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- 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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- 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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- French, Robert L
(författare)
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Automobile navigation safety issues
- 1991
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Ingår i: Proceedings of Strategic Highway Research Program and Traffic Safety on Two Continents. Conference in Gothenburg, Sweden, September 18-20, 1991. - Linköping : Statens väg- och transportforskningsinstitut. ; , s. 103-111
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 6. |
- Hellmark, Thomas, et al.
(författare)
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Comparison of anti-GBM antibodies in sera with or without ANCA
- 1997
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Ingår i: Journal of the American Society of Nephrology. - 1046-6673. ; 8:3, s. 376-385
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Tidskriftsartikel (refereegranskat)abstract
- An appreciable percentage of patients with serum anti-glomerular basement membrane (anti-GBM) antibodies also have antineutrophil cytoplasmic antibodies (ANCA), against either myeloperoxidase (MPO-ANCA), or proteinase 3 (PR3-ANCA). In sera without ANCA, the anti-GBM antibodies have been shown to react mainly with the noncollagenous domain (NC1) of Type IV collagen, and especially with its alpha 3 chain, alpha 3(IV)NC1. In most sera, the antibodies can be partially blocked by a monoclonal antibody (Mab17) against alpha 3(IV)NC1, suggesting that a limited region is recognized. Although there is evidence that some anti-GBM antibodies that coexist with ANCA react with alpha 3(IV)NC1, extensive analysis of the specificity of such anti-GBM antibodies has not been reported. In the study presented here, sera were analyzed from 332 patients tested both for anti-GBM antibodies and ANCA (MPO or PR3-ANCA) and found to have one or more positive tests. Of the 100 sera with anti-GBM antibodies, 38 also had ANCA-25 with MPO-ANCA (66%), 12 with PR3-ANCA (32%), and one with both (2%). Of the 232 sera with ANCA only, 153 had MPO-ANCA (66%), 75 had PR3-ANCA (32%), and four had both (2%). Sera was also analyzed from 259 other patients who had positive ANCA tests and were not tested for anti-GBM antibodies: 138 had MPO-ANCA (54%), and 121 had PR3-ANCA (46%). The relative frequencies of MPO or PR3-ANCA in patients with coexisting anti-GBM antibodies did not differ significantly from those in all patients with ANCA (P = 0.35). Seventeen sera with anti-GBM antibodies only and 16 sera with anti-GBM antibodies plus ANCA were selected for further studies to compare the specificity of anti-GBM antibodies in sera with or without ANCA. Using enzyme-linked immunosorbent assays (ELISA), all sera in both groups were found to react with the NC1 domain (as a hexamer) of bovine Type IV collagen and with alpha 3 (IV)NC1 monomers. Furthermore, all but six sera also reacted with one or more of the alpha 1, 2, and 4 (IV)NC1 monomers, generally with considerably lower titers. Reactivity to alpha 3(IV)NC1 was partially blocked by Mab17, with comparable degrees of inhibition in both groups. Western blot analysis with the human NC1 domains revealed no differences in reactivity between the two groups. Thus, differences in antigen specificities of anti-GBM antibodies in sera with or without ANCA were not detected. The anti-GBM response in both situations is hypothesized to be driven by the same immunogen, which is probably derived from NC1 domains of endogenous Type IV collagen.
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| 8. |
- Jern, Sverker, 1954, et al.
(författare)
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Swedish Isradipine Study in Hypertension: evaluation of quality of life, safety, and efficacy. SWISH Group.
