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Results for “Measuring algorithm”

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PubMed2006

Application and assessment of a robust elastic motion correction algorithm to dynamic MRI.

The purpose of this study was to assess the performance of a new motion correction algorithm. Twenty-five dynamic MR mammography (MRM) data sets and 25 contrast-enhanced three-dimensional peripheral MR angiographic (MRA) data sets which were affected by patient motion of varying severeness were selected retrospectively from routine examinations. Anonymized data were registered by a new experimental elastic motion correction algorithm. The algorithm works by computing a similarity measure for the two volumes that takes into account expected signal changes due to the presence of a contrast agent while penalizing other signal changes caused by patient motion. A conjugate gradient method is used to find the best possible set of motion parameters that maximizes the similarity measures across the entire volume. Images before and after correction were visually evaluated and scored by experienced radiologists with respect to reduction of motion, improvement of image quality, disappearance of existing lesions or creation of artifactual lesions. It was found that the correction improves image quality (76% for MRM and 96% for MRA) and diagnosability (60% for MRM and 96% for MRA).

Adult↗

PubMedDate not supplied

A maximum likelihood method for region-of-interest evaluation in emission tomography.

A maximum likelihood (ML) estimation method, called the ML-ROI algorithm, is presented for the calculation of region-of-interest (ROI) values from emission tomography scans. The EM algorithm is used to directly estimate ROI values from tomographic projection data given the location, size, and shape of all ROIs. The algorithm requires for the specification of a detailed model of the physical factors contributing to projection measurements including resolution and attenuation. The ML-ROI algorithm also provides an estimate of the variability of the ROI estimator (covariance matrix). The algorithm was tested with simulation and phantom data and compared with ROI estimation strategies using filtered backprojection (FBP) images. The ML-ROI estimates were unbiased, i.e., the partial volume effect was eliminated. Except for regions smaller than the detector resolution, the variability of the ML estimates was comparable to or less than the biased FBP estimators. Computation time for the ML-ROI algorithm was between 5 and 10 s/iteration. An evaluation of the sensitivity of the algorithm to misdefinition of the location and size of the ROIs was also performed.

Humans↗

PubMed2002

CX, an algorithm that identifies protruding atoms in proteins.

MOTIVATION: A simple and fast algorithm is described that calculates a measure of protrusion (cx) for atoms in protein structures, directly useable with the common molecular graphics programs. RESULTS: A sphere of predetermined radius is centered around each non-hydrogen atom, and the volume occupied by the protein and the free volume within the sphere (internal and external volumes, respectively) are calculated. Atoms in protruding regions have a high ratio (cx) between the external and the internal volume. The program reads a PDB file, and writes the output in the same format, with cx values in the B factor field. Output structure files can be directly displayed with standard molecular graphics programs like RASMOL, MOLMOL, Swiss-PDB Viewer and colored according to cx values. We show the potential use of this program in the analysis of two protein-protein complexes and in the prediction of limited proteolysis sites in native proteins. AVAILABILITY: The algorithm is implemented in a standalone program written in C and its source is freely available at ftp.icgeb.trieste.it/pub/CX or on request from the authors.

Algorithms↗

PubMed2002

Quantitative evaluation of nonablative laser technology.

