- Durham, North Carolina, United States
James Dobbins
Duke University, Radiology, Alumnus
Research Interests: Optics, Biomedical Engineering, Nuclear medicine, Medical Physics, Medicine, and 11 moreImage Quality, Humans, Digital Radiography, Radiologic Technology, Computed radiography, Reproducibility of Results, Sensitivity and Specificity, Equipment Design, Equipment Failure Analysis, Detective Quantum Efficiency, and Chest radiograph
Radiography of the chest is a fascinating topic. Volumes can be written about the application of the examination to modern clinical medicine (Fraser et al., 1999). The presentations of disease on chest radiographs are myriad and often... more
Radiography of the chest is a fascinating topic. Volumes can be written about the application of the examination to modern clinical medicine (Fraser et al., 1999). The presentations of disease on chest radiographs are myriad and often manifest the subtlety and nuance that many may still associate with radiological practice. Insight gained by practitioners long ago has equal relevance today and remains the basis for image interpretation to the present time. Students of medical radiographic science also find much of interest in the chest examination. No other radiographic examination has been studied as extensively. The application of image science to chest radiography produces many useful and informative results . At the same time, studies of chest radiography often demonstrate the limitations of radiological science, as the interaction between the image and the observer can still confound the best present analyses. This report describes the technical aspects of chest radiography, with emphasis on issues related to image quality. The discussions may therefore be of interest to radiologists and clinicians who diagnose chest disease, physicists, engineers and radiological technologists.
Az The area under an ROC curve, often used as an index of detectability or diagnostic accuracy. aliasing artifacts Artifacts that may arise when an image is sampled at a spatial frequency that is less than required by the spatial... more
Az The area under an ROC curve, often used as an index of detectability or diagnostic accuracy. aliasing artifacts Artifacts that may arise when an image is sampled at a spatial frequency that is less than required by the spatial frequency content of the image. The minimum sampling frequency needed to avoid aliasing artifacts is twice the maximum spatial frequency content of the image. auto-correlation function The auto-correlation function is the ensemble average of the joint second moment of an imaging process. The autocorrelation function of radiographic mottle indicates the magnitude and the texture of the noise pattern in a radiograph. bootstrap sensitometry A method to determine the H & D curve of a screen-film system by overlapping separate segments of the curve, where each segment is measured independently. This method was devised to measure the curve by using two parameter combinations such as tube voltage-time, tube currenttime, step wedgetime, step wedge-distance, instead of one parameter in order to cover a large range of X-ray exposure rates incident on the screen-film system. characteristic curve See H & D curve. contrast A broad concept representing the difference or the ratio in image signals, such as the optical density, transmittance or radiant exposure, at two selected locations. convolution In radiographic science, the mathematical procedure that transforms an object (or input) distribution by the line spread function or point spread function into an image (or output) distribution, when the imaging system is linear and shift invariant. crossover exposure The additional radiant exposure to the film emulsion caused by light that is emitted by the screen placed opposite that
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The concept of selective exposure radiography encompasses those techniques which spatially modulate the incident x-ray field to produce a more uniform exit field arising from the patient. The resulting reduction in the dynamic range of... more
The concept of selective exposure radiography encompasses those techniques which spatially modulate the incident x-ray field to produce a more uniform exit field arising from the patient. The resulting reduction in the dynamic range of the exposure field offers several advantages. In conventional radiography, selective exposure techniques allow all areas of the image to be placed in the linear portion of the film characteristic curve so that local contrast is maximized. With video systems, the reduction in dynamic range minimizes the impact of electronic noise behind the least transmissive regions of the patient. With both electronic and photographic detectors, selective exposure radiography is characterized by uniform quantum statistics and uniform scatter across the image. Several selective exposure techniques currently are being investigated. They include compensating filters placed manually in the x-ray field as well as fan-beam geometries in which the x-ray tube output is modulated with a feedback circuit to maintain constant exposure to the image receptor. At the University of Wisconsin, we have been investigating a digital system which uses an initial low-dose patient image to design an attenuator with transmission complimentary to that of the patient. The attenuator is fabricated for each patient and is positioned automatically in the x-ray beam prior to the acquisition of the final compensated image. The possible applications of this device include chest radiography, coronary angiography, subtraction angiography, and accurate digital videodensitometry.
