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Results for “Measuring algorithm”

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PubMed1988

Quantitative regional curvature analysis: a prospective evaluation of ventricular shape and wall motion measurements.

To overcome the assumptions and approximations mandated by the use of traditional wall motion methodologies, a method was recently developed for measuring ventricular shape based on quantitative curvature analysis of ventricular outlines. This study was designed to assess prospectively the performance of this algorithm, to compare it to traditional wall motion measurements (centerline method), and to determine the comparative degree to which each method mimicked the interpretation of wall motion by clinical observers. Semiquantitative visual grading of regional function in 52 patients was performed by four independent observers on two occasions. Anterior, apical, or inferior segments were judged to be normal (0 points) or abnormal (1 point) based on viewing nonrealigned, end-diastolic and end-systolic ventricular silhouettes from cineventriculograms obtained in the 30-degree right anterior oblique projection. Each segment was assigned a collated score ranging from 0 (all observers felt the region was normal on both readings) to 8 (all observers felt the region was abnormal on both readings). Quantitative regional curvature analysis and wall motion analysis (centerline method) were performed. Quantitative shape and wall motion scores correlated equally well with the semiquantitative visual scores. When a visual score of greater than or equal to 4 was used to designate an abnormal segment, both quantitative approaches demonstrated comparable sensitivity, specificity, and concordance rates. Both methods achieved optimal performance when maximum and minimum deviations from normal were recorded. Under these circumstances, the shape analysis demonstrated a greater concordance with the clinical diagnosis than did wall motion analysis (99% vs-93%, p less than 0.04).(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗

PubMed2006

What is the optimal clinical technique for measurement of left ventricular volume after myocardial infarction? A comparative study of 3-dimensional echocardiography, single photon emission computed tomography, and cardiac magnetic resonance imaging.

BACKGROUND: Left ventricular (LV) volumes have important prognostic implications, but are commonly underestimated. We sought accuracy and reproducibility of LV volume measurement by live 3-dimensional (3D) echocardiography (3DE) and TI-201 single photon emission computed tomography (SPECT), compared with cardiac magnetic resonance imaging (MRI). METHODS: In all, 30 patients (age 62 +/- 9 years, 23 men) underwent LV volume assessment with 3DE, SPECT, and cardiac MRI after myocardial infarction. LV volumes were measured using a semiautomated border detection algorithm for 3DE, gated SPECT software for SPECT, and a 3D display for MRI. Results of 3DE and SPECT volumes were compared with MRI as the standard of reference. RESULTS: The 3DE volumes showed excellent correlation with cardiac MRI (end-diastolic volume [EDV], r = 0.90, P = .001; end-systolic volume [ESV], r = 0.94, P = .001), as did SPECT (EDV, r = 0.89, P = .001; ESV, r = 0.95, P = .001). However, both 3DE and SPECT underestimated LV volumes. The mean MRI EDV was 179 +/- 56 mL compared with 3DE (mean difference, -10 +/- 26 mL, P = .04) and SPECT (mean difference, -58 +/- 28 mL, P < .001). There was a significant difference between SPECT EDV and 3DE (mean difference, -48 +/- 31 mL, P < .001). The mean MRI ESV was 96 +/- 54 mL and this was underestimated by SPECT (mean difference, -22 +/- 19 mL, P < .001), but not by 3DE (mean difference, -0.9 +/- 19 mL, P = not significant). ESV was also underestimated when SPECT was compared with 3DE (mean difference, -22 +/- 27 mL, P < .001). The results of 3DE were reproducible with excellent intraobserver (ESV, r = 0.98, -2 +/- 6 mL; EDV, r = 0.98, -1 +/- 6 mL, P = .001) and interobserver (ESV, r = 0.97, -2 +/- 6 mL; EDV, r = 0.95, -3 +/- 10 mL, P = .001) correlation. CONCLUSION: We have shown that 3DE is accurate and reproducible for the measurement of LV volumes for risk assessment in chronic ischemic heart disease and dilated cardiomyopathy. Furthermore, 3DE is more accurate than TI-201 SPECT with less underestimation of LV volumes.

