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| 2. |
- Fredenberg, Erik, PhD, 1979-, et al.
(författare)
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Photon-Counting Spectral Phase-Contrast Mammography
- 2012
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Ingår i: Medical Imaging 2012. - : SPIE - International Society for Optical Engineering. - 9780819489623
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Konferensbidrag (refereegranskat)abstract
- Phase-contrast imaging is an emerging technology that may increase the signal-difference-to-noise ratio in medical imaging. One of the most promising phase-contrast techniques is Talbot interferometry, which, combined with energy-sensitive photon-counting detectors, enables spectral differential phase-contrast mammography. We have evaluated a realistic system based on this technique by cascaded-systems analysis and with a task-dependent ideal-observer detectability index as a figure-of-merit. Beam-propagation simulations were used for validation and illustration of the analytical framework. Differential phase contrast improved detectability compared to absorption contrast, in particular for fine tumor structures. This result was supported by images of human mastectomy samples that were acquired with a conventional detector. The optimal incident energy was higher in differential phase contrast than in absorption contrast when disregarding the setup design energy. Further, optimal weighting of the transmitted spectrum was found to have a weaker energy dependence than for absorption contrast. Taking the design energy into account yielded a superimposed maximum on both detectability as a function of incident energy, and on optimal weighting. Spectral material decomposition was not facilitated by phase contrast, but phase information may be used instead of spectral information.
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| 4. |
- Norlin, P., et al.
(författare)
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Evaluation of junction termination for silicon X-ray detectors
- 2011
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 648, s. S68-S71
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Tidskriftsartikel (refereegranskat)abstract
- Junction terminations intended for silicon strip X-ray detectors were evaluated experimentally and with simulations, with respect to their tolerance to radiation-induced surface charge. The terminations were designed with an inner guard ring biased to the same potential as the active anode and multiple p+-doped rings with metallic field plates at floating potential. Two designs, one with 9 and one with 14 floating rings were evaluated and applied to simple non-segmented test diodes. The test diodes were irradiated with X-rays to 72-74 kGy, the surface charge was determined from capaciatance-voltage measurements, and reverse breakdown voltage was determined from I-V-curves. Both simulations and experiments showed superior performance of the 14-ring design. The experimentally determined surface charge density after irradiation was in the order of +5 x 10(11) cm(-2), and the breakdown voltages were similar to 900 and 1600 V for the 9-ring and 14-ring termination, respectively.
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| 5. |
- Borovok, I, et al.
(författare)
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Streptomyces spp. contain class Ia and class II ribonucleotide reductases: expression analysis of the genes in vegetative growth
- 2002
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Ingår i: Microbiology (Reading, England). - : Microbiology Society. - 1350-0872 .- 1465-2080. ; 148:Pt 2, s. 391-404
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Tidskriftsartikel (refereegranskat)abstract
- Genes encoding two ribonucleotide reductases (RNRs) were identified in members of the genusStreptomyces. One gene,nrdJ, encoded an oligomeric protein comprising four identical subunits each with a molecular mass of ∼108 kDa. The activity of this protein depended on the presence of 5′-deoxyadenosylcobalamine (coenzyme B12), establishing it as a class II RNR. TheStreptomyces clavuligerus nrdJgene was cloned, using internal peptide sequences from the purified protein, and was found to encode a polypeptide of 961 aa. Molecular phylogenetic analysis showed that theS. clavuligerusclass II RNR shares significant similarity with most other bacterial and archaeal class II RNRs. Two other genes,nrdAandnrdB, were initially identified in theStreptomyces coelicolorgenome database in unannotated ORFs as encoding a class Ia RNR. Southern analysis demonstrated that thenrdABgenes were present in differentStreptomycesspp. TheS. coelicolor nrdABgenes were cloned and expressed inEscherichia coli, and the recombinant proteins were shown to represent a class I RNR. It was shown, using quantitative real-time PCR, that theS. clavuligerusclass Ia and class II RNR genes were differentially transcribed during vegetative growth. The copy number of the class IInrdJtranscripts was approximately constant throughout the exponential phase of vegetative growth (3–5×105copies per 400 ng total RNA after reverse transcription). In contrast, the copy number of the class IanrdABtranscripts was some 10- to 20-fold less than that ofnrdJin the early-exponential growth phase (2·8×104copies), and decreased markedly at the mid-exponential (4×103copies) and late-exponential phases (1·1×103copies) of growth. A possible role for the involvement of two RNRs during vegetative growth is discussed.
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| 6. |
- El-Sayed, Najib M., et al.
(författare)
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The genome sequence of Trypanosoma cruzi, etiologic agent of Chagas disease.
- 2005
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 309:5733, s. 409-15
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Tidskriftsartikel (refereegranskat)abstract
- Whole-genome sequencing of the protozoan pathogen Trypanosoma cruzi revealed that the diploid genome contains a predicted 22,570 proteins encoded by genes, of which 12,570 represent allelic pairs. Over 50% of the genome consists of repeated sequences, such as retrotransposons and genes for large families of surface molecules, which include trans-sialidases, mucins, gp63s, and a large novel family (>1300 copies) of mucin-associated surface protein (MASP) genes. Analyses of the T. cruzi, T. brucei, and Leishmania major (Tritryp) genomes imply differences from other eukaryotes in DNA repair and initiation of replication and reflect their unusual mitochondrial DNA. Although the Tritryp lack several classes of signaling molecules, their kinomes contain a large and diverse set of protein kinases and phosphatases; their size and diversity imply previously unknown interactions and regulatory processes, which may be targets for intervention.
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| 8. |
- Aslund, Magnus, et al.
(författare)
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Detectors for the future of X-ray imaging
- 2010
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Ingår i: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 139:1-3, s. 327-333
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Tidskriftsartikel (refereegranskat)abstract
- In recent decades, developments in detectors for X-ray imaging have improved dose efficiency. This has been accomplished with for example, structured scintillators such as columnar CsI, or with direct detectors where the X rays are converted to electric charge carriers in a semiconductor. Scattered radiation remains a major noise source, and fairly inefficient anti-scatter grids are still a gold standard. Hence, any future development should include improved scatter rejection. In recent years, photon-counting detectors have generated significant interest by several companies as well as academic research groups. This method eliminates electronic noise, which is an advantage in low-dose applications. Moreover, energy-sensitive photon-counting detectors allow for further improvements by optimising the signal-to-quantum-noise ratio, anatomical background subtraction or quantitative analysis of object constituents. This paper reviews state-of-the-art photon-counting detectors, scatter control and their application in diagnostic X-ray medical imaging. In particular, spectral imaging with photon-counting detectors, pitfalls such as charge sharing and high rates and various proposals for mitigation are discussed.
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