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Results for “Measuring algorithm”

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PubMed2000

An analysis algorithm for measuring airway lumen and wall areas from high-resolution computed tomographic data.

High-resolution computed tomography (HRCT) has been used to examine airway narrowing. We developed an automated computed tomographic image analysis algorithm (computed tomographic airway morphometry; CTAM) to measure airway lumen area (Ai ), airway wall area (Awa), and airway angle of orientation. Tubes of varying size were embedded in Styrofoam and then scanned at angles between 0 degrees and 50 degrees to assess the accuracy of measurements made with CTAM. Two excised pig lungs were fixed in inflation, sectioned, and scanned. Ai and Awa were measured planimetrically from the cut surfaces to optimize CTAM measurement parameters. In CTAM, Ai was defined according to an airway-size-dependent threshold value, and total Awa was determined through a score-guided erosion method. Results were compared with measurements made through a previously validated method (manual method). CTAM provided accurate measurements of the tubes' Ai values at all angles; Awa was overestimated in direct relation to airway size. The manual method underestimated Ai and overestimated Awa in a manner directly related to airway size as well as to airway angle of orientation. In the excised lung, the mean errors of Ai and Awa measurements made with CTAM were 0.52 +/- 0.24 mm(2) and 0.17 +/- 0.32 mm(2) (mean +/- SEM), respectively. Ai errors with the manual method were similar, but Awa was overestimated to a greater degree (6.3 +/- 0.38 mm(2); p < 0.01) and the error was proportional to Awa (r = 0.64; p < 0.01). CTAM allows accurate measurements of airway dimensions and angle of orientation.

Airway Resistance↗

PubMed2004

Measurement of mesothelioma on thoracic CT scans: a comparison of manual and computer-assisted techniques.

Our purpose in this study was to evaluate the variability of manual mesothelioma tumor thickness measurements in computed tomography (CT) scans and to assess the relative performance of six computerized measurement algorithms. The CT scans of 22 patients with malignant pleural mesothelioma were collected. In each scan, an initial observer identified up to three sites in each of three CT sections at which tumor thickness measurements were to be made. At each site, five observers manually measured tumor thickness through a computer interface. Three observers repeated these measurements during three separate sessions. Inter- and intra-observer variability in the manual measurement of tumor thickness was assessed. Six automated measurement algorithms were developed based on the geometric relationship between a specified measurement site and the automatically extracted lung regions. Computer-generated measurements were compared with manual measurements. The tumor thickness measurements of different observers were highly correlated (r > or = 0.99); however, the 95% limits of agreement for relative inter-observer difference spanned a range of 30%. Tumor thickness measurements generated by the computer algorithms also correlated highly with the average of observer measurements (r > or = 0.93). We have developed computerized techniques for the measurement of mesothelioma tumor thickness in CT scans. These techniques achieved varying levels of agreement with measurements made by human observers.

Adult↗

PubMed1991

Some ways of measurement unification in testing ECG analysers on the basis of test signals normalized according to amplitude/parameters and medical indications.

An urgency of test method development for testing the automated ECG analysers is substantiated; a generalized measurement algorithm used in measuring devices testing is discussed with interpretation as applied to ECG analysers. A general measurement scheme in analyser testing is given, tasks to create test ECG signals and develop methods and means for storage, reproduction and transfer of ECG signals to ECG analysers are advanced. A method to create, organize, store and reproduce the ECG signal data bank with the use of measuring and computing complex (MCC) is developed. A device for ECG signal reproduction and transfer (a generator) is made, with its structural diagram, work principles and main technological (metrological) characteristics shown.

Algorithms↗

PubMed2005

Development and validation of algorithms for measuring G-protein coupled receptor activation in cells using the LSC-based imaging cytometer platform.

BACKGROUND: A cell-based assay system (Transfluor) has been developed for measurement of G-protein coupled receptor (GPCR) activity by using cells transfected to express a fusion protein of arrestin plus green fluorescent protein (GFP) and the target GPCR. Upon agonist stimulation, the arrestin-GFP translocates to and binds the activated GPCR at the plasma membrane. The receptor/arrestin-GFP complexes then localize in clathrin-coated pits and/or intracellular vesicles. This redistribution of arrestin-GFP into condensed fluorescent spots is useful for visually monitoring the active status of GPCRs and its quantitation is possible with certain types of digital image analysis systems. METHODS: We designed two lines of image processing algorithms to carry out quantitative measurement of the arrestin-GFP movement on an inverted version of laser scanning cytometry (iCyte) as an imaging platform. We used a cell line expressing arrestin-GFP and the wild-type beta2-adrenergic receptor or a modified version of this receptor with enhanced affinity for arrestin. Each cell line was challenged with various concentrations of agonist. RESULTS: A dose-dependent signal was measured and half-maximal effective concentration values were obtained that agreed well with results determined by other methods previously reported. CONCLUSIONS: The results indicate that the combination of Transfluor, iCyte, and our algorithms is suitable for robust and pharmacologically relevant GPCR ligand exploration.

