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At least 1,045 records · Page 58Linked to original sources
PubMed2002

The usefulness of dipyridamole thallium-201 single photon emission computed tomography for predicting perioperative cardiac events in patients undergoing non-cardiac vascular surgery.

UNLABELLED: The aim of this study was to evaluate the usefulness of dipyridamole Tl-201 myocardium single photon emission computed tomography (201Tl-SPECT) for predicting perioperative cardiac events in patients with arteriosclerosis obliterans (ASO) and abdominal aortic aneurysm (AAA) undergoing non-cardiac vascular surgery. METHODS: Preoperative dipyridamole 201Tl-SPECT imaging in association with clinical risk assessment was performed in 224 consecutive patients (97 ASO and 127 AAA). RESULTS: The patients were classified into three groups, including low-risk (n = 173, 77%), intermediate-risk (n = 39, 18%), and high-risk (n = 12, 5%) groups according to the clinical risk stratification. The prevalence of reversible Tl-201 defect was significantly higher in the high-risk group than that in the low-risk group (83% vs. 14%, p < 0.001). In 180 patients who underwent vascular surgery, 9 patients (5.0%) had perioperative cardiac events, including heart failure (n = 1), unstable angina (n = 2), and other cardiac events such as arrhythmias (n = 6). The clinical variables including the clinical risk stratification did not significantly correlate with the perioperative cardiac events. In contrast, the reversible defect on 201Tl-SPECT was the only variable to predict perioperative cardiac events by a stepwise logistic regression analysis (odds ratio 7.0, 95% confidence interval 1.7-28.0, p = 0.007). It was also a significant predictor of perioperative cardiac events in a subgroup of low risk patients (odds ratio 11.6, 95% confidence interval 2.3-57.4, p = 0.004). The sensitivity and specificity of the reversible defect for predicting perioperative cardiac events were 55.6% and 84.8% in all operated patients, and 57.1% and 89.7% in low risk patients, respectively. CONCLUSIONS: The preoperative dipyridamole 201Tl-SPECT was useful for predicting perioperative cardiac events in patients with vascular diseases, even in patients identified as having a low risk based on the clinical risk assessment.

Aged↗
PubMed1986

Comparison of four single-point phenytoin dosage prediction techniques using computer-simulated pharmacokinetic values.

The predictive abilities of the following four single-point phenytoin dosage adjustment methods were compared using computer-simulated data: the Bayesian feedback method of Vozeh et al. (B), a linearized version of the Bayesian method (LB), the population-clearance method of Graves et al. (G), and the Rambeck nomogram (R). A series of 512 "subjects" with normally distributed values for volume of distribution, weight, and the Michaelis-Menten variables Vmax and Km were simulated. The steady-state serum concentration (SSSC) resulting from the administration of a standard dose of phenytoin sodium (5 mg/kg/day) was calculated, and "subjects" with SSSCs less than or equal to 12 mg/L or greater than or equal to 17 mg/L were entered in the study. If the concentration was greater than 50 mg/L or the standard dosage exceeded Vmax, the dosage was reduced empirically by 25%. Normally distributed random errors were introduced into the SSSC values to simulate actual patient data. The pharmacokinetic values, dosages, and SSSCs were used for predicting the dosage required to attain an SSSC of 14.9 mg/L. In the unstratified population, the mean error and mean-squared error were lowest for methods G and B, followed by methods LB and R. Methods B and LB gave the highest percentages of satisfactory dosage predictions based on the resultant SSSC value. The performance of all methods was superior at initial SSSCs greater than 8 mg/L.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMed2004

Pollutant dispersion in a large indoor space. Part 2: Computational fluid dynamics predictions and comparison with a scale model experiment for isothermal flow.

