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Results for “Measuring algorithm”

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At least 793 records · Page 44Linked to original sources

PubMed1998

Assessment of telomere length in hematopoietic interphase cells using in situ hybridization and digital fluorescence microscopy.

Telomeres are G/C-rich repetitive DNA sequences at the end of all eukaryotic chromosomes. The loss of telomeric repeat sequences during cell divisions has been proposed as a possible mechanism for cell senescence. The standard procedure for measurement of telomere length is Southern blot (SB) hybridization with a telomere-specific probe. However, in using this technique no information can be obtained on variation in telomeric fragments due to interchromosomal, intrachromosomal, and intercellular differences. Lansdorp et al. (Hum Mol Genet 5:685-691, 1996) developed a method to measure individual telomeres, using in situ hybridization on metaphase chromosomes, employing peptide nucleic acid (PNA) probes and digital fluorescence microscopy. In this paper we describe a method that can be used to assess telomeric length in interphase cells. An algorithm was developed to measure the total intranuclear fluorescence in situ hybridization (FISH) signal, which features accurate correction for the local autofluorescence. Application of this methodology to samples of fetal liver, umbilical cord blood, and adult bone marrow cells showed a gradual decrease of average telomeric length. Southern blot analysis and PNA FISH measurements on chromosomes in the same samples showed similar results. Advantages of interphase measurements include the possibility of studying nonproliferating cells, thus avoiding selection and cell culturing.

Adult↗

PubMed2001

Closing the loop in ICU decision support: physiologic event detection, alerts, and documentation.

Automated physiologic event detection and alerting is a challenging task in the ICU. Ideally care providers should be alerted only when events are clinically significant and there is opportunity for corrective action. However, the concepts of clinical significance and opportunity are difficult to define in automated systems, and effectiveness of alerting algorithms is difficult to measure. This paper describes recent efforts on the Simon project to capture information from ICU care providers about patient state and therapy in response to alerts, in order to assess the value of event definitions and progressively refine alerting algorithms. Event definitions for intracranial pressure and cerebral perfusion pressure were studied by implementing a reliable system to automatically deliver alerts to clinical users alphanumeric pagers, and to capture associated documentation about patient state and therapy when the alerts occurred. During a 6-month test period in the trauma ICU at Vanderbilt University Medical Center, 530 alerts were detected in 2280 hours of data spanning 14 patients. Clinical users electronically documented 81% of these alerts as they occurred. Retrospectively classifying documentation based on therapeutic actions taken, or reasons why actions were not taken, provided useful information about ways to potentially improve event definitions and enhance system utility.

Decision Support Systems, Clinical↗

PubMed1993

Acoustic pattern recognition of /s/ misarticulation by the self-organizing map.

The [s] samples of 11 women, psychoacoustically classified as acceptable/unacceptable, were studied with the self-organizing map, the neural network algorithm of Kohonen. The measurement map had been previously computed with nondisordered speech samples. Fifteen-component spectral vectors, analyzed with the map, were calculated from short-time FFT spectra at 10-ms intervals. The degree of audible acceptability correlated with the location of the sample on the map. Spectral model vectors in different map locations depicted distinguishing spectral features in the [s] samples analyzed. The results demonstrate that self-organized maps are suitable for the extraction and measurement of acoustic features underlying psychoacoustic classifications, and for on-line visual imaging of speech.

Adolescent↗

PubMed2004

Reproducibility of left ventricular volume and ejection fraction measurements in rat using pinhole gated SPECT.

