| 511. |
- Jonsson, Joakim H, et al.
(författare)
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Registration accuracy for MR images of the prostate using a subvolume based registration protocol
- 2011
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Ingår i: Radiation Oncology. - 1748-717X. ; 6:1, s. 73-
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: In recent years, there has been a considerable research effort concerning the integration of magnetic resonance imaging (MRI) into the external radiotherapy workflow motivated by the superior soft tissue contrast as compared to computed tomography. Image registration is a necessary step in many applications, e.g. in patient positioning and therapy response assessment with repeated imaging. In this study, we investigate the dependence between the registration accuracy and the size of the registration volume for a subvolume based rigid registration protocol for MR images of the prostate.METHODS: Ten patients were imaged four times each over the course of radiotherapy treatment using a T2 weighted sequence. The images were registered to each other using a mean square distance metric and a step gradient optimizer for registration volumes of different sizes. The precision of the registrations was evaluated using the center of mass distance between the manually defined prostates in the registered images. The optimal size of the registration volume was determined by minimizing the standard deviation of these distances.RESULTS: We found that prostate position was most uncertain in the anterior-posterior (AP) direction using traditional full volume registration. The improvement in standard deviation of the mean center of mass distance between the prostate volumes using a registration volume optimized to the prostate was 3.9 mm (p < 0.001) in the AP direction. The optimum registration volume size was 0 mm margin added to the prostate gland as outlined in the first image series.CONCLUSIONS: Repeated MR imaging of the prostate for therapy set-up or therapy assessment will both require high precision tissue registration. With a subvolume based registration the prostate registration uncertainty can be reduced down to the order of 1 mm (1 SD) compared to several millimeters for registration based on the whole pelvis.
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| 512. |
- Jonsson, Jakob, et al.
(författare)
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Measuring Gambling Reinforcers, Over Consumption and Fallacies : The Psychometric Properties and Predictive Validity of the Jonsson-Abbott Scale
- 2017
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Ingår i: Frontiers in Psychology. - : Frontiers Media SA. - 1664-1078. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Traditionally, gambling and problem gambling research relies on cross-sectional and retrospective designs. This has compromised identification of temporal relationships and causal inference. To overcome these problems a new questionnaire, the Jonsson-Abbott Scale (JAS), was developed and used in a large, prospective, general population study, The Swedish Longitudinal Gambling Study (Swelogs). The JAS has 11 items and seeks to identify early indicators, examine relationships between indicators and assess their capacity to predict future problem progression. The aims of the study were to examine psychometric properties of the JAS (internal consistency and dimensionality) and predictive validity with respect to increased gambling risk and problem gambling onset. The results are based on repeated interviews with 3818 participants. The response rate from the initial baseline wave was 74%. The original sample consisted of a random, stratified selection from the Swedish population register aged between 16 and 84. The results indicate an acceptable fit of a three-factor solution in a confirmatory factor analysis with ‘Over consumption,’ ‘Gambling fallacies,’ and ‘Reinforcers’ as factors. Reinforcers, Over consumption and Gambling fallacies were significant predictors of gambling risk potential and Gambling fallacies and Over consumption were significant predictors of problem gambling onset (incident cases) at 12 month follow up. When controlled for risk potential measured at baseline, the predictor Over consumption was not significant for gambling risk potential at follow up. For incident cases, Gambling fallacies and Over consumption remained significant when controlled for risk potential. Implications of the results for the development of problem gambling, early detection, prevention, and future research are discussed.
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| 513. |
- Jonsson, Jakob, 1972-
(författare)
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Simplicial Complexes of Graphs
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Let G be a finite graph with vertex set V and edge set E. A graph complex on G is an abstract simplicial complex consisting of subsets of E. In particular, we may interpret such a complex as a family of subgraphs of G. The subject of this thesis is the topology of graph complexes, the emphasis being placed on homology, homotopy type, connectivity degree, Cohen-Macaulayness, and Euler characteristic. We are particularly interested in the case that G is the complete graph on V. Monotone graph properties are complexes on such a graph satisfying the additional condition that they are invariant under permutations of V. Some well-studied monotone graph properties that we discuss in this thesis are complexes of matchings, forests, bipartite graphs, disconnected graphs, and not 2-connected graphs. We present new results about several other monotone graph properties, including complexes of not 3-connected graphs and graphs not coverable by p vertices. Imagining the vertices as the corners of a regular polygon, we obtain another important class consisting of those graph complexes that are invariant under the natural action of the dihedral group on this polygon. The most famous example is the associahedron, whose faces are graphs without crossings inside the polygon. Restricting to matchings, forests, or bipartite graphs, we obtain other interesting complexes of noncrossing graphs. We also examine a certain "dihedral" variant of connectivity. The third class to be examined is the class of digraph complexes. Some well-studied examples are complexes of acyclic digraphs and not strongly connected digraphs. We present new results about a few other digraph complexes, including complexes of graded digraphs and non-spanning digraphs. Many of our proofs are based on Robin Forman's discrete version of Morse theory. As a byproduct, this thesis provides a loosely defined toolbox for attacking problems in topological combinatorics via discrete Morse theory. In terms of simplicity and power, arguably the most efficient tool is Forman's divide and conquer approach via decision trees, which we successfully apply to a large number of graph and digraph complexes.