UNLABELLED: This paper reports on an investigation of the adequacy of computational fluid dynamics (CFD), using a standard Reynolds Averaged Navier-Stokes (RANS) model, for predicting dispersion of neutrally buoyant gas in a large indoor space. We used CFD to predict pollutant (dye) concentration distribution in a water-filled scale model of an atrium with a continuous pollutant source in the absence of furniture and occupants. Predictions from the RANS formulation are comparable with an ensemble average of independent identical experiments. Model results were compared with pollutant concentration data in a horizontal plane from experiments in a scale model atrium. Predictions were made for steady-state (fully developed) and transient (developing) pollutant concentrations. Agreement between CFD predictions and ensemble averaged experimental measurements is quantified using the ratios of CFD-predicted and experimentally measured dye concentration at a large number of points in the measurement plane. Agreement is considered good if these ratios fall between 0.5 and 2.0 at all points in the plane. The standard k-epsilon two-equation turbulence model obtains this level of agreement and predicts pollutant arrival time to the measurement plane within a few seconds. These results suggest that this modeling approach is adequate for predicting isothermal pollutant transport in a large room with simple geometry. PRACTICAL IMPLICATIONS: CFD modeling of pollutant transport is becoming increasingly common but high quality comparisons between CFD and experiment remain rare. Our results provide such a comparison. We demonstrate that the standard k-epsilon model provides good predictions for both transient and fully developed pollutant concentrations for an isothermal large space where furnishings are unimportant. This model is less computationally intensive than a large eddy simulation or low Reynolds number k-epsilon model.

Air Movements↗
PubMed2006

Comparison between myocardial contrast echocardiography and single-photon emission computed tomography for predicting transmurality of acute myocardial infarction.

Contrast-enhanced cardiovascular magnetic resonance imaging (CMR) has been shown to accurately assess transmural extent of infarction, which is an excellent predictor of long-term improvement in contractile function. We assessed the relative accuracy of myocardial contrast echocardiography (MCE) and single-photon emission computed tomography (SPECT) to predict transmural extent of infarction after acute myocardial infarction. MCE, SPECT, and CMR were performed in 40 patients with acute myocardial infarction 7 to 10 days after thrombolysis. CMR was used to divide the transmural extent of infarction into 5 groups: 0%, 1% to 25%, 26% to 50%, 51% to 75%, and 76% to 100% in dysfunctional segments. MCE and SPECT were compared with assessment grades of transmural extent of infarction. There was a significant relation (p<0.0001) between decreasing contrast intensity as assessed qualitatively by MCE and increasing transmural extent of infarction on CMR as was the case for SPECT. The accuracy of MCE (77%) to predict>50% transmural extent of infarction (nonviable myocardium) was significantly (p=0.02) superior to that of SPECT (70%). Absence of uptake on MCE and SPECT virtually ruled out 25% transmural extent of infarction (84% vs 76%, p=0.03). MCE and SPECT correlate well with the transmural extent of infarction. However, MCE is significantly more accurate in predicting >50% of the transmural extent of infarction and more sensitive in identifying <or=25% of the transmural extent of infarction than SPECT.

Cohort Studies↗
PubMed2002

Usefulness of dobutamine Tc-99m sestamibi-gated single-photon emission computed tomography for prediction of left ventricular ejection fraction outcome after coronary revascularization for ischemic cardiomyopathy.

Gated single-photon emission computed tomography (SPECT) imaging allows analysis of myocardial perfusion and assessment of baseline global and regional left ventricular (LV) function and their changes during low-dose dobutamine infusion. The study examined whether the changes in LV ejection fraction induced by dobutamine and evaluated using technetium-99m sestamibi- gated SPECT predict the evolution of ejection fraction after revascularization in patients with ischemic cardiomyopathy. Thirty-seven patients underwent resting and dobutamine nitrate-enhanced sestamibi-gated SPECT before revascularization and baseline-resting sestamibi gated SPECT after intervention to assess global functional changes. A postrevascularization improvement in ejection fraction > or =5 U was defined as significant. At follow-up, ejection fraction increased significantly in 19 patients. According to receiver-operating characteristic curve analysis, an increase in ejection fraction > or =5 U during dobutamine was the optimal cutoff value for predicting a significant postrevascularization improvement, with 79% sensitivity, 78% specificity, and 78% accuracy. A significant correlation was found between dobutamine and postrevascularization ejection fraction (r = 0.85; p <0.0001). The increase in ejection fraction during dobutamine is a good predictor of an improvement in ejection fraction after revascularization. This represents another important diagnostic contribution obtained using gated SPECT imaging for the assessment of myocardial viability in patients with ischemic cardiomyopathy.

Adrenergic beta-Agonists↗
PubMed1999

Computational models of predictive and memory-related functions of the hippocampus.

We discuss the role of the hippocampus in information processing in the brain and hypothesise that the hippocampus monitors the stability of sensory cues it receives from the external world, using the current context to predict the next sensory event in the episodic sequence by learning from experience, and memorising these sequences of sensory events. Two computational models are presented here. The predictive theory and model are closely related to experimental evidence and use dynamic synapses with an asymmetric learning rule to develop predictive neural activity of a leaky integrate-and-fire model of a pyramidal CA3 cell. The oscillatory model of the hippocampus for memorising sequences of sensory events is developed as a chain of interacting neural oscillators forced by oscillatory inputs from the entorhinal cortex and from the medial septum.

