realistic demonstration and comparison, a digital chest phantom derived from clinical CT images was used for the simulation study. An anthropomorphic chest phantom was imaged for the experimental study. The resultant dual-view DTS images were visually compared with the single-view DTS images and CBCT images for the presence of image artifacts and accuracy of CT numbers and anatomy and quantitatively compared with root-mean-square-deviation (RMSD) values computed using the digital chest phantom or the CBCT images as the reference in the simulation and experimental study, respectively. High-contrast wires with vertical, oblique, and horizontal orientations in a PA view plane were also imaged to investigate the spatial resolutions and how the wire signals spread in the PA view and lateral view slice images. RESULTS Both the digital phantom images (simulated) and the anthropomorphic phantom images (experimentally generated) demonstrated that the dual-view DTS technique resulted in improved spatial resolution in the depth (PA) direction, more accurate representation of the anatomy, and significantly reduced artifacts. The RMSD values corroborate well with visual observations with substantially lower RMSD values measured for the dual-view DTS images as compared to those measured for the single-view DTS images. The imaging experiment with the high-contrast wires shows that while the vertical and oblique wires could be resolved in the lateral view in both single- and dual-view DTS images, the horizontal wire could only be resolved in the dual-view DTS images. This indicates that with single-view DTS, the wire signals spread liberally to off-fulcrum planes and generated wire shadow there. CONCLUSIONS The authors have demonstrated both visually and quantitatively that the dual-view DTS technique can be used to achieve more accurate rendition of the anatomy and to obtain slice images with improved resolution and reduced artifacts as compared to the single-view DTS technique, thus allowing the 3D image data to be viewed in views other than the PA view. These advantages could make the dual-view DTS technique useful in situations where better separation of the objects-of-interest from the off-fulcrum structures or more accurate 3D rendition of the anatomy are required while a regular CT examination is undesirable due to radiation dose considerations.
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Affiliation(s)
- Yuncheng Zhong
- Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77054
| | - Chao-Jen Lai
- Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77054
| | - Tianpeng Wang
- Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77054
| | - Chris C Shaw
- Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77054
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A Case for Wide-Angle Breast Tomosynthesis. Acad Radiol 2015; 22:860-9. [PMID: 25920335 DOI: 10.1016/j.acra.2015.02.015] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2014] [Revised: 02/13/2015] [Accepted: 02/18/2015] [Indexed: 11/27/2022]
Abstract
RATIONALES AND OBJECTIVES Conventional mammography is largely limited by superimposed anatomy. Digital breast tomosynthesis (DBT) and computed tomography (CT) alleviate this limitation but with added out-of-plane artifacts or limited chest wall coverage. This article presents a wide-angle breast tomosynthesis (WBT), aimed to provide a practical solution to these limitations, and offers an initial study of its utility in comparison with DBT and CT using a singular evaluation platform. MATERIALS AND METHODS Using an anthropomorphic virtual breast phantom, a Monte Carlo code modeled a breast imaging system for three modalities of DBT, WBT, and breast CT (44°, 99°, and 198° total angle range, respectively) at four breast compression levels, all at a constant mean glandular dose level of 1.5 mGy. Reconstructed volumes were generated using iterative reconstruction methods. Lesion detectability was estimated using contrast-to-noise ratio and a channelized Hotelling observer model in terms of the area under the receiver operating characteristic (AUC). RESULTS Results showed improved detection with increased angular span and compression. The estimated AUCs for WBT were similar to that of CT. Comparative performance averaged over all thicknesses between CT and WBT was 4.3 ± 3.0%, whereas that between WBT and DBT was 5.6 ± 1.0%. At compression levels reflective of the modality (7-, 5-, and 4-cm thickness for CT, WBT, and DBT, respectively), WBT yielded an AUC comparable to CT (performance difference of 1.2%) but superior to DBT (performance difference of 5.5%). CONCLUSIONS The proposed imaging modality showed significant advantages over conventional DBT. WBT exhibited superior imaging performance over DBT at lower compression levels, highlighting further potential for reduced breast compression.
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Barrett HH, Myers KJ, Hoeschen C, Kupinski MA, Little MP. Task-based measures of image quality and their relation to radiation dose and patient risk. Phys Med Biol 2015; 60:R1-75. [PMID: 25564960 PMCID: PMC4318357 DOI: 10.1088/0031-9155/60/2/r1] [Citation(s) in RCA: 79] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The theory of task-based assessment of image quality is reviewed in the context of imaging with ionizing radiation, and objective figures of merit (FOMs) for image quality are summarized. The variation of the FOMs with the task, the observer and especially with the mean number of photons recorded in the image is discussed. Then various standard methods for specifying radiation dose are reviewed and related to the mean number of photons in the image and hence to image quality. Current knowledge of the relation between local radiation dose and the risk of various adverse effects is summarized, and some graphical depictions of the tradeoffs between image quality and risk are introduced. Then various dose-reduction strategies are discussed in terms of their effect on task-based measures of image quality.