Female↗

PubMed1990

[Computer-assisted selection of therapeutic measures in ischemic heart disease and arterial hypertension during mass screening of a rural population].

Expert assessments of 537 case histories of patients with various coronary heart diseases made it possible to derive an algorithm for automatic choice of therapeutic and prophylactic measures. This approach was tested within the framework of the automatic system "Cardioscreening". It was shown that there was a good correlation between the automatic choice of therapeutic and prophylactic actions and the strategy of a skilled cardiologist.

Algorithms↗

PubMed1992

A linear scale for measuring vagal tone in man.

1. Different levels of parasympathetic control of the heart were measured using ratios of the longest to the shortest intervals between R-waves in the ECGs (R-R) recorded during a deep breathing exercise in the supine position (respiratory sinus arrhythmia). The mean of absolute differences in consecutive R-R intervals was also measured in the supine position during quiet breathing (beat-to-beat variation), in six healthy volunteers, after cumulative doses of atropine (0.1-2.0 mg 70 kg-1, i.v.). 2. Full atropinization was observed at 2.0 mg 70 kg-1 where the respiratory sinus arrhythmia decreased by 97%, and the beat-to-beat variation dropped by 94%. There was no further drop in both indices at doses above 2.0 mg 70 kg-1. The different levels of parasympathetic control of the heart were directly proportional to the equivalent levels of respiratory sinus arrhythmia or beat-to-beat variation. 3. A universal linear vagal scale was calculated for use with these non-invasive indices to assess the levels of parasympathetic control of the heart. Zero in this scale would represent no activities in the cardiac vagus nerve. 4. It was concluded that vagal tone could be selectively measured in an intact person using these simplified and fast algorithms for quantifying respiratory sinus arrhythmia or beat-to-beat variation. A linear scale for measuring the vagal tone was possible. This linear scale was called the linear vagal scale (LVS).

Adult↗

PubMed2007

A new analytical method to diagnose congenital myasthenia with stimulated single-fiber electromyography.

Stimulated single-fiber electromyography (SSF-EMG) is useful to assess neuromuscular junction (NMJ) abnormalities in children. Conventionally mean consecutive difference (MCD) analysis measures the jitter for each muscle-fiber potential. We present a new algorithm that analyzes the entire SSF-EMG waveform. Cross-correlational coefficients (between 0-1.0) are calculated for consecutive pairs of 100 SSF-EMG waveforms obtained at each needle position in orbicularis oculi, and averaged. A lower normal limit (0.722, mean -3 SD) was established from 123 SSF-EMG samples in 10 adult control subjects, and applied to SSF-EMG data from 23 children referred for a suspected myasthenic syndrome. Results were compared with MCD analysis and related to the final clinical diagnosis. Our results showed that compared with conventional MCD measurement, the new algorithm had better specificity (87% vs. 53%) but similar sensitivity (88% for both). These findings indicate that the cross-correlational method is a useful predictor of NMJ dysfunction in children.

Adolescent↗

PubMed2000

An automated procedure for identifying spontaneous otoacoustic emissions.

An algorithm is described for objectively identifying and measuring spontaneous otoacoustic emissions (SOAEs) using the spectrum that results from transformation of the acoustic waveform measured in the outer ear canal. Prior to spectral analysis, the rms level is calculated for successive short segments of the waveform and only the weakest 25% of the segments are retained for the spectral analysis [the quietest 150 when using 16k-point fast Fourier transforms (FFTs)]. The resulting initial spectrum is scanned for peaks (potential SOAEs) which are then deleted from the spectrum. New values are estimated for the deleted values using linear extrapolations from frequency ranges on either side of the deleted values. The end result is a smoothed spectrum devoid of all local peaks. The initial spectrum is then compared peak-by-peak with the smoothed spectrum, and those peaks having differences that exceed an objectively determined decision criterion are identified as likely SOAEs. The effects of varying some of the important parameter values of the algorithm are described, and the sensitivity of the procedure is evaluated by measuring the detection rate for a Lorentzian peak of known amplitude added to a spectrum otherwise devoid of SOAEs.

