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PubMed2003

Seizure detection: correlation of human experts.

OBJECTIVE: The description and application of a new, overlap-integral comparison method and the quantification of human vs. human accuracies that can be used as goals for algorithms. METHODS: Four human experts marked ten 8 h electroencephalography (EEG) records from seizure patients. The seizures varied in origin and type, including complex partial, generalized absence, secondarily generalized and primary generalized tonic-clonic. The traditional any-overlap comparison method is used in addition to the overlap-integral method, which is sensitive to the correct placement of the seizure endpoints. RESULTS: The number of events marked by each reader ranged from 57 to 77. The average any-overlap sensitivity and false positives per hour rate are 0.92 and 0.117. The average overlap-integral correlation, sensitivity and specificity are 0.80, 0.82 and 0.9926. As expected, the correspondence between readers is high, but confounding issues resulted in overlap-integral sensitivities less than 0.5 for 10% of the records. Seven percent of the any-overlap sensitivities are less than 0.5. A comparison of the methods by record shows that the overlap-integral specificity and the any-overlap false positive rate measure different features. CONCLUSIONS: There was little variation between readers and they were essentially interchangeable. High seizure rate (many per hour), short seizure durations (<10 s) and long seizure durations (approximately 10 min) with ambiguous offsets can complicate the analysis and result in poor correlation. There may be any number of unmarked events in rigorously marked records and it may be preferable to use records from non-epilepsy patients to compute the false positive rate. The any-overlap and overlap-integral comparison methods are complementary. SIGNIFICANCE: Correlation between expert human readers can be low on some records, which will complicate testing of seizure detection algorithms.

Algorithms↗

PubMed1991

Comparison of methods for measuring fractal dimension.

Fractal dimension has been proposed as a useful method for characterizing medical images. The fractal dimension is calculated from the average radial power spectrum of the image. However, simpler methods of calculation have been proposed. This paper examines a very simple and easily implemented method which has been proposed for the calculation of fractal dimensions. Comparisons are made between the more rigorous method and the proposed simplification. It is found that the simpler method is a useful technique for calculating estimates of fractal dimension provided the range of dimensions of interest is small.

Algorithms↗

PubMed1996

[Infrared temperature measurement in the ear canal with the DIATEK 9000 Instatemp and the DIATEK 9000 Thermoguide. Comparison with methods of temperature measurement in other body parts].

UNLABELLED: Temperature of the tympanic membrane is recommended as a "gold standard" of core-temperature recording. However, use of temperature probes in the auditory canal may lead to damage of tympanic membrane. Temperature measurement in the auditory canal with infrared thermometry does not pose this risk. Furthermore it is easy to perform and not very time-consuming. For this reason infrared thermometry of the auditory canal is becoming increasingly popular in clinical practice. We evaluated two infrared thermometers-the Diatek 9000 Thermoguide and the Diatek 9000 Instatemp-regarding factors influencing agreement with conventional tympanic temperature measurement and other core-temperature recording sites. In addition, we systematically evaluated user dependent factors that influence the agreement with the tympanic temperature. MATERIALS AND METHODS: In 20 volunteers we evaluated the influence of three factors: duration of the devices in the auditory canal before taking temperature (0 or 5 s), interval between two following recordings (30, 60, 90, 120, 180 s) and positioning of the grip relative to the auditory-canal axis (0, 60, 180 and 270 degrees). Agreement with tympanic contact probes (Mon-a-therm tympanic) in the contralateral ear was investigated in 100 postoperative patients. Comparative readings with rectal (YSI series 400) and esophageal (Mon-a-therm esophageal stethoscope with temperature sensor) probes were done in 100 patients in the ICU. The method of Bland and Altman was taken for comparison. RESULTS: Shortening of the interval between two consecutive readings led to increasing differences between the two measurements with the second reading decreasing. A similar effect was seen when positioning the infrared thermometers in the auditory canal before taking temperatures: after 5 s the recorded temperatures were significantly lower than temperature recordings taken immediately. Rotation of the devices out of the telephone handle position led to increasing lack of agreement between infrared thermometry and contact probes. Mean differences between infrared thermometry (Instatemp and Thermoguide, CAL-Mode) and tympanic probes were -0.41 +/- 0.67 degree C (2 SD) and -0.43 +/- 0.70 degree C, respectively. Mean differences between the Thermoquide (Rectal-Mode) and rectal probe were -0.19 +/- 0.72 degree C, and between the Thermoguide (Core Mode) and esophageal probe -0.13 +/- 0.74 degree C. DISCUSSION: Although easy to use, infrared thermometry requires careful handling. To obtain optimal recordings, the time between two consecutive readings should not be less than two min. Recordings should be taken immediately after positioning the devices in the auditory canal. Best results are obtained in the 60 degrees position with the grip of the devices following the ramus mandibulae (telephone handle position). The lower readings of infrared thermometry compared with tympanic contact probes indicate that the readings obtained represent the temperature of the auditory canal rather than of the tympanic membrane itself. To compensate for underestimation of core temperature by infrared thermometry, the results obtained are corrected and transferred into core-equivalent temperatures. This data correction reduces mean differences between infrared recordings and traditional core-temperature monitoring, but leaves limits of agreement between the two methods uninfluenced.