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Affiliation(s)
- Harrison H. Barrett
- College of Optical Sciences, University of Arizona, Tucson, AZ
- Center for Gamma-Ray Imaging, Department of Medical Imaging, University of Arizona, Tucson, AZ
| | - Kyle J. Myers
- Division of Imaging and Applied Mathematics, Office of Scientific and Engineering Laboratories, Center for Devices and Radiological Health, Food and Drug Administration, Silver Spring, MD
| | - Christoph Hoeschen
- Department of Electrical Engineering and Information Technology, Otto-von-Guericke University, Magdeburg, Germany
- Research unit Medical Radiation Physics and Diagnostics, Helmholtz Zentrum München, Oberschleissheim, Germany
| | - Matthew A. Kupinski
- College of Optical Sciences, University of Arizona, Tucson, AZ
- Center for Gamma-Ray Imaging, Department of Medical Imaging, University of Arizona, Tucson, AZ
| | - Mark P. Little
- Division of Cancer Epidemiology and Genetics, Radiation Epidemiology Branch, National Cancer Institute, Bethesda, MD
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Zeng R, Park S, Bakic P, Myers KJ. Evaluating the sensitivity of the optimization of acquisition geometry to the choice of reconstruction algorithm in digital breast tomosynthesis through a simulation study. Phys Med Biol 2015; 60:1259-88. [PMID: 25591807 DOI: 10.1088/0031-9155/60/3/1259] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Due to the limited number of views and limited angular span in digital breast tomosynthesis (DBT), the acquisition geometry design is an important factor that affects the image quality. Therefore, intensive studies have been conducted regarding the optimization of the acquisition geometry. However, different reconstruction algorithms were used in most of the reported studies. Because each type of reconstruction algorithm can provide images with its own image resolution, noise properties and artifact appearance, it is unclear whether the optimal geometries concluded for the DBT system in one study can be generalized to the DBT systems with a reconstruction algorithm different to the one applied in that study. Hence, we investigated the effect of the reconstruction algorithm on the optimization of acquisition geometry parameters through carefully designed simulation studies. Our results show that using various reconstruction algorithms, including the filtered back-projection, the simultaneous algebraic reconstruction technique, the maximum-likelihood method and the total-variation regularized least-square method, gave similar performance trends for the acquisition parameters for detecting lesions. The consistency of system ranking indicates that the choice of the reconstruction algorithm may not be critical for DBT system geometry optimization.
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Affiliation(s)
- Rongping Zeng
- Division of Imaging, Diagonistics and Software Reliability, Office of Science and Engineering Laboratories, Center for Devices and Radiological Health, FDA, Silver Spring, MD 20993, USA
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Goodsitt MM, Chan HP, Schmitz A, Zelakiewicz S, Telang S, Hadjiiski L, Watcharotone K, Helvie MA, Paramagul C, Neal C, Christodoulou E, Larson SC, Carson PL. Digital breast tomosynthesis: studies of the effects of acquisition geometry on contrast-to-noise ratio and observer preference of low-contrast objects in breast phantom images. Phys Med Biol 2014; 59:5883-902. [PMID: 25211509 PMCID: PMC4264665 DOI: 10.1088/0031-9155/59/19/5883] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The effect of acquisition geometry in digital breast tomosynthesis was evaluated with studies of contrast-to-noise ratios (CNRs) and observer preference. Contrast-detail (CD) test objects in 5 cm thick phantoms with breast-like backgrounds were imaged. Twelve different angular acquisitions (average glandular dose for each ~1.1 mGy) were performed ranging from narrow angle 16° with 17 projection views (16d17p) to wide angle 64d17p. Focal slices of SART-reconstructed images of the CD arrays were selected for CNR computations and the reader preference study. For the latter, pairs of images obtained with different acquisition geometries were randomized and scored by 7 trained readers. The total scores for all images and readings for each acquisition geometry were compared as were the CNRs. In general, readers preferred images acquired with wide angle as opposed to narrow angle geometries. The mean percent preferred was highly correlated with tomosynthesis angle (R = 0.91). The highest scoring geometries were 60d21p (95%), 64d17p (80%), and 48d17p (72%); the lowest scoring were 16d17p (4%), 24d9p (17%) and 24d13p (33%). The measured CNRs for the various acquisitions showed much overlap but were overall highest for wide-angle acquisitions. Finally, the mean reader scores were well correlated with the mean CNRs (R = 0.83).