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Digital breast tomosynthesis is a form of limited angle tomography, in which section (slice) images are produced from a series of discrete projection images acquired at different angles. Tomosynthesis can be useful in breast imaging by... more
Digital breast tomosynthesis is a form of limited angle tomography, in which section (slice) images are produced from a series of discrete projection images acquired at different angles. Tomosynthesis can be useful in breast imaging by providing potentially better visibility of lesions over conventional mammography, especially in patients with dense breasts. This talk will cover the various physics aspects of DBT, including reconstruction algorithms, the importance of deblurring, and optimizing image acquisition parameters. Remaining important research questions in DBT will be presented and discussed. The presentation will also discuss MQSA Certificate extension process for currently approved digital breast tomosynthesis (DBT) systems. Training requirements, manufacturer required tests for Mammography Equipment Evaluation (MEE) as acceptance tests, and phantom imaging for the purpose of approval of certificate extension will be described. The talk will emphasize the specific tests where special attention must be given and will discuss how the techs should be advised to perform these tests. LEARNING OBJECTIVES 1. To understand the fundamentals of tomosynthesis reconstruction, including deblurring, algorithm choice, and optimization 2. To understand FDA's certificate extension process for DBT 3. To understand the requirements for MEE 4. To understand the required AEC tracking data Research sponsored in part by NIH, Siemens, and GE Healthcare.
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Research Interests: Materials Science, Optics, Biomedical Engineering, Quantum Theory, Filtration, and 15 moreMedical Physics, Medicine, Low Frequency, Qualitative evaluation, Quantum Efficiency, Grain size, Internationality, Reproducibility of Results, Sensitivity and Specificity, Detector, Equipment Failure Analysis, Amorphous Silicon, Detective Quantum Efficiency, Reference standards, and guidelines as topic
The last few years have seen a rapid increase in the number of digital imaging devices produced for radiographic applications. With digitized video/image intensifiers, computed radiography (CR), and more recently the advent of... more
The last few years have seen a rapid increase in the number of digital imaging devices produced for radiographic applications. With digitized video/image intensifiers, computed radiography (CR), and more recently the advent of flat-panel imagers, an almost bewildering number of choices of digital imaging devices is available. The good news from this rapid progress in digital radiography is that devices are becoming available with image quality superior to that available just a few years ago. The challenge from this proliferation of digital devices is making the difficult decision about which device is most suitable for a particular application. Radiologists will rightly ask, âHow can I know which device I should purchase for my clinical imaging needs?â Imaging physicists, on the other hand, will be concerned with verifying the image quality specifications of the various manufacturers, developing appropriate algorithms to extend the utility of the devices, and developing appropriate clinical imaging protocols to take best advantage of the devices' imaging performance. Physicists and radiologists will need to work collaboratively to determine the appropriate applications for these devices, and the performance that may be expected from them. In order to assess the performance of these devices, it is necessary to consider both physical image-quality parameters as well as the observer's perceptual response. Both of these areas are more difficult with digital devices than with screen film. Because the image has been sampled, quantized, and processed, there are a number of changes necessary in traditional measurements of image-quality. Furthermore, because there is an almost unlimited degree of image processing that can be done to the images, it becomes more difficult to gauge observer acceptance of the resulting images. There are a number of physical and observer-based measurements which can be used to gauge image-quality, and these will be considered in this chapter. This chapter is divided into four sections. First, global measures of image-quality will be addressed, using measurements in Cartesian (or image-intensity) space. Second, measures in spatial frequency space will be considered. Third, methods of assessing image processing will be considered, and last, observer assessment will be addressed. Of course, the final stage in assessment of image-quality is the ability of a particular imaging device and clinical protocol to improve diagnostic accuracy. The issue of diagnostic accuracy, while very important, is an entire field of study in itself, and is therefore beyond the scope of this chapter. The interested reader is referred to other chapters in this volume on measuring diagnostic accuracy.
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Digital x-ray tomosynthesis is a technique for producing slice images using conventional x-ray systems. It is a refinement of conventional geometric tomography, which has been known since the 1930s. In conventional geometric tomography,... more
Digital x-ray tomosynthesis is a technique for producing slice images using conventional x-ray systems. It is a refinement of conventional geometric tomography, which has been known since the 1930s. In conventional geometric tomography, the x-ray tube and image receptor move in synchrony on opposite sides of the patient to produce a plane of structures in sharp focus at the plane containing the fulcrum of the motion; all other structures above and below the fulcrum plane are blurred and thus less visible in the resulting image. Tomosynthesis improves upon conventional geometric tomography in that it allows an arbitrary number of in-focus planes to be generated retrospectively from a sequence of projection radiographs that are acquired during a single motion of the x-ray tube. By shifting and adding these projection radiographs, specific planes may be reconstructed. This topical review describes the various reconstruction algorithms used to produce tomosynthesis images, as well as approaches used to minimize the residual blur from out-of-plane structures. Historical background and mathematical details are given for the various approaches described. Approaches for optimizing the tomosynthesis image are given. Applications of tomosynthesis to various clinical tasks, including angiography, chest imaging, mammography, dental imaging and orthopaedic imaging, are also described.
