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Results for “Measuring algorithm”

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PubMedDate not supplied

Automatic detection and measurement of EMG silent periods in masticatory muscles during chewing in man.

Silent periods are transient stops of muscle activity that are induced by mechanical or electrical stimulus. The current report describes a new algorithm which enables automatic detection and measurement of silent periods that occur in the EMG of human masticatory muscles during chewing efforts together with jaw positions in space at the occurrence of the silent periods. The EMG signal for detection of the silent period is modeled based on the observation of the EMG records induced from the jaw-closing muscles during chewing efforts in seven volunteer subjects. The algorithm for automatic detection and measurement of the EMG silent period has been applied successfully to real EMG data and the performance of the software was confirmed to be sufficiently reliable. The results of the analysis are stored in a biosignal database for possible clinical use.

Adult↗

PubMed1989

Case studies on the effect of exercise and hot water submersion on intracardiac temperature and the performance of a pacemaker which varies pacing rate based on temperature.

The effectiveness of using blood temperature change as an indicator to automatically vary heart rate physiologically was evaluated in 3 patients implanted with Model Sensor Kelvin 500 (Cook Pacemaker Corporation, Leechburg, PA, USA) pacemakers. Each patient performed two block-randomized treadmill exercise tests: one while programmed for temperature-based, rate-modulated pacing and the other while programmed without rate modulation. In 1 pacemaker patient and 4 volunteers, heart rates were recorded during exposure to a hot water bath. Blood temperature measured at 10 sec intervals and pacing rate measured at 1 min intervals were telemetered to a diagnostic programmer and data collector for storage and transfer to a computer. Observation comments and ECG-derived heart rates were manually recorded. The temperature-based pacemaker was shown to respond promptly not only to physical exertion but also to emotionally caused stress and submersion in a hot bath. These events cause increased heart rate in the normal heart. Using a suitable algorithm to process the measurement of blood temperature, it was possible to produce appropriate pacing rates in paced patients.

Aged↗

PubMed1997

An automatic six-degree-of-freedom image registration algorithm for image-guided frameless stereotaxic radiosurgery.

A frameless radiosurgical treatment system has been developed by coupling an orthogonal pair of real-time x-ray cameras to a robotically manipulated linear accelerator to guide the therapy beam to treatment sites within a patient's cranium. The two cameras observe the position and orientation of the patient's head in the treatment system coordinate frame. An image registration algorithm compares the two real-time radiographs to a corresponding pair of digitally synthesized radiographs derived from a CT study of the patient. The algorithm determines all six degrees of translational and rotational difference between the position of the head in the CT coordinate frame and its position in the treatment room coordinate frame. This allows translation of treatment planning coordinates into treatment room coordinates without rigidly fixing the patient's head position during either the CT scan or treatment. In this paper the image registration algorithm is described and measurements of the precision and speed with which the process can determine the patient's position are reported. The tests have demonstrated translational uncertainty of 0.5-1.0 mm per axis and rotational uncertainty of 0.6-1.3 degrees per axis, accomplished in approximately 2 s elapsed time.

Algorithms↗

PubMed2004

Effect of organ and tissue masses on resting energy expenditure in underweight, normal weight and obese adults.

BACKGROUND: In normal-weight subjects, resting energy expenditure (REE) can be accurately calculated from organ and tissue masses applying constant organ-specific metabolic rates. This approach allows a precise correction for between-subjects variation in REE, explained by body composition. Since a decrease in organ metabolic rate with increasing organ mass has been deduced from interspecies comparison including human studies, the validity of the organ- and tissue-specific REE calculation remains to be proved over a wider range of fat-free mass (FFM). DESIGN: In a cross-sectional study on 57 healthy adults (35 females and 22 males, 19-43 y; 14 underweight, 25 intermediate weight and 18 obese), magnetic resonance imaging (MRI) and dual-energy X-ray absorptiometry (DXA) were used to assess the masses of brain, internal organs, skeletal muscle (MM), bone and adipose tissue. REE was measured by indirect calorimetry (REEm) and calculated from detailed organ size determination by MRI and DXA (REEc1), or in a simplified approach exclusively from DXA (REEc2). RESULTS: We found a high agreement between REEm and REEc1 over the whole range of FFM (28-86 kg). REE prediction errors were -17 +/- 505, -145 +/- 514 and -141 +/- 1058 kJ/day in intermediate weight, underweight and obese subjects, respectively (n.s.). Regressing REEm on FFM resulted in a significant positive intercept of 1.6 MJ/day that could be reduced to 0.5 MJ/day by adjusting FFM for the proportion of MM/organ mass. In a multiple regression analysis, MM and liver mass explained 81% of the variance in REEm. DXA-derived REE prediction showed a good agreement with measured values (mean values for REEm and REEc2 were 5.72 +/- 1.87 and 5.82 +/- 1.51 MJ/day; difference n.s.). CONCLUSION: Detailed analysis of metabolically active components of FFM allows REE prediction over a wide range of FFM. The data provide indirect evidence for a view that, for practical purposes within humans, the specific metabolic rate is constant with increasing organ mass. Nonlinearity of REE on FFM was partly explained by FFM composition. A simplified REE prediction algorithm from regional DXA measurements has to be validated in future studies.