Body Temperature↗

PubMed1987

Comparison of methods for determining occupational exposure in a case-control interview study of chronic lymphocytic leukemia.

A comparison was made between two indirect methods for linking reported lifetime occupations and industries of employment with specific exposures and with directly reported exposure information, using data from a population-based case-control interview study of chronic lymphocytic leukemia (CLL). Exposures previously suspected of being associated with CLL were examined using a job-exposure matrix developed by Hoar et al and a linkage between observed occupational exposures and specific occupations, by industry, based on data collected in the National Occupational Hazard Survey (NOHS). In general, concordance on exposure for the two occupation-exposure linkage methods was fairly poor, although it was better for some of the exposures studied (butadiene and asbestos, for which most kappas were between 0.40 and 0.60) than for others (carbon tetrachloride and benzene with kappas ranging from 0.01 to 0.12). Higher proportions of cases and controls directly reported exposure to benzene and asbestos than was determined using the two more indirect methods, neither of which showed consistently greater agreement with direct reporting.

Epidemiologic Methods↗

PubMed1992

Quantitation of chronotropic response: comparison of methods for rate-modulating permanent pacemakers.

OBJECTIVES: The aim of this study was to develop a technique for quantitating chronotropic response. BACKGROUND: Although the importance of chronotropic response for optimizing cardiac output during exercise is widely recognized, methods for quantitating the rate-modulating behavior of permanent pacemakers have not been developed. For a method of quantitating chronotropic response to be clinically useful, the rate-modulating characteristics of a pacing system should be defined at the onset of exertion, over a variety of exercise work loads and during recovery. METHODS: Three methods for quantitation of rate modulation were assessed in 10 patients during treadmill exercise testing using the chronotropic assessment exercise protocol with expired gas exchange analysis. To compare the observed chronotropic response with a standard, the "expected" heart rate throughout exercise was calculated by using the concept of heart rate reserve as described by Wilkoff. The pacing rate observed during exercise was analyzed with 1) standard linear regression analysis, 2) comparison of observed and expected pacing rates at the midpoint and end of each quartile of exercise, and 3) integration of the area under the rate-response curve with comparison with the area under the expected curve. RESULTS: With use of a normalized scale relating change in heart rate to change in metabolic work load, with values of heart rate and metabolic work load at rest set to 0 and those at maximal exertion set to a value of 1, the mean y intercept for the study group was 0.10 +/- 0.20 (range -0.14 to +0.45), with a mean slope of 0.81 +/- 0.25 (range 0.31 to 1.19). The correlation coefficient relating change in heart rate to change in exercise work load was a mean of 0.90 +/- 0.09 (range 0.63 to 0.98). Integration of the area under the rate-response curve observed during exercise yielded a mean area that was 101 +/- 36% of that expected. When the range of exercise work loads was divided into quartiles, the area under the observed rate-response curve was 151 +/- 114% of that expected during the first quartile of exercise, 113 +/- 70% during the second, 96 +/- 38% during the third and 92 +/- 20% during the fourth. The mean area under the curve during recovery was 93 +/- 29% of that expected. Although calculation of the observed heart rate as a percent of that expected at the midpoint and end of each quartile of exercise used fewer observations, it provided similar results. CONCLUSIONS: Quantitation of the rate-response curve with comparison with the expected heart rate curve provides accurate methods for quantitation of chronotropic response. Adoption of this method would facilitate comparisons of artificial sensors and provide a framework to address issues of optimal rate modulation.

