| 1. |
- Fredenberg, Erik, PhD, 1979-, et al.
(författare)
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A photon-counting detector for dual-energy breast tomosynthesis
- 2009
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Ingår i: Medical Imaging 2009. - : SPIE. ; , s. 72581-
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Konferensbidrag (refereegranskat)abstract
- We present the first evaluation of a recently developed silicon-strip detector for photon-counting dual-energy breast tomosynthesis. The detector is well suited for tomosynthesis with high dose efficiency and intrinsic scatter rejection. A method was developed for measuring the spatial resolution of a system based on the detector in terms of the three-dimensional modulation transfer function (MTF). The measurements agreed well with theoretical expectations, and it was seen that depth resolution was won at the cost of a slightly decreased lateral resolution. This may be a justifiable trade-off as clinical images acquired with the system indicate improved conspicuity of breast lesions. The photon-counting detector enables dual-energy subtraction imaging with electronic spectrumsplitting. This improved the detectability of iodine in phantom measurements, and the detector was found to be stable over typical clinical acquisition times. A model of the energy resolution showed that further improvements are witn reach by optimization of the detector.
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| 2. |
- Fredenberg, Erik, PhD, 1979-, et al.
(författare)
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Contrast-enhanced spectral mammography with a photon-counting detector
- 2010
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Ingår i: Medical physics (Lancaster). - : Wiley. - 0094-2405. ; 37:5, s. 2017-2029
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Spectral imaging is a method in medical x-ray imaging to extract information about the object constituents by the material-specific energy dependence of x-ray attenuation. In particular, the detectability of a contrast agent can be improved over a lumpy background. We have investigated a photon-counting spectral imaging system with two energy bins for contrast-enhanced mammography. System optimization and the potential benefit compared to conventional non-energy-resolved imaging was studied.Methods: A framework for system characterization was set up that included quantum and anatomical noise, and a theoretical model of the system was benchmarked to phantom measurements.Results: It was found that optimal combination of the energy-resolved images corresponded approximately to minimization of the anatomical noise, and an ideal-observer detectability index could be improved more than a factor of two compared to absorption imaging in the phantom study. In the clinical case, an improvement close to 80% was predicted for an average glandularity breast, and a factor of eight for dense breast tissue. Another 70% was found to be within reach for an optimized system.Conclusions: Contrast-enhanced spectral mammography is feasible and beneficial with the current system, and there is room for additional improvements.
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| 3. |
- Bornefalk, hans, et al.
(författare)
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Contrast-enhanced dual-energy mammography using a scanned multi-slit system : valuation of a differential beam filtering technique
- 2007
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Ingår i: Journal of Electronic Imaging (JEI). - : SPIE-Intl Soc Optical Eng. - 1017-9909 .- 1560-229X. ; 16:2, s. 023006-
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes a method for single-exposure, contrast-enhanced dual-energy imaging of tumors utilizing a scanned multislit system for digital mammography. This photon-counting system employs an array of silicon strip detectors mounted in an edge-on geometry. The line detectors and pre- and post-collimator slits are carefully aligned, and the multislit setup allows differential filtering of the x-ray beam in the pre-collimator slits. A high-energy image is constructed from those lines where the filter material has been chosen to harden the x-ray beam and the low-energy image from the lines with a filter producing softer beams. Both images are obtained in the same scan, eliminating the need to change tube voltages and anode materials and minimizing the risk of motion artifacts. The method is illustrated on a purpose-built phantom, and logarithmic subtraction of the images produces images essentially free of anatomical clutter with the contrast-enhanced targets clearly visible.
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| 4. |
- Bornefalk, Hans, et al.