Cochlea↗

PubMed1998

Clinical evaluation of scanning laser polarimetry: II. Polar profile shape analysis.

AIMS: To devise a method to describe and quantify the shape of polar profiles obtained with the scanning laser polarimeter and to compare this measurement with other polar profile measurements in a series of normal subjects and glaucoma patients. METHODS: Scanning laser polarimetry was performed on 54 normal subjects and 74 glaucoma patients. The retardation values obtained from one randomly chosen eye of each subject were analysed using our own methods, including the use of an algorithm to remove blood vessels from the polar profiles, an algorithm to standardise the glaucoma profiles to a normal database, and a further algorithm to evaluate the profile shape. The measurements of profile shape were compared with measurements of the absolute and standardised retinal nerve fibre layer thickness obtained with the scanning laser polarimeter. RESULTS: There was no significant difference between the mean retardation values for the normal and glaucomatous subjects in either hemiretina. However, standardisation of the glaucoma retardation values to a normal database produced significant differences at p < 1 x 10-8 in the mean retardation values for these two groups in both hemiretinas. Profile shape measurement analysis produced similar significant differences between the mean retardation values for the normal and glaucomatous subjects in both hemiretinas, although the degree of separation was greater following standardisation of the retardation values. CONCLUSION: The use of an algorithm to standardise an individual's retardation values in conjunction with a blood vessel removal algorithm enables an improvement in the ability of the scanning laser polarimeter to discriminate between normal and glaucomatous patients. The polar profile shape algorithm is independent of standardisation and significantly improves the discrimination between normal and glaucomatous patients, as well as providing additional information regarding the retinal nerve fibre layer.

Adult↗

PubMed2001

Modelling variation of lower leg length growth in early life.

We consider the estimation of sources of variation for panel data with repeated measurements. With no repeated measurements and known measurement error, models for variation decomposition have been proposed when there are one or more types of measurements. Estimation was performed using the EM algorithm accompanied by model augmentation that demands more computational efforts. In this article we extend previous variation models and modify the estimation methods in order to estimate various variation components after eliminating the unknown effects of measurement error. Specifically, methods that dispense with model augmentation and estimation of time-dependent covariates are considered. A set of lower leg length data from Chinese infants is analysed by using the proposed model. Interestingly, our results are consistent with the well-accepted three-phase (infancy-childhood-puberty) growth transition proposition for human growth. Moreover, gender effect is found to be time-varying.

Anthropometry↗

PubMed2001

A comparison of quantitative coronary angiography systems using a unique set of in vivo coronary stenosis images.

OBJECTIVE: To compare the accuracy and precision of measurements of minimum lumen diameter (MLD) among two existing, and one new, quantitative coronary angiography systems. MATERIALS AND METHODS: The analysis was performed using in vivo cinearteriograms of precisely drilled, radiolucent plastic beads that were inserted percutaneously into the coronary arteries of canines. The existing algorithms compared were the ArTrek and the Coronary Measurement System (CMS). The latter was applied in two modes: a mode based on a minimal cost analysis algorithm and a mode based on a gradient field transform. The new algorithm (CorTrek) was also applied in two modes: a mode called the ArTrek compatible mode and a mode known as the 'regression' mode. The latter mode uses a look-up table, based on a phantom calibration step, to readjust the measured MLD to overcome system nonlinearities (overestimation of small diameters and underestimation of large diameters). RESULTS: In the absence of editing, the optimal accuracy (no significant bias) was achieved with the ArTrek compatible algorithm (-0.03 mm for an MLD between 0.83 and 1.83 mm). All other algorithms showed significant under- or overestimation of the MLD within this range. The precision ranged from 0.18 to 0.40 mm without editing, and was best with the ArTrek algorithm. CONCLUSIONS: The present study provides in vivo validation and comparative performance characteristics of a new, accurate coronary quantitative angiography system.