Age Factors↗

PubMed1996

A comparison of methods for measuring trunk list. A simple plumbline is the best.

STUDY DESIGN: Trunk list was measured using three different techniques to compare accuracy, precision, and ease of use. OBJECTIVE: To obtain a reproducible technique for further studies of the nature, cause, and clinical relevance of trunk list. SUMMARY OF BACKGROUND DATA: Gravity-induced trunk list is a clinical sign that is frequently observed in patients with low back pain and has been associated with intervertebral disc lesions. METHODS: Patients with trunk list participated in a comparison of three techniques to determine list magnitude and direction. Paired measurements of trunk list were obtained from each patient using three techniques: a plumbline, a projected shadow, and the 3SPACE Isotrak (McDonnell Douglas Electronics Company, Colchester, VT). In addition, intra- and interobserver reliability of list measurement was assessed by comparison of paired measurements by each of two observers. RESULTS: List measurements assessed by the plumbline and the projected shadow techniques were not significantly different, but the Isotrak produced data that differed significantly (P < 0.05) from both of these techniques. Comparison of intra- and interobserver repeatability of list measurement using the plumbline technique indicated no significant difference between repeated measures by each observer or between two observers. CONCLUSIONS: A plumbline is the most useful instrument for measuring static trunk list, but its limitations and the need for standardization of measurement technique must be recognized.

Adult↗

PubMed1994

Comparison of three methods for obtaining plantar pressures in nonpathologic subjects.

The purpose of this study was to determine if pressure data, collected after taking one step or two steps, were similar to values obtained by using the traditional midgait method. Ten healthy subjects, with a mean age of 27 years, walked across a sensor platform sampling at 70 Hz. Each subject was randomly assigned to take one step, two steps, or multiple steps (midgait method) across the sensor platform. The results of the study indicate that the two-step method, in comparison with the one-step method, provides pressure data more representative of the midgait method, and different values for pressure and force will be obtained, depending on the method of pressure data collection selected by the clinician.

Adult↗

PubMedDate not supplied

Interlaboratory comparison of methods for the determination of incurred tilmicosin residues in bovine liver.

The objective of this study was to compare 2 methods for the determination of tilmicosin residues in bovine liver samples. Three laboratories participated in the comparison of the 2 methods. The first method was described in a New Animal Drug Application (NADA 140-929), and the second was a modification of that method in which hexane was substituted for carbon tetrachloride in one cleanup step. Each of the 3 laboratories analyzed subsamples of 10 bovine livers containing incurred tilmicosin. Residues ranged from 2.3 to 81 ppm tilmicosin in the 10 liver samples with an 11.8% relative standard deviation obtained by using both methods. In addition, fortified-control liver tissue samples were analyzed concurrently with tissues containing incurred residues by using the modified method in one of the laboratories. The fortification levels ranged from 0.3 to 112 ppm, with recoveries ranging from 76 to 92%. The results from the 3 laboratories were comparable, indicating that the modified method was not only as effective as the original NADA method, but also more desirable because of the change to a less hazardous solvent.

Animals↗

PubMed1998

Comparison of methods for identifying transcription units and transcription map of the Werner syndrome gene region.

To isolate a human disease gene by positional cloning, a critical step is the identification of candidate genes from a targeted genomic region. We used cDNA selection, exon trapping, and genomic sequencing to identify 12 transcription units from a 1.4-Mb genomic region containing the Werner syndrome gene (WRN). This included sequencing of 650 kb in the region of the WRN gene, to date, the most DNA sequenced as part of a positional cloning effort. The result of this combined method was significant overlap among the transcription units identified by each method; yet, no one method identified all of the transcription units. We present here a comparison of the effectiveness and efficiency of these methods and present a transcription map of the Werner syndrome gene region.