Absorptiometry, Photon↗

PubMed1999

Use of a priori information in estimating tissue resistivities--application to measured data.

A statistically constrained minimum mean squares error estimator (MiMSEE) has been shown to be useful in estimating internal resistivity distribution by the use of simulated data. In this study, the performance of the MiMSEE algorithm is tested by using measured data from resistor phantoms. The MiMSEE uses a priori information on body geometry, electrode position, statistical properties of tissue resistivities, instrumentation noise and linearization error to calculate the optimum inverse matrix which maps the surface potentials to unknown regional resistivities. In this study, the MiMSEE is also constrained with the variance-covariance of the modelling error to improve the estimation accuracy. The data are obtained from two different phantom geometries, namely five-region and thorax. Using the measured data, the estimations are realized and errors are calculated. Then, the results are compared with the results obtained by using a conventional least squares error estimator (LSEE). The five-region model results show similarity with the simulation study results of Baysal and Eyüboğlu. On the thorax model, the total estimation error is 34.2% with the MiMSEE compared with 856% with the LSEE. It is concluded that the MiMSEE is more robust than the LSEE and applicable to measured data.

Algorithms↗

PubMed2005

Thermodynamically based DNA strand design.

We describe a new algorithm for design of strand sets, for use in DNA computations or universal microarrays. Our algorithm can design sets that satisfy any of several thermodynamic and combinatorial constraints, which aim to maximize desired hybridizations between strands and their complements, while minimizing undesired cross-hybridizations. To heuristically search for good strand sets, our algorithm uses a conflict-driven stochastic local search approach, which is known to be effective in solving comparable search problems. The PairFold program of Andronescu et al. [M. Andronescu, Z. C. Zhang and A. Condon (2005) J. Mol. Biol., 345, 987-1001; M. Andronescu, R. Aguirre-Hernandez, A. Condon, and H. Hoos (2003) Nucleic Acids Res., 31, 3416-3422.] is used to calculate the minimum free energy of hybridization between two mismatched strands. We describe new thermodynamic measures of the quality of strand sets. With respect to these measures of quality, our algorithm consistently finds, within reasonable time, sets that are significantly better than previously published sets in the literature.

Algorithms↗

PubMed2005

Sparse basis selection: new results and application to adaptive prediction of video source traffic.

Real-time prediction of video source traffic is an important step in many network management tasks such as dynamic bandwidth allocation and end-to-end quality-of-service (QoS) control strategies. In this paper, an adaptive prediction model for MPEG-coded traffic is developed. A novel technology is used, first developed in the signal processing community, called sparse basis selection. It is based on selecting a small subset of inputs (basis) from among a large dictionary of possible inputs. A new sparse basis selection algorithm is developed that is based on efficiently updating the input selection adaptively. When a new measurement is received, the proposed algorithm updates the selected inputs in a recursive manner. Thus, adaptability is not only in the weight adjustment, but also in the dynamic update of the inputs. The algorithm is applied to the problem of single-step-ahead prediction of MPEG-coded video source traffic, and the developed method achieves improved results, as compared to the published results in the literature. The present analysis indicates that the adaptive feature of the developed algorithm seems to add significant overall value.

Algorithms↗

PubMed1999

Brain tumor volume measurement: comparison of manual and semiautomated methods.