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Affiliation(s)
| | - Heang-Ping Chan
- University of Michigan, Department of Radiology, Ann Arbor, MI
| | | | | | - Santosh Telang
- University of Michigan, Department of Radiology, Ann Arbor, MI
| | | | - Kuanwong Watcharotone
- Michigan Institute for Clinical & Health Research (MICHR), University of Michigan, Ann Arbor, MI
| | - Mark A. Helvie
- University of Michigan, Department of Radiology, Ann Arbor, MI
| | | | - Colleen Neal
- University of Michigan, Department of Radiology, Ann Arbor, MI
| | | | | | - Paul L. Carson
- University of Michigan, Department of Radiology, Ann Arbor, MI
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Zhao C, Kanicki J. Amorphous In-Ga-Zn-O thin-film transistor active pixel sensor x-ray imager for digital breast tomosynthesis. Med Phys 2014; 41:091902. [DOI: 10.1118/1.4892382] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
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31
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Chan HP, Goodsitt MM, Helvie MA, Zelakiewicz S, Schmitz A, Noroozian M, Paramagul C, Roubidoux MA, Nees AV, Neal CH, Carson P, Lu Y, Hadjiiski L, Wei J. Digital breast tomosynthesis: observer performance of clustered microcalcification detection on breast phantom images acquired with an experimental system using variable scan angles, angular increments, and number of projection views. Radiology 2014; 273:675-85. [PMID: 25007048 DOI: 10.1148/radiol.14132722] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
PURPOSE To investigate the dependence of microcalcification cluster detectability on tomographic scan angle, angular increment, and number of projection views acquired at digital breast tomosynthesis ( DBT digital breast tomosynthesis ). MATERIALS AND METHODS A prototype DBT digital breast tomosynthesis system operated in step-and-shoot mode was used to image breast phantoms. Four 5-cm-thick phantoms embedded with 81 simulated microcalcification clusters of three speck sizes (subtle, medium, and obvious) were imaged by using a rhodium target and rhodium filter with 29 kV, 50 mAs, and seven acquisition protocols. Fixed angular increments were used in four protocols (denoted as scan angle, angular increment, and number of projection views, respectively: 16°, 1°, and 17; 24°, 3°, and nine; 30°, 3°, and 11; and 60°, 3°, and 21), and variable increments were used in three (40°, variable, and 13; 40°, variable, and 15; and 60°, variable, and 21). The reconstructed DBT digital breast tomosynthesis images were interpreted by six radiologists who located the microcalcification clusters and rated their conspicuity. RESULTS The mean sensitivity for detection of subtle clusters ranged from 80% (22.5 of 28) to 96% (26.8 of 28) for the seven DBT digital breast tomosynthesis protocols; the highest sensitivity was achieved with the 16°, 1°, and 17 protocol (96%), but the difference was significant only for the 60°, 3°, and 21 protocol (80%, P < .002) and did not reach significance for the other five protocols (P = .01-.15). The mean sensitivity for detection of medium and obvious clusters ranged from 97% (28.2 of 29) to 100% (24 of 24), but the differences fell short of significance (P = .08 to >.99). The conspicuity of subtle and medium clusters with the 16°, 1°, and 17 protocol was rated higher than those with other protocols; the differences were significant for subtle clusters with the 24°, 3°, and nine protocol and for medium clusters with 24°, 3°, and nine; 30°, 3°, and 11; 60°, 3° and 21; and 60°, variable, and 21 protocols (P < .002). CONCLUSION With imaging that did not include x-ray source motion or patient motion during acquisition of the projection views, narrow-angle DBT digital breast tomosynthesis provided higher sensitivity and conspicuity than wide-angle DBT digital breast tomosynthesis for subtle microcalcification clusters.
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Affiliation(s)
- Heang-Ping Chan
- From the Department of Radiology, University of Michigan Medical Center, 1500 E Medical Center Dr, Ann Arbor, MI 48109-5842 (H.P.C., M.M.G., M.A.H., M.N., C.P., M.A.R., A.V.N., C.H.N., P.C., Y.L., L.H., J.W.); and GE Global Research, Niskayuna, NY (S.Z., A.S.)
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Zhang Y, Leng S, Yu L, Carter RE, McCollough CH. Correlation between human and model observer performance for discrimination task in CT. Phys Med Biol 2014; 59:3389-404. [PMID: 24875060 DOI: 10.1088/0031-9155/59/13/3389] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Although physical metrics can objectively characterize computed tomography (CT) image quality, quantitative approaches to predict human observer performance are more accurate and clinically relevant. This study compared a modified channelized Hotelling model observer (CHO) with human observers in a shape discrimination task. Eight lesion-mimicking rods (two contrasts, two sizes and two shapes) were inserted into a 35 × 26 cm(2) torso-shaped water phantom and scanned 100 times on a 128-slice CT scanner at five dose levels. CT images were reconstructed using filtered backprojection (FBP) and iterative reconstruction (IR) techniques. Two-alternative forced choice studies were constructed with hexagonal and circular rod images put side-by-side in a randomized order. An edge mask was introduced to CHO to reflect the human observers' emphasis on lesion boundaries in discriminating shape. For small size lesions, the performance of three human observers and the modified CHO was highly correlated across lesion contrasts, CT doses and reconstruction algorithms; while for large size lesions, a ceiling effect was observed for both human and model observers' performance at high doses. Our result suggests the potential of CHO to predict human observer performance for both FBP and IR. For this shape discrimination task with uniform background, IR significantly improved human and model observer performance compared to FBP, with the amount of improvement depending on lesion size, contrast and dose.