Blotting, Northern↗

PubMed1987

Measurement of glomerular filtration rate with 99mTc-DTPA: a comparison of gamma camera methods.

A comparison has been made between three gamma camera methods for estimation of glomerular filtration rate (GFR) using 99mTc-DTPA in a group of 27 patients with widely different renal function. Plasma clearance of 99mTc-DTPA by multiple blood sampling was used as the reference. Percentage uptake of chelate in the bladder and kidneys at 20 min after injection gave the lowest standard error of 8.0 ml/min. Techniques using early uptake of isotope in the kidneys at 2 min after injection gave less accurate estimates. Correction for the vascular activity in the renal region of interest improved the results for the 2 min uptake technique. Gamma camera techniques provide rapid estimates of GFR which are less accurate than those obtained by plasma clearance of labelled chelate.

Glomerular Filtration Rate↗

PubMed1997

Comparison of methods of measuring pulmonary artery pressure.

BACKGROUND: Pulmonary artery waveforms fluctuate because of changes in intrathoracic pressure caused by respirations. Monitoring system algorithms determine digital displays of pressure measurements on the basis of recognition, analysis, and comparison of consecutive waveforms. OBJECTIVE: To compare three methods of measuring pulmonary artery pressure during mechanical ventilation and spontaneous breathing in cardiac surgery patients with stable hemodynamics. METHODS: Pulmonary artery pressure was measured during mechanical ventilation after cardiac surgery in 53 patients; 37 of the patients were studied again after extubation. Three monitoring methods were compared: graphic strip recording, the "stop cursor" (monitor screen freezing) method, and digital-display recording. Difference scores were calculated between the methods and analyzed for frequency and direction. RESULTS: All comparisons showed differences of at least +/-3 mm Hg in measurements obtained with the three methods. During mechanical ventilation, the digital and graphic measurements of systolic pressure varied most often; 57% (30/53) of the comparisons had difference scores of at least +/-3 mm Hg. The cursor and graphic measurements of diastolic pressures varied least often; 6% (3/53) of the comparisons had difference scores of at least +/-3 mm Hg. As expected, the digital method most often gave higher results than the graphic method. During spontaneous breathing, measurements of systolic pressure varied more often (38% to 53%) than did measurements of diastolic pressure (12% to 37%). Unexpectedly, for systolic pressures, the difference between digital and graphic measurements was 3 mm Hg or more 30% (11/37) of the time, and the difference between cursor and graphic measurements was 3 mm Hg or more 53% (17/32) of the time. CONCLUSIONS: Because of physiological and technical influences, measurements of systolic and diastolic pressures in the pulmonary artery made with the digital and cursor methods were not as reliable as measurements made with the graphic method. The findings support continued use of the graphic method for accurate measurements of pulmonary artery pressure.

Adult↗

PubMed1977

Estimation of composition of weight loss in man: a comparison of methods.

Five different procedures were used to estimate composition of weight loss by six obese individuals maintained on low-calorie regimens: 1) energy-nitrogen (E-N) balance; 2) total body water-nitrogen balance (TBW-N); 3) total body water (TBW); 4) total body potassium (TBK); and 5) an anthropometric method. Quantity of weight lost by obese subjects during comparison periods lasting 25-40 days ranged from 7.9 to 17.1 kg. Expressed as percent of aggregate weight loss, collective fat loss was 47.6 by E-N balance; 46.3 by TBW-N balance; 51.7 by TBK; 50.9 by anthrometry; and 33 by TBW. The E-N balance method yielded a tight cluster of individual means, whereas the other procedures gave a wide scatter of means. For short-term studies, the E-N balance procedure, although tedious and difficult, should yield results less variable than those generated by any of the other methods examined.

Adult↗

PubMed2001

Comparison of glucose levels in dermal interstitial fluid and finger capillary blood.