PURPOSE: The aim of this study was to investigate the intra-individual reproducibility of left ventricular volume and ejection fraction measurements in living rat using pinhole gated single-photon emission computed tomography (SPECT). METHODS: Eight normal male Wistar rats underwent four pinhole gated SPECT acquisitions over a 1-month period. Two pinhole gated myocardial perfusion SPECT studies were acquired at a 1-week interval after injecting the animals with 439+/-52 MBq of (99m)Tc-sestamibi. Subsequently, 1 week after the perfusion studies, two pinhole gated blood pool SPECT studies were acquired at a 1-week interval after in vivo labelling of the red blood cells using 520+/-49 MBq of (99m)Tc-pertechnetate. Pinhole gated SPECT acquisitions were done on a single-head gamma camera equipped with a pinhole collimator with a 3-mm opening and 165-mm focal length. Parameters of acquisition were as follows: 44 mm radius of rotation, 360 degrees rotation using a circular orbit, 64 projections, 64x64 matrix, gating using 16 time frames and 22-min acquisition time. The projection data were reconstructed with a modified version of OSEM taking into account the pinhole geometry and incorporating a prior assumption about the temporal properties of gated SPECT studies to reduce noise. Left ventricular volumes and ejection fraction were measured using automatic quantification algorithms. Inter-study, inter-observer and intra-observer reproducibility was investigated. RESULTS: Pinhole gated myocardial perfusion and pinhole gated blood pool images were of high quality in all animals. No significant differences were observed between the repeated measurements. The pinhole gated myocardial perfusion SPECT studies indicated that differences between repeated measurements larger than 41 microl for end-diastolic volume, 17 microl for end-systolic volume and 3% for ejection fraction were significant. The pinhole gated blood pool SPECT studies indicated that differences between repeated measurements larger than 42 microl for end-diastolic volume, 38 mul for end-systolic volume and 5% for ejection fraction were significant. In addition to the reproducibility measures, the accuracy of volume measurements in pinhole gated blood pool SPECT was confirmed by a phantom study. Excellent correlations were observed between the measured volumes and the actual phantom volumes. CONCLUSION: Pinhole gated SPECT is an accurate and reproducible technique for cardiac studies of small animals. Because this technique is non-invasive, the same animal can be imaged repetitively, allowing follow-up studies.

Animals↗

PubMed2004

Use of automatic threshold tracking function with non-low polarization leads: risk for algorithm malfunction.

The AutoCapture (AC) function of new pacemakers (PM) from St Jude Medical (SJM) was originally recommended for use with low polarization (LP) ventricular leads only.However, recent reports have encouraged the use of the AC function with various leads, including those lacking a special LP design. The objective of this study was to analyze the reliability and safety of the AC algorithm application with different types of pacing leads. The study group comprised 30 consecutive patients with AC PMs connected to three different types of non-LP leads. Ten patients with SJM LP leads served as the control group. The study protocol included a complete AC function test using four different pulse widths (PW). The pacing threshold was independently assessed by a manual/semiautomatic check. Erratic behavior of polarization measurements with increasing PWs was demonstrated in 43% (n = 13) of the study group. Invalid polarization measurements resulted in erroneous algorithm recommendation to apply AC function in 17% (n = 5) of the study patients. Subsequent AC function activation lead to incorrect threshold determination due to missed noncapture in three patients. AC function should be applied with caution with non-LP leads. "Off label" use of these leads may cause erroneous polarization signal measurements which, in some cases, may result in incorrect pacing threshold determination, rendering a potential risk to dependent patients.

Algorithms↗

PubMed1993

Can the same edge-detection algorithm be applied to on-line and off-line analysis systems? Validation of a new cinefilm-based geometric coronary measurement software.

In the Cardiovascular Measurement System (CMS) the edge-detection algorithm, which was primarily designed for the Philips digital cardiac imaging system (DCI), is applied to cinefilms. Comparative validation of CMS and DCI was performed in vitro and in vivo with intracoronary insertion of stenosis phantoms in anesthetized pigs. The "obstruction diameter" (OD) was measured at the artificial stenoses visualized by angiography with calibration at the isocenter (ISO) and catheter calibration (CATH) and compared with the true phantom diameters. A clinical comparison of OD, reference diameter (RD), and percentage diameter stenosis (DS) was performed on 70 corresponding images from post-PTCA angiograms. In vitro, OD (CMS) yielded an accuracy of 0.18 +/- 0.14 mm with 100% (correlation coefficient: r = 0.97, y = 0.06 + 0.75x, standard error of estimate [SEE] = 0.09) and 0.19 +/- 0.15 mm with 50% contrast (r = 0.94, y = 0.02 + 0.81 x). OD (DCI) yielded an accuracy of 0.11 +/- 0.06 mm with 100% (r = 0.99, y = -0.03 + 0.91 x, SEE = 0.05) and 0.24 +/- 0.13 mm with 50% contrast (r = 0.94, y = 0.29 + 6.69 x, SEE = 0.12). In vivo, OD (CMS) yielded an accuracy of 0.18 +/- 0.23 mm with ISO (r = 0.89, y = 0.02 + 0.83 x, SEE = 0.22) and 0.26 +/- 0.24 mm with CATH (r = 0.89, y = 0.06 + 0.72 x, SEE = 0.19). OD (DCI) yielded an accuracy of 0.08 +/- 0.15 mm with ISO (r = 0.96, y = 0.08 + 0.86 x, SEE = 0.14) and 0.18 +/- 0.21 mm with CATH (r = 0.92, y = 0.09 + 0.76 x, SEE = 0.17). The clinical comparison showed reasonable agreement for OD only (r = 0.81, y = 0.26 + 0.81 x, SEE = 0.29). Transformation of an edge-detection algorithm from a digital to a cinefilm-based system can lead to impairment of measurement reliability.