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Affiliation(s)
- Yi Zhang
- Department of Radiology, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA
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Park HS, Kim YS, Kim HJ, Choi YW, Choi JG. Optimization of configuration parameters in a newly developed digital breast tomosynthesis system. JOURNAL OF RADIATION RESEARCH 2014; 55:589-599. [PMID: 24297999 PMCID: PMC4014153 DOI: 10.1093/jrr/rrt130] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/08/2012] [Revised: 10/15/2013] [Accepted: 10/16/2013] [Indexed: 06/02/2023]
Abstract
The purpose of the present work was to investigate the effects of variable projection-view (PV) and angular dose (AD) distributions on the reconstructed image quality for improving microcalcification detection. The PV densities at central and peripheral sites were varied through the distribution of 21 PVs acquired over ± 25° angular range. To vary the AD distribution, 7 PVs in the central region were targeted with two, four and six times the peripheral dose, and the number of central PVs receiving four times the peripheral dose was increased from 3 to 11. The contrast-to-noise ratio (CNR) for in-focus plane quality and the full width at half maximum (FWHM) of artifact spread function (ASF) for resolution in the z-direction were used. Although the ASF improved with increasing PV densities at two peripheral sites, the CNRs were inferior to those obtained with other subsets. With increasing PV density in the central area, the vertical resolution decreased but the CNR increased. Although increasing the central PV or AD concentrations improved image quality, excessive central densities reduced image quality by increasing noise in peripheral views.
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Affiliation(s)
- Hye-Suk Park
- Department of Radiological Science and Research Institute of Health Science, Yonsei University, #137 Backun Hall, 234 Maeji, Heungup, Wonju, Gangwon 220-710, South Korea
| | - Ye-Seul Kim
- Department of Radiological Science and Research Institute of Health Science, Yonsei University, #137 Backun Hall, 234 Maeji, Heungup, Wonju, Gangwon 220-710, South Korea
| | - Hee-Joung Kim
- Department of Radiological Science and Research Institute of Health Science, Yonsei University, #137 Backun Hall, 234 Maeji, Heungup, Wonju, Gangwon 220-710, South Korea
| | - Young-Wook Choi
- Korea Electrotechnology Research Institute (KERI), Ansan, Geongki 426-170, South Korea
| | - Jae-Gu Choi
- Korea Electrotechnology Research Institute (KERI), Ansan, Geongki 426-170, South Korea
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Young S, Bakic PR, Myers KJ, Jennings RJ, Park S. A virtual trial framework for quantifying the detectability of masses in breast tomosynthesis projection data. Med Phys 2013; 40:051914. [PMID: 23635284 DOI: 10.1118/1.4800501] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
PURPOSE Digital breast tomosynthesis (DBT) is a promising breast cancer screening tool that has already begun making inroads into clinical practice. However, there is ongoing debate over how to quantitatively evaluate and optimize these systems, because different definitions of image quality can lead to different optimal design strategies. Powerful and accurate tools are desired to extend our understanding of DBT system optimization and validate published design principles. METHODS The authors developed a virtual trial framework for task-specific DBT assessment that uses digital phantoms, open-source x-ray transport codes, and a projection-space, spatial-domain observer model for quantitative system evaluation. The authors considered evaluation of reconstruction algorithms as a separate problem and focused on the information content in the raw, unfiltered projection images. Specifically, the authors investigated the effects of scan angle and number of angular projections on detectability of a small (3 mm diameter) signal embedded in randomly-varying anatomical backgrounds. Detectability was measured by the area under the receiver-operating characteristic curve (AUC). Experiments were repeated for three test cases where the detectability-limiting factor was anatomical variability, quantum noise, or electronic noise. The authors also juxtaposed the virtual trial framework with other published studies to illustrate its advantages and disadvantages. RESULTS The large number of variables in a virtual DBT study make it difficult to directly compare different authors' results, so each result must be interpreted within the context of the specific virtual trial framework. The following results apply to 25% density phantoms with 5.15 cm compressed thickness and 500 μm(3) voxels (larger 500 μm(2) detector pixels were used to avoid voxel-edge artifacts): 1. For raw, unfiltered projection images in the anatomical-variability-limited regime, AUC appeared to remain constant or increase slightly with scan angle. 2. In the same regime, when the authors fixed the scan angle, AUC increased asymptotically with the number of projections. The threshold number of projections for asymptotic AUC performance depended on the scan angle. In the quantum- and electronic-noise dominant regimes, AUC behaviors as a function of scan angle and number of projections sometimes differed from the anatomy-limited regime. For example, with a fixed scan angle, AUC generally decreased with the number of projections in the electronic-noise dominant regime. These results are intended to demonstrate the capabilities of the virtual trial framework, not to be used as optimization rules for DBT. CONCLUSIONS The authors have demonstrated a novel simulation framework and tools for evaluating DBT systems in an objective, task-specific manner. This framework facilitates further investigation of image quality tradeoffs in DBT.