(författare)
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Dual-energy imaging using a digital scanned multi-slit system for mammography : evaluation of a differential beam filtering technique - art. no. 61422O
- 2006
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Ingår i: Medical Imaging 2006: Physics of Medical Imaging, Pts 1-3. - BELLINGHAM, WA : SPIE-INT SOC OPTICAL ENGINEERING. - 0819461857 ; , s. O1422-O1422
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Konferensbidrag (refereegranskat)abstract
- This paper describes a method for single exposure contrast-enhanced dual-energy imaging of tumors utilizing a scanned multi-slit system for digital mammography. This photon counting system employs an array of silicon strip detectors in an edge-on geometry. In the multi-slit setup, the line detectors and pre-collimator slits are aligned orthogonal to the scan direction. This geometry is advantageous to dual-energy imaging, since it allows differential filtering of the x-ray beam in the pre-collimator slits. A high-energy image is constructed from those lines where the filter material has been chosen to harden the x-ray beam and the low-energy image from the lines with a filter producing softer beams. Both images are obtained in the same scan, eliminating the need to change tube voltages and anode materials and minimizing the risk of motion artifacts. The method is illustrated on a purpose-built phantom and logarithmic subtraction of the images produces images essentially free of anatomical clutter with the contrast-enhanced targets clearly visible.
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| 5. |
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| 6. |
- Hemmendorff, Magnus, 1972-
(författare)
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Motion estimation and compensation in medical imaging
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation presents a framework for estimation of motion fields in 2D images, 3D volumes and multi-dimensional signal registration. The primary application is motion compensation for sequences of medical images and volumes with contrast agents.The framework implies motion estimation in two steps where the intermediate result is constraints on the local motion vectors. One algorithm generates constraints and a second algorithm computes motion vector fields.We present two methods for generation of local motion constraints. The first method is based on phase from quadrature filters. The second method is based on canonical correlation and scalar products of quadrature filters. In both methods, a local confidence measure produced to increase accuracy and robustness.A mathematical result is a novel method for maximizing canonical correlation. The novel method can handle covariance matrices that are complex and singular.Parametric models, such as affine or finite elements, are used to estimate motion fields from local motion constraints and confidence measures. In order to control smoothness, the model is extended to incorporate stiffness and cost of deformations.Multiple layers of motion fields are estimated using implicit or explicit clustering of motion constraints. We also discuss some philosophical issues in the analysis of multiple motions. An extension of the known EM algorithm is presented together with experimental results on multiple layers for 2D images and 3D volumes. As an alternative to the EM algorithm, this thesis also introduces a method based on higher order outer products. In addition, we present a back projection algorithm for reconstruction of transparent layers.Clinical evaluation shows good results for 2D X-ray angiography images. Experimental results also show accurate motion estimates for 3D MRI mammograms and simulated images in 3D angiography.
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| 7. |
- Hemmendorff, Magnus, et al.
(författare)
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Phase-based Image Motion Estimation and Registration : Phoenix, AZ, USA
- 1999
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Ingår i: International Conference on Acoustics, Speech, and Signal Processing (ICASSP), 1999.
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Konferensbidrag (refereegranskat)abstract
- Conventional gradient methods (optical flow), for motion estimation assume intensity conservation between frames. This assumption is often violated in real applications. The remedy is a novel method that computes constraints on the local motion. These constraint are given on the same form as in conventional methods. Thus, it can directly substitute the gradient method in most applications. Experiments indicate a superior accuracy, even on synthetic images where the intensity conservation assumption is valid. The conventional gradient methods seem obsolete.
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| 8. |
- Hemmendorff, Magnus, et al.
(författare)
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Phase-based Multidimensional Volume Registration
- 2000
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Konferensbidrag (refereegranskat)abstract
- We present a method for accurate image registration and motion estimation in multidimensional volumes, such as 3D CT and MR images. The method is based on phase from quadrature filters, which makes it insensitive to variations in luminance and other disturbance in the images. The theory is not restricted to any particular kind of motion model or number of dimensions. Experimental results for affine motions in 3D show high accuracy.
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| 9. |
- Hemmendorff, Magnus, et al.
(författare)
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Phase-based multidimensional volume registration
- 2002
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Ingår i: IEEE Transactions on Medical Imaging. - 0278-0062 .- 1558-254X. ; 21:12, s. 1536-1543
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Tidskriftsartikel (refereegranskat)abstract
- We present a method for accurate image registration and motion compensation in multidimensional signals, such as two-dimensional (2-D) X-ray images and three-dimensional (3-D) computed tomography/magnetic resonance imaging volumes. The method is based on phase from quadrature filters, which makes it robust to noise and temporal intensity variations. The method is equally applicable to signals of two, three or higher number of dimensions. We use parametric models, e.g., affine models, finite elements or local affine models with global regularization. Experimental results show high accuracy for 2-D and 3-D motion compensation.