Algorithms↗

PubMed2007

10/20, 10/10, and 10/5 systems revisited: their validity as relative head-surface-based positioning systems.

With the advent of multi-channel EEG hardware systems and the concurrent development of topographic and tomographic signal source localization methods, the international 10/20 system, a standard system for electrode positioning with 21 electrodes, was extended to higher density electrode settings such as 10/10 and 10/5 systems, allowing more than 300 electrode positions. However, their effectiveness as relative head-surface-based positioning systems has not been examined. We previously developed a virtual 10/20 measurement algorithm that can analyze any structural MR head and brain image. Extending this method to the virtual 10/10 and 10/5 measurement algorithms, we analyzed the MR images of 17 healthy subjects. The acquired scalp positions of the 10/10 and 10/5 systems were normalized to the Montreal Neurological Institute (MNI) stereotactic coordinates and their spatial variability was assessed. We described and examined the effects of spatial variability due to the selection of positioning systems and landmark placement strategies. As long as a detailed rule for a particular system was provided, it yielded precise landmark positions on the scalp. Moreover, we evaluated the effective spatial resolution of 329 scalp landmark positions of the 10/5 system for multi-subject studies. As long as a detailed rule for landmark setting was provided, 241 scalp positions could be set effectively when there was no overlapping of two neighboring positions. Importantly, 10/10 positions could be well separated on a scalp without overlapping. This study presents a referential framework for establishing the effective spatial resolutions of 10/20, 10/10, and 10/5 systems as relative head-surface-based positioning systems.

Body Surface Area↗

PubMed2006

Automatic measurement of vertebral rotation in idiopathic scoliosis.

STUDY DESIGN: Development of an automatic measurement algorithm and comparison with manual measurement methods. OBJECTIVES: To develop a new computer-based method for automatic measurement of vertebral rotation in idiopathic scoliosis from computed tomography images and to compare the automatic method with two manual measurement techniques. SUMMARY OF BACKGROUND DATA: Techniques have been developed for vertebral rotation measurement in idiopathic scoliosis using plain radiographs, computed tomography, or magnetic resonance images. All of these techniques require manual selection of landmark points and are therefore subject to interobserver and intraobserver error. METHODS: We developed a new method for automatic measurement of vertebral rotation in idiopathic scoliosis using a symmetry ratio algorithm. The automatic method provided values comparable with Aaro and Ho's manual measurement methods for a set of 19 transverse computed tomography slices through apical vertebrae, and with Aaro's method for a set of 204 reformatted computed tomography images through vertebral endplates. RESULTS: Confidence intervals (95%) for intraobserver and interobserver variability using manual methods were in the range 5.5 degrees to 7.2 degrees . The mean (+/-SD) difference between automatic and manual rotation measurements for the 19 apical images was -0.5 degrees +/- 3.3 degrees for Aaro's method and 0.7 degrees +/- 3.4 degrees for Ho's method. The mean (+/-SD) difference between automatic and manual rotation measurements for the 204 endplate images was 0.25 degrees +/- 3.8 degrees . CONCLUSIONS: The symmetry ratio algorithm allows automatic measurement of vertebral rotation in idiopathic scoliosis without intraobserver or interobserver error due to landmark point selection.

Algorithms↗

PubMed2000

Strict reliance on a computer algorithm or measurable ST segment criteria may lead to errors in thrombolytic therapy eligibility.