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We have used a prototype digital beam attenuator (DBA) system to generate patient-specific digitally-prepared compensating filters for chest radiography of a human subject. The compensated radiographs demonstrate substantially more... more
We have used a prototype digital beam attenuator (DBA) system to generate patient-specific digitally-prepared compensating filters for chest radiography of a human subject. The compensated radiographs demonstrate substantially more information in areas such as the mediastinum and upper abdomen which normally are underpenetrated in conventional chest radiographs. The compensated image was acquired with high contrast, high speed film-screen receptors improving the visibility of pulmonary parenchymal detail while minimizing patient radiation exposure. Currently we are limited by a two-hour preparation time and position the attenuator manually. We are developing a second generation DBA system featuring fast (15 second) fabrication times and automatic positioning of the attenuator. We expect that these features will relieve some of the misregistration errors present in our initial examination.
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ABSTRACT Correlated-polarity noise reduction (CPNR) is a novel noise reduction technique that uses a statistical approach to reduce noise while maintaining excellent resolution and a “normal” noise appearance. It is applicable to any type... more
ABSTRACT Correlated-polarity noise reduction (CPNR) is a novel noise reduction technique that uses a statistical approach to reduce noise while maintaining excellent resolution and a “normal” noise appearance. It is applicable to any type of medical imaging, and we introduced it at SPIE 2011 for reducing dose three-fold in radiography while maintaining excellent image quality. In this current work, we demonstrate for the first time its use in reducing the noise in CT images as a means of reducing the dose in CT. Simulated chest CT images were generated using the XCAT phantom and Poisson noise was added to simulate a conventional full-dose CT image and a half-dose CT image. CPNR was applied to the half-dose images in projection image space, and then the images were reconstructed using filtered backprojection with a Feldkamp methodology. The resulting CPNR processed half-dose images showed essentially equivalent relative standard deviation in the central heart region to the full-dose images, and about 0.7 times that in half-dose images that were not processed with CPNR. This noise reduction was consistent with a two-fold reduction in dose that is possible with CPNR in CT. The CPNR images demonstrated virtually identical sharpness of vessels and no apparent artifacts. We conclude that CPNR shows strong promise as a new noise reduction method for dose reduction in CT. CPNR could also be used in combination with model-based iterative reconstruction techniques for yet further dose reduction.
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ABSTRACT Correlated-polarity noise reduction (CPNR) is a novel noise reduction technique that uses a statistical approach to reduce noise while maintaining excellent resolution and a “normal” noise appearance. It is applicable to any type... more
ABSTRACT Correlated-polarity noise reduction (CPNR) is a novel noise reduction technique that uses a statistical approach to reduce noise while maintaining excellent resolution and a “normal” noise appearance. It is applicable to any type of medical imaging, and we introduced it at SPIE 2011 for reducing dose three-fold in radiography while maintaining excellent image quality. In this current work, we demonstrate for the first time its use in reducing the noise in CT images as a means of reducing the dose in CT. Simulated chest CT images were generated using the XCAT phantom and Poisson noise was added to simulate a conventional full-dose CT image and a half-dose CT image. CPNR was applied to the half-dose images in projection image space, and then the images were reconstructed using filtered backprojection with a Feldkamp methodology. The resulting CPNR processed half-dose images showed essentially equivalent relative standard deviation in the central heart region to the full-dose images, and about 0.7 times that in half-dose images that were not processed with CPNR. This noise reduction was consistent with a two-fold reduction in dose that is possible with CPNR in CT. The CPNR images demonstrated virtually identical sharpness of vessels and no apparent artifacts. We conclude that CPNR shows strong promise as a new noise reduction method for dose reduction in CT. CPNR could also be used in combination with model-based iterative reconstruction techniques for yet further dose reduction.
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A circuit has been constructed to perform spatial frequency filtration on DSA images at real-time video rates. The 10-bit device performs low-pass or high-pass filtering, and with external memory can perform bandpass and more... more
A circuit has been constructed to perform spatial frequency filtration on DSA images at real-time video rates. The 10-bit device performs low-pass or high-pass filtering, and with external memory can perform bandpass and more sophisticated filtering. Pixels in the convolving kernel are weighted independendently in the x- and y-directions to provide a Gaussian-like convolving function. The kernel width ranges from 3-30 pixels and appropriate weighting yields a FWHM of the Gaussian kernel function as small as 0.85 pixel width for horizontal image widths of ≤256 pixels and as small as 1.25 pixel width for a horizontal image width of 512 pixels. Applications to be investigated include scatter and glare correction for videodensitometry, enhancement of arteries behind large opacified structures such as the ventricle and aorta, noise suppression in low-spatial frequency DSA exams, edge-enhancement of images, and partial-pixel shifting. Peli and Lim have suggested a more sophisticated algorithm which enhances high-pass filtration only in dark regions of an image. This and other techniques may be implemented with the current circuit to enhance small detail in highly opacified regions such as the ventricle, while leaving the rest of the image unaltered.