A new method for treating facial rhytides and acne scars with nonablative laser and light source techniques has recently been introduced. Given the inherent limitations of photographic and clinical evaluation to assess subtle changes in rhytides and surface topography, new noninvasive, objective instruments were used to accurately assess the outcome of these procedures. This study measures and objectively quantifies facial skin by using 2 novel, noninvasive measuring systems after 3 to 5 treatment sessions with the 1,064 nm QS Nd:YAG laser in patients with photodamage and acne scarring. One system measures the skin surface topography and the other characterizes the biomechanical properties of the skin. Patients undergoing facial rejuvenation procedures were analyzed before and after therapy with a 32 x 32 mm in vivo three-dimensional microtopography imaging system (PRIMOS, GFM, Teltow, Germany). The imaging system projects light on to a specific surface of the skin with a Digital Micromirror Device (DMD; Texas Instruments, Irving, TX) and records the image with a CCD camera. Skin Surface microtopography is reconstructed using temporal phase shift algorithms to generate three-dimensional images. Measurements were taken at baseline, at various times during the treatment protocol, and then at 3 and 6 month follow-up visits. Silicone skin replicas (FLEXICO, Herts, England) were also made before and after the laser treatment protocol for comparison to in vivo acquisition. Skin stiffness and compliance were measured with the BTC-2000 (BTC 2000, S.R.L.I. Inc. Nashville, TN). This instrument measures the response of the skin during dynamic stress created by suction. An infrared targeting laser measures the vertical displacement of the skin during the cycle. Pressure and deformation are graphically displayed on the monitor and embedded biomechanical algorithms determine the aforementioned parameters based on the average of 3 repetitive cycles. Four sites on the face were analyzed and compared including the right and left cheek and the right and left forehead. Measurements were taken at baseline and then at 1-, 3- and 6-month follow-up visits. Skin roughness decreased 11% from baseline in the patient with photodamaged skin, while the patients with acne scarring showed a 33% improvement from baseline after 3 treatment sessions. Six-months after the fifth treatment session, a 26% improvement in skin smoothness was documented in the patients with photodamaged skin, while a 61% improvement was recorded in the subject with acne scarring. Biomechanical analysis of the skin showed a 23% decrease in skin stiffness and a 30% increase in skin compliance at the 6-month follow-up in the patients with photodamage. Alternatively, the patient with acne scarring showed a 50% increase in skin stiffness, and a 30% decrease in skin compliance at the 6-month follow-up. Three-dimensional in vivo optical skin imaging provided a rapid and quantitative assessment of surface topography and facial fine lines after multiple treatment sessions with a 1064-nm QS Nd:YAG laser, correlating with clinical and subjective responses. Biomechanical analysis provided technical understanding of structural changes in photodamaged skin and acne scarring following nonablative laser treatment. Future applications of these devices may include comparison of nonablative laser technology, optimization of treatment regimens, and objective evaluation of other aesthetic procedures performed by dermatologists.

Cicatrix↗

PubMed2003

QT variability.

We hypothesized that temporal lability in ventricular repolarization is a marker for, and is mechanistically related to, increased risk of malignant ventricular arrhythmias. To assess repolarization lability in the surface electrocardiogram, we developed an automated algorithm, based on template matching, to measure beat-to-beat changes in QT interval. We calculate a QT variability index (QTVI) to quantify the relative magnitude of QT interval changes compared to heart rate variability. We found that QTVI is a reproducible measure. It is elevated in patients with ischemic and nonischemic dilated cardiomyopathy compared with age-matched controls (P<.00001). We have also shown that QTVI is elevated in patients with malignant beta-myosin heavy-chain mutations associated with hypertrophic cardiomyopathy. In a study of patients undergoing electrophysiologic testing, QTVI identified patients with cardiac arrest better than electrophysiologic test result and better than other risk stratifiers included in the analysis. QT variability is a marker of electrical disease in the ventricle and may be associated with enhanced risk of life-threatening arrhythmias.

Algorithms↗

PubMed1997

One step is not enough: making better use of association norms to predict cued recall.

Cued recall is strongly affected by the strength of the preexisting connection between the test cue and the information to be recalled, the target. In all past work, preexisting cue-to-target strength has been measured by the probability that the cue produced the target in free association. This paper presents four experiments showing that this use of such norms underestimates the strength of the connection and that a more accurate estimate can be obtained by incorporating indirect as well as direct connections in the estimate. Experiments 1 and 2 showed that in extralist cued recall both the strength and number of two-step indirect connections facilitate recall. Experiment 3 showed that three-step connections have negligible effects. Experiment 4 used an intralist task in which cue and target are first studied together, and the results showed once again that indirect connections can affect recall. In all of these experiments, indirect connections had an effect on recall that was larger when direct cue-to-target strength was weak than when it was strong. Implications for using association norms in research are described, and an algorithm for using association norms to measure cue-to-target strength is proposed.

