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At least 1,225 records · Page 68Linked to original sources
PubMed2006

Benchmarking matching pursuit to find sleep spindles.

The aim of this study is to evaluate performance of Matching Pursuit (MP) algorithm against visual analysis for automatic sleep spindle (SS) detection in a sample of sleep stages 2-4 and REM pertaining to nine healthy young subjects. MP-SS voltage, frequency and duration characteristics were investigated for the amplitude threshold (AT) that maximized yield between test sensitivity and specificity. Parameter distribution curves were also built for correctly detected (true positive) and false-positive events. For sleep stage 2, MP reached 80.6% sensitivity and specificity for an AT value of 58.8. For all stages together, 81.2% sensitivity and specificity were reached for an AT value of 46.6. Specificity curves were adequate for all stages; sensitivity was lower for S3+4. Sigma frequency range activity with atypical characteristics was detected within REM sleep. Prevalence indexes obtained with MP were much higher than visual prevalence indexes for all stages; similar voltage, frequency and duration distribution curves were obtained for true positive and false positive events. For this sample of young male healthy subjects, the free-ware MP algorithm showed satisfactory performance for SS detection in sleep stage 2 as reported earlier, acceptable performance in sleep stages 3+4, although with lowered sensitivity, and sigma frequency range activity within REM sleep that needs better understanding. Within NREM sleep, correspondence between the MP automatic and the visual method was supported.

Adult↗
PubMed2003

A systematic benchmark method for analysis and comparison of IMRT treatment planning algorithms.

Tools and procedures for evaluating and comparing different intensity-modulated radiation therapy (IMRT) systems are presented. IMRT is increasingly in demand and there are numerous systems available commercially. These programs introduce significantly different software to dosimetrists and physicists than conventional planning systems, and the options often seem initially overwhelmingly complex to the user. By creating geometric target volumes and critical normal tissues, the characteristics of the algorithms may be investigated, and the influence of the different parameters explored. Overall optimization strategies of the algorithm may be characterized by treating a square target volume (TV) with 2 perpendicular beams, with and without heterogeneities. A half-donut (hemi-annulus) TV with a "donut hole" (central cylinder) critical normal tissue (CNT) on a CT of a simulated quality assurance phantom is suggested as a good geometry to explore the IMRT algorithm parameters. Using this geometry, the order of varying parameters is suggested. First is to determine the effects of the number of stratifications of optimized intensity fluence on the resulting dose distribution, and selecting a fixed number of stratifications for further studies. To characterize the dose distributions, a dose-homogeneity index (DHI) is defined as the ratio of the dose received by 90% of the volume to the minimum dose received by the "hottest" 10% of the volume. The next step is to explore the effects of priority and penalty on both the TV and the CNT. Then, choosing and fixing these parameters, the effects of varying the number of beams can be looked at. As well as evaluating the dose distributions (and DHI), the number of subfields and the number of monitor units required for different numbers of stratifications and beams can be evaluated.

Algorithms↗
PubMed2001

Likelihood of conception with a single act of intercourse: providing benchmark rates for assessment of post-coital contraceptives.

Emergency post-coital contraceptives effectively reduce the risk of pregnancy, but their degree of efficacy remains uncertain. Measurement of efficacy depends on the pregnancy rate without treatment, which cannot be measured directly. We provide indirect estimates of such pregnancy rates, using data from a prospective study of 221 women who were attempting to conceive. We previously estimated the probability of pregnancy with an act of intercourse relative to ovulation. In this article, we extend these data to estimate the probability of pregnancy relative to intercourse on a given cycle day (counting from onset of previous menses). In assessing the efficacy of post-coital contraceptives, other approaches have not incorporated accurate information on the variability of ovulation. We find that the possibility of late ovulation produces a persistent risk of pregnancy even into the sixth week of the cycle. Post-coital contraceptives may be indicated even when intercourse has occurred late in the cycle.

