1
|
Song H, Lee C, Baek J. Full 3-D modulation transfer function estimation of tomosynthesis system using modified Richardson-Lucy deconvolution. Med Phys 2024; 51:2510-2525. [PMID: 38011539 DOI: 10.1002/mp.16843] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2023] [Revised: 10/12/2023] [Accepted: 11/02/2023] [Indexed: 11/29/2023] Open
Abstract
BACKGROUND Tomosynthesis systems are three-dimensional (3-D) medical imaging devices that operate over limited acquisition angles using low radiation dosages. To measure the spatial resolution performance of a tomosynthesis system, the modulation transfer function (MTF) is widely used as a quantitative evaluation metric. PURPOSE We previously introduced a method to estimate the full 3-D MTF of a cone-beam computed tomography system using two-dimensional (2-D) Richardson-Lucy (RL) deconvolution with Tikhonov-Miller regularization. However, this method can not be applied directly to estimate the 3-D MTF of a tomosynthesis system, since the unique artifacts (i.e., shadow artifacts, spreading tails, directional blurring, and high-level noise) of the system produce several errors that lower the estimation performance. Varying positions of the negative pixels due to shadow artifacts and spreading tails cause inconsistent deconvolution performances at each of the directional projections, and the severe noise in the reconstructed images cause noise amplification during estimation. This work proposes several modifications to the previous method to resolve the inconsistent performance and noise amplification errors to increase the full 3-D MTF estimation accuracy. METHODS Three modifications were introduced to the 2-D RL deconvolution to prevent estimation errors and improve MTF estimation performance: non-negativity relaxation function, cost function to terminate the iterative process of RL deconvolution, and regularization strength for noise control. To validate the effectiveness of the proposed modifications, we reconstructed sphere phantoms from simulation and experimental tomosynthesis studies in the iso-center and offset-center positions as well as estimated the full 3-D MTFs using the previous and proposed methods. We compared the 3-D render images, central plane images, and center profiles of the estimated 3-D MTFs and calculated the full widths at half and tenth maximum for quantitative evaluation. RESULTS The previous method cannot estimate the full 3-D MTF of a tomosynthesis system; its inaccurate negative pixel relaxation produces circular-shaped errors, and the mean squared error based simple cost function for termination causes inconsistent estimation at each directional projection to diminish the clear edges of the low-frequency drop and missing sample regions. Noise amplification from lack of noise regularization is also seen in the previous method results. Compared to the previous method, the proposed method shows superior estimation performance at reducing errors in both the simulation and experimental studies regardless of object position. The proposed method preserves the low-frequency drop, missing sample regions from the limited acquisition angles, and missing cone region from the offset-center position; the estimated MTFs also show FWHM and FWTM values close to those of the ideal MTFs than with the previous method. CONCLUSIONS This work presents a method to estimate the full 3-D MTF of a tomosynthesis system. The proposed modifications prevent circular-shaped errors and noise amplification due to the geometry for limited acquisition angles and high noise levels. Compared to our previous method, the proposed scheme show better performance for estimating the 3-D MTF of the tomosynthesis system.
Collapse
Affiliation(s)
- Hoondong Song
- School of Integrated Technology, Yonsei University, Incheon, South Korea
| | - Changwoo Lee
- Medical Metrology Team, Korea Research Institute of Standards and Science (KRISS), Daejeon, South Korea
| | - Jongduk Baek
- Department of Artificial intelligence, College of Computing, Yonsei University, Seoul, South Korea
| |
Collapse
|
2
|
Marshall NW, Bosmans H. Performance evaluation of digital breast tomosynthesis systems: physical methods and experimental data. Phys Med Biol 2022; 67. [DOI: 10.1088/1361-6560/ac9a35] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2022] [Accepted: 10/13/2022] [Indexed: 11/17/2022]
Abstract
Abstract
Digital breast tomosynthesis (DBT) has become a well-established breast imaging technique, whose performance has been investigated in many clinical studies, including a number of prospective clinical trials. Results from these studies generally point to non-inferiority in terms of microcalcification detection and superior mass-lesion detection for DBT imaging compared to digital mammography (DM). This modality has become an essential tool in the clinic for assessment and ad-hoc screening but is not yet implemented in most breast screening programmes at a state or national level. While evidence on the clinical utility of DBT has been accumulating, there has also been progress in the development of methods for technical performance assessment and quality control of these imaging systems. DBT is a relatively complicated ‘pseudo-3D’ modality whose technical assessment poses a number of difficulties. This paper reviews methods for the technical performance assessment of DBT devices, starting at the component level in part one and leading up to discussion of system evaluation with physical test objects in part two. We provide some historical and basic theoretical perspective, often starting from methods developed for DM imaging. Data from a multi-vendor comparison are also included, acquired under the medical physics quality control protocol developed by EUREF and currently being consolidated by a European Federation of Organisations for Medical Physics working group. These data and associated methods can serve as a reference for the development of reference data and provide some context for clinical studies.
Collapse
|
3
|
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.