Algorithms↗

PubMed1994

Beam profiles along the nonwedged direction for large wedged fields.

Beam profiles along the nonwedged direction of a wedged field produced by a linear accelerator exhibit more "sagging" than that of an open field at the same depth. For large fields, the profiles of open and wedged fields can differ by as much as 7%. The extra "sagging" of wedged profiles is mainly due to the difference in penetration between on- and off-axis rays caused by the variation of beam quality across the field. An algorithm was developed to estimate an "effective" depth such that the profile of a wedged field can be approximated by the open-field profile at the effective depth. The algorithm was verified by measured beam profiles for 6- and 15-MV x-ray beams for 15 degree, 30 degree, 45 degree, and 60 degree wedges.

Algorithms↗

PubMed2002

Phase-shifting algorithms for electronic speckle pattern interferometry.

A set of innovative phase-shifting algorithms developed to facilitate metrology based on electronic speckle pattern interferometry (ESPI) are presented. The theory of a phase-shifting algorithm, called a (5,1) algorithm, that takes five phase-shifted intensity maps before a specimen is deformed and one intensity map after a specimen is deformed is presented first. Because a high-speed camera can be used to record the dynamic image of the specimen, this newly developed algorithm has the potential to retain the phase-shifting capability for ESPI in dynamic measurements. Also shown is an algorithm called a (1,5) algorithm that takes five phase-shifted intensity maps after the specimen is deformed. In addition, a direct-correlation algorithm was integrated with these newly developed (5,1) or (1,5) algorithms to form DC-(5,1) and DC-(1,5) algorithms, which are shown to improve significantly the quality of the phase maps. The theoretical and experimental aspects of these two newly developed techniques, which can extend ESPI to areas such as high-speed dynamic measurements, are examined in detail.

Journal Article↗

PubMed2000

Use of Monte Carlo computation in benchmarking radiotherapy treatment planning system algorithms.

Radiotherapy treatments are becoming more complex, often requiring the dose to be calculated in three dimensions and sometimes involving the application of non-coplanar beams. The ability of treatment planning systems to accurately calculate dose under a range of these and other irradiation conditions requires evaluation. Practical assessment of such arrangements can be problematical, especially when a heterogeneous medium is used. This work describes the use of Monte Carlo computation as a benchmarking tool to assess the dose distribution of external photon beam plans obtained in a simple heterogeneous phantom by several commercially available 3D and 2D treatment planning system algorithms. For comparison, practical measurements were undertaken using film dosimetry. The dose distributions were calculated for a variety of irradiation conditions designed to show the effects of surface obliquity, inhomogeneities and missing tissue above tangential beams. The results show maximum dose differences of 47% between some planning algorithms and film at a point 1 mm below a tangentially irradiated surface. Overall, the dose distribution obtained from film was most faithfully reproduced by the Monte Carlo N-Particle results illustrating the potential of Monte Carlo computation in evaluating treatment planning system algorithms.

Algorithms↗

PubMed2006

Inspiratory flow shape clustering: an automated method to monitor upper airway performance during sleep.

We describe an automated method for monitoring airflow dynamics in the upper airway of a sleeping subject. Its main task is to determine a set of inspiratory flow shape representatives and their relative incidence in a given respiratory airflow material. The flow shape clustering aims at reducing redundant information in the data, and thereby decreases the time needed to score overnight sleep recordings. Compared with previous computer-assisted systems, built on a pre-defined classification of prototype shapes, we require no a priori assumptions of the flow shape clusters to be discovered. The intrinsic flow shape clustering is performed with a modification of the Isodata algorithm, and the K-means clustering is used as a reference in comparison studies. The operation of the method is demonstrated on clinical sleep recordings both from patients with nocturnal breathing disorders and from non-symptomatic individuals. The feasible results obtained in the practical research design suggest that application of clustering algorithms to respiratory airflow measurements could give important insights into the subtle flow shape abnormalities underlying obstructive sleep-disordered breathing.

Algorithms↗

PubMed2006

Parameter incremental learning algorithm for neural networks.