Animals↗
PubMed1984

Computer programme statistically predicting folding structure of nucleic acids of any length: and examples of calculation.

We devised a computer programme which calculates "folding probabilities" of single stranded nucleic acids of any length which we want to analyze. The "folding probability" defined by equation (7) (see below) reflects approximate probability of generation of intrastrand annealing in a given region. With this programme, we analyzed Escherichia coli 23S ribosomal RNA, and cucumber mosaic virus RNA segment 3. The calculated data of Escherichia coli 23S ribosomal RNA agreed approximately well with Klein et al.'s electronmicroscopical data [7].

Computers↗
PubMed2002

Computational antisense oligo prediction with a neural network model.

MOTIVATION: The expression of a gene can be selectively inhibited by antisense oligonucleotides (AOs) targeting the mRNA. However, if the target site in the mRNA is picked randomly, typically 20% or less of the AOs are effective inhibitors in vivo. The sequence properties that make an AO effective are not well understood, thus many AOs need to be tested to find good inhibitors, which is time consuming and costly. So far computational models have been based exclusively on RNA structure prediction or motif searches while ignoring information from other aspects of AO design into the model. RESULTS: We present a computational model for AO prediction based on a neural network approach using a broad range of input parameters. Collecting sequence and efficacy data from AO scanning experiments in the literature generated a database of 490 AO molecules. Using a set of derived parameters based on AO sequence properties we trained a neural network model. The best model, an ensemble of 10 networks, gave an overall correlation coefficient of 0.30 (p=10(-8)). This model can predict effective AOs (>50% inhibition of gene expression) with a success rate of 92%. Using these thresholds the model predicts on average 12 effective AOs per 1000 base pairs, making it a stringent yet practical method for AO prediction.

Algorithms↗
PubMed2002

Computational design and prediction of interesting not-yet-synthesized structures of inorganic materials by using building unit concepts.

The computational design of new and interesting inorganic materials is still an ongoing challenge. The motivation of these efforts is to aid the often difficult task of crystal structure determination, to rationalize different but related structure types, or to help limit the domain of structures that are possible in a given system. Over the past decade, simulation methods have continuously evolved towards the prediction of new structures using minimal input information in terms of symmetry, cell parameters, or chemical composition. So far, this task of identifying candidate structures through an analysis of the energy landscape of chemical systems has been particularly successful for predominantly ionic systems with relatively small numbers of atoms or ions in the simulation cell. After an introductory section, the second section of this work presents the historical developments of such simulation methods in this area. The following sections of the work are dedicated to the introduction of the building unit concept in simulation methods: we present simulation approaches to structure prediction employing both primary (aggregate of atoms) and secondary (aggregate of coordination polyhedra) building units. While structure prediction with primary units is a straightforward extension of established approaches, the AASBU method (automated asssembly of secondary building units) focusses on the topology of network-based structures. This method explores the possible ways to assemble predefined inorganic building units in three-dimensional space, opening the way to the manipulation of very large building units (up to 84 atoms in this work). As illustrative examples we present the prediction of candidate structures for Li(4)CO(4), the identification of topological relationships within a family of metalphosphates, ULM-n and MIL-n, and finally the generation of new topologies by using predefined large building units such as a sodalite or a double-four-ring cage, for the prediction of new and interesting zeolite-type structures.

Journal Article↗
PubMed2006

Use of computed tomography to predict failure of nonoperative treatment of unilateral facet fractures of the cervical spine.