Coitus↗
PubMed2003

Contemporary utilization and outcomes of intra-aortic balloon counterpulsation in acute myocardial infarction: the benchmark registry.

OBJECTIVES: We sought to examine contemporary utilization patterns and clinical outcomes in patients with acute myocardial infarction (AMI) requiring intra-aortic balloon pump (IABP) counterpulsation. BACKGROUND: Despite increasing experience with and broadened indications for intra-aortic counterpulsation, the current indications, associated complications, and clinical outcomes of IABP use in AMI are unknown. METHODS: Between June 1996 and August 2001, data were prospectively collected from 22,663 consecutive patients treated with aortic counterpulsation at 250 medical centers worldwide; 5,495 of these patients had AMI. RESULTS: Placement of an IABP in AMI patients was most frequently indicated for cardiogenic shock (27.3%), hemodynamic support during catheterization and/or angioplasty (27.2%) or prior to high-risk surgery (11.2%), mechanical complications of AMI (11.7%), and refractory post-myocardial infarction unstable angina (10.0%). Balloon insertions were successful in 97.7% of patients. Diagnostic catheterization was performed in 96% of patients, and 83% underwent coronary revascularization before hospital discharge. The in-hospital mortality rate was 20.0% (38.7% in patients with shock) and varied markedly by indication and use of revascularization procedures. Major IABP complications occurred in only 2.7% of patients, despite median use for three days, and early IABP discontinuation was required in only 2.1% of patients. CONCLUSIONS: With contemporary advances in device technology, insertion technique, and operator experience, IABP counterpulsation may be successfully employed for a wide variety of conditions in the AMI setting, providing significant hemodynamic support with rare major complications in a high-risk patient population.

Adult↗
PubMed1997

Benchmarking the perioperative process. I. Patient routing systems: a method for continual improvement of patient flow and resource utilization.

The article presents an overview of the design and application of a real-time patient routing system, based on barcode and local area network technology, that was designed to track the progress of patients during the perioperative process. We present data on all patients undergoing ambulatory surgery. Patients' progress during their surgical stay was recorded at 17 strategic events using this real-time patient tracking technology. These times were used to identify inefficiencies in the perioperative process by identifying bottlenecks and areas of high variation. We found that both raw and actual operating room (OR) utilization efficiency was less than 50%. Points of high variation in a patient's progress occurred during the time from admit to the hospital until the patient was ready for the OR; the time from when a patient was ready for the OR until they were called for; and the time a patient spends in the OR preoperative holding room. Causes for variation were identified and traced back to individual procedures, activities, and work processes. Multidisciplinary improvement teams were created to improve the pinpointed problem areas. The real-time patient routing system is a process that has proven to be highly valuable to all participants in the surgical process in bringing about rational, data driven efficiencies in perioperative services. This process has the potential to facilitate multidisciplinary cooperation in efforts to contain and reduce costs of perioperative services.

Appointments and Schedules↗
PubMed2002

Gamma irradiator dose mapping simulation using the MCNP code and benchmarking with dosimetry.

The Monte Carlo transport code, MCNP, has been applied in simulating dose rate distribution in the IR-136 gamma irradiator system. Isodose curves, cumulative dose values, and system design data such as throughputs, over-dose-ratios, and efficiencies have been simulated as functions of product density. Simulated isodose curves, and cumulative dose values were compared with dosimetry values obtained using polymethyle-methacrylate, Fricke, ethanol-chlorobenzene, and potassium dichromate dosimeters. The produced system design data were also found to agree quite favorably with those of the system manufacturer's data. MCNP has thus been found to be an effective transport code for handling of various dose mapping excercises for gamma irradiators.

Journal Article↗
PubMed2005

Structural analysis of silanediols as transition-state-analogue inhibitors of the benchmark metalloprotease thermolysin.