Adult↗

PubMed1999

[An algorithm for real-time quantitative analysis of remote detection spectrum of chemical vapor with passive Fourier-transform infrared spectroscopy].

The algorithm for quantitative analysis of passive Fourier-transform infrared spectum (FTIR) of a chemical vapor is given. It can be applied to both real-time processing for chemical vapor and quantitative measurements of chemical vapor column density. The algorithm simultaneously achieves quantitation of the vapor spectral transmission, background removal, real-time calibration for FTIR. Finally, we discuss in detail an example of the use of the algorithm to a simulant DMMP.

Air Pollutants↗

PubMed1999

Uni- and bipolar pacing threshold measurements with capturecontrol, a new automatic pacemaker function for capture verification. Comparison of the automatic and the manual pacing threshold measurement.

It is mandatory in pacemaker patients to determine the pacing threshold at each follow-up visit. To facilitate the pacing threshold measurements, complete automatic pacemaker tests are being developed. A new pacemaker algorithm for automatic capture verification (Capturecontrol) detects the presence of the evoked response signal 70-100 ms after the pacing pulse. The aim of this study was to determine the uni- and bipolar pacing thresholds using this automatic pacemaker function and compare them with the manually determined threshold. The study included 14 patients with the DDD pacemaker Logos (Biotronik) connected to the high-ohmic ventricular pacing lead Synox SX 60-BP (Biotronik). At predischarge and 8, 14, 20 and 26 weeks after implantation the uni- and bipolar pacing thresholds were assessed manually and with the automatic pacemaker function at 0.4 ms duration. Mean pacing thresholds determined with the automatic pacemaker function were not different from the manually measured values. This applied to uni- and bipolar pacing. Seventy percent of all unipolar and 67% of all bipolar measurements had no deviation. A deviation of 0.1 V between manual and automatic threshold measurement was observed in 25% (unipolar) and 28% (bipolar), respectively. A 0.2-volt difference occurred in 3% in the unipolar measurements. Deviations >/=0.3 V were found in 2% of all unipolar and in 5% of all bipolar measurements. In conclusion, automatic pacing threshold measurements using the Capturecontrol algorithm were similar compared to the manually determined thresholds. The excellent agreement between the two methods was observed for bipolar as well as unipolar pacing and on condition that all patients had a high-ohmic ventricular pacing lead. Therefore, fewer requirements are necessary for Capturecontrol than for presently available systems. Such pacemaker functions can help to speed up the measurements during follow-up visits.

Aged↗

PubMed2004

Fourier transform infrared spectroscopy as a new tool to determine rosmarinic acid in situ.

A new procedure has been developed for the in situ FT-IR determination of rosmarinic acid (RA) in suspension cultures of Lavandula officinalis. The method involves sample preparation on ZnSe crystals or microplates from silicon, and measuring absorbance spectra between 4000 and 700 cm(-1). First derivative spectra were analysed after normalisation using partial least square (PLS) algorithm. The correlation between spectral analysis and HPLC measurements of cell extracts shows that the FT-IR procedure is suitable for qualitative and quantitative analyses of RA in cell suspension cultures.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed1993

Differences in CT density between dependent and nondependent portions of the lung: influence of lung volume.