Algorithms↗

PubMed2000

Treatment planning algorithm corrections accounting for random setup uncertainties in fractionated stereotactic radiotherapy.

A number of relocatable head fixation systems have become commercially available or developed in-house to perform fractionated stereotactic radiotherapy (SRT) treatment. The uncertainty usually quoted for the target repositioning in SRT is over 2 mm, more than twice that of stereotactic radiosurgery (SRS) systems. This setup uncertainty is usually accounted for at treatment planning by outlining extra target margins to form the planning target volume (PTV). It was, however, shown by Lo et al. [Int. J. Radiat. Oncol., Biol., Phys. 34, 1113-1119 (1996)] that these extra margins partly offset the radiobiological advantages of SRT. The present paper considers dose calculations in SRT and shows that the dose predictions could be made at least as accurate as in SRS with no extra margins required. It is shown that the dose distribution from SRT can be calculated using the same algorithms as in SRS, with the measured off-axis ratios (OARs) replaced by "effective" OARs. These are obtained by convolving the probability density distribution of the isocenter positions (assumed to be normal) and the original OARs. An additional output correction factor has also been introduced accounting for the isocenter dose reduction (2.4% for a 7 mm collimator) due to the OARs "blurring." Another correction factor accommodates for the reduced (by 1% for 6 MV beam) dose rate at the isocenter due to x-ray absorption in the relocatable mask. Mean dose profiles and the standard deviations of the dose (STD) were obtained through simulating SRT treatment by a combination of normally distributed isocenters. These dose distributions were compared with those calculated using the convolution approach. Agreement of the dose distributions was within 1%. Since standard deviation reduces with the number of fractions, N, as STD/square root(N), the planning predictions in fractionated stereotactic radiotherapy can be made more accurate than in SRS by increasing N and using "effective" OARs along with corrected dose output.

Algorithms↗

PubMed2000

Specific versus nonspecific brain activity in a parametric N-back task.

In this study functional magnetic resonance imaging (fMRI) was used to examine cerebral activity patterns in relation to increasing mental load of a working memory task. Aim of the experiment was to distinguish nonspecific task-related processes from specific workload processes analytically. Twelve healthy volunteers engaged in a spatial n-back task with four levels. FMRI data were acquired with the 3D-PRESTO pulse sequence. Analysis entailed a two-step multiple regression algorithm, which was specifically designed to measure and separate load-sensitive and load-insensitive activity simultaneously, while preserving the original high spatial resolution of the fMRI signal. Load-sensitive and load-insensitive activity was found in both dorsolateral-prefrontal and parietal cortex, predominantly bilaterally, and in the anterior cingulate. As expected, the left primary sensorimotor cortex showed predominantly load-insensitive activity. Load-sensitive activity reflects specific working memory functions, such as temporary retention and manipulation of information, while load-insensitive activity reflects supportive functions, such as visual orientation, perception, encoding, and response selection and execution. Good performance was correlated with a large area of load-sensitive activity in anterior cingulate, and with a small area of load-insensitive activity in the right parietal cortex. The findings indicate that nonspecific and specific working memory processes colocalize and are represented in multiple frontal and parietal regions. Implication of this analytical strategy for application in research on psychiatric disorders is discussed.

Adult↗

PubMed1989

A generalised algorithm for spectral reconstruction in Compton spectroscopy with corrections for coherent scattering.

Reconstruction of primary-photon energy spectra from pulse-height distributions obtained in a Compton spectrometer has earlier been performed under the assumption that coherent scattering in the scatterer is negligible. This holds for most clinical x-ray units operated in the range 40-150 kV. In mammography, and to some extent in dental radiography, the relatively high frequency of low-energy photons (less than 30 keV) in the primary beam makes it necessary to extend the algorithms to allow for significant contribution of coherent scattering. This extension is performed as a perturbation calculation to the algorithms developed earlier in which a modified Klein-Nishina scattering cross section was taken as the total scattering cross section. Comparison with energy spectra measured in the primary beam indicates that the Compton spectrometer with the extended algorithm is an excellent instrument for measuring energy spectra with energies down to a few keV.