- 1991
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Ingår i: Journal of cardiovascular pharmacology. - 0160-2446. ; 18 Suppl 3
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Tidskriftsartikel (refereegranskat)abstract
- This was a double-blind multicenter study to compare the efficacy, tolerability and effects on the quality of life with isradipine and atenolol in the treatment of essential hypertension. Of 588 patients entering the 6-week placebo run-in period, 549 were eligible for randomization to receive either isradipine or atenolol for 8 weeks. If, at the end of this period, diastolic blood pressure (DBP) remained greater than 90 mm Hg, then both agents were given in combination for a further 10 weeks. Tolerability and quality of life were assessed repeatedly during the placebo and active-treatment phases. A subgroup of 30 patients were followed by 24-h ambulatory blood pressure monitoring, and their results are now being analyzed. In another subgroup of 26 patients, maximum exercise capacity, as determined by ergometer bicycle-testing, was measured once during placebo and twice during active treatment. At the end of the 24-week study period, both isradipine and atenolol as monotherapy had produced significant decreases in blood pressure. There were no significant differences overall between the compounds in quality-of-life and side-effect profiles, although there was a relative absence of ankle edema and headache with isradipine. Furthermore, patients receiving isradipine had no change in performance on exercise testing whereas patients on atenolol had a significant decrease (p less than 0.01).
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| 9. |
- Johnsson, Lennart, et al.
(författare)
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Communication Efficient Multi–Processor FFT
- 1992
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Ingår i: Journal of Computational Physics. - 0021-9991 .- 1090-2716. ; 102:2, s. 381-397
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Tidskriftsartikel (refereegranskat)abstract
- Computing the fast Fourier transform on a distributed memory architecture by a direct pipelined radix-2, a bi-section, or a multisection algorithm, all yield the same communications requirement, if communication for all FFT stages can be performed concurrently, the input data is in normal order, and the data allocation is consecutive. With a cyclic data allocation, or bit-reversed input data and a consecutive allocation, multi-sectioning offers a reduced communications requirement by approximately a factor of two. For a consecutive data allocation, normal input order, a decimation-in-time FFT requires that P/N + d−2 twiddle factors be stored for P elements distributed evenly over N processors, and the axis that is subject to transformation be distributed over 2d processors. No communication of twiddle factors is required. The same storage requirements hold for a decimation-in-frequency FFT, bit-reversed input order, and consecutive data allocation. The opposite combination of FFT type and data ordering requires a factor of log2N more storage for N processors. The peak performance for a Connection Machine system CM-200 implementation is 12.9 Gflops/s in 32-bit precision, and 10.7 Gflops/s in 64-bit precision for unordered transforms local to each processor. The corresponding execution rates for ordered transforms are 11.1 Gflops/s and 8.5 Gflops/s, respectively. For distributed one- and two-dimensional transforms the peak performance for unordered transforms exceeds 5 Gflops/s in 32-bit precision and 3 Gflops/s in 64-bit precision. Three-dimensional transforms execute at a slightly lower rate. Distributed ordered transforms execute at a rate of about 1/2 to 2/3 of the unordered transforms.
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| 10. |
- Johnsson, Lennart, et al.
(författare)
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Cooley–Tukey FFT on the Connection Machine
- 1992
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Ingår i: Parallel Computing. - 0167-8191 .- 1872-7336. ; 18:11, s. 1201-1221
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Tidskriftsartikel (refereegranskat)abstract
- We describe an implementation of the Cooley-Tukey complex-to-complex FFT on the Connection Machine. The implementation is designed to make effective use of the communications bandwidth of the architecture, its memory bandwidth, and storage with precomputed twiddle factors. The peak data motion rate that is achieved for the interprocessor communication stages is in excess of 7 Gbytes/s for a Connection Machine system CM-200 with 2048 floating-point processors. The peak rate of FFT computations local to a processor is 12.9 Gflops/s in 32-bit precision, and 10.7 Gflops/s in 64-bit precision. The same FFT routine is used to perform both one- and multi-dimensional FFT without any explicit data rearrangement. The peak performance for a one-dimensional FFT on data distributed over all processors is 5.4 Gflops/s in 32-bit precision and 3.2 Gflops/s in 64-bit precision. The peak performance for square, two-dimensional transforms, is 3.1 Gflops/s in 32-bit precision, and for cubic, three dimensional transforms, the peak is 2.0 Gflops/s in 64-bit precision. Certain oblong shapes yield better performance. The number of twiddle factors stored in each processor is P/2N + log2 N for an FFT on P complex points uniformly distributed among N processors. To achieve this level of storage efficiency we show that a decimation-in-time FFT is required for normal order input, and a decimation-in-frequency FFT is required for bit-reversed input order.
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