In this paper, a novel stochastic (or online) training algorithm for neural networks, named parameter incremental learning (PIL) algorithm, is proposed and developed. The main idea of the PIL strategy is that the learning algorithm should not only adapt to the newly presented input-output training pattern by adjusting parameters, but also preserve the prior results. A general PIL algorithm for feedforward neural networks is accordingly presented as the first-order approximate solution to an optimization problem, where the performance index is the combination of proper measures of preservation and adaptation. The PIL algorithms for the multilayer perceptron (MLP) are subsequently derived. Numerical studies show that for all the three benchmark problems used in this paper the PIL algorithm for MLP is measurably superior to the standard online backpropagation (BP) algorithm and the stochastic diagonal Levenberg-Marquardt (SDLM) algorithm in terms of the convergence speed and accuracy. Other appealing features of the PIL algorithm are that it is computationally as simple as the BP algorithm, and as easy to use as the BP algorithm. It, therefore, can be applied, with better performance, to any situations where the standard online BP algorithm is applicable.

Algorithms↗

PubMed1994

Estimation of peripheral dose from two linacs: Mevatron MX6700 and Mevatron KDS.

An empirical calculation method for high-energy beam peripheral dose estimation is described. The peripheral dose has been measured for a Siemens Mevatron MX6700 (6 MV) and a Siemens Mevatron KDS (6 and 18 MV) linear accelerators. The dose distribution is parameterized for each beam energy as a function of depth, distance from the edge of the field, and field size. A simple algorithm has been developed for dose calculation up to 100 cm from the field central axes. Predictions by this algorithm are compared with measurements in an Alderson phantom.

Particle Accelerators↗

PubMed1994

The use of urinary hormonal assessments in human studies.

The collection and analysis of urine samples provides a practical method for monitoring female reproductive events in non-laboratory and non-clinic populations. Collection of biologic samples permits objective assessment of reproductive health endpoints in epidemiologic studies and for epidemiologic research purposes can provide validation of information provided by the subjects, especially outcomes which are usually concealed and thus unknown to the participant. Urine sampling has several advantages over the collection of blood samples, such as simplicity, non-invasiveness, and cost efficiency. Several studies have shown that endocrine information similar to that obtained in blood samples can be obtained from assays of daily urine samples. The measurement of human chorionic gonadotropin in daily and selected urine samples has been incorporated into several recent epidemiologic studies focusing on early fetal loss, and ovarian and pituitary hormone metabolites have been measured in daily urine samples to evaluate ovarian function in studies focusing on women's reproductive health. As the strategy of urinary monitoring becomes more accepted as a legitimate research tool, laboratory methods are being modified to improve performance, reduce costs and adapted to sophisticated algorithms using multiple hormonal measurements to identify a number of end-points.

Biomarkers↗

PubMed1993

A method for dose calculation for high energy photon beams based on measurements performed at reference depth.

An algorithm is proposed to calculate the dose per monitor unit at any point along the beam axis for blocked or unblocked fields. The proposed formalism takes into consideration the beam measurements performed at the reference depth as recommended by most dosimetry protocols (5 cm or 10 cm depending on the beam quality). The only parameters which cannot be measured at the reference depth are the peak scatter factors, but they appear only as a ratio of two peak scatter factors for two slightly different field sizes. A correction factor is proposed when the distance of one shielding block to the beam axis is smaller than 5 cm. An agreement better than 1% has been obtained between calculations and measurements in the range of beam qualities, distances to the source and field sizes defined by typical collimators or shielding blocks, usually encountered in clinical practice.

Calibration↗

PubMed1994

Development of an advanced digital image processor for real-time speckle suppression in routine ultrasonic scanning.

This paper describes a digital image processor for ultrasonic speckle suppression that was explicitly designed to satisfy the requirements of detail preservation, adequate smoothing and real-time operation. The first two of these requirements were addressed by selecting a nonlinear adaptive algorithm, which uses a measure of local homogeneity to adjust the amount of smoothing performed at each point of the scan, and employing a large (9 x 9 pixels) filtering window. Real-time operation was achieved by developing a highly concurrent systolic architecture that allowed the efficient mapping of the algorithm into low-cost high-density hardware. Initial experience, obtained by interfacing the processor to a scanner, suggests that this type of processing is capable of enhancing the visibility of subtle differences in echogenicity while retaining genuine image detail, as judged by the preservation of the small vessels and ducts. In addition to its impact on contrast resolution, this form of real-time speckle suppression should also prove valuable as a preprocessing stage before performing other digital image processing operations that are sensitive to noise, such as segmentation and three-dimensional rendering.