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Affiliation(s)
- Stefano Young
- College of Optical Sciences, University of Arizona, Tucson, Arizona 85721, USA
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Park HS, Kim YS, Kim HJ, Choi JG, Choi YW. Optimization of the key imaging parameters for detection of microcalcifications in a newly developed digital breast tomosynthesis system. Clin Imaging 2013; 37:993-9. [DOI: 10.1016/j.clinimag.2013.06.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2012] [Revised: 03/26/2013] [Accepted: 06/11/2013] [Indexed: 10/26/2022]
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Tucker AW, Lu J, Zhou O. Dependency of image quality on system configuration parameters in a stationary digital breast tomosynthesis system. Med Phys 2013; 40:031917. [PMID: 23464332 DOI: 10.1118/1.4792296] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
PURPOSE In principle, a stationary digital breast tomosynthesis (s-DBT) system has better image quality when compared to continuous motion DBT systems due to zero motion blur of the source. The authors have developed a s-DBT system by using a linear carbon nanotube x-ray source array. The purpose of the current study was to quantitatively evaluate the performance of the s-DBT system; and investigate the dependence of imaging quality on the system configuration parameters. METHODS Physical phantoms were used to assess the image quality of each configuration including inplane resolution as measured by the modulation transfer function (MTF), inplane contrast as measured by the signal difference to noise ratio (SdNR), and depth resolution as measured by the z-axis artifact spread function. Five parameters were varied to create five groups of configurations: (1) total angular span; (2) total number of projection images; (3) distribution of exposure (mAs) across the projection images; (4) entrance dose; (5) detector pixel size. RESULTS It was found that the z-axis depth resolution increased with the total angular span but was insensitive to the number of projection images, mAs distribution, entrance dose, and detector pixel size. The SdNR was not affected by the angular span or the number of projection images. A decrease in SdNR was observed when the mAs was not evenly distributed across the projection images. As expected, the SdNR increased with entrance dose and when larger pixel sizes were used. For a given detector pixel size, the inplane resolution was found to be insensitive to the total angular span, number of projection images, mAs distribution, and entrance dose. A 25% increase in the MTF was observed when the detector was operating in full resolution mode (70 μm pixel size) compared to 2 × 2 binned mode (140 μm pixel size). CONCLUSIONS The results suggest that the optimal imaging configuration for a s-DBT system is a large angular span, an intermittent number of projection views, and a uniform mAs distribution over all views. With the detector operating at full resolution, a stationary DBT system can achieve an inplane resolution of 5.1 cycles per mm, which is significantly better than continuous motion DBT systems.
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Affiliation(s)
- Andrew W Tucker
- Department of Biomedical Engineering, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
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Levakhina YM, Duschka RL, Vogt FM, Barkhausen J, Buzug TM. A dual-axis tilt acquisition geometry for digital musculoskeletal tomosynthesis. Phys Med Biol 2013; 58:4827-48. [DOI: 10.1088/0031-9155/58/14/4827] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Sechopoulos I. A review of breast tomosynthesis. Part I. The image acquisition process. Med Phys 2013; 40:014301. [PMID: 23298126 PMCID: PMC3548887 DOI: 10.1118/1.4770279] [Citation(s) in RCA: 240] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2012] [Revised: 11/16/2012] [Accepted: 11/16/2012] [Indexed: 12/11/2022] Open
Abstract
Mammography is a very well-established imaging modality for the early detection and diagnosis of breast cancer. However, since the introduction of digital imaging to the realm of radiology, more advanced, and especially tomographic imaging methods have been made possible. One of these methods, breast tomosynthesis, has finally been introduced to the clinic for routine everyday use, with potential to in the future replace mammography for screening for breast cancer. In this two part paper, the extensive research performed during the development of breast tomosynthesis is reviewed, with a focus on the research addressing the medical physics aspects of this imaging modality. This first paper will review the research performed on the issues relevant to the image acquisition process, including system design, optimization of geometry and technique, x-ray scatter, and radiation dose. The companion to this paper will review all other aspects of breast tomosynthesis imaging, including the reconstruction process.
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Affiliation(s)
- Ioannis Sechopoulos
- Department of Radiology and Imaging Sciences, Emory University, Atlanta, GA, USA
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40
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Shaheen E, Van Ongeval C, Zanca F, Cockmartin L, Marshall N, Jacobs J, Young KC, R Dance D, Bosmans H. The simulation of 3D microcalcification clusters in 2D digital mammography and breast tomosynthesis. Med Phys 2012; 38:6659-71. [PMID: 22149848 DOI: 10.1118/1.3662868] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
PURPOSE This work proposes a new method of building 3D models of microcalcification clusters and describes the validation of their realistic appearance when simulated into 2D digital mammograms and into breast tomosynthesis images. METHODS A micro-CT unit was used to scan 23 breast biopsy specimens of microcalcification clusters with malignant and benign characteristics and their 3D reconstructed datasets were segmented to obtain 3D models of microcalcification clusters. These models were then adjusted for the x-ray spectrum used and for the system resolution and simulated into 2D projection images to obtain mammograms after image processing and into tomographic sequences of projection images, which were then reconstructed to form 3D tomosynthesis datasets. Six radiologists were asked to distinguish between 40 real and 40 simulated clusters of microcalcifications in two separate studies on 2D mammography and tomosynthesis datasets. Receiver operating characteristic (ROC) analysis was used to test the ability of each observer to distinguish between simulated and real microcalcification clusters. The kappa statistic was applied to assess how often the individual simulated and real microcalcification clusters had received similar scores ("agreement") on their realistic appearance in both modalities. This analysis was performed for all readers and for the real and the simulated group of microcalcification clusters separately. "Poor" agreement would reflect radiologists' confusion between simulated and real clusters, i.e., lesions not systematically evaluated in both modalities as either simulated or real, and would therefore be interpreted as a success of the present models. RESULTS The area under the ROC curve, averaged over the observers, was 0.55 (95% confidence interval [0.44, 0.66]) for the 2D study, and 0.46 (95% confidence interval [0.29, 0.64]) for the tomosynthesis study, indicating no statistically significant difference between real and simulated lesions (p > 0.05). Agreement between allocated lesion scores for 2D mammography and those for the tomosynthesis series was poor. CONCLUSIONS The realistic appearance of the 3D models of microcalcification clusters, whether malignant or benign clusters, was confirmed for 2D digital mammography images and the breast tomosynthesis datasets; this database of clusters is suitable for use in future observer performance studies related to the detectability of microcalcification clusters. Such studies include comparing 2D digital mammography to breast tomosynthesis and comparing different reconstruction algorithms.