Alternative methods for self-monitoring of blood glucose have been pursued by many researchers, largely in response to evidence gathered in several long-term studies of patients with diabetes mellitus. These studies suggest that long-term complications of the disease may be mitigated if the disease is intensively managed, a component of which is increased monitoring. Many of the alternative methods utilize interstitial fluid (ISF) as the diagnostic fluid, rather than finger blood. A time lag in the distribution of glucose from blood to the interstitium has been observed by many, with estimates of lag time varying from none to 45 min. Dermal ISF was sampled from diabetic subjects in two tests and compared to finger blood glucose. In the first test, data were collected over time in a manner that allowed a cross-correlation analysis to predict an average lag time. Information from this test was then used as input to a data collection format for a method comparison test of 691 patients with diabetes in which ISF data were collected immediately after the finger blood reference and 15 min after the reference. An average lag time of about 25 min was determined from the cross-correlation analysis, with the correlation error reduced by three-fourths within a 15-min lag time. In the method comparison test, the correlation coefficient between finger blood glucose and ISF glucose improved from 0.923 to 0.951, and the percentage of data in the A zone of the Clarke Error Grid rose from 80.2% to 90.6% for the ISF glucose data collected at no lag and 15-min lag, respectively. Dermal ISF glucose measurement might be a reasonable alternative to blood glucose measurement for patients routinely monitoring ambient glycemia, although more testing in the sensitive hypoglycemic range is needed to clarify what might happen in cases of rapidly changing glucose.

Blood Glucose↗

PubMed1999

[Tracheotomy: discussion of various surgical procedures using argon plasma coagulation].

BACKGROUND: At present there is a discernible lack of consensus among different medical specialties regarding methods of tracheotomy in an intensive care setting. There is an obvious preference for percutaneous dilatational tracheotomy methods. Comparison of different methods are necessary to determine whether this trend is justified. METHOD: ENT and intensive care departments together performed 270 tracheotomies using different techniques in longtime-intubated adults over a period of 4 years. Severe complications were compared. Twenty conventional surgical tracheotomies were performed by using argon-plasma coagulation (APC). RESULTS: Comparison of 2175 percutaneous and 3263 conventional surgical tracheotomies reveals a nearly identical rate of severe perioperative complications. Percutaneous methods are most frequently used in patients with initially uncomplicated conditions. CONCLUSIONS: On the basis of our experience with 270 tracheotomies we have found there are clear indications for the various methods of tracheotomy. They depend on both the history of the disorder and its course and on the known contraindications to percutaneous tracheotomy methods. For safety reasons, we do not perform percutaneous tracheotomies on patients with severe brain damage who tend to aspirate and require prolonged neurological rehabilitation. Preoperative bleeding in percutaneous tracheostomies is the most important complication. It led to a life-threatening situation in 2.4% of our cases. Preoperative neck ultrasound may decrease the risks due to unusual anatomical conditions. Comparison of significant perioperative complications does not appear to favor any one method at present. In light of our effective cooperation with other specialties in planning and performing tracheotomies we do not feel that the current general preference for percutaneous methods in intensive care medicine is justified. Initial experience with APC shows promising results concerning its use in conventional tracheotomies. However, we noticed a shorter operation time, reduction of bleeding complications, and use of less suture material. The effectiveness of surgical intervention is improved by a number of factors.

Adult↗

PubMed2001

Interpreting epidemiological research: blinded comparison of methods used to estimate the prevalence of inherited mutations in BRCA1.

While sequence analysis is considered by many to be the most sensitive method of detecting unknown mutations in large genes such as BRCA1, most published estimates of the prevalence of mutations in this gene have been derived from studies that have used other methods of gene analysis. In order to determine the relative sensitivity of techniques that are widely used in research on BRCA1, a set of blinded samples containing 58 distinct mutations were analysed by four separate laboratories. Each used one of the following methods: single strand conformational polymorphism analysis (SSCP), conformation sensitive gel electrophoresis (CSGE), two dimensional gene scanning (TDGS), and denaturing high performance liquid chromatography (DHPLC). Only the laboratory using DHPLC correctly identified each of the mutations. The laboratory using TDGS correctly identified 91% of the mutations but produced three apparent false positive results. The laboratories using SSCP and CSGE detected abnormal migration for 72% and 76% of the mutations, respectively, but subsequently confirmed and reported only 65% and 60% of mutations, respectively. False negatives therefore resulted not only from failure of the techniques to distinguish wild type from mutant, but also from failure to confirm the mutation by sequence analysis as well as from human errors leading to misreporting of results. These findings characterise sources of error in commonly used methods of mutation detection that should be addressed by laboratories using these methods. Based upon sources of error identified in this comparison, it is likely that mutations in BRCA1 and BRCA2 are more prevalent than some studies have previously reported. The findings of this comparison provide a basis for interpreting studies of mutations in susceptibility genes across many inherited cancer syndromes.