BACKGROUND: There is accumulating evidence that thrombolytic therapy is underused among eligible patients with acute myocardial infarction. We sought to determine whether potential errors in electrocardiographic diagnosis might be a contributing factor. METHODS: Seventy-five electrocardiograms were interpreted on 2 separate occasions by 3 cardiologists. Two criteria were compared for thrombolysis eligibility: (1) measurement of > or =1 mm ST-segment elevation in 2 contiguous leads (measured) and (2) criterion 1 plus the subjective opinion that the changes represented acute transmural injury (interpretive). The results were compared with computerized interpretations by the Marquette 12SL system. RESULTS: Raw agreement and agreement corrected for chance between raters for both criteria were excellent and tended to be better for interpretive compared with measured criteria (kappa = 0.89 vs 0.78, respectively). Strict reliance on measured electrocardiographic criteria alone would have resulted in overuse of thrombolysis among all 3 raters. Based on the consensus opinion, the absolute overuse of thrombolysis would have been approximately 15% (P <.0034). The computer algorithm had a specificity of 100% and a sensitivity of 61.5%. Reliance on the computerized interpretation alone would have lead to underuse of thrombolytic therapy compared with consensus opinion (21.3% vs 34. 6%; P <.005). CONCLUSION: Agreement for suspected acute myocardial infarction tended to be better when the appearance of the ST segments was added to measurable ST elevation criteria. Strict reliance on measurable criteria may lead to the inappropriate overuse of thrombolysis. Although the Marquette 12SL system has excellent specificity, it has poor sensitivity for the diagnosis of thrombolysis-eligible AMI. Reliance on computerized electrocardiographic interpretation would lead to the inappropriate underuse of thrombolytic therapy in situations in which qualifying electrocardiographic criteria are actually met.

Algorithms↗

PubMed2002

Quantification of distention in CT colonography: development and validation of three computer algorithms.

Three bowel distention-measuring algorithms for use at computed tomographic (CT) colonography were developed, validated in phantoms, and applied to a human CT colonographic data set. The three algorithms are the cross-sectional area method, the moving spheres method, and the segmental volume method. Each algorithm effectively quantified distention, but accuracy varied between methods. Clinical feasibility was demonstrated. Depending on the desired spatial resolution and accuracy, each algorithm can quantitatively depict colonic diameter in CT colonography.

Algorithms↗

PubMed2006

Four methods of measuring tidal volume during high-frequency oscillatory ventilation.

OBJECTIVE: Assess the accuracy of four different methods of measuring tidal volume during simulated high-frequency oscillatory ventilation. DESIGN: In vitro study. SETTING: Research laboratory. SUBJECTS: Three differential pressure pneumotachometers, a modified Pitot tube, an ultrasound flowmeter, and an adult hot wire anemometer. INTERVENTIONS: Each device was placed in series with a Sensormedics 3100B high-frequency ventilator and an 8.0-mm endotracheal tube attached to a 48.9-L plethysmograph. Inspiratory/expiratory ratio was fixed at 1:1 and mean airway pressure at 10 cm H2O. Tidal volumes were calculated at each combination of frequency (f: 3, 4, 6, 8, 10, 12 Hz) and pressure amplitude (DeltaP: 30, 60, 90 cm H2O) by digital integration of the sampled flow signals from each device and compared with those calculated from pressure changes within the plethysmograph. The protocol was repeated after incorporation of frequency-specific calibrations to the flow-measuring algorithm of each device. The hot wire anemometer was further evaluated at Fio2 of 1.0, 37 degrees C, 80% humidity, mean airway pressure of 20 cm H2O, and an inspiratory/expiratory ratio of 1:2. MEASUREMENTS AND MAIN RESULTS: Tidal volumes were 36-305 mL. Bland-Altman analysis demonstrated that each device exhibited systematic bias before frequency-specific adjustment. After frequency-specific adjustment of the flow-measuring algorithm, the two most accurate and precise devices were the Hans Rudolph pneumotachometer, which exhibited a mean error of 0.2% (95% confidence interval, -3.0% to 3.4%), and the hot wire anemometer, which had a mean error of -1.1% (95% confidence interval, -5.5% to 3.3%). The hot wire anemometer remained accurate at Fio2 1.0, 37 degrees C, 80% humidity, mean airway pressure of 20 cm H2O, and an inspiratory/expiratory ratio of 1:2. CONCLUSIONS: Tidal volume can be measured during high-frequency oscillatory ventilation using a variety of techniques. Frequency-specific calibration improves the accuracy and precision of tidal volume measurements. Hot wire anemometry exhibits stable performance characteristics across the range of temperature, humidity, Fio2, and inspiratory/expiratory ratios encountered clinically, has a small deadspace, is unaffected by mean airway pressure, and is therefore suitable for clinical applications.

Adult↗

PubMed2006

[Application of wavelength selection algorithm to measure the effective component of Chinese medicine based on near-infrared spectroscopy].