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Affiliation(s)
- Eman Shaheen
- Department of Radiology, University Hospitals Leuven, Herestraat 49, 3000 Leuven, Belgium.
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Lu Y, Chan HP, Wei J, Goodsitt M, Carson PL, Hadjiiski L, Schmitz A, Eberhard JW, Claus BEH. Image quality of microcalcifications in digital breast tomosynthesis: effects of projection-view distributions. Med Phys 2011; 38:5703-12. [PMID: 21992385 DOI: 10.1118/1.3637492] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE To analyze the effects of projection-view (PV) distribution on the contrast and spatial blurring of microcalcifications on the tomosynthesized slices (X-Y plane) and along the depth (Z) direction for the same radiation dose in digital breast tomosynthesis (DBT). METHODS A GE GEN2 prototype DBT system was used for acquisition of DBT scans. The system acquires PV images from 21 angles in 3° increments over a ±30° range. From these acquired PV images, the authors selected six subsets of PV images to simulate DBT of different angular ranges and angular increments. The number of PV images in each subset was fixed at 11 to simulate a constant total dose. These different PV distributions were subjectively divided into three categories: uniform group, nonuniform central group, and nonuniform extreme group with different angular ranges and angular increments. The simultaneous algebraic reconstruction technique (SART) was applied to each subset to reconstruct the DBT slices. A selective diffusion regularization method was employed to suppress noise. The image quality of microcalcifications in the reconstructed DBTs with different PV distributions was compared using the DBT scans of an American College of Radiology phantom and three human subjects. The contrast-to-noise ratio (CNR) and the full width at half maximum (FWHM) of the line profiles of microcalcifications within their in-focus DBT slices (parallel to detector plane) and the FWHMs of the interplane artifact spread function (ASF) in the Z-direction (perpendicular to detector plane) were used as image quality measures. RESULTS The results indicate that DBT acquired with a large angular range or, for an equal angular range,with a large fraction of PVs at large angles yielded superior ASF with smaller FWHM in the Z-direction. PV distributions with a narrow angular range or a large fraction of PVs at small angles had stronger interplane artifacts. In the X-Y focal planes, the effect of PV distributions on spatial blurring depended on the directions. In the X-direction (perpendicular to the chestwall), the normalized line profiles of the calcifications reconstructed with the different PV distributions were similar in terms of FWHM; the differences in the FWHMs between the different PV distributions were less than half a pixel. In the Y-direction (x-ray source motion), the normalized line profiles of the calcifications reconstructed with PVs acquired with a narrow angular range or a large fraction of PVs at small angles had smaller FWHMs and thus less blurring of the line profiles. In addition, PV distributions with a narrow angular range or a large fraction of PVs at small angles yielded slightly higher CNR than those with a wide angular range for small, subtle microcalcifications; however, PV distributions had no obvious effect on CNR for relatively large microcalcifications. CONCLUSIONS PV distributions affect the image quality of DBT. The relative importance of the impact depends on the characteristics of the signal and the direction (perpendicular or parallel) relative to the direction of x-ray source motion. For a given number of PVs, the angular range and the distribution of the PVs affect the degree of in-plane and interplane blurring in opposite ways. The design of the scan parameters of tomosynthesis systems would require proper consideration of the characteristics of the signals of interest and the potential trade-off of the image quality of different types of signals.
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Affiliation(s)
- Yao Lu
- Department of Radiology, University of Michigan, Ann Arbor, MI 48109-5842, USA.