PURPOSE: To compare the reliability of two approaches to measuring enhancing brain tumor volumes--the conventional manual trace method and a threshold-based, semiautomated computer software method. MATERIALS AND METHODS: Two operators rated contrast material-enhanced, T1-weighted axial magnetic resonance (MR) image data sets from 16 patients aged 21-71 years with high-grade gliomas. Each MR data set was rated twice by using manual tracing and twice by using the semiautomated method. The semiautomated measurement method involved a thresholding algorithm based on mixture modeling. The data collection time for each method was recorded. Reliability was measured by using inter- and intraoperator agreement indexes. RESULTS: Mean intraoperator agreement indexes (+/- SD) were 0.90 +/- 0.09 (operator 1) and 0.83 +/- 0.15 (operator 2) for the manual trace method and 0.83 +/- 0.17 (operator 1) and 0.84 +/- 0.16 (operator 2) for the semiautomated measurement method. The mean interoperator agreement was 0.85 +/- 0.14 for the manual method and 0.82 +/- 0.18 for the semiautomated method. The semiautomated method was faster than the manual trace method by an average of 4.6 minutes per patient. CONCLUSION: The semiautomated computer method of measuring tumor volume was faster than the manual trace method. Semiautomated computer approaches offer an alternative to manual tracing for measuring serial tumor volumes in patients with high-grade brain neoplasms.

Adult↗

PubMed1996

Measures of uncertainty of pharmacokinetic and pharmacodynamic parameter estimates: a new computerized algorithm.

Numerous algorithms exist to fit data to nonlinear models of the type used in chemistry, pharmacology, physiology, etc. Most include modules that provide some measure of the reliability of the estimated model parameters. The variance-covariance matrix (VCM) is the common tabulation of information that is used to quantify the parameter uncertainty as well as correlations between parameters. The VCM has its mathematical foundation in the linear regression world, where the dependent variable is a linear function of the parameters. However, when the model is not linear in its parameters, then the VCM is no longer an absolute quantitative measure of reliability of the parameter estimates and should be interpreted with caution. If the goal is to obtain a realistic and quantitative rather than a qualitative measurement of the parameter reliability, then it is necessary to have an alternative approach to describe the parameter likelihood region. We present a computerized algorithm that fills that need, and we compare its performance with the traditional VCM approach for different data sets. We also discuss criteria that may be used to determine when the VCM approach should and should not be used.

Algorithms↗

PubMed2006

Performance comparison of independent component analysis algorithms for fetal cardiac signal reconstruction: a study on synthetic fMCG data.

Independent component analysis (ICA) algorithms have been successfully used for signal extraction tasks in the field of biomedical signal processing. We studied the performances of six algorithms (FastICA, CubICA, JADE, Infomax, TDSEP and MRMI-SIG) for fetal magnetocardiography (fMCG). Synthetic datasets were used to check the quality of the separated components against the original traces. Real fMCG recordings were simulated with linear combinations of typical fMCG source signals: maternal and fetal cardiac activity, ambient noise, maternal respiration, sensor spikes and thermal noise. Clusters of different dimensions (19, 36 and 55 sensors) were prepared to represent different MCG systems. Two types of signal-to-interference ratios (SIR) were measured. The first involves averaging over all estimated components and the second is based solely on the fetal trace. The computation time to reach a minimum of 20 dB SIR was measured for all six algorithms. No significant dependency on gestational age or cluster dimension was observed. Infomax performed poorly when a sub-Gaussian source was included; TDSEP and MRMI-SIG were sensitive to additive noise, whereas FastICA, CubICA and JADE showed the best performances. Of all six methods considered, FastICA had the best overall performance in terms of both separation quality and computation times.

Algorithms↗

PubMedDate not supplied

Construct validity of the stages of change of exercise adoption for different intensities of physical activity in four samples of differing age groups.

PURPOSE: To examine whether the stages of change of exercise adoption appropriately address strenuous, moderate, and mild intensities of physical activity. DESIGN AND SETTING: Secondary analysis of four data sets investigating transtheoretical model (TTM) constructs for exercise adoption. SUBJECTS: Four samples of differing age groups (adolescents, n = 400; college students, n = 240; adults, n = 346; seniors, n = 504). MEASURES: Stage of change algorithm for exercise adoption and self-reported physical activity. RESULTS: Multivariate analysis of variance (MANOVA) results showed that stages of change were distinguished by strenuous and moderate but not mild exercise in the adolescent, college student, and adult sample. In the senior sample, stage differences were found in the frequency of exercising (equivalent for moderate to strenuous exercise) and the frequency of walking (equivalent for mild exercise). Bivariate correlation coefficients as well as sensitivity, specificity, and related quality indices decreased respectively from strenuous to moderate to mild exercise and from exercising to walking. CONCLUSIONS: Results provide additional support for the construct validity of the stages of change for strenuous and moderate intensities of physical activity. Development of a new stage assessment instrument for mild intensities of physical activity is recommended. Limitations include use of a different validation measure of exercise behavior in the senior sample.

