| 1. |
- Agell, Jonas, et al.
(författare)
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Labor Supply Prediction when Tax Avoidance Matters
- 1999
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We examine how tax avoidance in the form of trade in well-functioning asset markets affects the emipircal study of labor supply. We discuss the implications for tax policy analysis, and we show that a failure to account for avoidance responses may lead to huge errors when predicting how tax reform affects labor supply, tax revenue, and the welfare cost of taxation. in conclusion we argue that our model may explain a number of otherwise hard to understand dimensions of tax payer response.
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| 2. |
- Agell, Jonas, et al.
(författare)
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Labor supply prediction when tax avoidance matters
- 1999
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Labor Supply Prediction when Tax Avoidance Matters Jonas Agell, Mats Persson and Hans Sacklén, 1999/16, September 1999 We examine how tax avoidance in the form of trade in well-functioning asset markets affects the empirical study of labor supply. We di
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| 3. |
- Bornefalk, Hans, 1974-, et al.
(författare)
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Allowable forward model misspecification for accurate basis decomposition in a silicon detector based spectral CT
- 2015
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Ingår i: IEEE Transactions on Medical Imaging. - : IEEE Press. - 0278-0062 .- 1558-254X. ; 34:3, s. 788-795
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Tidskriftsartikel (refereegranskat)abstract
- Material basis decomposition in the sinogram domain requires accurate knowledge of the forward model in spectral computed tomography (CT). Misspecifications over a certain limit will result in biased estimates and make quantum limited (where statistical noise dominates) quantitative CT difficult. We present a method whereby users can determine the degree of allowed misspecification error in a spectral CT forward model and still have quantification errors that are limited by the inherent statistical uncertainty. For a particular silicon detector based spectral CT system, we conclude that threshold determination is the most critical factor and that the bin edges need to be known to within 0.15 keV in order to be able to perform quantum limited material basis decomposition. The method as such is general to all multibin systems.
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| 4. |
- Bornefalk, Hans, et al.
(författare)
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Effect of Temperature Variation on the Energy Response of a Photon Counting Silicon CT Detector
- 2013
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Ingår i: IEEE Transactions on Nuclear Science. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9499 .- 1558-1578. ; 60:2, s. 1442-1449
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Tidskriftsartikel (refereegranskat)abstract
- The effect of temperature variation on pulse height determination accuracy is determined for a photon counting multibin silicon detector developed for spectral CT. Theoretical predictions of the temperature coefficient of the gain and offset are similar to values derived from synchrotron radiation measurements in a temperature controlled environment. By means of statistical modeling, we conclude that temperature changes affect all channels equally and with separate effects on gain and threshold offset. The combined effect of a 1 degrees C temperature increase is to decrease the detected energy by 0.1 keV for events depositing 30 keV. For the electronic noise, no statistically significant temperature effect was discernible in the data set, although theory predicts a weak dependence. The method is applicable to all x-ray detectors operating in pulse mode.
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| 5. |
- Bornefalk, Hans, et al.
(författare)
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Necessary forward model specification accuracy for basis material decomposition in spectral CT
- 2014
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Ingår i: Medical Imaging 2014. - : SPIE - International Society for Optical Engineering. - 9780819498267 ; , s. 90332I-
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Konferensbidrag (refereegranskat)abstract
- Material basis decomposition in the sinogram domain requires accurate knowledge of the forward model in spectral CT. Misspecifications over a certain limit will result in biased estimates and make quantum limited quantitative CT difficult. We present a method whereby users can determine the degree of allowed misspecification error in a spectral CT forward model, and still have quantification errors that are quantum limited.
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| 6. |
- Bornefalk, Hans, et al.
(författare)
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Theoretical Comparison of the Iodine Quantification Accuracy of Two Spectral CT Technologies
- 2014
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Ingår i: IEEE Transactions on Medical Imaging. - 0278-0062 .- 1558-254X. ; 33:2, s. 556-565
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Tidskriftsartikel (refereegranskat)abstract
- We compare the theoretical limits of iodine quantification for the photon counting multibin and dual energy technologies. Dual energy systems by necessity have to make prior assumptions in order to quantify iodine. We explicitly allow the multibin system to make the same assumptions and also allow them to be wrong. We isolate the effect of technology from imperfections and implementation issues by assuming both technologies to be ideal, i.e., without scattered radiation, unity detection efficiency and perfect energy response functions, and by applying the Cramer-Rao lower bound methodology to assess the quantification accuracy. When priors are wrong the maximum likelihood estimates will be biased and the mean square error of the quantification error is a more appropriate figure of merit. The evaluation assumes identical X-ray spectra for both methodologies and for that reason a sensitivity analysis is performed with regard to the assumed X-ray spectrum. We show that when iodine is quantified over regions of interest larger than 6 cm, multibin systems benefit by independent estimation of three basis functions. For smaller regions of interest multibin systems can increase quantification accuracy by making the same prior assumptions as dual energy systems.
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| 7. |
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| 8. |
- Grönberg, Fredrik, et al.
(författare)
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Dimensionality and Background Cancellation in Energy Selective X-Ray Imaging
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Purpose: The set of linear attenuation coefficients that belong to materials in the human body is commonly assumed to be spanned by two basis functions in the range of clinical x-ray energies, even though there is evidence that the dimensionality of this set is greater than two. It has not yet been clear that the use of a third basis function could be beneficial in absence of contrast agents.Approach: In this work, the choice of the number of basis functions used in the basis decomposition method is studied for the task of producing an image where a third material is separated from a background of two other materials, in a case where none of the materials have a K-edge in the range of considered x-ray energies (20-140 keV). The case of separating iron from mixtures of liver and adipose tissue is studied with a simulated phantom which incorporates random and realistic tissue variability.Results: Inclusion of a third basis function improves the quantitative estimate of iron concentration by several orders of magnitude in terms of mean squared error in the resulting image.Conclusions: The inclusion of a third basis function in the basis decomposition is essential for the studied imaging task and could have potential application for quantitative estimation of iron concentration from material decomposed images.
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| 9. |
- Grönberg, Fredrik, et al.
(författare)
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Image reconstruction based on energy-resolved image data from a photon-counting multi-bin detector
- 2015
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Patent (populärvet., debatt m.m.)abstract
- There is provided a method of image reconstruction based on energy-resolved image data from a photon-counting multi-bin detector or an intermediate storage. The method comprises processing (S1) the energy-resolved image data by performing at least two separate basis decompositions using different number of basis functions for modeling linear attenuation, wherein a first basis decomposition is performed using a first smaller set of basis functions to obtain at least one first basis image representation, and wherein a second basis decomposition is performed using a second larger set of basis functions to obtain at least one second basis image representation. The method also comprises reconstructing a first image based on said at least one first basis image representation obtained from the first basis decomposition, and combining the first image with information representative of said at least one second basis image representation.
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| 10. |
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