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42
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Baker JA, Lo JY. Breast tomosynthesis: state-of-the-art and review of the literature. Acad Radiol 2011; 18:1298-310. [PMID: 21893296 DOI: 10.1016/j.acra.2011.06.011] [Citation(s) in RCA: 104] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2011] [Revised: 05/07/2011] [Accepted: 06/20/2011] [Indexed: 10/17/2022]
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Tingberg A, Zackrisson S. Digital mammography and tomosynthesis for breast cancer diagnosis. ACTA ACUST UNITED AC 2011; 5:517-26. [DOI: 10.1517/17530059.2011.616492] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
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Webb LJ, Samei E, Lo JY, Baker JA, Ghate SV, Kim C, Soo MS, Walsh R. Comparative performance of multiview stereoscopic and mammographic display modalities for breast lesion detection. Med Phys 2011; 38:1972-80. [PMID: 21626930 DOI: 10.1118/1.3562901] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Mammography is known to be one of the most difficult radiographic exams to interpret. Mammography has important limitations, including the superposition of normal tissue that can obscure a mass, chance alignment of normal tissue to mimic a true lesion and the inability to derive volumetric information. It has been shown that stereomammography can overcome these deficiencies by showing that layers of normal tissue lay at different depths. If standard stereomammography (i.e., a single stereoscopic pair consisting of two projection images) can significantly improve lesion detection, how will multiview stereoscopy (MVS), where many projection images are used, compare to mammography? The aim of this study was to assess the relative performance of MVS compared to mammography for breast mass detection. METHODS The MVS image sets consisted of the 25 raw projection images acquired over an arc of approximately 45 degrees using a Siemens prototype breast tomosynthesis system. The mammograms were acquired using a commercial Siemens FFDM system. The raw data were taken from both of these systems for 27 cases and realistic simulated mass lesions were added to duplicates of the 27 images at the same local contrast. The images with lesions (27 mammography and 27 MVS) and the images without lesions (27 mammography and 27 MVS) were then postprocessed to provide comparable and representative image appearance across the two modalities. All 108 image sets were shown to five full-time breast imaging radiologists in random order on a state-of-the-art stereoscopic display. The observers were asked to give a confidence rating for each image (0 for lesion definitely not present, 100 for lesion definitely present). The ratings were then compiled and processed using ROC and variance analysis. RESULTS The mean AUC for the five observers was 0.614 +/- 0.055 for mammography and 0.778 +/- 0.052 for multiview stereoscopy. The difference of 0.164 +/- 0.065 was statistically significant with a p-value of 0.0148. CONCLUSIONS The differences in the AUCs and the p-value suggest that multiview stereoscopy has a statistically significant advantage over mammography in the detection of simulated breast masses. This highlights the dominance of anatomical noise compared to quantum noise for breast mass detection. It also shows that significant lesion detection can be achieved with MVS without any of the artifacts associated with tomosynthesis.
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Affiliation(s)
- Lincoln J Webb
- Medical Physics Graduate Program, Carl E. Ravin Advanced Imaging Laboratories, Duke University, Durham, North Carolina 27705, USA
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Chen B, Shorey J, Saunders RS, Richard S, Thompson J, Nolte LW, Samei E. An anthropomorphic breast model for breast imaging simulation and optimization. Acad Radiol 2011; 18:536-46. [PMID: 21397528 DOI: 10.1016/j.acra.2010.11.009] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2010] [Revised: 11/09/2010] [Accepted: 11/09/2010] [Indexed: 11/19/2022]
Abstract
RATIONALE AND OBJECTIVES Optimization studies for x-ray-based breast imaging systems using computer simulation can greatly benefit from a phantom capable of modeling varying anatomical variability across different patients. This study aimed to develop a three-dimensional phantom model with realistic and randomizable anatomical features. MATERIALS AND METHODS A voxelized breast model was developed consisting of an outer layer of skin and subcutaneous fat, a mixture of glandular and adipose, stochastically generated ductal trees, masses, and microcalcifications. Randomized realization of the breast morphology provided a range of patient models. Compression models were included to represent the breast under various compression levels along different orientations. A Monte Carlo (MC) simulation code was adapted to simulate x-ray based imaging systems for the breast phantom. Simulated projections of the phantom at different angles were generated and reconstructed with iterative methods, simulating mammography, breast tomosynthesis, and computed tomography (CT) systems. Phantom dose maps were further generated for dosimetric evaluation. RESULTS Region of interest comparisons of simulated and real mammograms showed strong similarities in terms of appearance and features. Noise-power spectra of simulated mammographic images demonstrated that the phantom provided target properties for anatomical backgrounds. Reconstructed tomosynthesis and CT images and dose maps provided corresponding data from a single breast enabling optimization studies. Dosimetry result provided insight into the dose distribution difference between modalities and compression levels. CONCLUSION The anthropomorphic breast phantom, combined with the MC simulation platform, generated a realistic model for a breast imaging system. The developed platform is expected to provide a versatile and powerful framework for optimizing volumetric breast imaging systems.
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Affiliation(s)
- Baiyu Chen
- Medical Physics Graduate Program, Duke University, Durham, NC, 27705, USA
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Das M, Gifford HC, O'Connor JM, Glick SJ. Penalized maximum likelihood reconstruction for improved microcalcification detection in breast tomosynthesis. IEEE TRANSACTIONS ON MEDICAL IMAGING 2011; 30:904-14. [PMID: 21041158 PMCID: PMC3398486 DOI: 10.1109/tmi.2010.2089694] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
We examined the application of an iterative penalized maximum likelihood (PML) reconstruction method for improved detectability of microcalcifications (MCs) in digital breast tomosynthesis (DBT). Localized receiver operating characteristic (LROC) psychophysical studies with human observers and 2-D image slices were conducted to evaluate the performance of this reconstruction method and to compare its performance against the commonly used Feldkamp FBP algorithm. DBT projections were generated using rigorous computer simulations that included accurate modeling of the noise and detector blur. Acquisition dose levels of 0.7, 1.0, and 1.5 mGy in a 5-cm-thick compressed breast were tested. The defined task was to localize and detect MC clusters consisting of seven MCs. The individual MC diameter was 150 μm. Compressed-breast phantoms derived from CT images of actual mastectomy specimens provided realistic background structures for the detection task. Four observers each read 98 test images for each combination of reconstruction method and acquisition dose. All observers performed better with the PML images than with the FBP images. With the acquisition dose of 0.7 mGy, the average areas under the LROC curve (A(L)) for the PML and FBP algorithms were 0.69 and 0.43, respectively. For the 1.0-mGy dose, the values of A(L) were 0.93 (PML) and 0.7 (FBP), while the 1.5-mGy dose resulted in areas of 1.0 and 0.9, respectively, for the PML and FBP algorithms. A 2-D analysis of variance applied to the individual observer areas showed statistically significant differences (at a significance level of 0.05) between the reconstruction strategies at all three dose levels. There were no significant differences in observer performance for any of the dose levels.
