37 research outputs found
Whipworms in humans and pigs: origins and demography
No full text© 2016 Hawash et al. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
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(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. The attached file is the published version of the article.NHM Repositor
MBF: a real matrix bloom filter representation method on dynamic set
No full textBloom Filter is a simple space-efficient randomized data structure for representing a set in order to support membership queries, which uses an m-bit array to represent a data set. In order to support representing dynamic set, dynamic bloom filter (DBF) and split bloom filter (SBF) have been developed Both DBF and SBF can support concisely representation and approximate membership queries of dynamic set instead of static set. SBF declares that it uses an s Xm bit matrix that consists of s bloom filters to represent a dynamic set, so DBF dose. But in fact, both the two bloom filters are not matrix representation method at all. They are just a set of s bloom filters whose length is in, and they have got a departure from the original idea of bloom filter: the constant query time cost. This paper points out the fact, and then introduce a truly matrix representation method of bloom filter to represent a dynamic set. We call it the Matrix Bloom Filter (MBF). Then, we will analysis the algorithm of MBF and study the average time complexity and the false positive probability.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000251390000125&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Computer Science, Hardware & ArchitectureComputer Science, Theory & MethodsEngineering, Electrical & ElectronicCPCI-S(ISTP)
Improved reproducibility for myocardial ASL: Impact of physiological and acquisition parameters
No full textPurpose: To investigate and mitigate the influence of physiological and acquisition-related parameters on myocardial blood flow (MBF) measurements obtained with myocardial Arterial Spin Labeling (myoASL). Methods: A Flow-sensitive Alternating Inversion Recovery (FAIR) myoASL sequence with bSSFP and spoiled GRE (spGRE) readout is investigated for MBF quantification. Bloch-equation simulations and phantom experiments were performed to evaluate how variations in acquisition flip angle (FA), acquisition matrix size (AMS), heart rate (HR) and blood (Formula presented.) relaxation time ((Formula presented.)) affect quantification of myoASL-MBF. In vivo myoASL-images were acquired in nine healthy subjects. A corrected MBF quantification approach was proposed based on subject-specific (Formula presented.) values and, for spGRE imaging, subtracting an additional saturation-prepared baseline from the original baseline signal. Results: Simulated and phantom experiments showed a strong dependence on AMS and FA ((Formula presented.) >0.73), which was eliminated in simulations and alleviated in phantom experiments using the proposed saturation-baseline correction in spGRE. Only a very mild HR dependence ((Formula presented.) >0.59) was observed which was reduced when calculating MBF with individual (Formula presented.). For corrected spGRE, in vivo mean global spGRE-MBF ranged from 0.54 to 2.59 mL/g/min and was in agreement with previously reported values. Compared to uncorrected spGRE, the intra-subject variability within a measurement (0.60 mL/g/min), between measurements (0.45 mL/g/min), as well as the inter-subject variability (1.29 mL/g/min) were improved by up to 40% and were comparable with conventional bSSFP. Conclusion: Our results show that physiological and acquisition-related factors can lead to spurious changes in myoASL-MBF if not accounted for. Using individual (Formula presented.) and a saturation-baseline can reduce these variations in spGRE and improve reproducibility of FAIR-myoASL against acquisition parameters.ImPhys/Weingärtner groupImPhys/Tao grou
Quantitative analysis of coronary endothelial function with generator-produced 82Rb PET : comparison with 15O-labelled water PET