Dialkylsilanediols have been found to be an effective functional group for the design of active-site-directed protease inhibitors, including aspartic (HIV protease) and metallo (ACE and thermolysin) proteases. The use of silanediols is predicated on its resemblance to the hydrated carbonyl transition-state structure of amide hydrolysis. This concept has been tested by replacing the presumed tetrahedral carbon of a thermolysin substrate with a silanediol group, resulting in an inhibitor with an inhibition constant K(i) = 40 nM. The structure of the silanediol bound to the active site of thermolysin was found to have a conformation very similar to that of a corresponding phosphonamidate inhibitor (K(i) = 10 nM). In both cases, a single oxygen is within bonding distance to the active-site zinc ion, mimicking the presumed tetrahedral transition state. There are binding differences that appear to be related to the presence or absence of protons on the oxygens attached to the silicon or phosphorus. This is the first crystal structure of an organosilane bound to the active site of a protease.

Bacillus↗
PubMedDate not supplied

Benchmarking of model core potentials: application to the halogen complexes of group 4 metals.

The reliability of the model core potential (MCP) method was probed in a systematic RHF and MP2 study of the geometries of the group 4 metal halogen complexes (MX4; M = Ti, Zr, Hf and X = F, Cl, Br, I). The computed bond lengths were compared with experimental values, as well as those predicted using effective core potentials. Provided that electrons from the outermost core shell of the metal atom are treated explicitly in the calculation, both the MCP and ECP methods predict M-X bond lengths within 0.02-0.03 A of experiment. The reaction energies for a simple set of halogen substitution reactions of the MX4 complexes leading to the mixed halogen complex, MX2Y2, were also studied. Although no experimental values are available for these reactions, comparison was made with the values computed using effective core potentials. The predictability of the different pseudopotential techniques and the importance of the metal atom valence basis set contraction scheme and polarization space are discussed.

Journal Article↗
PubMedDate not supplied

QSAR study of steroid benchmark and dipeptides based on MEDV-13.

A molecular electronegativity distance vector based on 13 atomic types, called MEDV-13, is a descriptor for predicting the biological activities of molecules based on the quantitative structure-activity relations (QSAR). The MEDV-13 uses a modified electrotopological state (E-state) index to substitute for the relative eletronegativity (q) of non-hydrogen atoms in the molecule of interest in the MEDV and a topological distance for the relative distance (d) in the MEDV. For an organic molecule containing several chemical elements such as C, H, O, N, S, F, Cl, Br, I, and P, the MEDV-13 includes at best 91 descriptors. Then it is essential to employ a principal component regression (PCR) technique to derive a QSAR model relating the biological activities to the MEDV-13. The MEDV-13 is used to study the QSAR of the corticosteroid-binding globulin (CBG) binding affinity of the steroids and the activity inhibiting angiotensin-converting enzyme (ACE) of dipeptides, and resulting models have a comparable quality to the current three-dimensional (3D) methods such as CoMFA though the MEDV-13 is a descriptor based on two-dimensional topological information.

Angiotensin-Converting Enzyme Inhibitors↗
PubMedDate not supplied

Predictive toxicology: benchmarking molecular descriptors and statistical methods.

The development of drugs depends on finding compounds that have beneficial effects with a minimum of toxic effects. The measurement of toxic effects is typically time-consuming and expensive, so there is a need to be able to predict toxic effects from the compound structure. Predicting toxic effects is expected to be challenging because there are usually multiple toxic mechanisms involved. In this paper, combinations of different chemical descriptors and popular statistical methods were applied to the problem of predictive toxicology. Four data sets were collected and cleaned, and four different sets of chemical descriptors were calculated for the compounds in each of the four data sets. Three statistical methods (recursive partitioning, neural networks, and partial least squares) were used to attempt to link chemical descriptors to the response. Good predictions were achieved in the two smaller data sets; we found for large data sets that the results were less effective, indicating that new chemical descriptors or statistical methods are needed. All of the methods and descriptors worked to a degree, but our work hints that certain descriptors work better with specific statistical methods so there is a need for better understanding and for continued methods development.

Drug Design↗