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ABSTRACT Assessment of the resolution properties of nonlinear imaging systems is a useful but challenging task. While the modulation transfer function (MTF) fully describes contrast resolution as a function of spatial frequency for linear... more
ABSTRACT Assessment of the resolution properties of nonlinear imaging systems is a useful but challenging task. While the modulation transfer function (MTF) fully describes contrast resolution as a function of spatial frequency for linear systems, an equivalent metric does not exist for systems with significant nonlinearity. Therefore, this preliminary investigation attempts to classify and quantify the amount of scaling and distortion imposed on a given image signal as the result of a nonlinear process (nonlinear image processing algorithm). As a proof-of-concept, a median filter is assessed in terms of its principle frequency response (PFR) and distortion response (DR) functions. These metrics are derived in frequency space using a sinusoidal basis function, and it is shown that, for a narrow-band sinusoidal input signal, the scaling and distortion properties of the nonlinear filter are described exactly by PFR and DR, respectively. The use of matched sinusoidal basis and input functions accurately reveals the frequency response to long linear structures of different scale. However, when more complex (multi-band) input signals are considered, PFR and DR fail to adequately characterize the frequency response due to nonlinear interaction effects between different frequency components during processing. Overall, the results reveal the context-dependent nature of nonlinear image processing algorithm performance, and they emphasize the importance of the basis function choice in algorithm assessment. In the future, more complex forms of nonlinear systems analysis may be necessary to fully characterize the frequency response properties of nonlinear algorithms in a context-dependent manner.
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ABSTRACT We previously proposed a three-dimensional computerized breast phantom that combines empirical data with the flexibility of mathematical models1. The goal of this project is to enhance the breast phantom to include a more... more
ABSTRACT We previously proposed a three-dimensional computerized breast phantom that combines empirical data with the flexibility of mathematical models1. The goal of this project is to enhance the breast phantom to include a more detailed anatomy than currently visible and create additional phantoms from different breast CT data. To improve the level of detail in our existing segmentations, the breast CT data is reconstructed at a higher resolution and additional image processing techniques are used to correct for noise and scatter in the image data. A refined segmentation algorithm is used that incorporates more detail than previously defined. To further enhance high-resolution detail, mathematical models, implementing branching algorithms to extend the glandular tissue throughout the breast and to define Cooper's ligaments, are under investigation. We perform the simulation of mammography and tomosynthesis using an analytical projection algorithm that can be applied directly to the mathematical model of the breast without voxelization2. This method speeds up image acquisition, reduces voxelization artifacts, and produces higher resolution images than the previously used method. The realistic 3D computerized breast phantom will ultimately be incorporated into the 4DXCAT phantom3-5 to be used for breast imaging research.
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ABSTRACT Reduction of image noise is an important goal in producing the highest quality medical images. A very important benefit of reducing image noise is the ability to reduce patient exposure while maintaining adequate image quality.... more
ABSTRACT Reduction of image noise is an important goal in producing the highest quality medical images. A very important benefit of reducing image noise is the ability to reduce patient exposure while maintaining adequate image quality. Various methods have been described in the literature for reducing image noise by means of image processing, both deterministic and statistical. Deterministic methods tend to degrade image resolution or lead to artifacts or non-uniform noise texture that does not look "natural" to the observer. Statistical methods, including Bayesian estimation, have been successfully applied to image processing, but may require more time-consuming steps of computing priors. The approach described in this paper uses a new statistical method we have developed in our laboratory to reduce image noise. This approach, Correlated-Polarity Noise Reduction (CPNR), makes an estimate of the polarity of noise at a given pixel, and then subtracts a random value from a normal distribution having a sign that matches the estimated polarity of the noise in the pixel. For example, if the noise is estimated to be positive in a given pixel, then a random number that is also positive will be subtracted from that pixel. The CPNR method reduces the noise in an image by about 20% per iteration, with little negative impact on image resolution, few artifacts, and final image noise characteristics that appears "normal." Examples of the feasibility of this approach are presented in application to radiography and CT, but it also has potential utility in tomosynthesis and fluoroscopy.
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Since the early 1970's, Edholm and others have shown that compensation attenuators can provide fundamental improvements in radiographic image formation by modifying patient dose-distribution, reducing scatter fractions in dark regions... more
Since the early 1970's, Edholm and others have shown that compensation attenuators can provide fundamental improvements in radiographic image formation by modifying patient dose-distribution, reducing scatter fractions in dark regions of the image, and easing dynamic range requirements for film and video systems. Compensating attenuators have not yet been used widely in diagnostic radiology because of the difficulties of forming masks to compensate for the anatomical variations of individual patients. We have designed a software-based system which forms a heavy-metal attenuator from a digital image of the patient. At present, the attenuators are constructed manually from a pattern generated by the computer, but several techniques are being investigated which may permit fabrication and positioning during suspension of respiration. Phantom studies demonstrate that, in nonsubtractive applications, unsharp masking by the x-ray beam attenuator enhances local contrast, while in digitally subtracted images, attenuators eliminate dark regions where iodine signals otherwise are degraded by video and quantum noise. The technique can be used to reduce patient exposure in highly transmissive areas or, at the expense of increased tube loading, to increase exposure to highly attenuating areas in order to reduce image noise. Anticipated applications of this technique include chest radiography as well as conventional and digital subtraction angiography.