No full textPurpose: Endothelial dysfunction is the earliest abnormality in the development of coronary atherosclerosis. Rubidium-82 (82Rb) is a generator-produced positron emission tomography (PET) myocardial perfusion tracer that is becoming more widely used. We aimed to develop a method for quantitative assessment of coronary endothelial function using the myocardial blood flow (MBF) response during a cold pressor test (CPT) in smokers, measured using 82Rb PET and ii) compare the results with those measured using 15O-water PET. Methods: MBF was assessed at rest and during CPT with 82Rb and 15O-water in 9 controls and 10 smokers. A one-compartment model with tracer extraction correction was used to estimate MBF with both tracers. CPT response was calculated as the ratio of MBF during CPT to MBF at rest. Results: At rest, measurements of MBF for smokers vs. controls were not different using 15O-water (0.86 ± 0.18 vs. 0.70 ± 0.13, p = 0.426) than they were using 82Rb (0.83 ± 0.23 vs. 0.62 ± 0.20, p = 0.051). Both methods showed a reduced CPT response in smokers vs. controls (15O-water, 1.03 ± 0.21 vs. 1.42 ± 0.29, p = 0.006; 82Rb, 1.02 ± 0.28 vs. 1.70 ± 0.52, p < 0.001). There was high reliability [intra-class correlation coefficients: 0.48 (0.07, 0.75)] of MBF measurement between 82Rb and 15O-water during CPT. Conclusions: Using CPT, 82Rb MBF measurements detected coronary endothelial dysfunctions in smokers. 82Rb MBF measurements were comparable to those made using the 15O-water approach. Thus, 82Rb PET may be applicable for risk assessments or evaluation of risk factor modification in subjects with coronary risk factors
Quantification of myocardial blood flow using dynamic 320-row multi-detector CT as compared with O-15-H2O PET
No full textThis study introduces a method to calculate myocardium blood flow (MBF) and coronary flow reserve (CFR) using the relatively low-dose dynamic 320-row multi-detector computed tomography (MDCT), validates the method against O-15-H2O positron-emission tomography (PET) and assesses the CFRs of coronary artery disease (CAD) patients. Thirty-two subjects underwent both dynamic CT perfusion (CTP) and PET perfusion imaging at rest and during pharmacological stress. In 12 normal subjects (pilot group), the calculation method for MBF and CFR was established. In the other 13 normal subjects (validation group), MBF and CFR obtained by dynamic CTP and PET were compared. Finally, the CFRs obtained by dynamic CTP and PET were compared between the validation group and CAD patients (n = 7). Correlation between MBF of MDCT and PET was strong (r = 0.95, P < 0.0001). CFR showed good correlation between dynamic CTP and PET (r = 0.67, P = 0.0126). CFRCT in the CAD group (2.3 +/- 0.8) was significantly lower than that in the validation group (5.2 +/- 1.8) (P = 0.0011). We established a method for measuring MBF and CFR with the relatively low-dose dynamic MDCT. Lower CFR was well demonstrated in CAD patients by dynamic CTP. aEuro cent MBF and CFR can be calculated using dynamic CTP with 320-row MDCT. aEuro cent MBF and CFR showed good correlation between dynamic CTP and PET. aEuro cent Lower CFR was well demonstrated in CAD patients by dynamic CTP
Classification of hemodynamically significant stenoses from dynamic CT perfusion and CTA myocardial territories
No full textPurposeMyocardial blood flow (MBF) obtained by dynamic CT perfusion (CTP) has been recently introduced to assess hemodynamic significance of coronary stenosis in coronary artery disease. The diagnostic performance of dynamic CTP MBF is limited due to subjective interpretation of MBF maps and MBF variations caused by physiological, methodological, and technical issues. In this paper, we introduce a novel method to quantify the hypoperfused volume (HPV) in myocardial territories derived from CT angiography (CTA) to overcome the limitations of current dynamic CTP MBF analysis methods.MethodsThe diagnostic performance of HPV in classifying significant stenoses was evaluated on 22 patients (57 vessels) that underwent CTA, CTP and invasive fractional flow reserve (FFR). FFR was used as the standard of reference to determine stenosis significance. The diagnostic performance was compared to that of the mean MBF computed in regions manually annotated by an expert (MA-MBF). HPV was derived by thresholding the MBF in myocardial territories constructed from CTA by locating the closest artery. Diagnostic performance was evaluated using leave-one-case out cross-validation. Inter-observer reproducibility was assessed by performing annotations of coronary seeds (HPV) and manual regions (MA-MBF) with two users. In addition, the influence of different parameter settings on the diagnostic performance of HPV was