Collapse
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
| |
Collapse
|
4
|
Acciavatti RJ, Maidment ADA. Non-stationary model of oblique x-ray incidence in amorphous selenium detectors: I. Point spread function. Med Phys 2019; 46:494-504. [PMID: 30488462 PMCID: PMC6467228 DOI: 10.1002/mp.13313] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2018] [Revised: 10/02/2018] [Accepted: 11/16/2018] [Indexed: 01/05/2023] Open
Abstract
PURPOSE In previous work, a theoretical model of the point spread function (PSF) for oblique x-ray incidence in amorphous selenium (a-Se) detectors was proposed. The purpose of this paper is to develop a complementary model that includes two additional features. First, the incidence angle and the directionality of ray incidence are calculated at each position, assuming a divergent x-ray beam geometry. This approach allows the non-stationarity of the PSF to be modeled. Second, this paper develops a framework that is applicable to a digital system, unlike previous work which did not model the presence of a thin-film transistor (TFT) array. METHODS At each point on the detector, the incidence angle and the ray incidence direction are determined using ray tracing. Based on these calculations, an existing model for the PSF of the x-ray converter (Med Phys. 1995;22:365-374) is generalized to a non-stationary model. The PSF is convolved with the product of two rectangle functions, which model the sampling of the TFT array. The rectangle functions match the detector element (del) size in two dimensions. RESULTS It is shown that the PSF can be calculated in closed form. This solution is used to simulate a digital mammography (DM) system at two x-ray energies (20 and 40 keV). Based on the divergence of the x-ray beam, the direction of ray incidence varies with position. Along this direction, the PSF is broader than the reference rect function matching the del size. The broadening is more pronounced with increasing obliquity. At high energy, the PSF deviates more strongly from the reference rect function, indicating that there is more blurring. In addition, the PSF is calculated along the polar angle perpendicular to the ray incidence direction. For this polar angle, the shape of the PSF is dependent upon whether the ray incidence direction is parallel with the sides of the detector. If the ray incidence direction is parallel with either dimension, the PSF is a perfect rectangle function, matching the del size. However, if the ray incidence direction is at an oblique angle relative to the sides of the detector, the PSF is not rectangular. These results illustrate the non-stationarity of the PSF. CONCLUSIONS This paper demonstrates that an existing model of the PSF of a-Se detectors can be generalized to include the effects of non-stationarity and digitization. The PSF is determined in closed form. This solution offers the advantage of shorter computation time relative to approaches that use numerical methods. This model is a tool for simulating a-Se detectors in future work, such as in virtual clinical trials with computational phantoms.
Collapse
Affiliation(s)
- Raymond J. Acciavatti
- Department of RadiologyPerelman School of Medicine at the University of PennsylvaniaPhiladelphiaPA19104‐4206USA
| | - Andrew D. A. Maidment
- Department of RadiologyPerelman School of Medicine at the University of PennsylvaniaPhiladelphiaPA19104‐4206USA
| |
Collapse
|
5
|
Berggren K, Cederström B, Lundqvist M, Fredenberg E. Characterization of photon-counting multislit breast tomosynthesis. Med Phys 2017; 45:549-560. [DOI: 10.1002/mp.12684] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2016] [Revised: 11/10/2017] [Accepted: 11/10/2017] [Indexed: 12/11/2022] Open
Affiliation(s)
- Karl Berggren
- Physics of Medical Imaging; Royal Institute of Technology; AlbaNova University Center; 106 91 Stockholm Sweden
- Philips Mammography Solutions; 164 40 Kista Sweden
| | | | | | | |
Collapse
|
6
|
Howansky A, Peng B, Lubinsky AR, Zhao W. Deriving depth-dependent light escape efficiency and optical Swank factor from measured pulse height spectra of scintillators. Med Phys 2017; 44:847-860. [PMID: 28039881 DOI: 10.1002/mp.12083] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2016] [Revised: 11/28/2016] [Accepted: 12/22/2016] [Indexed: 01/04/2023] Open
Abstract
PURPOSE Pulse height spectroscopy has been used by investigators to deduce the imaging properties of scintillators. Pulse height spectra (PHS) are used to compute the Swank factor, which describes the variation in scintillator light output per x-ray interaction. The spread in PHS measured below the K-edge is related to the optical component of the Swank factor, i.e., variations in light escape efficiency from different depths of x-ray interaction in the scintillator, denoted ε¯(z). Optimizing scintillators for medical imaging applications requires understanding of these optical properties, as they determine tradeoffs between parameters such as x-ray absorption, light yield, and spatial resolution. This work develops a model for PHS acquisition such that the effect of measurement uncertainty can be removed. This method allows ε¯(z) to be quantified on an absolute scale and permits more accurate estimation of the optical Swank factor of scintillators. METHODS The pulse height spectroscopy acquisition chain was modeled as a linear system of stochastic gain stages. Analytical expressions were derived for signal and noise propagation through the PHS chain, accounting for deterministic and stochastic aspects of x-ray absorption, scintillation, and light detection with a photomultiplier tube. The derived expressions were used to calculate PHS of thallium-doped cesium iodide (CsI) scintillators using parameters that were measured, calculated, or known from literature. PHS were measured at 25 and 32 keV of CsI samples designed with an optically reflective or absorptive backing, with or without a fiber-optic faceplate (FOP), and with thicknesses ranging from 150-1000 μm. Measured PHS were compared with calculated PHS, then light escape model parameters were varied until measured and modeled results reached agreement. Resulting estimates of ε¯(z) were used to calculate each scintillator's optical Swank factor. RESULTS For scintillators of the same optical design, only minor differences in light escape efficiency were observed between samples with different thickness. As thickness increased, escape efficiency decreased by up to 20% for interactions furthest away from light collection. Optical design (i.e., backing and FOP) predominantly affected the magnitude and relative variation in ε¯(z). Depending on interaction depth and scintillator thickness, samples with an absorptive backing and FOP were estimated to yield 4.1-13.4 photons/keV. Samples with a reflective backing and FOP yielded 10.4-18.4 keV-1 , while those with a reflective backing and no FOP yielded 29.5-52.0 keV-1 . Optical Swank factors were approximately 0.9 and near-unity in samples featuring an absorptive or reflective backing, respectively. CONCLUSIONS This work uses a modeling approach to remove the noise introduced by the measurement apparatus from measured PHS. This method allows absolute quantification of ε¯(z) and more accurate estimation of the optical Swank factor of scintillators. The method was applied to CsI scintillators with different thickness and optical design, and determined that optical design more strongly affects ε¯(z) and Swank factor than differences in CsI thickness. Despite large variations in ε¯(z) between optical designs, the Swank factor of all evaluated samples is above 0.9. Information provided by this methodology can help validate Monte Carlo simulations of structured CsI and optimize scintillator design for x-ray imaging applications.