Algorithms↗

PubMed1992

Models of the actin monomer and filament from fluorescence resonance-energy transfer.

We have developed algorithms for combining fluorescence resonance-energy transfer (FRET) efficiency measurements into structural models which predict the relative positions of the chemical groups used in FRET. We used these algorithms to construct models of the actin monomer and filament derived solely from FRET measurements based on seven distinct loci. We found a mirror-image pair of monomer models which best fit the FRET data. One of these models agrees well with the atomic-resolution crystal structure recently published by Kabsch et al. in Heidelberg [Kabsch, W., Mannherz, H. G., Suck, D., Pai, E. F. & Holmes, K. C. (1990) Nature 347, 37-44]. The root-mean-square deviation between this FRET model and the crystal structure was about 0.9 nm. Other macromolecular models assembled from FRET measurements are likely to have a similar resolution. The largest discrepancy was for the Cys10 locus which deviated 1.44 nm from the crystal position. We discuss the limitations of the FRET method that may have contributed to this discrepancy, and conclude that the Cys10 FRET data have probably located Cys10 incorrectly in the FRET monomer model. Using the FRET monomer models, we found three orientations in the filament which best fit the intermonomer FRET data. These orientations differ substantially from the atomic-resolution filament model proposed by the Heidelberg group [Holmes, K., Popp, D., Gebhard, W. & Kabsch, W. (1990) Nature 347, 44-49], largely because of the discrepancies in the Cys10 data. These data should probably be excluded from the analysis; however, this would leave too few measurements to assemble a filament model. In the near future, we hope to obtain additional FRET measurements to other actin loci so that the filament modelling can be done without the Cys10 data.

Actins↗

PubMed1988

On estimating the number density of random scatterers from backscattered acoustic signals.

When an acoustic pulse interacts with an inhomogeneous, attenuating medium, the backscattered signals exhibit random fluctuations which are correlated with the physical properties of the medium. This paper proposes a robust model for characterizing the statistical nature of these backscattered signals. This model takes into account frequency-dependent attenuation, spatially varying media statistics, arbitrary beam geometries, and arbitrary pulse shapes. Based on this model, statistical estimation schemes are proposed for estimating both the attenuation coefficient and scatterer number density of the medium. Using appropriate simplifying assumptions, it is shown that this model is consistent with attenuation estimation algorithms currently used for ultrasonic tissue characterization. A statistical approach for estimating the number density of scatterers is described and its theoretical performance is evaluated. The algorithm for estimating the scatterer number density incorporates measurements of both the statistical moments of the backscattered signals and the point spread function of the acoustic system. The number density algorithm has been applied to simulated waveforms, waveforms obtained from ultrasonic phantoms with known number densities, and in vitro mammalian tissues. There is an excellent agreement between theoretical, simulation, and experimental results. The application of this technique to ultrasonic tissue characterization is also discussed.

Algorithms↗

PubMed2002

Slower treatment response in bipolar depression predicted by lower pretreatment thyroid function.

OBJECTIVE: Because treatment of the depressed phase of bipolar disorder is a clinical challenge and hypothyroidism is known to be associated with depression, the authors examined the relationship between pretreatment thyroid values and response to antidepressant treatment. It was hypothesized that subjects with lower thyroid function, even within the normal range, would have a poorer response to initial treatment. METHOD: The subjects were 65 patients in the depressed phase of bipolar I disorder who were enrolled in a larger ongoing study. A panel of thyroid measures, including thyroid-stimulating hormone (TSH), thyroxine, triiodothyronine resin uptake, and free thyroxine index (FTI), were determined before initiation of algorithm-guided treatment. The effect of each thyroid measurement on time to remission was estimated by using the Cox proportional hazards model. RESULTS: Both lower values of FTI and higher values of TSH were significantly associated with longer times to remission, i.e., slower response to treatment. Outcomes were relatively poor unless patients had FTI values above the median and TSH values below the median. Patients with this optimal profile experienced remission 4 months faster than the remainder of the study group. CONCLUSIONS: This study provides further evidence that patients with bipolar disorder are particularly sensitive to variations in thyroid function within the normal range. Our results suggest that nearly three-quarters of patients with bipolar disorder have a thyroid profile that may be suboptimal for antidepressant response. It remains to be seen whether pharmacological enhancement of thyroid function will facilitate recovery from bipolar depression.

