| 1. |
- Häggmark, Ilian, et al.
(author)
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Phase-contrast chest radiography
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Other publication (other academic/artistic)abstract
- Respiratory X-ray imaging with phase contrast leads to improved sensitivity, as demonstrated in animal models to date. The translation to humans is limited by currently available technology, leaving the future clinical impact of the technique an open question. Here we demonstrate phase-contrast chest radiography using a proof-of-principle in silico framework. Specifically, we apply our previously developed preprocessing strategy to state-of-the-art realistic virtual human torso phantoms, then generate virtual chest radiographs through wave-propagation simulations. From a blind reader study conducted with clinical radiologists, we predict that phase contrast edge-enhancement has negligible impact for pulmonary nodule detection (6-20 mm). However, edge-enhancement of bronchial walls can visualize small airways (< 2 mm) invisible in conventional radiography. Our results predict that phase-contrast chest radiography could play a future role in diagnosis of small-airway obstruction (e.g., in asthma or chronic obstructive pulmonary disease) thereby motivating the experimental development needed for clinical translation.
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| 2. |
- Häggmark, Ilian, et al.
(author)
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Phase-contrast virtual chest radiography
- 2023
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In: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 120:1
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Journal article (peer-reviewed)abstract
- Respiratory X-ray imaging enhanced by phase contrast has shown improved airway visualization in animal models. Limitations in current X-ray technology have nevertheless hindered clinical translation, leaving the potential clinical impact an open question. Here, we explore phase-contrast chest radiography in a realistic in silico framework. Specifically, we use preprocessed virtual patients to generate in silico chest radiographs by Fresnel-diffraction simulations of X-ray wave propagation. Following a reader study conducted with clinical radiologists, we predict that phase-contrast edge enhancement will have a negligible impact on improving solitary pulmonary nodule detection (6 to 20 mm). However, edge enhancement of bronchial walls visualizes small airways (<2 mm), which are invisible in conventional radiography. Our results show that phase-contrast chest radiography could play a future role in observing small-airway obstruction (e.g., relevant for asthma or early-stage chronic obstructive pulmonary disease), which cannot be directly visualized using current clinical methods, thereby motivating the experimental development needed for clinical translation. Finally, we discuss quantitative requirements on distances and X-ray source/detector specifications for clinical implementation of phase-contrast chest radiography.
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| 3. |
- Häggmark, Ilian, et al.
(author)
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Propagation-based phase-contrast CXR: a virtual clinical study
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Other publication (other academic/artistic)abstract
- Background: Phase-contrast X-ray techniques are known to improve contrast for soft-tissueimaging but has yet to reach the clinical setting due to limitations of available technology. Virtual clinical studies serve as important tools for exploring the potential impact of new imaging technologies. Recent progress in X-ray imaging simulations has enabled virtual studies of propagation-based phase-contrast in clinical imaging. Purpose: To explore if propagation-based phase-contrast chest X-ray providing edge-enhancement of features can improve radiological diagnosis, specifically studying ifdetection sensitivity of pulmonary nodules can be increased. Materials and Methods: A virtual extended cardiac-torso (XCAT) phantom was used to simulate anteroposterior chest X-ray (CXR) images from virtual patients (n = 5) each withthree different settings: 1) Conventional (120 kV tungsten spectrum, patient next to detector), 2) Control (60 keV monochromatic, patient next to detector) and 3) Phase-contrast (60 keV monochromatic, patient 12 m before detector). Simulated images were post-processed using Siemens software for clinical CXR. The images were used to conduct a blind reader study with two radiologists, where 80 image sections (8×8 cm2) containing 0, 1, 2 or 3 pulmonary nodules (n = 20 each) were extracted for each setting (n = 240 sections in total). The sections were presented randomly to the radiologists, who reviewed the sections and potential findings with a degree of malignant suspicion (1-5 scale). The perceived image quality of each section was also reviewed ( 1-5 scale).Result: The radiologists perceived the simulated CXR as realistic enough to be used in a virtual clinical study. P hase-contrast CXR showed the same sensitivity in pulmonary nodule detection as conventional CXR (0.84 and 0.83, respectively). The number of false positives were also similar. The image quality of phase-contrast CXR was perceived worse on average compared to conventional CXR. Conclusion: Virtual clinical studies can be used to explore potential future impact of clinical phase-contrast X-ray imaging. For the task of pulmonary nodule detection, radiologists had similar benefit of propagation-based phase-contrast CXR as conventional CXR. The strong enhancement of airways and pulmonary vasculature did not increase false positives
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| 4. |
- Andersson, Jonas, 1975-, et al.