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| 514. |
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| 515. |
- Jonsson, Karin, 1974-
(författare)
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Effect of Hyporheic Exchange on Conservative and Reactive Solute Transport in Streams : Model Assessments Based on Tracer Tests
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Understanding of the processes affecting solute transport in flowing water is important for the possibility to predict the evolution with time of polluted stream systems. This thesis presents tracer experiment methodology and model developments for solute transport in streams, with special focus on retention processes and their effect on solute stream transport. Results are presented from a tracer experiment in the Säva Stream, Uppland County, Sweden, where both a conservative (3H as tritiated water) and a reactive (51Cr as trivalent chromium ion) tracer were injected simultaneously. The time and length scales of the experiment were prolonged compared to previous studies, which allowed for new critical tests of different model concepts. It was found that the hyporheic exchange greatly affected the solute transport of both tracers. However, the retention of chromium was significantly more pronounced. About 76% of the injected chromium was lost from the stream water phase directly after the passage of the pulse 30 km downstream of the injection point. The inventory of chromium in the sediments indicated that the main part was retrieved in the hyporheic zone. Both a diffusive and an advective hyporheic exchange model were developed and evaluated versus independent observations in the stream water and hyporheic zone. Analytical expressions for the central temporal moments of the breakthrough curve and semi-analytical solutions for the solute concentration in the Laplace domain were derived. Both models were found useful in representing the observations.For the transport of the reactive solute, it was found essential to consider a kinetic sorption on to particulate matter in the hyporheic zone. The time needed for a wash-out of 75% of the maximum uptake in the hyporheic zone was found to be ~85 times longer for the reactive solute, compared to the conservative solute. Neglecting the sorption kinetics in the transport model yielded significant errors in the central temporal moments, which implied an incorrect description of the wash-out process from the hyporheic zone. Independent observations in the stream water and hyporheic zone as well as choice of evaluation method are essential for a correct interpretation of the processes.A first attempt was also made to link model parameters such as the residence time in the hyporheic zone with measurable parameters of the stream. Such a relationship offers the possibility to generalize results for other streams and stream conditions. A generic study of the transport of an inert solute in the Lule River, Sweden, using this kind of relationship, indicated that the hyporheic exchange can have a large practical implication.
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| 516. |
- Jonsson, K., et al.
(författare)
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Effect of sorption kinetics on the transport of solutes in streams
- 2001
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Ingår i: Science of the Total Environment. - 0048-9697 .- 1879-1026. ; 266:03-jan, s. 239-247
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Tidskriftsartikel (refereegranskat)abstract
- To provide an appropriate description of the transport of a reactive substance in a stream, it is important to include a kinetic description of sorption in a transport model. In this study, first-order sorption kinetics was taken into account in both the transient storage zone and the stream water, and analytical expressions for relative error in statistical moments of the residence time PDF, resulting from disregarding sorption kinetics, were derived. The sorption rate coefficient in the water was found to influence the error in the expected value, and the error was found to approach infinity as the travel distance or sorption rate coefficient approaches zero. The sorption rate coefficient in the storage zone influences only higher-order moments. For sufficiently long distances, the error in the variance was found to be more pronounced when sorption kinetics in the storage zone was disregarded, than when sorption kinetics in the stream water was disregarded. Parameter values from a tracer experiment with Cr-51 revealed that the relative error in the variance could be more than 100%, if sorption kinetics in the storage zone is disregarded.
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| 517. |
- Jonsson, K., et al.
(författare)
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Hyporheic exchange of reactive and conservative solutes in streams - tracer methodology and model interpretation
- 2003
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 278:04-jan, s. 153-171
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Tidskriftsartikel (refereegranskat)abstract
- A transient storage model is evaluated using results from a tracer experiment, where a conservative and a reactive tracer (H-3 and Cr-51(III)) were injected simultaneously and monitored in stream water and bed sediment. About 76% of the chromium was lost from the stream water on the reach 30 km downstream of the injection point directly after the passage of the pulse in the flowing water. The bed sediment hosted the main part of the retained chromium. The time to washout 75% of the maximum solute uptake in the sediment was similar to 85 times longer for chromium than for tritium (i.e. similar to 45 days). It was possible to describe the sediment-water exchange with a diffusive flux formulation that could be evaluated using tritium breakthrough curves in the stream water or the tritium inventory breakthrough curves in the sediment. This experiment revealed further that observations of chromium concentrations in the sediment were essential for the quantifying of sorption properties, as it was not possible to catch accurately the time scale of sorption within the duration of the breakthrough curves in the stream water. There was a clear need for a rate-limited description of the sorption of chromium in the sediment. We found that a first-order kinetic description of the sorption process could acceptably describe the breakthrough curves in both the stream water and the bed sediment.
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| 518. |
- Jonsson, Karin, et al.
(författare)
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Hyporheic Exchange of Reactive and Conservative Solutes in Streams - Tracer Methodology and Model Interpretation
- 2003
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Ingår i: Journal of Hydrology. - 0022-1694 .- 1879-2707. ; 278:1-4, s. 153-171
-
Tidskriftsartikel (refereegranskat)abstract
- A transient storage model is evaluated using results from a tracer experiment, where a conservative and a reactive tracer (3H and 51Cr(III)) were injected simultaneously and monitored in stream water and bed sediment. About 76% of the chromium was lost from the stream water on the reach 30 km downstream of the injection point directly after the passage of the pulse in the flowing water. The bed sediment hosted the main part of the retained chromium. The time to washout 75% of the maximum solute uptake in the sediment was ∼85 times longer for chromium than for tritium (i.e. ∼45 days). It was possible to describe the sediment-water exchange with a diffusive flux formulation that could be evaluated using tritium breakthrough curves in the stream water or the tritium inventory breakthrough curves in the sediment. This experiment revealed further that observations of chromium concentrations in the sediment were essential for the quantifying of sorption properties, as it was not possible to catch accurately the time scale of sorption within the duration of the breakthrough curves in the stream water. There was a clear need for a rate-limited description of the sorption of chromium in the sediment. We found that a first-order kinetic description of the sorption process could acceptably describe the breakthrough curves in both the stream water and the bed sediment.
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| 519. |
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| 520. |
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