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Although image quality in chest radiography can be improved dramatically with compensating attenuators, it is difficult to match attenuator geometry to that of the patient and to properly position the filter in the x-ray beam. We are... more
Although image quality in chest radiography can be improved dramatically with compensating attenuators, it is difficult to match attenuator geometry to that of the patient and to properly position the filter in the x-ray beam. We are developing a system which will fabricate a compensating filter specific for individual patient anatomy and position the filter automatically. A low-dose image is acquired from which the attenuator is designed using a hardwired algorithm. The attenuator then is typed in multiple layers of a cerium oxide material onto a sheet of paper with a dotmatrix printer. Following positioning of the attenuator in the x-ray beam, the final compensated image is acquired with a photographic or electronic detector. Initial studies with our prototype digital beam attenuator have produced images with improved image quality. The improvement occurs because the attenuator allows the entire image to be placed in the linear portion of the film characteristic curve. In addition, decreased scatter fractions and increased signal-to-noise contribute to improved visualization of low-contrast signals behind the most attenuating regions of the patient.
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Arthritis is a painful condition with enormous societal impact. Arthritis damages the articular cartilage between adjacent bones in a joint, which is seen radiographically as narrowing of the joint space width (JSW). JSW is an important... more
Arthritis is a painful condition with enormous societal impact. Arthritis damages the articular cartilage between adjacent bones in a joint, which is seen radiographically as narrowing of the joint space width (JSW). JSW is an important arthritis outcome measure however a single radiographic image is a 2D projection of a D structure and diseased areas can be obscured. To quantify the JSW in three dimensions we have applied digital tomosynthesis imaging to hand radiography. A tomosynthesis algorithm, developed for use in chest radiography, was modified to provide reconstructed slices through the bones that formed joints of the hand. The methodology was tested using simulated radiographs of dry-bone specimens from 3 hand skeletons. Estimates to the JSW in 3D were made from the reconstructed slices. The algorithm produced tomographic slices through the bones of the joint with minimal loss of spatial resolution. We discovered that hand radiography is ideally suited for tomosynthesis imaging due to the small amount of scatter and lack of truncation artifacts. We have demonstrated the utility of digital tomosynthesis for use in quantifying JSW for arthritis assessment. The method shows promise for improving the assessment of disease progression.
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ABSTRACT Physical phantoms are essential for the development, optimization, and clinical evaluation of x-ray systems. These phantoms are used for various tests such as quality assurance testing, system characterization, reconstruction... more
ABSTRACT Physical phantoms are essential for the development, optimization, and clinical evaluation of x-ray systems. These phantoms are used for various tests such as quality assurance testing, system characterization, reconstruction evaluation, and dosimetry. They should ideally be capable of serving as ground truth for purposes such as virtual clinical trials. Currently, there is no anthropomorphic 3D physical phantom commercially available. We present our development of a new suite of physical breast phantoms based on real patient data. The phantoms were generated from the NURBS-based extended cardiac-torso (XCAT) breast phantoms, which were segmented from patient dedicated breast computed tomography data. High-resolution multi-material 3D printing technology was used to fabricate the physical models. Glandular tissue and skin were presented by the most radiographically dense photopolymer available to the printer, mimicking a 75% glandular tissue. Adipose tissue was presented by the least radiographically dense photopolymer, mimicking a 35% glandular tissue. The glandular equivalency was measured by comparing x-ray images of samples of the photopolymers available to the printer with those of breast tissue-equivalent materials. The mammographic projections and tomosynthesis reconstructed images of fabricated models showed great improvement over available phantoms, presenting a more realistic breast background.
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Digital tomosynthesis is an imaging technique that reconstructs tomographic planes in an object from a set of projection images taken over a fixed angle1. Preliminary results show that this technique increases the detectability of lung... more
Digital tomosynthesis is an imaging technique that reconstructs tomographic planes in an object from a set of projection images taken over a fixed angle1. Preliminary results show that this technique increases the detectability of lung nodules2. Current settings acquire images with approximately the same exposure as a screen-film lateral. However, due to the increased detectability of lung nodules from the removal of overlying structures, patient dose may be reduced while still maintaining increased sensitivity and specificity over conventional chest radiographs. This study describes a simulation method that provides realistic reduced dose images by adding noise to digital chest tomosynthesis images in order to simulate lower exposure settings for the purpose of dose optimization. Tomosynthesis projections of human subjects were taken at dose levels which were specified based on either patient thickness or a photo-timed digital chest radiograph acquired prior to tomosynthesis acquisition. For the purposes of this study, subtle nodules of varying size were simulated in the image for demonstration purposes before the noise simulation in order to have a known truth for nodule location and to evaluate the effect of additive noise on tumor detection. Noise was subsequently added in order to simulate 3/4, 1/2, and 1/4 of the original exposure in each projection. The projections were then processed with the MITS algorithm to produce slice images. This method will be applied to a study of dose reduction in the future using human subject cases.