Algorithms↗

PubMed2004

Spurious hypocalcemia after Omniscan- or OptiMARK-enhanced magnetic resonance imaging: an algorithm for minimizing a false-positive laboratory value.

Contrast-enhanced magnetic resonance imaging has become a routine diagnostic imaging procedure. Reports in the literature document that 2 of the 4 available gadolinium-based magnetic resonance imaging contrast agents, gadodiamide (Omniscan) and gadoversetamide (OptiMARK), are less stable and readily undergo dechelation. In vitro, this dechelation can result in interference with the most common laboratory methods used to measure total plasma or serum calcium. The result of total calcium measurement soon after contrast-enhanced magnetic resonance imaging with these interfering contrast agents is a spurious lowering of the total calcium level. This low calcium measurement may result in a value consistent with hypocalcemia and can persist in patients with renal insufficiency and in patients receiving higher doses of contrast agent. Alternatively, a clinically significant elevated calcium level may be overlooked because of the artificially lowered value. Two of the available gadolinium-based contrast agents, gadoteridol (ProHance) and gadopentetate dimeglumine (Magnevist), have not been to shown to interfere with total calcium measurement. A clinical practice algorithm for the laboratorian, the radiologist, and the clinician is presented to minimize the occurrence and consequences of a spuriously lowered total calcium level due to Omniscan- or OptiMARK-enhanced magnetic resonance imaging.

Algorithms↗

PubMed1998

Thermoluminescence dosimetry applied to in vivo dose measurements for total body irradiation techniques.

BACKGROUND AND PURPOSE: In total body irradiation (TBI) treatments in vivo dosimetry is recommended because it makes it possible to ensure the accuracy and quality control of dose delivery. The aim of this work is to set up an in vivo thermoluminescence dosimetry (TLD) system to measure the dose distribution during the TBI technique used prior to bone marrow transplant. Some technical problems due to the presence of lung shielding blocks are discussed. MATERIALS AND METHODS: Irradiations were performed in the Hospital de la Santa Creu i Sant Pau by means of a Varian Clinac-1800 linear accelerator with 18 MV X-ray beams. Different TLD calibration experiments were set up to optimize in vivo dose assessment and to analyze the influence on dose measurement of shielding blocks. An algorithm to estimate midplane doses from entrance and exit doses is proposed and the estimated dose in critical organs is compared to internal dose measurements performed in an Alderson anthropomorphic phantom. RESULTS: The predictions of the dose algorithm, even in heterogeneous zones of the body such as the lungs, are in good agreement with the experimental results obtained with and without shielding blocks. The differences between measured and predicted values are in all cases lower than 2%. CONCLUSIONS: The TLD system described in this work has been proven to be appropriate for in vivo dosimetry in TBI irradiations. The described calibration experiments point out the difficulty of calibrating an in vivo dosimetry system when lung shielding blocks are used.

Algorithms↗

PubMed1999

Evidence-based organ allocation.

BACKGROUND: There are not enough cadaveric kidneys to meet the demands of transplant candidates. The equity and efficiency of alternative organ allocation strategies have not been rigorously compared. METHODS: We developed a five-compartment Monte Carlo simulation model to compare alternative organ allocation strategies, accommodating dynamic changes in recipient and donor characteristics, patient and graft survival rates, and quality of life. The model simulated the operations of a single organ procurement organization and attempted to predict the evolution of the transplant waiting list for 10 years. Four allocation strategies were compared: a first-come first-transplanted system; a point system currently utilized by the United Network of Organ Sharing; an efficiency-based algorithm that incorporated correlates of patient and graft survival; and a distributive efficiency algorithm, which had an additional goal of promoting equitable allocation among African-American and other candidates. RESULTS: A 10-year computer simulation was performed. The distributive efficiency policy was associated with a 3.5%+/-0.8% (mean +/- SD) increase in quality-adjusted life expectancy (33.9 months vs 32.7 months), a decrease in the median waiting time to transplantation among those who were transplanted (6.6 months vs 16.3 months), and an increase in the overall likelihood of transplantation (61% vs 45%), compared with the United Network of Organ Sharing algorithm. Improved equity and efficiency were also seen by race (African-American vs other), sex, and age (<50 or > or =50 years). Sensitivity analyses did not appreciably change the qualitative results. CONCLUSION: Evidence-based organ allocation strategies in cadaveric kidney transplantation would yield improved equity and efficiency measures compared with existing algorithms.

Algorithms↗