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| 10. |
- Hemmendorff, Magnus, 1972-
(författare)
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Single and Multiple Motion Field Estimation
- 1999
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents a framework for estimation of motion fields both for single and multiple layers. All the methods have in common that they generate or use constraints on the local motion. Motion constraints are represented by vectors whose directions describe one component of the local motion and whose magnitude indicate confidence.Two novel methods for estimating these motion constraints are presented. Both methods take two images as input and apply orientation sensitive quadrature filters. One method is similar to a gradient method applied on the phase from the complex filter outputs. The other method is based on novel results using canonical correlation presented in this thesis.Parametric models, e.g. affine or FEM, are used to estimate motion from constraints on local motion. In order to estimate smooth fields for models with many parameters, cost functions on deformations are introduced.Motions of transparent multiple layers are estimated by implicit or explicit clustering of motion constraints into groups. General issues and difficulties in analysis of multiple motions are described. An extension of the known EM algorithm is presented together with experimental results on multiple transparent layers with affine motions. Good accuracy in estimation allows reconstruction of layers using a backprojection algorithm. As an alternative to the EM algorithm, this thesis also introduces a method based on higher order tensors.A result with potential applicatications in a number of diffeerent research fields is the extension of canonical correlation to handle complex variables. Correlation is maximized using a novel method that can handle singular covariance matrices.
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| 11. |
- Hjärn, Torbjörn, et al.
(författare)
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Method and arrangement relating to x-ray imaging
- 2005
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Patent (populärvet., debatt m.m.)abstract
- novel X-ray apparatus is provided for three-dimensional imaging and in particular for tomosynthesis examination, which includes an X-ray source having a focal spot, a collimator including a plurality of slits, a detector assembly including a plurality of line detectors corresponding to respective ones of the plurality of slits and an exposure volume arranged between the collimator and the detector assembly. The X-ray source, the collimator and the detector assembly are arranged in series, so that each line detector is aligned with the corresponding collimator slit and the focal spot, and is simultaneously displaceable by a scan motion relative to the exposure volume. The scan motion is primarily a rotation around a rotation axis arranged such that the detector assembly is situated essentially between the rotation axis and the X-ray source.; Combined two and three-dimensional examination are also permitted according to the disclosed methods and apparatus.
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| 12. |
- Knutsson, Hans, et al.
(författare)
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Digital Adaptive Angiocardiography
- 1998
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Ingår i: Proceedings of the SSAB symposium on image analysis. ; , s. 65-68
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Konferensbidrag (refereegranskat)
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| 13. |
- Knutsson, Hans, et al.
(författare)
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Spatio-temporal filtering of digital angiography image data
- 1998
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Ingår i: Computer Methods and Programs in Biomedicine. - 0169-2607 .- 1872-7565. ; 57:1-2, s. 115-123
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Tidskriftsartikel (refereegranskat)abstract
- As welfare diseases become more common all over the world the demand for angiography examinations is increasing rapidly. The development of advanced medical signal processing methods has with few exceptions been concentrated towards CT and MR while traditional contrast based radiology depend on methods developed for ancient photography techniques despite the fact that angiography sequences are generally recorded in digital form. This article presents a new approach for processing of angiography sequences based on advanced image processing methods. The developed algorithm automatically processes angiography sequences containing motion artifacts that cannot be processed by conventional methods like digital subtraction angiography (DSA) and pixel shift due to non uniform motions. The algorithm can in simple terms be described as an ideal pixelshift filter carrying out shifts of different directions and magnitude according to the local motions in the image. In difference to conventional methods it is fully automatic, no mask image needs to be defined and the manual pixelshift operations, which are extremely time consuming, are eliminated. The algorithm is efficient and robust and is designed to run on standard hardware of a powerful workstation which excludes the need for expensive dedicated angiography platforms. Since there is no need to make additional recordings if the patient moves, the patient is exposed to less amount of radiation and contrast fluid. The most exciting benefits by this method are, however, that it opens up new areas for contrast based angiography that are not possible to process with conventional methods e.g. nonuniform motions and multiple layers of moving tissue. Advanced image processing methods provide significantly better image quality and noise suppression but do also provide the means to compute flow velocity and visualize the flow dynamics in the arterial trees by e.g. using color. Initial tests have proven that it is possible to discriminate capillary blood flow from angiography data which opens up interesting possibilities for estimating the blood flow in the heart muscle without use of nuclear methods.