OBJECTIVE: Lung tissue, blood, and air determine the physical density of the lung and hence the attenuation measured on CT scans. These components are not homogeneously distributed throughout the lungs, and their relative proportion changes continuously during respiration. The objective of this study was to measure densities in various areas of the normal lung with CT and to examine the influences of gravity and of the degree of lung inflation on these densities. SUBJECTS AND METHODS: The subjects in the study were six healthy male volunteers. CT scans were obtained at the level of the aortic arch and 2 cm above the expiratory level of the diaphragm with the subjects supine and then with them prone. Scans were obtained at lung volumes of 10%, 50%, and 90% vital capacity by using a respiratory gating device connected to the CT scanner. The overall density of the lungs at these two levels and the densities in the dependent (posterior in supine, and anterior in prone body position) and nondependent (anterior in supine and posterior in prone body position) areas were measured by using a semiautomatic evaluation algorithm. RESULTS: Changes in lung volume caused the same changes in lung density in the right and left lungs and in the upper and lower parts of the lungs. For both body positions (supine and prone), the difference between lung density at 10% vital capacity and that at 90% vital capacity was significantly larger (p < .05) in the dependent parts of the lung than in the nondependent parts. In both positions, differences in density between dependent and nondependent regions were significantly (p < .05) greater at 10% vital capacity than at 90% vital capacity, and the differences became small when the volume of the lung was near total lung capacity. CONCLUSION: Changes in lung volume have different effects on changes in lung density in dependent and nondependent parts of the lung. The largest changes in lung density occur in the dependent regions. The difference in density between dependent and nondependent lung regions is smallest for lung volumes near total lung capacity. These findings may be useful as a baseline for interpreting CT measurements of regional lung density in suspected cases of lung disease, which would alter the physical density of lung tissue. Our results also suggest that measurements near total lung capacity should be included.

Adult↗

PubMed2005

Effect of co-substrate, biomass and sulfate concentration on the performance of a control strategy used to determine the anaerobic stage length of an anaerobic/aerobic SBR degrading p-nitrophenol.

The effect of the p-nitrophenol to propionic acid ratio, the biomass concentration, and the presence of sulfates on the performance of a control strategy of an anaerobic/aerobic SBR degrading p-nitrophenol was studied. The duration of the anaerobic stage was controlled by an algorithm based on the on-line measurement of the oxidation-reduction potential, which indicates the end of the reduction of p-nitrophenol to p-aminophenol. It was observed that no significant influence on the performance of the algorithm was found when the co-substrate, the biomass concentration and the presence of sulfates were varied, indicating the robustness of the control strategy. Only for the case when a low concentration of cosubstrate was used, was there no transformation of p-nitrophenol.

Aerobiosis↗

PubMed2007

Cortical abnormalities in epilepsy revealed by local EEG synchrony.

Abnormally strong functional linkage between cortical areas has been postulated to play a role in the pathogenesis of partial epilepsy. We explore the possibility that such linkages may be manifest in the interictal EEG apart from epileptiform disturbances or visually evident focal abnormalities. We analyzed samples of interictal intracranial EEG (ICEEG) recorded from subdural grids in nine patients with medically intractable partial epilepsy, measuring interelectrode synchrony using the mean phase coherence algorithm. This analysis revealed areas of elevated local synchrony, or "hypersynchrony" which had persistent spatiotemporal characteristics that were unique to each patient. Measuring local synchrony in a subdural grid results in a map of the cortical surface that provides information not visually apparent on either EEG or structural imaging. We explore the relationship of hypersynchronous areas to the clinical evidence of seizure localization in each case, and speculate that local hypersynchrony may be a marker of epileptogenic cortex, and may prove to be a valuable aid to clinical ICEEG interpretation.

Adolescent↗

PubMed2002

Developments in radar and remote-sensing methods for measuring and forecasting rainfall.