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ABSTRACT Mammography is currently the most widely accepted tool for detection and diagnosis of breast cancer. However, the sensitivity of mammography is reduced in women with dense breast tissue due to tissue overlap, which may obscure... more
ABSTRACT Mammography is currently the most widely accepted tool for detection and diagnosis of breast cancer. However, the sensitivity of mammography is reduced in women with dense breast tissue due to tissue overlap, which may obscure lesions. Digital breast tomosynthesis with contrast enhancement reduces tissue overlap and provides additional functional information about lesions (i.e. morphology and kinetics), which in turn may improve lesion characterization. The performance of such techniques is highly dependent on the structural composition of the breast, which varies significantly across patients. Therefore, optimization of breast imaging systems should be done with respect to this patient versatility. Furthermore, imaging techniques that employ contrast require the inclusion of a temporally varying breast composition with respect to the contrast agent kinetics to enable the optimization of the system. To these ends, we have developed a dynamic 4D anthropomorphic breast phantom, which can be used for optimizing a breast imaging system by incorporating material characteristics. The presented dynamic phantom is based on two recently developed anthropomorphic breast phantoms, which can be representative of a whole population through their randomized anatomical feature generation and various compression levels. The 4D dynamic phantom is incorporated with the kinetics of contrast agent uptake in different tissues and can realistically model benign and malignant lesions. To demonstrate the utility of the proposed dynamic phantom, contrast-enhanced digital mammography and breast tomosynthesis were simulated where a ray-tracing algorithm emulated the projections, a filtered back projection algorithm was used for reconstruction, and dual-energy and temporal subtractions were performed and compared.
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In digital radiography, conventional DQE evaluations are performed under idealized conditions that do not reflect typical clinical operating conditions. For this reason, we have developed and evaluated an experimental methodology for... more
In digital radiography, conventional DQE evaluations are performed under idealized conditions that do not reflect typical clinical operating conditions. For this reason, we have developed and evaluated an experimental methodology for measuring theeffective detective quantum efficiency (eDQE) of digital radiographic systems and its utility in chest imaging applications.To emulate the attenuation and scatter properties of the human thorax across a
Research Interests: Engineering, Physics, Optics, Image Quality, X Rays, and 13 moreDigital Radiography, Opacity, Quantum Efficiency, Spatial Frequency, Radiography, Modulation Transfer Function, Operant Conditioning, Attenuation, Reference Point, Detective Quantum Efficiency, Magnification, Scatter, and Experimental Methodology
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Digital tomosynthesis is a method for reconstructing arbitrary planes in an object from a series of projection radiographs, acquired with limited angle tube movement. Conventional 'shift and... more
Digital tomosynthesis is a method for reconstructing arbitrary planes in an object from a series of projection radiographs, acquired with limited angle tube movement. Conventional 'shift and add' tomosynthesis suffers from the presence of blurring artifacts, created by objects ...
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Research Interests: Computer Science, Algorithms, Artificial Intelligence, Computer Vision, Biomedical Engineering, and 14 moreMedical Physics, Medicine, X Rays, Humans, Calibration, Female, Three Dimensional Imaging, Breast, Mammography, Calcinosis, Reproducibility of Results, Tomosynthesis, Digital Breast Tomosynthesis, and Breast Neoplasms
A photostimulable storage phosphor (PSP) digital radiography system was evaluated regarding the signal-to-noise ratio (S/N) on chest images acquired at differing peak kilovoltage settings but with matched risk from radiation exposure.... more
A photostimulable storage phosphor (PSP) digital radiography system was evaluated regarding the signal-to-noise ratio (S/N) on chest images acquired at differing peak kilovoltage settings but with matched risk from radiation exposure. Images of two chest phantoms were acquired by using bedside (portable) imaging equipment at tube voltages ranging from 60 to 120 kV. Exposure factors were set so that the effective dose equivalent, a risk estimator weighted for various organs, was approximately equal in all exposures. The S/N in the lung-equivalent regions was found to be slightly higher (maximum, 15%) in the low-energy exposures, while the S/N values in the mediastinum- and subdiaphragm-equivalent regions were approximately equal at all kilovoltage settings. The absence of a high sensitivity of S/N to kilovoltage in risk-matched PSP images should enable institutions to select x-ray beam quality on the basis of other imaging criteria.