Near infrared (NIR) spectroscopy has raised a lot of interest in the pharmaceutical industry because it is a rapid and cost-effective analytical type of spectroscopy with no need for extensive sample preparation, and with the easy-realizable ability of on-line application. The NIR technology can increase the quality control standard of the Chinese medicine and accelerate the entry into the international market. In the present paper, two methods for wavelength selection are applied to the measurement of borneol, one of which is the multiple-chain stepwise, which tends to select many variables in the same area containing valuable information, and the other is the mixture genetic algorithm, which incorporates simulated annealing so as to improve the local searching ability while maintaining the global searching ability. The results present that the number of wavelength is reduced to 16% compared with the original number of wavelength, and the prediction accuracy has increased 47.6%. Therefore, the method of wavelength selection is a good way to enhance the prediction accuracy and simplify the model in NIR region.

Algorithms↗

PubMed1993

Optimal sampling interval and edge detection algorithm for measurement of blood vessel diameter on a cineangiogram.

RATIONALE AND OBJECTIVES: The authors studied the effects of image magnification and the type of edge detection filter on the precision of measuring blood vessel diameters on coronary angiograms. METHOD: A blood vessel phantom containing five channels of various diameters filled with contrast medium was filmed. The magnifications examined were x4, x10, and x20, and the edge detection filters used were the first derivative, second derivative, composite, and entropy filters. The regression line y = a+bx was introduced, where x represents the nominal diameter and y the diameter measured by the edge-detection filters. Determination criteria were the offset, slope, and residual variance from the regression equation. RESULTS: The best value among three criteria was obtained with a magnification of x10 or x20. The entropy filter gave the best value of slope and residual variance. The composite filter gave the best value of offset. CONCLUSION: The most precise measurement is obtained when the entropy filter and a magnification of x10 or x20 are applied.

Algorithms↗

PubMed1993

An algorithm for measurement of expiratory flow rate parameters on the partial expiratory flow-volume curve.

Partial expiratory flow-volume (PEFV) curves are a useful tool in airway challenge studies, but unlike the maximal expiratory flow-volume (MEFV) curve, lung function parameters require manual calculation from the flow-volume tracing. We describe an algorithm written in QuickBASIC that analyzes a PEFV curve superimposed on a MEFV curve by (1) identifying the PEFV curve, (2) locating the maximal expiratory flow at the point on the PEFV curve that corresponds to 60% of the baseline forced vital capacity (FVC) below total lung capacity (TLC), termed MEF40%(P), and (3) identifying the size of the PEFV curve along the TLC axis. A report of these parameters is also provided. This algorithm was validated using flow-volume curves from a clinical study in which eight subjects performed two sets of MEFV and PEFV curves separated by approximately 1 hr. Paired comparison of MEF40%(P) determined by the algorithm and two independent manual calculations correlated strongly and yielded no statistically significant differences between the two methods. We conclude that this algorithm provides rapid and accurate determinations of PEFV parameters.

Algorithms↗

PubMed1995

A PC based neural network algorithm for measurement of heart rate variability.

Heart Rate Variability has recently been shown as a viable index to predict sudden cardiac death. The goal of this research is to investigate the use of neural network technique to classify detected QRS complexes into normal and abnormal ones. A single layer perceptron neural network is used for this QRS pattern learning and classification. Results with real data showed that the algorithm gives a 99% correct QRS detection rate.

Algorithms↗

PubMed2006

Creating and validating an algorithm to measure AIDS mortality in the adult population using verbal autopsy.

BACKGROUND: Vital registration and cause of death reporting is incomplete in the countries in which the HIV epidemic is most severe. A reliable tool that is independent of HIV status is needed for measuring the frequency of AIDS deaths and ultimately the impact of antiretroviral therapy on mortality. METHODS AND FINDINGS: A verbal autopsy questionnaire was administered to caregivers of 381 adults of known HIV status who died between 1998 and 2003 in Manicaland, eastern Zimbabwe. Individuals who were HIV positive and did not die in an accident or during childbirth (74%; n = 282) were considered to have died of AIDS in the gold standard. Verbal autopsies were randomly allocated to a training dataset (n = 279) to generate classification criteria or a test dataset (n = 102) to verify criteria. A rule-based algorithm created to minimise false positives had a specificity of 66% and a sensitivity of 76%. Eight predictors (weight loss, wasting, jaundice, herpes zoster, presence of abscesses or sores, oral candidiasis, acute respiratory tract infections, and vaginal tumours) were included in the algorithm. In the test dataset of verbal autopsies, 69% of deaths were correctly classified as AIDS/non-AIDS, and it was not necessary to invoke a differential diagnosis of tuberculosis. Presence of any one of these criteria gave a post-test probability of AIDS death of 0.84. CONCLUSIONS: Analysis of verbal autopsy data in this rural Zimbabwean population revealed a distinct pattern of signs and symptoms associated with AIDS mortality. Using these signs and symptoms, demographic surveillance data on AIDS deaths may allow for the estimation of AIDS mortality and even HIV prevalence.