Chromatography, High Pressure Liquid↗

PubMed1999

Stability indicating assays for the determination of piroxicam--comparison of methods.

Photodegradation of piroxicam, a 1,2-benzothiazine oxicam, is studied laying special emphasis on the investigation of the correlation between concentration of the sample solution and stability. A comparison of three different methods (HPTLC/densitometry, HPLC, CE) developed for the photostability testing of the title compound is presented. The stability indicating capability of the assays is proved using forced degradation by exposing a sample solution to artificial irradiation from a xenon source. The chromatograms and the electropherogram of the resulting solution show piroxicam well resolved from the degradation products. For quantitation external calibration is employed, all calibration curves being linear in the respective concentration range of interest. Piroxicam solutions of three different concentrations (2 mg ml(-1); 250 microg ml(-1); 40 microg ml(-1)) are subjected to simulated sunlight for 480 min. The stability is investigated by quantitation of piroxicam by the methods mentioned. The methods are compared in respect of performance and precision. Costs and time of analysis are regarded also.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed1980

[Comparison of methods of determination of serum doxycyline assessing relative bioavailability of two commercial formulations (author's transl)].

The present study was undertaken to evaluate the accuracy of the analytical results of an investigation of relative bioavailability of two doxycycline preparations. Six methods in four laboratories were applied: one fluorimetric, three high-pressure-liquid-chromatographic and three microbiological methods. The analyses were performed after coding the samples. In all cases the two preparations were bioequivalent. When comparing the methods, it could be shown that the fluorimetric method was slightly more accurate than the others. The HPLC-methods were almost as accurate. The results of the microbiological determinations showed the lowest accuracy. Two of the results were in good agreement with the biochemical methods, whereas the third showed such a high deviation that a comparison was no longer possible. Altogether a good agreement of all compared methods (except one) could be demonstrated.

Biological Assay↗

PubMed2004

Comparison of methods for finding saddle points without knowledge of the final states.

Within the harmonic approximation to transition state theory, the biggest challenge involved in finding the mechanism or rate of transitions is the location of the relevant saddle points on the multidimensional potential energy surface. The saddle point search is particularly challenging when the final state of the transition is not specified. In this article we report on a comparison of several methods for locating saddle points under these conditions and compare, in particular, the well-established rational function optimization (RFO) methods using either exact or approximate Hessians with the more recently proposed minimum mode following methods where only the minimum eigenvalue mode is found, either by the dimer or the Lanczos method. A test problem involving transitions in a seven-atom Pt island on a Pt(111) surface using a simple Morse pairwise potential function is used and the number of degrees of freedom varied by varying the number of movable atoms. In the full system, 175 atoms can move so 525 degrees of freedom need to be optimized to find the saddle points. For testing purposes, we have also restricted the number of movable atoms to 7 and 1. Our results indicate that if attempting to make a map of all relevant saddle points for a large system (as would be necessary when simulating the long time scale evolution of a thermal system) the minimum mode following methods are preferred. The minimum mode following methods are also more efficient when searching for the lowest saddle points in a large system, and if the force can be obtained cheaply. However, if only the lowest saddle points are sought and the calculation of the force is expensive but a good approximation for the Hessian at the starting position of the search can be obtained at low cost, then the RFO approaches employing an approximate Hessian represent the preferred choice. For small and medium sized systems where the force is expensive to calculate, the RFO approaches employing an approximate Hessian is also the more efficient, but when the force and Hessian can be obtained cheaply and only the lowest saddle points are sought the RFO approach using an exact Hessian is the better choice. These conclusions have been reached based on a comparison of the total computational effort needed to find the saddle points and the number of saddle points found for each of the methods. The RFO methods do not perform very well with respect to the latter aspect, but starting the searches further away from the initial minimum or using the hybrid RFO version presented here improves this behavior considerably in most cases.

Journal Article↗