Adolescent↗

PubMed2002

Measurement and mapping of pH in hydrating pharmaceutical pellets using confocal laser scanning microscopy.

PURPOSE: pH modifiers are often used to promote drug solubility/ stability in dosage forms, but predicting the extent and duration of internal pH modification is difficult. Here, a noninvasive technique is developed for the spatial and temporal mapping of pH in a hydrated pharmaceutical pellet, within a pH range appropriate for microenvironmental pH control by weak acids. METHODS: Confocal dual excitation imaging (Ex 488/Ex 568) of pellets containing a single, soluble, pH-sensitive fluorophore with cross-validation from a pH microelectrode. The technique was used to investigate the changing pH distribution in hydrating pellets containing two weak acids of differing solubility. RESULTS: The algorithm developed provided pH measurements over the range pH 3.5-5.5 with a typical accuracy of 0.1 pH units and with excellent correlation with pH microelectrode measurements. The method showed how pellets containing 25%w/w tartaric acid exhibited a rapid but transient fall in internal pH, in contrast to a slower more prolonged reduction with fumaric acid. CONCLUSIONS: Spatial and temporal monitoring of pH in pellets was achieved with good accuracy within a pH range appropriate to pH modification by weak acids. However, the method developed is also generic and with suitable fluorophores will be applicable to other pH ranges and other dosage forms.

Cellulose↗

PubMed2000

Novel methods to evaluate controlled reperfusion techniques in cardiac surgery.

BACKGROUND: This manuscript describes two novel techniques that may be useful for comparing methods to reperfuse the heart during cardiac operations. These techniques are based on measurements of intra-myocyte ion content and the analysis of reperfusion arrhythmias. METHODS: Myocyte ion content was measured in normal porcine hearts before and after ischemia (cardioplegic arrest, CP arrest) using atomic absorption spectroscopy. A cobalt-EDTA complex served as the extra-cellular marker. Cobalt-EDTA was infused into the aorta together with blood or cardioplegia (CP) solution. Myocardial biopsies were taken prior to CP arrest and upon successful defibrillation 5 min after initiating reperfusion. Ventricular fibrillation (VF) was recorded prior to ischemia, and then during reperfusion. VF wavefront (WF) morphology and propagation patterns were analyzed using computer algorithms. Electrophysiologic variables for measuring VF included the multiplicity index (a descriptor of VF organization), the number of WFs detected (nwaves/s) and the mean peak first derivative of electrogram voltage with respect to time (mp d V/dt). RESULTS: Intra-cellular sodium content increased, while intra-cellular magnesium content decreased between control and reperfusion measurements (p < 0.05). Electrophysiologic recovery was characterized by increasingly rapid depolarization (i.e. more negative mp d V/dt) and an increasing nwaves/s during the first minute of post-CP reperfusion. CONCLUSIONS: Atomic absorption spectroscopy and computer-based analysis of reperfusion VF successfully measured metabolic and electrophysiologic events that occurred during controlled reperfusion. These methods may be useful for comparing controlled reperfusion techniques.

Animals↗

PubMed1995

Self organizing maps for the analysis of high resolution ECG in acute myocardial infarction.

An approach for an all-embracing ECG signal analysis is introduced. Self organizing maps are applied to spatial high resolution multilead ECG (body surface ECG) recorded during the acute phase of myocardial infarction to detect characteristic changes. The algorithm deals with the measurement of similarity between different pathological signal types. In opposition to other techniques, the whole ECG-signal coded as a feature vector is used as input for the self organizing map. The results show that this approach is suitable for handling unsharp class transitions common to several problems from the medical domain.

Algorithms↗

PubMed2004

Investigation of photon beam models in heterogeneous media of modern radiotherapy.