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A number of digital imaging techniques in medicine require the combination of multiple images. Using these techniques, it is essential that the images be adequately aligned and registered prior to addition, subtraction, or any other... more
A number of digital imaging techniques in medicine require the combination of multiple images. Using these techniques, it is essential that the images be adequately aligned and registered prior to addition, subtraction, or any other combination of the images. This paper describes an alignment routine developed to register an image of a fixed object containing a global offset error, rotation error, and magnification error relative to a second image. The described routine uses sparsely sampled regional correlation in a novel way to reduce computation time and avoid the use of markers and human interaction. The result is a fast, robust, and automatic alignment algorithm, with accuracy better than about 0.2 pixel in a test with clinical computed radiography images.
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There have been many remarkable advances in conventional thoracic imaging over the past decade. Perhaps the most remarkable is the rapid conversion from film-based to digital radiographic systems. Computed radiography is now the preferred... more
There have been many remarkable advances in conventional thoracic imaging over the past decade. Perhaps the most remarkable is the rapid conversion from film-based to digital radiographic systems. Computed radiography is now the preferred imaging modality for bedside chest imaging. Direct radiography is rapidly replacing film-based chest units for in-department posteroanterior and lateral examinations. An exciting aspect of the conversion to digital radiography is the ability to enhance the diagnostic capabilities and influence of chest radiography. Opportunities for direct computer-aided detection of various lesions may enhance the radiologist's accuracy and improve efficiency. Newer techniques such as dual-energy and temporal subtraction radiography show promise for improved detection of subtle and often obscured or overlooked lung lesions. Digital tomosynthesis is a particularly promising technique that allows reconstruction of multisection images from a short acquisition at very low patient dose. Preliminary data suggest that, compared with conventional radiography, tomosynthesis may also improve detection of subtle lung lesions. The ultimate influence of these new technologies will, of course, depend on the outcome of rigorous scientific validation.
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It is unnecessary to conduct complicated measurements of image chain performance in the clinical setting. The precision required in making intelligent design decisions for radiographic equipment must give way to practical considerations... more
It is unnecessary to conduct complicated measurements of image chain performance in the clinical setting. The precision required in making intelligent design decisions for radiographic equipment must give way to practical considerations of cost and convenience in the field. Selection of equipment or imaging strategies can properly rely on laboratory measures made available to the knowledgeable practitioner, but field assessment is still necessary to ensure that general expectations of performance are met on an ongoing basis (Hendee and Rossi, 1979; Linton et al ., 1979; WHO, 1982; Gray et al., 1983; NCRP, 1988).
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Portable or bedside chest radiography is a very common procedure that may account for as many as 50% of chest radiographs in large hospitals (Wandtke, 1994; MacMahon and Giger, 1996). Portable examinations are obtained for monitoring of... more
Portable or bedside chest radiography is a very common procedure that may account for as many as 50% of chest radiographs in large hospitals (Wandtke, 1994; MacMahon and Giger, 1996). Portable examinations are obtained for monitoring of patients in intensive care units, patients after surgery or patients who are unable to stand upright (Alter, 1980; Goodman, 1992, Maffessanti et al., 1998). Clinically significant findings are common and may be present in 18-65% of patients (Janower et al., 1984; Hall et al.; 1991, Henschke et al., 1996; Brainsky et al. , 1997; Marik and Janower, 1997). Additional clinical indications and clinical findings are discussed in Section 2.3.2.6. The quality of portable chest radiographs can be degraded significantly compared to conventional chest radiographs. The main limitations are increased scatter, inconstant film optical density and inconsistent patient positioning.
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Imaging procedures are an essential part of the diagnostic evaluation of a wide variety of chest diseases. Examples include various infections, malignancies, toxic effects, immunological disease and cardiovascular conditions. Indications... more
Imaging procedures are an essential part of the diagnostic evaluation of a wide variety of chest diseases. Examples include various infections, malignancies, toxic effects, immunological disease and cardiovascular conditions. Indications include the detection of suspected disease, the monitoring of known disease, and the discovery of asymptomatic disease. Low cost and general availability are major advantages. Chest radiography is a simple technique. The diagnostic yield of chest radiography is dependent on image quality, however, and constant attention to the technical aspects of the examination is essential. Chest radiography is the imaging study of choice for initial evaluation of chest disease worldwide and represents a substantial portion all radiographic examinations. During the 1970s and 1980s, chest examinations accounted for as many as half of the X-ray studies performed (Johnson and Abernathy, 1983; WHO, 1983; Bunge and Herman, 1987; Mettler, 1987). This percentage is nearer 25% in the recent survey by the United Nations (UNSCEAR, 2000). Changes in patient demographics and medical practice should continue to influence the use of chest radiography in years to come (Stieve, 1995). This section gives a brief overview of the role of chest radiography in clinical practice today.