Collapse
Affiliation(s)
- Adrian Howansky
- Department of Radiology, State University of New York at Stony Brook, Stony Brook, NY, 11790-8460, USA
| | - Boyu Peng
- Department of Radiology, State University of New York at Stony Brook, Stony Brook, NY, 11790-8460, USA
| | - Anthony R Lubinsky
- Department of Radiology, State University of New York at Stony Brook, Stony Brook, NY, 11790-8460, USA
| | - Wei Zhao
- Department of Radiology, State University of New York at Stony Brook, Stony Brook, NY, 11790-8460, USA
| |
Collapse
|
7
|
Vedantham S, Karellas A, Vijayaraghavan GR, Kopans DB. Digital Breast Tomosynthesis: State of the Art. Radiology 2016; 277:663-84. [PMID: 26599926 DOI: 10.1148/radiol.2015141303] [Citation(s) in RCA: 126] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
This topical review on digital breast tomosynthesis (DBT) is provided with the intent of describing the state of the art in terms of technology, results from recent clinical studies, advanced applications, and ongoing efforts to develop multimodality imaging systems that include DBT. Particular emphasis is placed on clinical studies. The observations of increase in cancer detection rates, particularly for invasive cancers, and the reduction in false-positive rates with DBT in prospective trials indicate its benefit for breast cancer screening. Retrospective multireader multicase studies show either noninferiority or superiority of DBT compared with mammography. Methods to curtail radiation dose are of importance. (©) RSNA, 2015.
Collapse
Affiliation(s)
- Srinivasan Vedantham
- From the Department of Radiology, University of Massachusetts Medical School, 55 Lake Ave North, Worcester, MA 01655 (S.V., A.K., G.R.V.); and Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, Mass (D.B.K.)
| | - Andrew Karellas
- From the Department of Radiology, University of Massachusetts Medical School, 55 Lake Ave North, Worcester, MA 01655 (S.V., A.K., G.R.V.); and Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, Mass (D.B.K.)
| | - Gopal R Vijayaraghavan
- From the Department of Radiology, University of Massachusetts Medical School, 55 Lake Ave North, Worcester, MA 01655 (S.V., A.K., G.R.V.); and Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, Mass (D.B.K.)
| | - Daniel B Kopans
- From the Department of Radiology, University of Massachusetts Medical School, 55 Lake Ave North, Worcester, MA 01655 (S.V., A.K., G.R.V.); and Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, Mass (D.B.K.)
| |
Collapse
|
8
|
Lee C, Baek J. A Sphere Phantom Approach to Measure Directional Modulation Transfer Functions for Tomosynthesis Imaging Systems. IEEE TRANSACTIONS ON MEDICAL IMAGING 2016; 35:871-881. [PMID: 26571519 DOI: 10.1109/tmi.2015.2498930] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We propose a sphere phantom approach to measure spatially varying directional modulation transfer functions (MTFs) for tomosynthesis imaging systems. Since the reconstructed tomosynthesis images contain significant artifacts, traditional background detrending techniques may not be effective to estimate the background trends accurately, which is essential to acquire sphere only data. A background detrending technique optimized for local volumes with different cone angles is presented. To measure directional MTFs, we calculate plane integrals of ideal sphere phantom and sphere only data. To minimize the effects of the high level of noise in tomosynthesis images, Richardson-Lucy deconvolution with Tikhonov-Miller is used to estimate directional plane spread function (PlSF). Then, directional MTFs are calculated by taking the modulus of the Fourier transform of the directional PlSFs. The measured directional MTFs are compared with the ideal directional MTFs calculated from a simulated point object. Our results show that the proposed method reliably measures directional MTFs along any desired directions, especially near low frequency regions.
Collapse
|
9
|
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).
Collapse
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
| |
Collapse
|
10
|
Liu H, Chakrabarti K, Kaczmarek RV, Benevides L, Gu S, Kyprianou IS. Evaluation of clinical full field digital mammography with the task specific system-model-based Fourier Hotelling observer (SMFHO) SNR. Med Phys 2014; 41:051907. [PMID: 24784386 DOI: 10.1118/1.4870377] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
PURPOSE The purpose of this work is to evaluate the performance of the image acquisition chain of clinical full field digital mammography (FFDM) systems by quantifying their image quality, and how well the desired information is captured by the images. METHODS The authors present a practical methodology to evaluate FFDM using the task specific system-model-based Fourier Hotelling observer (SMFHO) signal to noise ratio (SNR), which evaluates the signal and noise transfer characteristics of FFDM systems in the presence of a uniform polymethyl methacrylate phantom that models the attenuation of a 6 cm thick 20/80 breast (20% glandular/80% adipose). The authors model the system performance using the generalized modulation transfer function, which accounts for scatter blur and focal spot unsharpness, and the generalized noise power spectrum, both estimated with the phantom placed in the field of view. Using the system model, the authors were able to estimate system detectability for a series of simulated disk signals with various diameters and thicknesses, quantified by a SMFHO SNR map. Contrast-detail (CD) curves were generated from the SNR map and adjusted using an estimate of the human observer efficiency, without performing time-consuming human reader studies. Using the SMFHO method the authors compared two FFDM systems, the GE Senographe DS and Hologic Selenia FFDM systems, which use indirect and direct detectors, respectively. RESULTS Even though the two FFDM systems have different resolutions, noise properties, detector technologies, and antiscatter grids, the authors found no significant difference between them in terms of detectability for a given signal detection task. The authors also compared the performance between the two image acquisition modes (fine view and standard) of the GE Senographe DS system, and concluded that there is no significant difference when evaluated by the SMFHO. The estimated human observer efficiency was 30 ± 5% when compared to the SMFHO. The results showed good agreement when compared to other model observers as well as previously published human observer data. CONCLUSIONS This method generates CD curves from the SMFHO SNR that can be used as figures of merit for evaluating the image acquisition performance of clinical FFDM systems. It provides a way of creating an empirical model of the FFDM system that accounts for patient scatter, focal spot unsharpness, and detector blur. With the use of simulated signals, this method can predict system performance for a signal known exactly/background known exactly detection task with a limited number of images, therefore, it can be readily applied in a clinical environment.