Adolescent↗

PubMed2002

The influences of ambiguity phase aberration profiles on focusing quality in the very near field--part I: single range focusing on transmission.

Most phase aberration measurement algorithms have an ambiguity for constant and tilted phase aberration profiles. Based on the Fresnel (near field) approximation with single range focusing and the Fraunhofer (far field) approximation, constant and tilted phase aberration profiles change the position of the focal point only and do not influence the image focusing quality. Therefore, ambiguity phase aberration profiles are generally considered to be harmless and ignored in those algorithms and related theoretical analyses. However, Fresnel and Fraunhofer approximations may become invalid under many medical ultrasound imaging situations, e.g., when the imaging field is in the very near field (f-number approximately 1). In the very near field, although it is known that constant and tilted phase aberration profiles may degrade the focusing quality, it seems that there is a lack of quantitative analysis results in the literature about their influences, and this is the purpose of the current paper. In this paper, a quantitative analysis with a very near field approximation is performed for single range focusing on transmission, which is a commonly used transmission focusing method in medical ultrasound imaging. The tolerable levels of constant and tilted phase aberration profiles are derived as a function of the imaging system's f-number and wavelength. Because some phase aberration measurement algorithms may also have an ambiguity for quadratic phase aberration profiles, they are also included in the analysis. The theoretical results are compared with numerical and simulation results. These results have shown that the influences of tilted and quadratic phase-aberration profiles can be ignored only under certain conditions in the very near field.

Algorithms↗

PubMed2000

An efficient algorithm for measurement and correction of chromatic aberrations in fluorescence microscopy.

Even the best optical microscopes available on the market exhibit chromatic aberrations to some extent. In some types of study, chromatic aberrations of current optics cannot be neglected and a software correction is highly desirable. This paper describes a novel method of chromatic aberration measurement and software correction using sub-resolution bead imaging and computer image analysis. The method is quick, precise and enables the determination of both longitudinal and lateral chromatic aberrations. Correction function can be computed in about half an hour, including image acquisition. Using this approach, chromatic aberrations can be reduced to 10-20 nm laterally and 10-60 nm axially depending on the type of optical set-up. The method is especially suitable for fluorescence microscopy, where a limited number of wavelengths are observed.

Journal Article↗

PubMed2005

An information fusion framework for robust shape tracking.

Abstract-Existing methods for incorporating subspace model constraints in shape tracking use only partial information from the measurements and model distribution. We propose a unified framework for robust shape tracking, optimally fusing heteroscedastic uncertainties or noise from measurement, system dynamics, and a subspace model. The resulting nonorthogonal subspace projection and fusion are natural extensions of the traditional model constraint using orthogonal projection. We present two motion measurement algorithms and introduce alternative solutions for measurement uncertainty estimation. We build shape models offline from training data and exploit information from the ground truth initialization online through a strong model adaptation. Our framework is applied for tracking in echocardiograms where the motion estimation errors are heteroscedastic in nature, each heart has a distinct shape, and the relative motions of epicardial and endocardial borders reveal crucial diagnostic features. The proposed method significantly outperforms the existing shape-space-constrained tracking algorithm. Due to the complete treatment of heteroscedastic uncertainties, the strong model adaptation, and the coupled tracking of double-contours, robust performance is observed even on the most challenging cases.

Algorithms↗

PubMedDate not supplied

Automated electrocardiogram analysis: the state of the art.

The overwhelming number of electrocardiograms (ECGs) now recorded routinely has prompted the development of computer analysis which in turn has benefited electrocardiography with important technological advances. All automated ECG analysis systems adopt a similar approach: a measurement program and a program that interprets the clinical significance of these measurements along with a rhythm analysis algorithm. Measurement, selection and classification of parameters vary according to the program used. Data compression is applied to the signal to reduce processing time and allow long-term storage. Diagnostic accuracy, however, is not greatly improved over that of experienced cardiologists. Programs studied using a validated data bank provided by an international group of cardiologists show a variability not only in parameter measurement but also in diagnostic statement and in the way in which such statements are expressed. Recommendations for measurement standards have been made to fulfil the need for exchange of diagnostic criteria. No recommendations concerning the selection of parameters have been proposed, and so new parameters or combinations of parameters can be introduced with the ultimate aim of increased diagnostic performance.

Diagnosis, Computer-Assisted↗