(author)
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Estimating Patient Organ Dosewith Computed Tomography: A Review of Present Methodologyand Required DICOM Information : A Joint Report ofAAPM Task Group 246 and the European Federationof Organizations for Medical Physics (EFOMP)
- 2019
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Reports (peer-reviewed)abstract
- The purpose of this report is (1) to summarize the current state of the art in estimating organ doses from CT examinations and (2) to outline a road map for standardized reporting of essential parameters necessary for estimation of organ doses from CT imaging in the DICOM standard. To address these purposes, the report includes a comprehensive discussion of (1) the various metrics, concepts, and methods that may be used to achieve estimates of patient organ dose and (2) the DICOM standard for CT.This Joint Report of the American Association of Physicists in Medicine (AAPM) Task Group 246 and the European Federation of Organizations for Medical Physics (EFOMP) contains three major sections and an appendix. Section 2 (with additional material in the appendix) provides a review of basic CT dosimetry metrics, their uses and limitations in the context of organ dosimetry, and the DICOM information currently associated with parameters that affect CT dose metrics and, consequently, organ dose estimates. Section 3 provides an overview of present and emerging organ dose estimation methods reported in the literature, e.g., for the lens of the eye, breast tissue, colon, and skin. Finally, the report concludes with section 4, which provides a discussion on the sources and magnitudes of uncertainty for different organ dose estimation methods.Ongoing efforts to facilitate routine standardized estimation of patient organ doses from CT are dependent, in large part, on the availability of the DICOM Radiation Dose Structured Report (RDSR), which provides a host of information pertinent to radiation dose calculations. This report, therefore, includes detailed information on DICOM header content in CT images and how it can be used in organ dose estimation. The RDSR markedly expands the abilities of the clinical medical physicist to estimate doses at the patient, device, and protocol level
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| 5. |
- Ba, Alexandre, et al.
(author)
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Inter-laboratory comparison of channelized hotelling observer computation
- 2018
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In: Medical Physics. - : Wiley. - 0094-2405 .- 2473-4209. ; 45:7, s. 3019-3030
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Journal article (peer-reviewed)abstract
- Purpose: The task-based assessment of image quality using model observers is increasingly used for the assessment of different imaging modalities. However, the performance computation of model observers needs standardization as well as a well-established trust in its implementation methodology and uncertainty estimation. The purpose of this work was to determine the degree of equivalence of the channelized Hotelling observer performance and uncertainty estimation using an intercomparison exercise. Materials and Methods: Image samples to estimate model observer performance for detection tasks were generated from two-dimensional CT image slices of a uniform water phantom. A common set of images was sent to participating laboratories to perform and document the following tasks: (a) estimate the detectability index of a well-defined CHO and its uncertainty in three conditions involving different sized targets all at the same dose, and (b) apply this CHO to an image set where ground truth was unknown to participants (lower image dose). In addition, and on an optional basis, we asked the participating laboratories to (c) estimate the performance of real human observers from a psychophysical experiment of their choice. Each of the 13 participating laboratories was confidentially assigned a participant number and image sets could be downloaded through a secure server. Results were distributed with each participant recognizable by its number and then each laboratory was able to modify their results with justification as model observer calculation are not yet a routine and potentially error prone. Results: Detectability index increased with signal size for all participants and was very consistent for 6 mm sized target while showing higher variability for 8 and 10 mm sized target. There was one order of magnitude between the lowest and the largest uncertainty estimation. Conclusions: This intercomparison helped define the state of the art of model observer performance computation and with thirteen participants, reflects openness and trust within the medical imaging community. The performance of a CHO with explicitly defined channels and a relatively large number of test images was consistently estimated by all participants. In contrast, the paper demonstrates that there is no agreement on estimating the variance of detectability in the training and testing setting.
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| 6. |
- Ruschin, Mark, et al.
(author)
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Dose dependence of mass and microcalcification detection in digital mammography: free response human observer studies.