Collapse
Affiliation(s)
- Haimo Liu
- FDA Center for Devices and Radiological Health, Silver Spring, Maryland 20993-0002 and Department of Bioengineering, University of Maryland, College Park, Maryland 20742
| | - Kish Chakrabarti
- US FDA Center for Devices and Radiological Health, Silver Spring, Maryland 20993-0002
| | - Richard V Kaczmarek
- US FDA Center for Devices and Radiological Health, Silver Spring, Maryland 20993-0002
| | - Luis Benevides
- Radiological Controls, Naval Sea Systems Command, Washington, DC 20376
| | - Songxiang Gu
- US FDA Center for Devices and Radiological Health, Silver Spring, Maryland 20993-0002
| | - Iacovos S Kyprianou
- US FDA Center for Devices and Radiological Health, Silver Spring, Maryland 20993-0002 and Department of Bioengineering, University of Maryland, College Park, Maryland 20742
| |
Collapse
|
11
|
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.
Collapse
Affiliation(s)
- Stefano Young
- College of Optical Sciences, University of Arizona, Tucson, Arizona 85721, USA
| | | | | | | | | |
Collapse
|
12
|
Sharma D, Badano A. Validation of columnar CsI x-ray detector responses obtained with hybridMANTIS, a CPU-GPU Monte Carlo code for coupled x-ray, electron, and optical transport. Med Phys 2013; 40:031907. [PMID: 23464322 DOI: 10.1118/1.4791642] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
PURPOSE hybridMANTIS is a Monte Carlo package for modeling indirect x-ray imagers using columnar geometry based on a hybrid concept that maximizes the utilization of available CPU and graphics processing unit processors in a workstation. METHODS The authors compare hybridMANTIS x-ray response simulations to previously published MANTIS and experimental data for four cesium iodide scintillator screens. These screens have a variety of reflective and absorptive surfaces with different thicknesses. The authors analyze hybridMANTIS results in terms of modulation transfer function and calculate the root mean square difference and Swank factors from simulated and experimental results. RESULTS The comparison suggests that hybridMANTIS better matches the experimental data as compared to MANTIS, especially at high spatial frequencies and for the thicker screens. hybridMANTIS simulations are much faster than MANTIS with speed-ups up to 5260. CONCLUSIONS hybridMANTIS is a useful tool for improved description and optimization of image acquisition stages in medical imaging systems and for modeling the forward problem in iterative reconstruction algorithms.
Collapse
Affiliation(s)
- Diksha Sharma
- Division of Imaging and Applied Mathematics, Center for Devices and Radiological Health, Food and Drug Administration, Silver Spring, Maryland 20993, USA
| | | |
Collapse
|
13
|
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.
Collapse
Affiliation(s)
- Ioannis Sechopoulos
- Department of Radiology and Imaging Sciences, Emory University, Atlanta, GA, USA
| |
Collapse
|
14
|
Tibbelin S, Nillius P, Danielsson M. Simulation of HyperSPECT: a high-resolution small-animal system with in-line x-ray optics. Phys Med Biol 2012; 57:1617-29. [PMID: 22398032 DOI: 10.1088/0031-9155/57/6/1617] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
SPECT has become an important tool in pre-clinical applications. Small-animal imaging systems based on the use of one or more pinhole collimators now reach sub-half-mm resolution but unfortunately suffer from a compromise between sensitivity and resolution due to the pinhole collimators. We propose a small-animal SPECT system based not on pinholes but on in-line x-ray optics, which is rare in medical imaging systems for nuclear medicine. The x-ray lenses are optimized for 27 keV for low-energy imaging with iodine-125. We believe that this new system, HyperSPECT, can simultaneously improve on sensitivity and resolution compared to today's state-of-the-art systems. A full three-dimensional simulation of the system has been performed including the prism-array lenses, pre- and post-collimators and scintillator-based detector. Images of capillary phantoms have been reconstructed using an iterative image reconstruction method. Sensitivity was uniformly 0.37% throughout the 1 cm diameter spherical field of view and rod sizes of around 100 μm diameter were distinguishable in the images of simulated capillary phantoms. These results indicate an increase in resolution by a factor of 5 during a simultaneous increase in sensitivity by a factor of 2 compared to the current state-of-the-art small-animal SPECT systems.