STUDY DESIGN: Retrospective review. OBJECTIVES: To determine whether radiographic measurements derived from standard computed tomography (CT) evaluation can be used to predict failure of nonoperative treatment in patients with unilateral facet fractures. SUMMARY OF BACKGROUND DATA: There is no consensus regarding treatment of unilateral cervical spine facet fractures. Management of this injury is based primarily on the presence of neurologic deficits and the degree of perceived spinal instability. CT-based criteria for predicting failure of nonoperative treatment in this patient population have not been examined. METHODS: Initial CT scans of all patients with unilateral cervical facet fractures were reviewed. Direct measurements included height and width of the facet fracture fragment, fracture displacement, and angulation. Calculated data included percent height and width of the fracture fragment based on the height and width of the contralateral intact facet. RESULTS: A total of 24 patients with 26 unilateral facet fractures were identified. Five patients with 5 facet fractures failed nonoperative management and required delayed surgical stabilization. Comparing patients successfully treated nonoperatively to those failing nonoperative management, a significant difference was found in absolute height of the fracture fragment (P = 0.0002), articular fracture height (P = 0.008), and height of the fracture fragment expressed as a percentage of the contralateral intact lateral mass (P = 0.026). CONCLUSION: The only significant risk factors identified for failure of nonoperative treatment were craniocaudal height of the fracture fragment and relative height of the fracture fragment expressed as a percentage of the intact lateral mass. This study suggests that patients with unilateral cervical facet fractures involving >40% of the absolute height of the intact lateral mass or an absolute height >1 cm are at increased risk for failure of nonoperative treatment. Failure of nonoperative treatment was not observed in any patient with a fracture involving less than 40% of the height of the lateral mass or an absolute height <1 cm.

Adolescent↗
PubMedDate not supplied

Reliability of quantitative computed tomography to predict postoperative lung function in patients with chronic obstructive pulmonary disease having a lobectomy.

OBJECTIVE: To verify the reliability of quantitative computed tomography (CT) to estimate the postoperative lung function in patients with mild to severe chronic obstructive pulmonary disease (COPD) who underwent a lobectomy. METHODS: Nine COPD patients with lung cancer having a lung lobectomy with preoperative CT were enrolled. By applying a density mask technique and a specific equation, predicted postoperative forced expiratory volume in 1 second (FEV1) and vital capacity (VC) were calculated. Predicted values were correlated with postoperative measured values. RESULTS: Estimated FEV1 and VC were always significantly lower than the corresponding postoperative values; however, CT-estimated postresection FEV1 values were better than the postresection VC values (biases between estimated and measured values were -0.14 and -0.536 L, respectively, according to the Bland-Altman method). Quantitative CT predicted postoperative FEV1 (r = 0.97, P < 0.001) and VC (r = 0.93, P < 0.001) well in all patients, however. CONCLUSIONS: Quantitative CT may be an alternative tool to perfusion scan to predict postresection lung function, even in patients with borderline pulmonary function undergoing a lobectomy.

Aged↗
PubMed1998

Dipyridamole thallium-201 single-photon emission computed tomography for prediction of perioperative cardiac events in patients with arteriosclerosis obliterans undergoing vascular surgery.

The aim of the study was to determine whether or not dipyridamole thallium-201 single-photon emission computed tomography (201Tl-SPECT) has significant additive value for predicting perioperative cardiac events in patients with arteriosclerosis obliterans (ASO) undergoing vascular surgery. Routine preoperative 201Tl-SPECT was performed in 106 consecutive patients with ASO (age 68+/-8.9 years; 91 men and 15 women). The frequency of reversible defects in a clinical high-risk group (n=44) was significantly higher than in a low-risk group (n=62; 55% vs 24%, p<0.01). Perioperative cardiac events occurred in 9 patients, including 4 cardiac deaths, 1 non-fatal myocardial infarction, and 4 cases of unstable angina. Although clinical risk stratification was useful in predicting cardiac events (19% in the high-risk group vs 2% in the low-risk group, p<0.01), the positive predictive value was low. When considering a combination of 2 or more than 2 risk factors and a large reversible defect as a predictor, the positive predictive value and specificity increased from 19% to 47% and from 64% to 91%, respectively, whereas the sensitivity remained unchanged (89%). These results suggest that the addition of 201Tl-SPECT data to clinical risk-stratified patients with ASO allows better prediction of perioperative cardiac events.

Adult↗
PubMed2006

A novel computational method to predict transcription factor DNA binding preference.

Transcription factor binds to sequence specific sites in regulatory region to control nearby gene's expression. It is termed as the major regulator of transcription. However, identifying DNA binding preference of transcription factors systematically is still a challenge. By using the nearest neighbor algorithm, a novel computational approach was developed to predict transcription factor DNA binding preference based on the gene ontology [M. Ashburner, C.A. Ball, J.A. Blake, D. Botstein, H. Butler, J.M. Cherry, A.P. Davis, K. Dolinski, S.S. Dwight, J.T. Eppig, M.A. Harris, D.P. Hill, L. Issel-Tarver, A. Kasarskis, S. Lewis, J.C. Matese, J.E. Richardson, M. Ringwald, G.M. Rubin, G. Sherlock, Gene Ontology: tool for the unification of biology, Nat. Genet. 25 (2000) 25-29.] and 0/1 encoding system of nucleotide. The overall success rate of Jackknife cross-validation test for our predictor reaches 76.6%, which indicates the DNA binding preference is closely correlated with its biological functions and computational method developed in this contribution could be a powerful tool to investigate transcription factor DNA binding preference, especially for those novel transcription factors with little prior knowledge on its DNA binding preference.