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| 14. |
- Norrlid, Lilian del Risco, et al.
(författare)
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Imaging of small children prototype for photon counting tomosynthesis
- 2009
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Ingår i: Medical Imaging 2009. - : SPIE-Intl Soc Optical Eng.
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Konferensbidrag (refereegranskat)abstract
- We present data on a first prototype for photon counting tomosynthesis imaging of small children, which we call photoncounting tomosynthesis (PCT). A photon counting detector can completely eliminate electronic noise, which makes it ideal for tomosynthesis because of the low dose in each projection. Another advantage is that the detector allows for energy sensitivity in later versions, which will further lower the radiation dose. In-plane resolution is high and has been measured to be 5lp/mm, at least 4 times better than in CT, while the depth resolution was significantly lower than typical CT resolution. The image SNR decreased from 30 to 10 for a detail of 10 mm depth in increasing thickness of PMMA from 10 to 80 mm. The air kerma measured for PCT was 5.2 mGy, which leads to an organ dose to the brain of approximately 0.7 mGy. This dose is 96 % lower than a typical CT dose. PCT can be appealing for pediatric imaging since young children have an increased sensitivity to radiation induced cancers. We have acquired post mortem images of a newborn with the new device and with a state-of-the-art CT and compared the diagnostic information and dose levels of the two modalities. The results are promising but more work is needed to provide input to a next generation prototype that would be suitable for clinical trials.
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| 15. |
- Schmitzberger, Florian F, et al.
(författare)
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Development of low-dose photon-counting contrast-enhanced tomosynthesis with spectral imaging
- 2011
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Ingår i: Radiology. - : Radiological Society of North America (RSNA). - 0033-8419 .- 1527-1315. ; 259:2, s. 558-564
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To demonstrate the feasibility of low-dose photon-counting tomosynthesis in combination with a contrast agent (contrast material-enhanced tomographic mammography) for the differentiation of breast cancer. Materials and Methods: All studies were approved by the institutional review board, and all patients provided written informed consent. A phantom model with wells of iodinated contrast material (3 mg of iodine per milliliter) 1, 2, 5, 10, and 15 mm in diameter was assessed. Nine patients with malignant lesions and one with a high-risk lesion (atypical papilloma) were included (all women; mean age, 60 7 years). A multislit photon-counting tomosynthesis system was utilized (spectral imaging) to produce both low- and high-energy tomographic data (below and above the k edge of iodine, respectively ) in a single scan, which allowed for dual-energy visualization of iodine. Images were obtained prior to contrast material administration and 120 and 480 seconds after contrast material administration. Four readers independently assessed the images along with conventional mammograms, ultrasonographic images, and magnetic resonance images. Glandular dose was estimated. Results: Contrast agent was visible in the phantom model with simulated spherical tumor diameters as small as 5 mm. The average glandular dose was measured as 0.42 mGy per complete spectral imaging tomosynthesis scan of one breast. Because there were three time points (prior to contrast medium administration and 120 and 480 seconds after contrast medium administration), this resulted in a total dose of 1.26 mGy for the whole procedure in the breast with the abnormality. Seven of 10 cases were categorized as Breast Imaging Reporting and Data System score of 4 or higher by all four readers when reviewing spectral images in combination with mammograms. One lesion near the chest wall was not captured on the spectral image because of a positioning problem. Conclusion: The use of contrast-enhanced tomographic mammography has been demonstrated successfully in patients with promising diagnostic benefit. Further studies are necessary to fully assess diagnostic sensitivity and specificity.
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