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- West, Jay B., et al.
(författare)
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Comparison and evaluation of retrospective intermodality image registration techniques
- 1997
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Ingår i: SPIE - The International Society for Optical Engineering. - : SPIE - International Society for Optical Engineering. ; , s. 332-347
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Konferensbidrag (refereegranskat)abstract
- All retrospective image registration methods have attached to them some intrinsic estimate of registration error. However, this estimate of accuracy may not always be a good indicator of the distance between actual and estimated positions of targets within the cranial cavity. This paper describes a project whose principal goal is to use a prospective method based on fiducial markers as a ’gold standard’ to perform an objective, blinded evaluation of the accuracy of several retrospective image-to-image registration techniques. Image volumes of three modalities – CT, MR, and PET – were taken of patients undergoing neurosurgery at Vanderbilt University Medical Center. These volumes had all traces of the fiducial markers removed, and were provided to project collaborators outside Vanderbilt, who then performed retrospective registrations on the volumes, calculating transformations from CT to MR and/or from PET to MR, and communicated their transformations to Vanderbilt where the accuracy of each registration was evaluated. In this evaluation the accuracy is measured at multiple ’regions of interest,’ i.e. areas in the brain which would commonly be areas of neurological interest. A region is defined in the MR image and its centroid C is determined. Then the prospective registration is used to obtain the corresponding point C’ in CT or PET. To this point the retrospective registration is then applied, producing C’ in MR. Statistics are gathered on the target registration error (TRE), which is the disparity between the original point C and its corresponding point C’. A second goal of the project is to evaluate the importance of correcting geometrical distortion in MR images, by comparing the retrospective TRE in the rectified images, i.e., those which have had the distortion correction applied, with that of the same images before rectification. This paper presents preliminary results of this study along with a brief description of each registration technique and an estimate of both preparation and execution time needed to perform the registration.
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| 3. |
- Clarke, Robert, et al.
(författare)
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Lowering blood homocysteine with folic acid based supplements : Meta-analysis of randomised trials
- 1998
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Ingår i: British Medical Journal. - : BMJ. - 0959-8146. ; 316:7135, s. 894-898
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Forskningsöversikt (refereegranskat)abstract
- Objective: To determine the size of reduction in homocysteine concentrations produced by dietary supplementation with folic acid and with vitamins B-12 or B-6. Design: Meta-analysis of randomised controlled trials that assessed the effects of folic acid based supplements on blood homocysteine concentration. Multivariate regression analysis was used to determine the effects on homocysteine concentrations of different doses of folic acid and of the addition of vitamin B-12 or B-6. Subjects: Individual data on 1114 people included in 12 trials. Findings: The proportional and absolute reductions in blood homocysteine produced by folic acid supplements were greater at higher pretreatment blood homocysteine concentrations (P < 0.001) and at lower pretreatment blood folate concentrations (P < 0.001). After standardisation to pretreatment blood concentrations of homocysteine of 12 μmol/l and of folate of 12 nmol/l (approximate average concentrations for Western populations), dietary folic acid reduced blood homocysteine concentrations by 25% (95% confidence interval 23% to 28%; P < 0.001), with similar effects in the range of 0.5-5 mg folic acid daily. Vitamin B-12 (mean 0.5 mg daily) produced an additional 7% (3% to 10%) reduction in blood homocysteine. Vitamin B-6 (mean 16.5 mg daily) did not have a significant additional effect. Conclusions: Typically in Western populations, daily supplementation with both 0.5-5 mg folic acid and about 0.5 mg vitamin B-12 would be expected to reduce blood homocysteine concentrations by about a quarter to a third (for example, from about 12 μmol/l to 8-9 μmol/l). Large scale randomised trials of such regimens in high risk populations are now needed to determine whether lowering blood homocysteine concentrations reduces the risk of vascular disease.
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| 4. |
- Nguyen, N, et al.
(författare)
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Chromosomal sequencing using a PCR-based biotin-capture method allowed isolation of the complete gene for the outer membrane protein A of Klebsiella pneumoniae
- 1998
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Ingår i: Gene. - 0378-1119 .- 1879-0038. ; 210:1, s. 93-101
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Tidskriftsartikel (refereegranskat)abstract
- By employing a novel biotin-and PCR-assisted capture method, which allows determination of unknown sequences on chromosomal DNA. the gene for the outer membrane protein A (OmpA) of Klebsiella pneumoniae has been isolated and sequenced to completion. The method involves linear amplification of DNA from a biotinylated primer annealing to a region with known sequence. After capture of the amplified single-stranded DNA on to paramagnetic beads, unspecifically annealing primers, i.e. arbitrary primers, were used to generate fragments with only partly determined nt sequences. The homology of the sequenced gene to ompAs of related bacteria is discussed. The ompA gene was assembled for intracellular expression in Escherichia coli, and two different fusion proteins were produced and recovered with good yields. The importance of the novel chromosomal sequencing method for gene isolation in general and the potential use of the OmpA fusion proteins are discussed. (C) 1998 Elsevier Science B.V.
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| 5. |
- Prestigiacomo, Anthony F., et al.