Collapse
Affiliation(s)
- Sandra Tibbelin
- Department of Physics, The Royal Institute of Technology, AlbaNova University Center, 106 91 Stockholm, Sweden.
| | | | | |
Collapse
|
15
|
Kontos D, Ikejimba LC, Bakic PR, Troxel AB, Conant EF, Maidment ADA. Analysis of parenchymal texture with digital breast tomosynthesis: comparison with digital mammography and implications for cancer risk assessment. Radiology 2011; 261:80-91. [PMID: 21771961 DOI: 10.1148/radiol.11100966] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
PURPOSE To correlate the parenchymal texture features at digital breast tomosynthesis (DBT) and digital mammography with breast percent density (PD), an established breast cancer risk factor, in a screening population of women. MATERIALS AND METHODS This HIPAA-compliant study was approved by the institutional review board. Bilateral DBT images and digital mammograms from 71 women (mean age, 54 years; age range, 34-75 years) with negative or benign findings at screening mammography were retrospectively collected from a separate institutional review board-approved DBT screening trial (performed from July 2007 to March 2008) in which all women had given written informed consent. Parenchymal texture features of skewness, coarseness, contrast, energy, homogeneity, and fractal dimension were computed from the retroareolar region. Principal component analysis (PCA) was applied to obtain orthogonal texture components. Mammographic PD was estimated with software. Correlation analysis and multiple linear regression with generalized estimating equations were performed to determine the association between texture features and breast PD. Regression was adjusted for age to determine the independent association of texture to breast PD when age was also considered as a predictor variable. RESULTS Texture feature correlations to breast PD were stronger with DBT than with digital mammography. Statistically significant correlations (P < .001) were observed for contrast (r = 0.48), energy (r = -0.47), and homogeneity (r = -0.56) at DBT and for contrast (r = 0.26), energy (r = -0.26), and homogeneity (r = -0.33) at digital mammography. Multiple linear regression analysis of PCA texture components as predictors of PD also demonstrated significantly stronger associations with DBT. The association was strongest when age was also considered as a predictor of PD (R² = 0.41 for DBT and 0.28 for digital mammography; P < .001). CONCLUSION Parenchymal texture features are more strongly correlated to breast PD in DBT than in digital mammography. The authors' long-term hypothesis is that parenchymal texture analysis with DBT will result in quantitative imaging biomarkers that can improve the estimation of breast cancer risk.
Collapse
Affiliation(s)
- Despina Kontos
- Department of Radiology, University of Pennsylvania Health System, Philadelphia PA 19104-4206, USA.
| | | | | | | | | | | |
Collapse
|
16
|
Badano A, Freed M, Fang Y. Oblique incidence effects in direct x-ray detectors: a first-order approximation using a physics-based analytical model. Med Phys 2011; 38:2095-8. [PMID: 21626942 DOI: 10.1118/1.3567497] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
PURPOSE The authors describe the modifications to a previously developed analytical model of indirect CsI:Tl-based detector response required for studying oblique x-ray incidence effects in direct semiconductor-based detectors. This first-order approximation analysis allows the authors to describe the associated degradation in resolution in direct detectors and compare the predictions to the published data for indirect detectors. METHODS The proposed model is based on a physics-based analytical description developed by Freed et al. ["A fast, angle-dependent, analytical model of CsI detector response for optimization of 3D x-ray breast imaging systems," Med. Phys. 37(6), 2593-2605 (2010)] that describes detector response functions for indirect detectors and oblique incident x rays. The model, modified in this work to address direct detector response, describes the dependence of the response with x-ray energy, thickness of the transducer layer, and the depth-dependent blur and collection efficiency. RESULTS The authors report the detector response functions for indirect and direct detector models for typical thicknesses utilized in clinical systems for full-field digital mammography (150 microm for indirect CsI:Tl and 200 microm for a-Se direct detectors). The results suggest that the oblique incidence effect in a semiconductor detector differs from that in indirect detectors in two ways: The direct detector model produces a sharper overall PRF compared to the response corresponding to the indirect detector model for normal x-ray incidence and a larger relative increase in blur along the x-ray incidence direction compared to that found in indirect detectors with respect to the response at normal incidence angles. CONCLUSIONS Compared to the effect seen in indirect detectors, the direct detector model exhibits a sharper response at normal x-ray incidence and a larger relative increase in blur along the x-ray incidence direction with respect to the blur in the orthogonal direction. The results suggest that the oblique incidence effect in direct detectors can be considered to be caused mostly by the geometry of the path where the x-ray beam and its secondary particles deposit energy in the semiconductor layer.
Collapse
Affiliation(s)
- Aldo Badano
- Division of Imaging and Applied Mathematics, Office of Science and Engineering Laboratories, Center for Devices and Radiological Health, FDA, Silver Spring, Maryland 20993, USA.
| | | | | |
Collapse
|
17
|
Park S, Jennings R, Liu H, Badano A, Myers K. A statistical, task-based evaluation method for three-dimensional x-ray breast imaging systems using variable-background phantoms. Med Phys 2010; 37:6253-70. [PMID: 21302782 PMCID: PMC3188657 DOI: 10.1118/1.3488910] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2009] [Revised: 08/16/2010] [Accepted: 08/17/2010] [Indexed: 12/26/2022] Open
Abstract
PURPOSE For the last few years, development and optimization of three-dimensional (3D) x-ray breast imaging systems, such as digital breast tomosynthesis (DBT) and computed tomography, have drawn much attention from the medical imaging community, either academia or industry. However, there is still much room for understanding how to best optimize and evaluate the devices over a large space of many different system parameters and geometries. Current evaluation methods, which work well for 2D systems, do not incorporate the depth information from the 3D imaging systems. Therefore, it is critical to develop a statistically sound evaluation method to investigate the usefulness of inclusion of depth and background-variability information into the assessment and optimization of the 3D systems. METHODS In this paper, we present a mathematical framework for a statistical assessment of planar and 3D x-ray breast imaging systems. Our method is based on statistical decision theory, in particular, making use of the ideal linear observer called the Hotelling observer. We also present a physical phantom that consists of spheres of different sizes and materials for producing an ensemble of randomly varying backgrounds to be imaged for a given patient class. Lastly, we demonstrate our evaluation method in comparing laboratory mammography and three-angle DBT systems for signal detection tasks using the phantom's projection data. We compare the variable phantom case to that of a phantom of the same dimensions filled with water, which we call the uniform phantom, based on the performance of the Hotelling observer as a function of signal size and intensity. RESULTS Detectability trends calculated using the variable and uniform phantom methods are different from each other for both mammography and DBT systems. CONCLUSIONS Our results indicate that measuring the system's detection performance with consideration of background variability may lead to differences in system performance estimates and comparisons. For the assessment of 3D systems, to accurately determine trade offs between image quality and radiation dose, it is critical to incorporate randomness arising from the imaging chain including background variability into system performance calculations.
