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| 3. |
- Apostolakis, A., et al.
(författare)
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Measurement of the energy dependence of the form factor f+ in K 0 e3 decay
- 2000
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Ingår i: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 473:1, s. 186-192
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Tidskriftsartikel (refereegranskat)abstract
- Neutral-kaon decays to πeν were analysed to determine the q2 dependence of the K0e3 electroweak form factor f+. Based on 365612 events, this form factor was found to have a linear dependence on q2 with a slope λ+=0.0245±0.0012stat±0.0022syst.
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| 4. |
- Arlig, A, et al.
(författare)
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Attenuation correction in quantitative SPECT of cerebral blood flow: a Monte Carlo study
- 2000
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 45:12, s. 3847-3859
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Tidskriftsartikel (refereegranskat)abstract
- Monte Carlo simulation has been used to produce projections from a voxel-based brain phantom, simulating a 99mTc-HMPAO single photon emission computed tomography (SPECT) brain investigation. For comparison, projections free from the effects of attenuation and scattering were also simulated, giving ideal transaxial images after reconstruction. Three methods of attenuation correction were studied: (a) a pre-processing method, (b) a post-processing uniform method and (c) a post-processing non-uniform method using a density map. The accuracy of these methods was estimated by comparison of the reconstructed images with the ideal images using the normalized mean square error, NMSE, and quantitative values of the regional cerebral blood flow, rCBF. A minimum NMSE was achieved for the effective linear attenuation coefficient mu(eff) = 0.07 (0.09) cm(-1) for the uniform(pre) method, the effective mass attenuation coefficient mu(eff)/rho = 0.08 (0.10) cm2 g(-1) for the uniform(post) method and mu(eff)/rho = 0.12 (0.13) cm2 g(-1) for the non-uniform(post) method. Values in parentheses represent the case of dual-window scatter correction. The non-uniform(post) method performed better, as measured by the NMSE, both with and without scatter correction. Furthermore, the non-uniform(post) method gave, on average, more accurate rCBF values. Although the difference in rCBF accuracy was small between the various methods, the same method should be used for patient studies as for the reference material.
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- Bååth, Lars, 1948-
(författare)
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To See What You Cannot See
- 2003
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Ingår i: Image Analysis. - Heidelberg : Springer. - 9783540406013 ; , s. 108-108
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Bokkapitel (populärvet., debatt m.m.)abstract
- This paper discusses imaging with complex data from micro-wave, mm-wave, and optical interferometers. An overview of methods to extract physical parameters as images from interferometer data is made and two- and three-dimensional images of gas flows, quasi-stellar objects, steel melts, and fiber material such as wood are presented.
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| 7. |
- Börlin, Niclas, 1968-, et al.
(författare)
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The precision of radiostereometric measurements : manual vs. digital measurements
- 2002
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Ingår i: Journal of Biomechanics. - : Elsevier. - 0021-9290 .- 1873-2380. ; 35:1, s. 69-79
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Tidskriftsartikel (refereegranskat)abstract
- The precision of digital vs. manual radiostereometric measurements in total hip arthroplasty was evaluated using repeated stereoradiographic exposures with an interval of 10–15 min. Ten Lubinus SP2 stems cemented into bone specimens and 12 patients with the same stem design were used to evaluate the precision of stem translations and rotations. The precision of translations and rotations of the cup and femoral head penetration was studied in 12 patients with whole polyethylene cups.The use of a measurement method based on digitised radiographs improved the precision for some of the motion parameters, whereas many of them did not change. A corresponding pattern was observed for both the intra- and interobserver error. Of the wear parameters, the most pronounced improvements were the 3D wear and in the proximal-distal direction, although the anterior-posterior precision was also improved. The mean errors of rigid body and elliptic fitting decreased in all evaluations but one, consistent with a more reproducible identification of the markers centres and the edge of the femoral head.Increased precision of radiostereometric measurements may be used to increase the statistical power of future randomised studies and to study new fields in orthopaedics requiring higher precision than has been available with RSA based on manual measurements.
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- Eriksson-Bylund, Nina, 1971-
(författare)
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Spatio-temporal filtering of ultrasound image sequences
- 2004
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A number of diseases result in reduced perfusion of the vital organs of the body. Measures of the blood flow in the small vessels (the perfusion) of these organs would contribute significantly to a clinical diagnosis. Myocardial contrast echocardiography is a rapidly developing technique for non-invasive ultrasound imaging of perfusion. The work presented in this thesis is related to the preprocessing of the ultrasound data in order to facilitate the segmentation of the heart walls in which the perfusion is to be estimated.In an ultrasound image artifacts can occur for a number of reasons. These lead to a more complicated interpretation procedure as important information may be obscured or lost. One of the most frequently occuring artifacts in diagnostic ultrasound imaging is reverberation. This type of artifact is caused by the incorrect assumption that the ultrasound pulse's propagation path is always straight to a backscattering target and straight back to the transducer. Reverberation artifacts may be seen as multiple ghost structures in the ultrasound image.A method to detect these reverberation artifacts has been developed and tested on three different ultrasound image sequences. The method uses ratios of lognormal quadrature filter responses to estimate the local bandwidth of the ultrasound signal. For the in-vivo sequences the result is a "map" indicating the artifact locations.In order to reduce the reverberation artifacts an interactive procedure for estimating two dimensional and three-dimensional Wiener filters has been developed. The design procedure used is a weighted least squares approach, in which both a frequency and a spatiotemporal weighting function are used to optimize the filter. In the results after filtering with the optimized filters the magnitude of the artifact is significantly reduced. For the in-vivo sequences the 3D approach display a better selection capability compared to the 2D approach.The results from these studies show that the proposed methods constitute a promising basis for a useful clinical tool.
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