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- Gustafsson, Agnetha, et al.
(författare)
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Evaluation of attenuation corrections using Monte Carlo simulated lung SPECT
- 1998
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 43:8, s. 2325-2336
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Tidskriftsartikel (refereegranskat)abstract
- SPECT (single photon emission computed tomography) images are distorted by photon attenuation. The effect is complex in the thoracic region due to different tissue densities. This study compares the effect on the image homogeneity of two different methods of attenuation correction in lung SPECT; one pre-processing and one post-processing method. This study also investigates the impact of attenuation correction parameters such as lung contour, body contour, density of the lung tissue and effective attenuation coefficient. The Monte Carlo technique was used to simulate SPECT studies of a digital thorax phantom containing a homogeneous activity distribution in the lung. Homogeneity in reconstructed images was calculated as the coefficient of variation (CV). The isolated effect of the attenuation correction was assessed by normalizing pixel values from the attenuation corrected lung by pixel values from the lung with no attenuation effects. Results show that the CV decreased from 12.8% with no attenuation correction to 4.4% using the post-processing method and true densities in the thoracic region. The impact of variations in the definition of the body contour was found to be marginal while the corresponding effect of variations in the lung contour was substantial
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- Hanson, Maj, et al.
(författare)
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The influence of particle size interactions on the magnetization susceptibility of nanometre-size particles
- 1995
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Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 7, s. 9269-9277
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Tidskriftsartikel (refereegranskat)abstract
- We studied the magnetic properties of frozen magnetic liquids containing amorphous Fe1-xCx particles. By varying the particle size and concentration, we could separate single particle effects from interactions. In samples containing particles with median diameters 5.0 nm and 3.8 nm and with spontaneous saturation magnetizations 7.1 kA m-1 and 9.2 kA m -1, effects of particle interactions are observed. For 3.2 nm no interactions were observed. In samples with negligible interactions the superparamagnetic blocking temperature increases with the particle size. The effective anisotropy constant increases with decreasing particle size, implying that the anisotropy is enhanced by surface effects.
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- Lindberg, A. Michael, et al.
(författare)
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Echovirus 5 : infectious transcripts and complete nucleotide sequence from uncloned cDNA
- 1999
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Ingår i: Virus Research. - 0168-1702. ; 59:1, s. 75-87
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Tidskriftsartikel (refereegranskat)abstract
- Echovirus 5 (EV5) may be isolated from various neurological and exanthematic diseases. To determine the relationship of EV5 to other enteroviruses and for studies of its interactions with the target cell, the complete nucleotide sequence of EV5 was determined. Three overlapping fragments, collectively representing the complete genome, were amplified with RT–PCR and sequenced. Analysis of the EV5 sequence revealed a typical enterovirus-like organization of the genome. To verify that the cDNA generated sequence was derived from infectious viruses, complete EV5 genomes were amplified in one amplicon by long distance PCR. Transfection of in vitro transcribed RNA from these amplicons into cell cultures resulted in replicating EV5. Comparison of the overall nucleotide and amino acid sequences demonstrates that EV5 can be regarded as a coxsackievirus B-like enterovirus. Variable sequences between EV5 and the well characterized coxsackievirus B3 (CVB3) are for the most part observed for amino acid residues that correspond to exposed sequences in the CVB3 capsid. This observation indicates that the reported EV5 strain recently diverged from group B coxsackieviruses.
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