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Affiliation(s)
- Mini Das
- Department of Radiology, University of Massachusetts Medical School, Worcester, MA 01655, USA.
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A novel approach to digital breast tomosynthesis for simultaneous acquisition of 2D and 3D images. Eur Radiol 2010; 21:1207-13. [PMID: 21193910 DOI: 10.1007/s00330-010-2041-y] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2010] [Revised: 10/06/2010] [Accepted: 10/28/2010] [Indexed: 10/18/2022]
Abstract
OBJECTIVE The complexity of anatomical structure within the breast represents the ultimate limit to signal detection on a mammogram. To increase lesion conspicuity Digital Breast Tomosynthesis (DBT) has been recently proposed and several manufacturers are currently performing clinical trials. In this study we investigate the potential of DBT with variable dose distribution by using a phantom in which details of interest are within a heterogeneous background. METHODS To compare the performance of a commercial digital mammography unit and a DBT prototype, 2D and 3D images of the breast phantom were obtained at similar dose levels. RESULTS As expected, DBT showed superior performance over digital mammography. Although certain details of interest are not detectable with digital mammography, DBT can reveal their signal by reducing the complexity of tissue structures. Additionally, the potential of the central projection in variable dose DBT is similar to the standard projection obtained with digital mammography. Finally, the uniform and variable dose approaches provided almost identical reconstructed slices. CONCLUSION This preliminary investigation demonstrates that breast tomosynthesis acquired with variable dose distribution exhibits inherent 3D reconstruction advantages for structure noise removal and provides a 2D projection with a physical image quality close to that of standard mammography.
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Burvall A, Barrett HH, Myers KJ, Dainty C. Singular-value decomposition of a tomosynthesis system. OPTICS EXPRESS 2010; 18:20699-711. [PMID: 20940966 PMCID: PMC2958053 DOI: 10.1364/oe.18.020699] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Tomosynthesis is an emerging technique with potential to replace mammography, since it gives 3D information at a relatively small increase in dose and cost. We present an analytical singular-value decomposition of a tomosynthesis system, which provides the measurement component of any given object. The method is demonstrated on an example object. The measurement component can be used as a reconstruction of the object, and can also be utilized in future observer studies of tomosynthesis image quality.
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Affiliation(s)
- Anna Burvall
- Biomedical and X-Ray Physics, Royal Institute of Technology, AlbaNova University Center, SE-10691 Stockholm, Sweden.
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Reiser I, Nishikawa RM. Task-based assessment of breast tomosynthesis: effect of acquisition parameters and quantum noise. Med Phys 2010; 37:1591-600. [PMID: 20443480 DOI: 10.1118/1.3357288] [Citation(s) in RCA: 105] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
PURPOSE Tomosynthesis is a promising modality for breast imaging. The appearance of the tomosynthesis reconstructed image is greatly affected by the choice of acquisition and reconstruction parameters. The purpose of this study was to investigate the limitations of tomosynthesis breast imaging due to scan parameters and quantum noise. Tomosynthesis image quality was assessed based on performance of a mathematical observer model in a signal-known exactly (SKE) detection task. METHODS SKE detectability (d') was estimated using a prewhitening observer model. Structured breast background was simulated using filtered noise. Detectability was estimated for designer nodules ranging from 0.05 to 0.8 cm in diameter. Tomosynthesis slices were reconstructed using iterative maximum-likelihood expectation-maximization. The tomosynthesis scan angle was varied between 15 degrees and 60 degrees, the number of views between 11 and 41 and the total number of x-ray quanta was infinity, 6 X 10(5), and 6 x 10(4). Detectability in tomosynthesis was compared to that in a single projection. RESULTS For constant angular sampling distance, increasing the angular scan range increased detectability for all signal sizes. Large-scale signals were little affected by quantum noise or angular sampling. For small-scale signals, quantum noise and insufficient angular sampling degraded detectability. At high quantum noise levels, angular step size of 3 degrees or below was sufficient to avoid image degradation. At lower quantum noise levels, increased angular sampling always resulted in increased detectability. The ratio of detectability in the tomosynthesis slice to that in a single projection exhibited a peak that shifted to larger signal sizes when the angular range increased. For a given angular range, the peak shifted toward smaller signals when the number of views was increased. The ratio was greater than unity for all conditions evaluated. CONCLUSION The effect of acquisition parameters on lesion detectability depends on signal size. Tomosynthesis scan angle had an effect on detectability for all signals sizes, while quantum noise and angular sampling only affected the detectability small-scale signals.
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Affiliation(s)
- I Reiser
- Department of Radiology, The University of Chicago, Chicago, Illinois 60637, USA.
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