Algorithms↗
PubMed2000

Comparison of simultaneous dobutamine echocardiography and thallium-201 stress-reinjection single-photon emission computed tomography in predicting improvement of chronic myocardial dysfunction after revascularization.

Previous studies have shown that ultrasonic integrated backscatter is valuable in characterizing stunned myocardium. Recent investigations have demonstrated that resting cardiac cycle-dependent variation of integrated backscatter closely paralleled the contractile reserve in patients with chronic left ventricular ischemic dysfunction. The purpose of this study was to validate whether ultrasonic tissue characterization (UTC) compared with dobutamine stress echocardiography (DSE) and thallium-201 stress-reinjection single-photon emission computed tomography (Tl-SPECT) could predict reversible myocardial dyssynergy in patients with chronic coronary artery disease. Forty-eight patients with stable coronary artery disease underwent UTC, DSE, and Tl-SPECT simultaneously before successful coronary revascularization and were followed up with echocardiograms at rest >3 months later. Among the 58 investigated segments, the weighted amplitude, a composite parameter derived from the integrated backscatter power curve, was larger for those groups with greater functional recovery (p <0.001). For the persistent akinetic segments, the weighted amplitudes were small with large deviations of the nadir ratios that represented the asynchrony between the intramural contractile events and the global systole. Using the cut-off value 2.0 of the weighted amplitude, the sensitivity and specificity for predicting functional improvement after revascularization were both 82.8% (kappa = 0.66) and comparable to the sensitivity and specificity of DSE and Tl-SPECT. UTC, delineating the myocardial physical state and intramural contraction, can be a novel approach in predicting functional improvement of chronic dyssynergy after revascularization.

Adult↗
PubMed2006

Computational modeling to predict the temporal regulation of chondrocyte metabolism in response to various dynamic compression regimens.

Based on previously published experimental work, computational models were developed to simulate the effect of different dynamic compression regimens on the activity of chondrocytes seeded in agarose constructs. In particular, the balance between proliferation and matrix synthesis can be adjusted by applying different intervals of continuous or intermittent mechanical compression. A phenomenological compartment based-modeling approach was used as first model. A more mechanistic cell cycle model was used as the second model. The compartment-based modeling approach was found to be useful in representing a balance between proliferation and proteoglycan synthesis, when the effect of a certain stimulation protocol is known. In order to predict the response to different intervals of mechanical stimulation, however, a more mechanistic cell cycle-based approach is required. The cell cycle model supports an important role of the onset of loading. In addition, an inhibitory effect of further loading is required, which is more likely to be related to cell cycle progression velocity than to a decreased probability of commitment to the cell cycle. The mechanisms behind this inhibitory effect and the computational implementation, however, require further investigation.

Animals↗
PubMed1985

Computer program for prediction of the optimal and suboptimal secondary structures of long RNA molecules.

We present an algorithm for prediction of RNA secondary structures. The program consists of three parts: the first computes location and free energy of every possible stem-loop structure, the second computes probability of its formation, and the third lists the positions and free energies of all the stem-loops in the order of their probability sizes. The circular RNA molecule of chrysanthemum stunt viroid was used as an input data for demonstrating the operation of the program.

Algorithms↗
PubMed1995

A computer program for predicting recovery of SDS-protein in the automated HPGE-1000 apparatus.

The commercial automated gel electrophoresis apparatus (HPGE-1000 of LabIntelligence, Menlo Park, CA) allows one to recover the material migrating and visualized as a fluorescent-labeled band by electrophoresis into a collection cup located above the band at a right angle to the orientation of the separation path. The degree of recovery is a function of sample load (peak area), electrophoresis time at constant field strength, the mobility of the material and band width. Neglecting the latter, recovery of several SDS-proteins was measured as a function of the first three parameters. These measurements were used as a data base for a computer program capable of predicting, by interpolation of the experimental values, the time of electrophoresis needed to obtain a specified degree of recovery, or the degree of recovery obtained after a desired time of electrophoresis into the collection cup.

Autoanalysis↗