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The transfer characteristics of a radiographic imaging chain are accessible, either directly or indirectly, to laboratory assessment. Such measurements, when properly performed, yield the most precise available information about the... more
The transfer characteristics of a radiographic imaging chain are accessible, either directly or indirectly, to laboratory assessment. Such measurements, when properly performed, yield the most precise available information about the performance of a radiographic system. This information has been used in the past not only for evaluating system performance, but also for establishing the basis for a practical theoretical framework in which to consider radiographic imaging. Laboratory assessment can also guide product design and optimisation.
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The existence of chest radiographs in digital format allows application of a number of techniques that create images which may be more easily interpreted by human observers. Beyond this, the rapid application of computer vision and... more
The existence of chest radiographs in digital format allows application of a number of techniques that create images which may be more easily interpreted by human observers. Beyond this, the rapid application of computer vision and artificial intelligence methods in radiography has resulted in efforts to automate a variety of interpretative functions in chest radiography (Giger and MacMahon, 1996; Doi, 1999; MacMahon, 2000; Van Ginneken et al., 2001). The development of computer based methods is timely, given the ever more widespread use of digital chest radiography. Computer based techniques may one day be automatically and routinely applied to the images between the times of acquisition and interpretation.
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A general discussion of the use of phantoms in diagnostic radiography can be found in ICRU Report 48 (1992b). Specifications are presented here for selected phantoms used in the evaluation or maintenance of radiographic equipment and... more
A general discussion of the use of phantoms in diagnostic radiography can be found in ICRU Report 48 (1992b). Specifications are presented here for selected phantoms used in the evaluation or maintenance of radiographic equipment and image quality in chest radiography. A summary of these phantoms is given in Table A5. l. Further information may be obtained from manufacturers using the contact information provided.
Research Interests: Engineering and Appendix
The final diagnosis rendered on the basis of a radiograph depends on the physical quality of the image and the observer of the image. Although clinical radiographs are the final standard by which image quality must be assessed, much can... more
The final diagnosis rendered on the basis of a radiograph depends on the physical quality of the image and the observer of the image. Although clinical radiographs are the final standard by which image quality must be assessed, much can be learned about observer performance under more controlled conditions. This has the obvious benefits of allowing the detection of abnormalities to be assessed, as parameters of the radiographic process are varied. Phantom studies, for example, permit not only the properties of the lesion type under study to be precisely determined but, as is also important in the chest, their location on a simulated anatomical background to be varied. Clinical radiographs obtained with different imaging strategies can also be compared in the evaluation of image quality. These provide the radiologist with more realistic images, but must rely on available patients or available pathology, the latter of which is generally not at the limits of detectability.
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As discussed throughout the report, the most difficult technical challenge in chest radiography is the very large range of X-ray radiation transmitted by the human thorax. This dynamic range can easily exceed 50, greater than the... more
As discussed throughout the report, the most difficult technical challenge in chest radiography is the very large range of X-ray radiation transmitted by the human thorax. This dynamic range can easily exceed 50, greater than the recording latitude of conventional radiographic film. Radiographic technique factors are typically selected so that the lung is imaged in the optimum linear portion of the H & D curve, giving good contrast in the lung region. However, this forces the mediastinum and retrodiaphragmatic regions into the toe of the H & D curve (Figure 4.2), resulting in the familiar under-exposed appearance in those areas. Film manufacturers have addressed this problem by producing special wide-latitude films for use in chest radiography, but this solution has the drawback of improving contrast in the mediastinum at the expense of reduced contrast in the lungs. The wide range of transmitted X-ray intensities also results in a wide range of signal-to-noise levels over the chest radiographic image. The signal-tonoise ratio in the dense mediastinum and obscured lung can be many times worse than in the unobscured lung because of poor X-ray statistics. This makes it more difficult for observers to detect subtle abnormalities in the poorly penetrated regions, a difficulty compounded by poor radiographic contrast in these areas.
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The New New Symposium is a symposium for members relatively new to the organization to learn about the organizational structure and operational procedures of the society; how decisions are made, how the council and committee leadership is... more
The New New Symposium is a symposium for members relatively new to the organization to learn about the organizational structure and operational procedures of the society; how decisions are made, how the council and committee leadership is appointed and operates, opportunities for volunteer involvement, and a brief overview of the services and efforts provided by the HQ staff and the website. Attendees will hear from council chairs, key staff and chairs, and members with volunteer experience. After the symposium a social hour ensues with opportunities to interact with key AAPM members. The New Member Symposium is a (free) ticket option when you register online for the Annual Meeting. And don't forget registrants receive one (free) ticket for a beverage of your choice during the social afterwards.