Over the last 25 years or so, weather-radar networks have become an integral part of operational meteorological observing systems. While measurements of rainfall made using radar systems have been used qualitatively by weather forecasters, and by some operational hydrologists, acceptance has been limited as a consequence of uncertainties in the quality of the data. Nevertheless, new algorithms for improving the accuracy of radar measurements of rainfall have been developed, including the potential to calibrate radars using the measurements of attenuation on microwave telecommunications links. Likewise, ways of assimilating these data into both meteorological and hydrological models are being developed. In this paper we review the current accuracy of radar estimates of rainfall, pointing out those approaches to the improvement of accuracy which are likely to be most successful operationally. Comment is made on the usefulness of satellite data for estimating rainfall in a flood-forecasting context. Finally, problems in coping with the error characteristics of all these data using both simple schemes and more complex four-dimensional variational analysis are being addressed, and are discussed briefly in this paper.

Algorithms↗

PubMed2002

Missed opportunities to treat atherosclerosis in patients undergoing peripheral vascular interventions: insights from the University of Michigan Peripheral Vascular Disease Quality Improvement Initiative (PVD-QI2).

BACKGROUND: Peripheral vascular disease is a manifestation of systemic atherosclerosis and is associated with an increased risk of cardiovascular morbidity and mortality. METHODS AND RESULTS: We examined clinical outcomes in 66 consecutive patients undergoing peripheral vascular interventions at our institution between January 2001 and October 2001. At hospital discharge and at 6 months, lifestyle modifications and use of evidence-based therapy was suboptimal. At 6 months, a significant proportion continued to smoke (22.7%) and only half of the patients exercised, controlled their weight, or modified their diet for lipid control. The use of antiplatelet therapy was 77.2%; of angiotensin-converting enzyme, 35.9%; of beta-blockers, 42.5%; and of statins, 50%. Twelve of the 66 patients (18.2%) had a clinical event of death, myocardial infarction, or stroke. An appropriateness algorithm for use of secondary prevention measures was created with the use of evidence-based therapy guidelines, and a composite appropriateness variable was also created. The use of evidence-based therapy was associated with a significant reduction of the composite of death, myocardial infarction, and stroke at 6 months (OR 0.02, 95% CI 0.01 to 0.44, P=0.01). CONCLUSIONS: Atherosclerosis risk factors are very prevalent in patients with peripheral vascular disease, but these patients receive less than optimal treatment after a predominantly technical vascular intervention. Effective secondary prevention with appropriate lifestyle interventions and evidence-based medical therapy needs to be strongly encouraged and implemented in these patients.

Algorithms↗

PubMed2004

Characterisation of SNP haplotype structure in chemokine and chemokine receptor genes using CEPH pedigrees and statistical estimation.

Chemokine signals and their cell-surface receptors are important modulators of HIV-1 disease and cancer. To aid future case/control association studies, aim to further characterise the haplotype structure of variation in chemokine and chemokine receptor genes. To perform haplotype analysis in a population-based association study, haplotypes must be determined by estimation, in the absence of family information or laboratory methods to establish phase. Here, test the accuracy of estimates of haplotype frequency and linkage disequilibrium by comparing estimated haplotypes generated with the expectation maximisation (EM) algorithm to haplotypes determined from Centre d'Etude Polymorphisme Humain (CEPH) pedigree data. To do this, they have characterised haplotypes comprising alleles at 11 biallelic loci in four chemokine receptor genes (CCR3, CCR2, CCR5 and CCRL2), which span 150 kb on chromosome 3p21, and haplotyes of nine biallelic loci in six chemokine genes [MCP-1(CCL2), Eotaxin(CCL11), RANTES(CCL5), MPIF-1(CCL23), PARC(CCL18) and MIP-1alpha(CCL3)] on chromosome 17q11-12. Forty multi-generation CEPH families, totalling 489 individuals, were genotyped by the TaqMan 5'-nuclease assay. Phased haplotypes and haplotypes estimated from unphased genotypes were compared in 103 grandparents who were assumed to have mated at random. For the 3p21 single nucleotide polymorphism (SNP) data, haplotypes determined by pedigree analysis and haplotypes generated by the EM algorithm were nearly identical. Linkage disequilibrium, measured by the D' statistic, was nearly maximal across the 150 kb region, with complete disequilibrium maintained at the extremes between CCR3-Y17Y and CCRL2-I243V. D'-values calculated from estimated haplotypes on 3p21 had high concordance with pairwise comparisons between pedigree-phased chromosomes. Conversely, there was less agreement between analyses of haplotype frequencies and linkage disequilibrium using estimated haplotypes when compared with pedigree-phased haplotypes of SNPs on chromosome 17q11-12. These results suggest that, while estimations of haplotype frequency and linkage disequilibrium may be relatively simple in the 3p21 chemokine receptor cluster in population samples, the more complex environment on chromosome 17q11-12 will require a higher resolution haplotype analysis.