assessed.ResultsLeave-one-case out cross-validation showed that HPV has an accuracy of 72% (58–83%) with sensitivity of 72% (47–90%) and specificity of 72% (58–83%). The accuracy of MA-MBF was 70% (57–82%) with a sensitivity of 50% (26–74%) and a specificity of 79% (64–91%). The Spearman correlation and the kappa statistic was (ρ = 0.94, κ = 0.86) for HPV and (ρ = 0.72, κ = 0.82) for MA-MBF. The influence of parameter settings on HPV based diagnostic performance was not significant.ConclusionsThe proposed HPV accurately classifies hemodynamically significant stenoses with a level of accuracy comparable to the mean MBF in regions annotated by an expert. HPV improves inter-observer reproducibility as compared to MA-MBF by providing a more objective criterion to associate the stenotic coronary with the supplied myocardial territory.ImPhys/Quantitative Imagin
Improved spillover correction model to quantify myocardial blood flow by C-11-acetate PET : comparison with O-15-H2O PET
No full textC-11-acetate has been applied for evaluation of myocardial oxidative metabolism and can simultaneously estimate myocardial blood flow (MBF). We developed a new method using two-parameter spillover correction to estimate regional MBF (rMBF) with C-11-acetate PET in reference to MBF derived from O-15-H2O PET. The usefulness of our new approach was evaluated compared to the conventional method using one-parameter spillover correction. Sixty-three subjects were examined with C-11-acetate and O-15-H2O dynamic PET at rest. Inflow rate of C-11-acetate (K1) was compared with MBF derived from O-15-H2O PET. For the derivation, the relationship between K1 and MBF from O-15-H2O was linked by the Renkin-Crone model in 20 subjects as a pilot group. One-parameter and two-parameter corrections were applied to suppress the spillover between left ventricular (LV) wall and LV cavity. Validation was set using the other 43 subjects' data. Finally, rMBFs were calculated using relational expression derived from the pilot-group data. The relationship between K1 and MBF derived from O-15-H2O PET was approximated as K1 = [1-0.764 x exp(-1.001/MBF)] MBF from the pilot data using the two-parameter method. In the validation set, the correlation coefficient between rMBF from C-11-acetate and O-15-H2O demonstrated a significantly higher relationship with the two-parameter spillover correction method than the one-parameter spillover correction method (r = 0.730, 0.592, respectively, p < 0.05). In C-11-acetate PET study, the new two-parameter spillover correction method dedicated more accurate and robust myocardial blood flow than the conventional one-parameter method
Reduced 123I-BMIPP uptake implies decreased myocardial flow reserve in patients with chronic stable angina
No full textPurpose Long-chain fatty acid (LCFA) is the main energy source for normal myocardium at rest, but in ischemic myocardium, the main energy substrate shifts from LCFA to glucose. 123I-BMIPP is a radiolabeled LCFA analog. In chronic stable angina without previous infarction, we suppose that reduced 123I-BMIPP uptake is related to the substrate shift in myocardium with decreased myocardial flow reserve (MFR). The purpose of this study was to relate 123I-BMIPP uptake to rest myocardial blood flow (MBF), hyperemic MBF, and MFR assessed with 15O-water positron emission tomography (PET).
Methods We enrolled 21 patients with chronic stable angina without previous infarction, all of whom underwent 123I-BMIPP single-photon emission computed tomography (SPECT) and 15O-water PET. The left ventricle was divided into 13 segments. In each segment, rest MBF and hyperemic MBF were measured by PET. 123I-BMIPP uptake was evaluated as follows: score 0=normal, 1=slightly decreased uptake, 2=moderately decreased uptake, 3=severely decreased uptake, and 4=complete defect. 123I-BMIPP uptake was compared with rest MBF, hyperemic MBF, and MFR.
Results The numbers of segments with 123I-BMIPP scores 0, 1, 2, 3, and 4 were 178, 40, 25, 24, and 0, respectively. The rest MBFs for scores 0, 1, 2, and 3 were 0.93±0.25, 0.86±0.21, 0.97±0.30, and 0.99±0.37 ml/min/g, respectively. The hyperemic MBFs for scores 0, 1, 2, and 3 were 2.76±1.29, 1.84±0.74, 1.37±0.39, and 1.08±0.40 ml/min/g, respectively. The MFRs for scores 0, 1, 2, and 3 were 3.01±1.38, 2.20±0.95, 1.44±0.22, and 1.10±0.26, respectively. As 123I-BMIPP uptake declined, hyperemic MBF and MFR decreased.