Collapse
Affiliation(s)
- Subok Park
- Division of Imaging Applied Mathematics, OSEL/CDRH/FDA, Silver Spring, Maryland 20993, USA.
| | | | | | | | | |
Collapse
|
18
|
Freed M, Park S, Badano A. A fast, angle-dependent, analytical model of CsI detector response for optimization of 3D x-ray breast imaging systems. Med Phys 2010; 37:2593-605. [PMID: 20632571 DOI: 10.1118/1.3397462] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
PURPOSE Accurate models of detector blur are crucial for performing meaningful optimizations of three-dimensional (3D) x-ray breast imaging systems as well as for developing reconstruction algorithms that faithfully reproduce the imaged object anatomy. So far, x-ray detector blur has either been ignored or modeled as a shift-invariant symmetric function for these applications. The recent development of a Monte Carlo simulation package called MANTIS has allowed detailed modeling of these detector blur functions and demonstrated the magnitude of the anisotropy for both tomosynthesis and breast CT imaging systems. Despite the detailed results that MANTIS produces, the long simulation times required make inclusion of these results impractical in rigorous optimization and reconstruction algorithms. As a result, there is a need for detector blur models that can be rapidly generated. METHODS In this study, the authors have derived an analytical model for deterministic detector blur functions, referred to here as point response functions (PRFs), of columnar CsI phosphor screens. The analytical model is x-ray energy and incidence angle dependent and draws on results from MANTIS to indirectly include complicated interactions that are not explicitly included in the mathematical model. Once the mathematical expression is derived, values of the coefficients are determined by a two-dimensional (2D) fit to MANTIS-generated results based on a figure-of-merit (FOM) that measures the normalized differences between the MANTIS and analytical model results averaged over a region of interest. A smaller FOM indicates a better fit. This analysis was performed for a monochromatic x-ray energy of 25 keV, a CsI scintillator thickness of 150 microm, and four incidence angles (0 degrees, 15 degrees, 30 degrees, and 45 degrees). RESULTS The FOMs comparing the analytical model to MANTIS for these parameters were 0.1951 +/- 0.0011, 0.1915 +/- 0.0014, 0.2266 +/- 0.0021, and 0.2416 +/- 0.0074 for 0 degrees, 15 degrees, 30 degrees, and 45 degrees, respectively. As a comparison, the same FOMs comparing MANTIS to 2D symmetric Gaussian fits to the zero-angle PRF were 0.6234 +/- 0.0020, 0.9058 +/- 0.0029, 1.491 +/- 0.012, and 2.757 +/- 0.039 for the same set of incidence angles. Therefore, the analytical model matches MANTIS results much better than a 2D symmetric Gaussian function. A comparison was also made against experimental data for a 170 microm thick CsI screen and an x-ray energy of 25.6 keV. The corresponding FOMs were 0.3457 +/- 0.0036, 0.3281 +/- 0.0057, 0.3422 +/- 0.0023, and 0.3677 +/- 0.0041 for 0 degrees, 15 degrees, 30 degrees, and 45 degrees, respectively. In a previous study, FOMs comparing the same experimental data to MANTIS PRFs were found to be 0.2944 +/- 0.0027, 0.2387 +/- 0.0039, 0.2816 +/- 0.0025, and 0.2665 +/- 0.0032 for the same set of incidence angles. CONCLUSIONS The two sets of derived FOMs, comparing MANTIS-generated PRFs and experimental data to the analytical model, demonstrate that the analytical model is able to reproduce experimental data with a FOM of less than two times that comparing MANTIs and experimental data. This performance is achieved in less than one millionth the computation time required to generate a comparable PRF with MANTIS. Such small computation times will allow for the inclusion of detailed detector physics in rigorous optimization and reconstruction algorithms for 3D x-ray breast imaging systems.
Collapse
Affiliation(s)
- Melanie Freed
- Division of Imaging and Applied Mathematics, Office of Science and Engineering Laboratories, Center for Devices and Radiological Health, U.S. Food and Drug Administration, 10903 New Hampshire Avenue, Silver Spring, Maryland 20993-0002, USA.