- 2007
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In: Medical physics. - : Wiley. - 0094-2405. ; 34:2, s. 400-7
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Journal article (peer-reviewed)abstract
- The purpose of this study was to evaluate the effect of dose reduction in digital mammography on the detection of two lesion types-malignant masses and clusters of microcalcifications. Two free-response observer studies were performed-one for each lesion type. Ninety screening images were retrospectively selected; each image was originally acquired under automatic exposure conditions, corresponding to an average glandular dose of 1.3 mGy for a standard breast (50 mm compressed breast thickness with 50% glandularity). For each study, one to three simulated lesions were added to each of 40 images (abnormals) while 50 were kept without lesions (normals). Two levels of simulated system noise were added to the images yielding two new image sets, corresponding to simulated dose levels of 50% and 30% of the original images (100%). The manufacturer's standard display processing was subsequently applied to all images. Four radiologists experienced in mammography evaluated the images by searching for lesions and marking and assigning confidence levels to suspicious regions. The search data were analyzed using jackknife free-response (JA-FROC) methodology. For the detection of masses, the mean figure-of-merit (FOM) averaged over all readers was 0.74, 0.71, and 0.68 corresponding to dose levels of 100%, 50%, and 30%, respectively. These values were not statistically different from each other (F= 1.67, p=0.19) but showed a decreasing trend. In contrast, in the microcalcification study the mean FOM was 0.93, 0.67, and 0.38 for the same dose levels and these values were all significantly different from each other (F = 109.84, p < 0.0001). The results indicate that lowering the present dose level by a factor of two compromised the detection of microcalcifications but had a weaker effect on mass detection.
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| 7. |
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| 8. |
- Wang, Adam, et al.
(author)
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Science and practice of imaging physics through 50 years of SPIE Medical Imaging conferences
- 2022
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In: Journal of Medical Imaging. - : SPIE-Intl Soc Optical Eng. - 2329-4302 .- 2329-4310. ; 9:S1
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Journal article (peer-reviewed)abstract
- Purpose: For 50 years now, SPIE Medical Imaging (MI) conferences have been the premier forum for disseminating and sharing new ideas, technologies, and concepts on the physics of MI. Approach: Our overarching objective is to demonstrate and highlight the major trajectories of imaging physics and how they are informed by the community and science present and presented at SPIE MI conferences from its inception to now. Results: These contributions range from the development of image science, image quality metrology, and image reconstruction to digital x-ray detectors that have revolutionized MI modalities including radiography, mammography, fluoroscopy, tomosynthesis, and computed tomography (CT). Recent advances in detector technology such as photon-counting detectors continue to enable new capabilities in MI. Conclusion: As we celebrate the past 50 years, we are also excited about what the next 50 years of SPIE MI will bring to the physics of MI.
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| 9. |
- Åslund, Magnus
(author)
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Digital Mammography with a Photon Counting Detector in a Scanned Multislit Geometry
- 2007
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Doctoral thesis (other academic/artistic)abstract
- Mammography screening aims to reduce the number of breast cancer deaths by early detection of the disease, which is one of the leading causes of deaths for middle aged women in the western world. The risk from the x-ray radiation in mammography is relatively low but still a factor in the benefit-risk ratio of screening. The characterization and optimization of a digital mammography system is presented in this thesis. The investigated system is shown to be highly dose efficient by employing a photon counting detector in a scanning multislit geometry. A novel automatic exposure control (AEC) is proposed and validated in clinical practise. The AEC uses the leading detector edge to measure the transmission of the breast. The exposure is modulated by altering the scan velocity during the scan. A W-Al anode-filter combination is proposed. The characterization of the photon counting detector is performed using the detective quantum efficiency. The effect of the photon counting detector and the multislit geometry on the measurement method is studied in detail. It is shown that the detector has a zero-frequency DQE of over 70\% and that it is quantum limited even at very low exposures. Efficient rejection of image-degrading secondary radiation is fundamental for a dose efficient system. The efficiency of the scatter rejection techniques currently used are quantified and compared to the multislit geometry. A system performance metric with its foundation in statistical decision theory is discussed. It is argued that a photon counting multislit system can operate at approximately half the dose compared to several other digital mammography techniques.
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