Conclusion In chronic stable angina without previous infarction, reduced 123I-BMIPP uptake implies decreased MFR
Improved regionalmyocardial blood flow and flow reserve after coronary revascularization as assessed by serial O-15-water positron emission tomography/computed tomography
No full textAims Myocardial perfusion imaging without and with quantitative myocardial blood flow (MBF) and myocardial flow reserve (MFR) plays an important role in the diagnosis and risk stratification of patients with stable coronary artery disease (CAD). We aimed to quantify the effects of coronary revascularization on regional stress MBF and MFR and to determine whether the presence of subendocardial infarction was associated with these changes. Methods and results Forty-seven patients with stable CAD were prospectively enrolled. They underwent 15O-water positron emission tomography at baseline and 6 months after optimal medical therapy alone (n = 16), percutaneous coronary intervention (PCI) (n = 18), or coronary artery bypass grafting (CABG) (n = 13). Stenosis of >= 50% diameter was detected in 98/141 vessels (70%). The regional MFR was significantly increased from baseline to follow-up [1.84 (interquartile range, IQR 1.28-2.17) vs. 2.12 (IQR 1.69-2.63), P < 0.001] in vessel territories following PCI or CABG due to an increase in the stress MBF [1.33 (IQR 0.97-1.67) mL/g/min vs. 1.64 (IQR 1.38-2.17) mL/g/min, P < 0.001], whereas there was no significant change in the regional stress MBF or MFR in vessel territories without revascularization. A multilevel mixed-effects models adjusted for baseline characteristics, subendocardial infarction assessed by cardiovascular magnetic resonance imaging, and intra-patient correlation showed that the degree of angiographic improvement after coronary revascularization was significantly associated with increased regional stress MBF and MFR (P < 0.05 for all). Conclusion Coronary revascularization improved the regional stress MBF and MFR in patients with stable CAD. The magnitude of these changes was associated with the extent of revascularization independent of subendocardial infarction
High-Resolution Free-Breathing Quantitative First-Pass Perfusion Cardiac MR Using Dual-Echo Dixon With Spatio-Temporal Acceleration
No full textIntroduction: To develop and test the feasibility of free-breathing (FB), high-resolution quantitative first-pass perfusion cardiac MR (FPP-CMR) using dual-echo Dixon (FOSTERS; Fat-water separation for mOtion-corrected Spatio-TEmporally accelerated myocardial peRfuSion). Materials and Methods: FOSTERS was performed in FB using a dual-saturation single-bolus acquisition with dual-echo Dixon and a dynamically variable Cartesian k-t undersampling (8-fold) approach, with low-rank and sparsity constrained reconstruction, to achieve high-resolution FPP-CMR images. FOSTERS also included automatic in-plane motion estimation and T (Formula presented.) correction to obtain quantitative myocardial blood flow (MBF) maps. High-resolution (1.6 x 1.6 mm2) FB FOSTERS was evaluated in eleven patients, during rest, against standard-resolution (2.6 x 2.6 mm2) 2-fold SENSE-accelerated breath-hold (BH) FPP-CMR. In addition, MBF was computed for FOSTERS and spatial wavelet-based compressed sensing (CS) reconstruction. Two cardiologists scored the image quality (IQ) of FOSTERS, CS, and standard BH FPP-CMR images using a 4-point scale (1–4, non-diagnostic – fully diagnostic). Results: FOSTERS produced high-quality images without dark-rim and with reduced motion-related artifacts, using an 8x accelerated FB acquisition. FOSTERS and standard BH FPP-CMR exhibited excellent IQ with an average score of 3.5 ± 0.6 and 3.4 ± 0.6 (no statistical difference, p > 0.05), respectively. CS images exhibited severe artifacts and high levels of noise, resulting in an average IQ score of 2.9 ± 0.5. MBF values obtained with FOSTERS presented a lower variance than those obtained with CS. Discussion: FOSTERS enabled high-resolution FB FPP-CMR with MBF quantification. Combining motion correction with a low-rank and sparsity-constrained reconstruction results in excellent image quality.ImPhys/Medical Imagin