Algorithms↗

PubMed2001

[A research on the quantification of retinal blood vessels in cases of arteriovenous crossing pressure syndrome caused by hypertension].

The method for quantification of retinal blood vessels in cases of arteriovenous crossing pressure syndrome caused by hypertension was studied. The matched filtering pre-processing of image enhancement for local retinal blood vessels and closing of mathematical morphology for image smoothing, and the method of scale-up lineation for contour determination of retinal blood vessels and optimal seeking algorithm with reversible quantification were used to measure the pathological deformation of vessel, thus providing a computer method for auxiliary diagnosis of relative diseases.

Algorithms↗

PubMed1994

Sonographic evaluation of gallstone burden in humans.

A prospective blind study was performed to compare sonographic with postoperative findings of gallstone burden in 34 patients (10 males, 24 females; mean age 52 years). Gallstone size was assessed in single calculi (n = 15) by measuring the largest diameter by ultrasonography (US). The ellipsoid algorithm was used to estimate US volume for both single and multiple gallstones. After cholecystectomy, diameters were measured in single stones; stone volume was assessed by the ellipsoid formula (single stones) and fluid displacement (single and multiple stones). Stone volumes assessed by the ellipsoid formula and fluid displacement correlated closely (r = 0.98; p < 0.0001, n = 15). In the case of single gallstones, the mean length assessed by US was 25.3 +/- 3.2 mm and compared well with the value measured "in vitro" (24.8 +/- 3.1 mm). A highly significant and positive relationship existed between the sonographic size and the true stone size (r = 0.93; p < 0.0001, n = 15). Stone volumes assessed "in vivo" and by fluid displacement were comparable and correlated for both single (US: 6.6 +/- 1.3 vs fluid displacement: 5.8 +/- 1.4 ml; r = 0.79; p < 0.0005, n = 15) and multiple stones (US: 3.8 +/- 0.8 vs fluid displacement: 3.7 +/- 0.8 ml; r = 0.85; p < 0.0001, n = 19).(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗

PubMed2001

Experimental evaluation of an environmental CAT scanning system for mapping chemicals in air in real-time.

An innovative method is being developed which creates real-time, two-dimensional maps of chemical concentrations in air for environmental and occupational applications. This method, we call environmental CAT scanning, combines the real-time measuring technique of open-path Fourier transform infrared spectroscopy with the mapping capabilities of computed tomography to produce accurate spatial and temporal information about contaminant concentrations and dispersion patterns. With this system, a network of open-path measurements is obtained over an area; measurements are then processed using a tomographic algorithm to reconstruct the concentrations. This article describes a thorough experimental evaluation of an environmental CAT scanning system using a field-ready prototype system deployed in a room-size exposure chamber; point sample measurements were taken simultaneously in the chamber along with the CAT measurements. Twenty-eight experiments were performed using single or multiple plumes of a tracer gas in the chamber. Tomographic maps were compared with the point sample reference maps to evaluate the CAT scanning system for accuracy of concentration measurement and plume location. Quantitative agreement was very good; concentrations reconstructed with the tomographic maps agreed to within 17 percent of the point sample maps, and plume locations were reconstructed to within six inches of the plumes in the point sample maps. This technique shows real promise as a rapid and accurate method for mapping chemicals over large areas.

Air Pollutants↗