| | | | | |
Collapse
|
19
|
Freed M, Miller S, Tang K, Badano A. Experimental validation of Monte Carlo (MANTIS) simulated x-ray response of columnar CsI scintillator screens. Med Phys 2010; 36:4944-56. [PMID: 19994503 DOI: 10.1118/1.3233683] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
PURPOSE MANTIS is a Monte Carlo code developed for the detailed simulation of columnar CsI scintillator screens in x-ray imaging systems. Validation of this code is needed to provide a reliable and valuable tool for system optimization and accurate reconstructions for a variety of x-ray applications. Whereas previous validation efforts have focused on matching of summary statistics, in this work the authors examine the complete point response function (PRF) of the detector system in addition to relative light output values. METHODS Relative light output values and high-resolution PRFs have been experimentally measured with a custom setup. A corresponding set of simulated light output values and PRFs have also been produced, where detailed knowledge of the experimental setup and CsI:Tl screen structures are accounted for in the simulations. Four different screens were investigated with different thicknesses, column tilt angles, and substrate types. A quantitative comparison between the experimental and simulated PRFs was performed for four different incidence angles (0 degrees, 15 degrees, 30 degrees, and 45 degrees) and two different x-ray spectra (40 and 70 kVp). The figure of merit (FOM) used measures the normalized differences between the simulated and experimental data averaged over a region of interest. RESULTS Experimental relative light output values ranged from 1.456 to 1.650 and were in approximate agreement for aluminum substrates, but poor agreement for graphite substrates. The FOMs for all screen types, incidence angles, and energies ranged from 0.1929 to 0.4775. To put these FOMs in context, the same FOM was computed for 2D symmetric Gaussians fit to the same experimental data. These FOMs ranged from 0.2068 to 0.8029. Our analysis demonstrates that MANTIS reproduces experimental PRFs with higher accuracy than a symmetric 2D Gaussian fit to the experimental data in the majority of cases. Examination of the spatial distribution of differences between the PRFs shows that the main reason for errors between MANTIS and the experimental data is that MANTIS-generated PRFs are sharper than the experimental PRFs. CONCLUSIONS The experimental validation of MANTIS performed in this study demonstrates that MANTIS is able to reliably predict experimental PRFs, especially for thinner screens, and can reproduce the highly asymmetric shape seen in the experimental data. As a result, optimizations and reconstructions carried out using MANTIS should yield results indicative of actual detector performance. Better characterization of screen properties is necessary to reconcile the simulated light output values with experimental data.
Collapse
Affiliation(s)
- Melanie Freed
- CDRH/NIBIB Laboratory for the Assessment of Medical Imaging Systems, Division of Imaging and Applied Mathematics, Office of Science and Engineering Laboratories, Center for Devices and Radiological Health, U.S. Food and Drug Administration, 10903 New Hampshire Avenue, Silver Spring, Maryland 20993-0002, USA.
| | | | | | | |
Collapse
|
20
|
Sechopoulos I, Ghetti C. Optimization of the acquisition geometry in digital tomosynthesis of the breast. Med Phys 2009; 36:1199-207. [PMID: 19472626 DOI: 10.1118/1.3090889] [Citation(s) in RCA: 112] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Digital tomosynthesis of the breast continues to be intensively studied as an adjunct or replacement of conventional mammography. Although many of the acquisition parameters found in tomosynthesis imaging are also found in conventional mammography and therefore most of the traditional values from mammography have been used in the former, two acquisition geometry parameters, the angular range covered during acquisition and the number of projections per projection set, are applicable only to tomosynthesis. Therefore, in the preclinical and clinical studies reported on tomosynthesis of the breast, a wide variety of values have been used for these two parameters. In this study, 63 different combinations of angular range and number of projections were evaluated using computer simulation methods to characterize how these two parameters affect reconstruction quality and to find which of these combinations maximize it. For this, a computer simulation of a digital tomosynthesis system that included empirically determined system response characteristics was developed and used to generate 9450 different breast tissue volume reconstructions. These reconstructions were analyzed objectively using metrics for in-plane lesion visibility and vertical resolution in the form of the contrast-to-noise ratio and artifact spread function (ASF). It was found that although maximizing the angular range covered does always increase the vertical resolution in tomosynthesis, increasing the number of projections in the acquisition set beyond a relatively low threshold does not further improve the vertical resolution. This threshold value for the minimal number of projections needed to minimize the ASF was found to vary proportionally with angular range. For example, for a 60 degrees angular range, the threshold number of projections was found to be 13. Given the clear inverse relationship between the number of projections and in-plane reconstruction quality under a limited total glandular dose condition, the optimum acquisition geometry in tomosynthesis imaging of the breast is that which maximizes the angular range while maintaining the number of projections close to the threshold values found. Finally, of the 63 acquisition geometries studied, the one that resulted in the highest quality reconstruction, considering both in-plane quality and vertical resolution, consisted of the acquisition of 13 projections over a 60 degrees angular range.
Collapse
Affiliation(s)
- Ioannis Sechopoulos
- Department of Radiology and Winship Cancer Institute, Emory University School of Medicine, 1701 Upper Gate Drive, Suite 5018, Atlanta, Georgia 30322, USA.
| | | |
Collapse
|
21
|
Badano A, Kyprianou IS, Freed M, Jennings RJ, Sempau J. Effect of oblique X-ray incidence in flat-panel computed tomography of the breast. IEEE TRANSACTIONS ON MEDICAL IMAGING 2009; 28:696-702. [PMID: 19272986 DOI: 10.1109/tmi.2008.2010443] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
We quantify the variation in resolution due to anisotropy caused by oblique X-ray incidence in indirect flat-panel detectors for computed tomography breast imaging systems. We consider a geometry and detector type utilized in breast computed tomography (CT) systems currently being developed. Our methods rely on mantis, a combined X-ray, electron, and optical Monte Carlo transport open source code. The physics models are the most accurate available in general-purpose Monte Carlo packages in the diagnostic energy range. We consider maximum-obliquity angles of 10 ( degrees ) and 13 ( degrees ) at the centers of the 30 and 40 cm detector edges, respectively, and 16 ( degrees ) at the corner of the detector. Our results indicate that blur is asymmetric and that the resolution properties vary significantly with the angle (or location) of incidence. Our results suggest that the asymmetry can be as high as a factor of 2.6 between orthogonal directions. Anisotropy maps predicted by mantis provide an understanding of the effect that such variations have on the imaging system and allow more accurate modeling and optimization of breast CT systems. These maps of anisotropy across the detector could lead to improved reconstruction and help motivate physics-based strategies for computer detection of breast lesions.