This study investigates the performance of photon beam models in dose calculations involving heterogeneous media in modern radiotherapy. Three dose calculation algorithms implemented in the CMS FOCUS treatment planning system have been assessed and validated using ionization chambers, thermoluminescent dosimeters (TLDs) and film. The algorithms include the multigrid superposition (MGS) algorithm, fast Fourier Transform Convolution (FFTC) algorithm and Clarkson algorithm. Heterogeneous phantoms used in the study consist of air cavities, lung analogue and an anthropomorphic phantom. Depth dose distributions along the central beam axis for 6 MV and 10 MV photon beams with field sizes of 5 cm x 5 cm and 10 cm x 10 cm were measured in the air cavity phantoms and lung analogue phantom. Point dose measurements were performed in the anthropomorphic phantom. Calculated results with three dose calculation algorithms were compared with measured results. In the air cavity phantoms, the maximum dose differences between the algorithms and the measurements were found at the distal surface of the air cavity with a 10 MV photon beam and a 5 cm x 5 cm field size. The differences were 3.8%. 24.9% and 27.7% for the MGS. FFTC and Clarkson algorithms. respectively. Experimental measurements of secondary electron build-up range beyond the air cavity showed an increase with decreasing field size, increasing energy and increasing air cavity thickness. The maximum dose differences in the lung analogue with 5 cm x 5 cm field size were found to be 0.3%. 4.9% and 6.9% for the MGS. FFTC and Clarkson algorithms with a 6 MV photon beam and 0.4%. 6.3% and 9.1% with a 10 MV photon beam, respectively. In the anthropomorphic phantom, the dose differences between calculations using the MGS algorithm and measurements with TLD rods were less than +/-4.5% for 6 MV and 10 MV photon beams with 10 cm x 10 cm field size and 6 MV photon beam with 5 cm x 5 cm field size, and within +/-7.5% for 10 MV with 5 cm x 5 cm field size, respectively. The FFTC and Clarkson algorithms overestimate doses at all dose points in the lung of the anthropomorphic phantom. In conclusion, the MGS is the most accurate dose calculation algorithm of investigated photon beam models. It is strongly recommended for implementation in modern radiotherapy with multiple small fields when heterogeneous media are in the treatment fields.

Algorithms↗

PubMed1997

Accuracy of ultrasonography in assessing spleen and liver size in patients with Gaucher disease: comparison to computed tomographic measurements.

A comparison was made between volume measurements of spleen and liver by ultrasonography and by computed tomography, the two most common modes of assessment of organ size in patients with Gaucher disease, who require frequent follow-up measurements. The two measurements showed a high degree of correlation within a broad range for both spleen and liver volumes. An algorithm for conversion of one measurement to the other was derived for both spleen and liver.

Adolescent↗

PubMed1994

Dosimetry of large, irregularly shaped fields by the circle method. A feasibility study.

The Circle Method is an algorithm for dose calculation in an irregularly shaped field. The algorithm is based on measurements of circle fields at the therapy machine in use. A separation into primary and scattered radiation components is not necessary. Clarkson's sector-integration method and an off-axis correction are embodied. Experimental and calculated dose values agree within +/- 2.8% in the treatment field and under block shieldings.

Algorithms↗

PubMed2005

Quantitative comparison of algorithms for inter-subject registration of 3D volumetric brain MRI scans.

The objective of inter-subject registration of three-dimensional volumetric brain scans is to reduce the anatomical variability between the images scanned from different individuals. This is a necessary step in many different applications such as voxelwise group analysis of imaging data obtained from different individuals. In this paper, the ability of three different image registration algorithms in reducing inter-subject anatomical variability is quantitatively compared using a set of common high-resolution volumetric magnetic resonance imaging scans from 17 subjects. The algorithms are from the automatic image registration (AIR; version 5), the statistical parametric mapping (SPM99), and the automatic registration toolbox (ART) packages. The latter includes the implementation of a non-linear image registration algorithm, details of which are presented in this paper. The accuracy of registration is quantified in terms of two independent measures: (1) post-registration spatial dispersion of sets of homologous landmarks manually identified on images before or after registration; and (2) voxelwise image standard deviation maps computed within the set of images registered by each algorithm. Both measures showed that the ART algorithm is clearly superior to both AIR and SPM99 in reducing inter-subject anatomical variability. The spatial dispersion measure was found to be more sensitive when the landmarks were placed after image registration. The standard deviation measure was found sensitive to intensity normalization or the method of image interpolation.

Adult↗