(författare)
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A comparison of the free fraction of serum prostate specific antigen in men with benign and cancerous prostates : The best case scenario
- 1996
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Ingår i: Journal of Urology. - 0022-5347. ; 156:2, s. 350-354
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: In most previous studies of free-to-total serum prostate specific antigen (PSA) ratios, the specimens from patients with prostate cancer or those with benign prostatic hyperplasia (BPH) have not been highly characterized. We compared preoperative sera from post-radical prostatectomy patients with clinically significant cancers of at least 2 cm.3 to sera from those with BPH and large, biopsy negative prostates. Materials and Methods: We used 2 different time resolved immunofluorometric assays for free and total PSA, and a combination of a chemoluminescent immunoassay for free PSA detection with an immunoradiometric assay for total PSA to measure free and total PSA. The serum ratios of free-to-total PSA in these assays were compared to those obtained previously from gel filtration studies. Sera from 51 men with prostate cancer volumes of 2 to 18 cm.3 were compared to those from 48 men with BPH and a mean prostate volume of 78 ± 7 cm.3. The respective mean serum PSA levels plus or minus standard deviation were 10.0 ± 6.3 and 8.9 ± 7.2 ng./ml. Results: Monoclonal assays for free PSA confirmed the previous study with gel filtration. For PSA 4 to 10 ng./ml., 94 to 95% of the men with prostate cancer were correctly diagnosed, with a cutoff of less than 15% for free-to-total PSA on immunofluorometric assay and less than 14% for chemoluminescent immunoassay with immunoradiometric assay. However, 46% (immunofluorometric assay) and 36% (chemoluminescent immunoassay and immunoradiometric assay) of men with BPH did not have enough free PSA for diagnosis of BPH (that is 36 to 46% false-positive rate). Conclusions: For total PSA 4 to 10 ng./ml., the sensitivity of approximately 15% free-to-total PSA for prostate cancer is high (94 to 95%) but 36 to 46% of men with BPH and a large gland will not be correctly identified. For PSA 2 to 4 ng./ml., no ratio of percent free-to-total PSA discriminated BPH from prostate cancer.
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- Syväjärvi, Mikael, 1968-
(författare)
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High growth rate epitaxy of SiC: growth processes and structural quality
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Silicon carbide (SiC) is a promising wide-bandgap semiconductor for applications such as high-power devices, high-voltage switches, high-temperature electronics and microwave components. The prospect of using this material is a large driving force for improving the material growth which is still quite immature in comparison with established semiconductor materials (e.g. silicon). There is an increasing number of reports in growth of large area boules and epilayers, but the fundamental growth issues are often not discussed (or not known) which holds back the advancement in the growth technology.Chemical vapor deposition (CVD) is the technique which has achieved epitaxial layers with low residual doping (<1015cm-3) and smooth surface morphology, two requirements for device quality material. The drawback of CVD is the low growth rate (<5 μm/hr). Since material cost is one limitation for industrial applications, increased growth rates would be preferred.Two epitaxial techniques which yield high growth rates (several tens or hundreds of μm/hr) are liquid phase epitaxy and sublimation epitaxy, both of which have been investigated within the present work. The first method is appealing since growth from the liquid phase is a growth technique under near equilibrium conditions thus providing a base for growth of high-quality material. In paper I a SiC liquid phase epitaxy technique is described. The growth process and the quality of the grown material are investigated to gain understanding of this high growth rate technique. Several factors affect the quality of the grown material. One important parameter is the quality of the interface at the growing crystal surface. This is studied in paper II for liquid phase growth where the SiC/solvent interfacial properties are investigated. The results are used for estimating the surface free energy of 4H-SiC. In liquid phase epitaxy the influence of gravity induced convection is more pronounced than in vapor phase growth. This effect was studied in paper III where comparisons in growth rate, doping incorporation and structural quality of layers grown on-ground and for the first time for SiC layers grown under microgravity conditions were made.In liquid phase epitaxy with high growth rates, a smooth surface morphology is difficult to achieve due to increased step heights (up to 1 μm) caused by pronounced stepbunching. For further understanding of SiC epitaxial growth with high growth rates, the sublimation epitaxy growth technique was studied in paper IV. It is shown that growth rates up to 2 mm/hr are achieved and the surface is smooth without observation of macrosteps using optical microscopy. The limitations in growth conditions for morphological stable growth are investigated for 6H and 4H-SiC. Studies of the kinetics show that the growth rate limiting process is sublimation of the SiC source material.Defects are often observed on as-grown surfaces but for deeper understanding of the formation mechanisms involved, cross-sections of epitaxial layers are important to study. Application of cross-sectional cleavages for investigating SiC epitaxial layers has been investigated in paper V. The preferred cleavage planes are related to the crystal structure of SiC. Appearance of defects and other polytypes than given by the substrate is a difficult matter in the growth process. Fundamentals in formation of these imperfections have been investigated in paper VI for growth using on-axis and offoriented substrates. These issues are more crucial in bulk growth where improper growth behaviour may lead to morphologically unstable growth and a phase transition from 4H-SiC polytype to 6H-SiC during the first millimeters of growth. The initial stages of crystal formation in seeded sublimation bulk growth are studied in paper VII and single 4H-SiC boules without polytype conversion were grown.The structural quality of the grown material is a fundamental property in growth. In paper VIII structural improvement, as compared with the substrates used, is demonstrated for sublimation epitaxy. Different misoriented domains in the substrate merge into one with one major orientation. A mechanism for this process is proposed. The as-grown surfaces are free of morphological defects which typically appear in SiC epitaxy. It is also shown that the improvement in structural quality is maintained when growth is performed on substrates containing a layer grown by liquid phase epitaxy. This is a technique for reducing micropipe densities in the substrates. Even though starting from a LPE layer surface showing steps, smooth surfaces were achieved using sublimation epitaxy. This finding may have an important practical impact.
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