Collapse
Affiliation(s)
- Aldo Badano
- NIBIB/CDRH Laboratory for the Assessment of Medical Imaging Systems, Division of Imaging and Applied Mathematics, Office of Science and Engineering Laboratories, US FDA, Silver Spring, MD 20993 USA.
| | | | | | | | | |
Collapse
|
22
|
Karellas A, Vedantham S. Breast cancer imaging: a perspective for the next decade. Med Phys 2009; 35:4878-97. [PMID: 19070222 DOI: 10.1118/1.2986144] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Breast imaging is largely indicated for detection, diagnosis, and clinical management of breast cancer and for evaluation of the integrity of breast implants. In this work, a prospective view of techniques for breast cancer detection and diagnosis is provided based on an assessment of current trends. The potential role of emerging techniques that are under various stages of research and development is also addressed. It appears that the primary imaging tool for breast cancer screening in the next decade will be high-resolution, high-contrast, anatomical x-ray imaging with or without depth information. MRI and ultrasonography will have an increasingly important adjunctive role for imaging high-risk patients and women with dense breasts. Pilot studies with dedicated breast CT have demonstrated high-resolution three-dimensional imaging capabilities, but several technological barriers must be overcome before clinical adoption. Radionuclide based imaging techniques and x-ray imaging with intravenously injected contrast offer substantial potential as a diagnostic tools and for evaluation of suspicious lesions. Developing optical and electromagnetic imaging techniques hold significant potential for physiologic information and they are likely to be of most value when integrated with or adjunctively used with techniques that provide anatomic information. Experimental studies with breast specimens suggest that phase-sensitive x-ray imaging techniques can provide edge enhancement and contrast improvement but more research is needed to evaluate their potential role in clinical breast imaging. From the technological perspective, in addition to improvements within each modality, there is likely to be a trend towards multi-modality systems that combine anatomic with physiologic information. We are also likely to transition from a standardized screening, where all women undergo the same imaging exam (mammography), to selection of a screening modality or modalities based an individual-risk or other classification.
Collapse
Affiliation(s)
- Andrew Karellas
- Department of Radiology, University of Massachusetts Medical School, Worcester, MA 01655, USA.
| | | |
Collapse
|
23
|
Hajdok G, Battista JJ, Cunningham IA. Fundamental x-ray interaction limits in diagnostic imaging detectors: spatial resolution. Med Phys 2008; 35:3180-93. [PMID: 18697543 DOI: 10.1118/1.2924219] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
The practice of diagnostic x-ray imaging has been transformed with the emergence of digital detector technology. Although digital systems offer many practical advantages over conventional film-based systems, their spatial resolution performance can be a limitation. The authors present a Monte Carlo study to determine fundamental resolution limits caused by x-ray interactions in four converter materials: Amorphous silicon (a-Si), amorphous selenium, cesium iodide, and lead iodide. The "x-ray interaction" modulation transfer function (MTF) was determined for each material and compared in terms of the 50% MTF spatial frequency and Wagner's effective aperture for incident photon energies between 10 and 150 keV and various converter thicknesses. Several conclusions can be drawn from their Monte Carlo study. (i) In low-Z (a-Si) converters, reabsorption of Compton scatter x rays limits spatial resolution with a sharp MTF drop at very low spatial frequencies (< 0.3 cycles/mm), especially above 60 keV; while in high-Z materials, reabsorption of characteristic x rays plays a dominant role, resulting in a mid-frequency (1-5 cycles/mm) MTF drop. (ii) Coherent scatter plays a minor role in the x-ray interaction MTF. (iii) The spread of energy due to secondary electron (e.g., photoelectrons) transport is significant only at very high spatial frequencies. (iv) Unlike the spread of optical light in phosphors, the spread of absorbed energy from x-ray interactions does not significantly degrade spatial resolution as converter thickness is increased. (v) The effective aperture results reported here represent fundamental spatial resolution limits of the materials tested and serve as target benchmarks for the design and development of future digital x-ray detectors.
Collapse
Affiliation(s)
- G Hajdok
- Imaging Research Laboratories, Robarts Research Institute, P.O. Box 5015, London, Ontario N6A 5K8, Canada.
| | | | | |
Collapse
|
24
|
Pan X, Siewerdsen J, La Riviere PJ, Kalender WA. Anniversary paper. Development of x-ray computed tomography: the role of medical physics and AAPM from the 1970s to present. Med Phys 2008; 35:3728-39. [PMID: 18777932 PMCID: PMC3910137 DOI: 10.1118/1.2952653] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2008] [Revised: 06/09/2008] [Accepted: 06/09/2008] [Indexed: 01/17/2023] Open
Abstract
The AAPM, through its members, meetings, and its flagship journal Medical Physics, has played an important role in the development and growth of x-ray tomography in the last 50 years. From a spate of early articles in the 1970s characterizing the first commercial computed tomography (CT) scanners through the "slice wars" of the 1990s and 2000s, the history of CT and related techniques such as tomosynthesis can readily be traced through the pages of Medical Physics and the annals of the AAPM and RSNA/AAPM Annual Meetings. In this article, the authors intend to give a brief review of the role of Medical Physics and the AAPM in CT and tomosynthesis imaging over the last few decades.
Collapse
Affiliation(s)
- Xiaochuan Pan
- Department of Radiology, University of Chicago, Chicago, Illinois 60637, USA.
| | | | | | | |
Collapse
|
25
|
Hajdok G, Battista JJ, Cunningham IA. Fundamental x-ray interaction limits in diagnostic imaging detectors: Frequency-dependent Swank noise. Med Phys 2008; 35:3194-204. [PMID: 18697544 DOI: 10.1118/1.2936412] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Affiliation(s)
- G Hajdok
- Imaging Research Laboratories, Robarts Research Institute, P.O. Box 5015, London, Ontario N6A 5K8, Canada.
| | | | | |
Collapse
|