Adult↗

PubMed1994

Visual field analysis using artificial neural networks.

There have been several reports on the application of artificial neural networks (ANNs) to visual field classification. While these have demonstrated that neural networks can be used with good results they have not explored the effects that the training set can have upon network performance nor emphasized the unique value of ANNs in visual field analysis. This paper considers the problem of differentiating normal and glaucomatous visual fields and explores different training set characteristics using field data collected from a Henson CFS2000 perimeter. Training set properties including size, balance between normals and glaucomas, extent of field loss and the spatial location of glaucomatous defects are explored. A multilayer network with 132 input nodes, 20 hidden layer nodes and 2 output nodes in trained using an error backpropagation algorithm. Both sensitivity and specificity are measured during testing. The results demonstrate that large random sets are better than small random sets since sensitivity improves with size and specificity is not adversely affected. The variability in performance also reduces as training set size increases. In addition, sets that are biased towards glaucoma examples are more sensitive and less specific, while sets biased with normal examples are more specific and less sensitive than balanced sets. Thus large training sets with class balance are generally desirable for good sensitivities and specificities. The actual glaucoma examples contained in the set are also important. A training set deficient in examples has no detrimental effect on sensitivity or specificity. The spatial distribution of defects is also crucial. Spatially biased sets are unable to recognize defects that occur in locations where no previous defect has been presented while more balanced sets lead to better performance. In conclusion the 'ideal' training set should contain many examples of early defects that represent the full range of locations where these defects may occur.

Algorithms↗

PubMed1993

Early reocclusion after successful thrombolysis is related to lesion length and roughness.

BACKGROUND: Reocclusion is a significant problem after thrombolysis. Results of previous studies conflict regarding the association of various features of postlytic lesions that might predict reocclusion. METHODS: A computer-assisted algorithm was therefore used to quantitatively measure edge roughness in the 90-minute postlysis angiogram of 84 patients receiving recombinant tissue plasminogen activator within 6 hours of chest pain. RESULTS: Twenty-five patients had reocclusion, and 59 did not. The baseline angiogram showed no differences between these two groups with respect to minimal dimensions or relative percentage of stenosis. Length was greater in the reocclusion group (12.2 +/- 5.0 vs 10.0 +/- 4.2 mm, P < 0.05). Three of four roughness indices based on curvature analysis indicated greater roughness in those patients with reocclusion. These differences were largely due to the increased length of these lesions. The scaled edge-length ratio, an index of roughness that is independent of length, was, however, significantly greater in the reocclusion group (1.15 +/- 0.10 vs 1.09 +/- 0.08, P < 0.006). Multiple regression analysis showed that lesion length, the scaled edge-length ratio, and the number of features (invaginations and evaginations) per cm correlated independently with the risk for reocclusion. CONCLUSIONS: The length and roughness of postlytic residual lesions are determinants of reocclusion.

Algorithms↗

PubMed1994

Evaluation of algorithms for tomographic reconstruction of chemical concentrations in indoor air.

Numerical studies were performed to evaluate and compare four different algorithms for tomographically reconstructing pollutant concentrations in indoor air measured with an optical remote sensing system. With a remote sensing/computed tomography system, two-dimensional maps of air concentrations can be created for an entire room with good spatial and temporal resolution. The success of such a system for characterizing the flow of contaminants in air, exposure assessment, and leak detection depends on the choice of tomographic reconstruction algorithm. A systematic method was developed to evaluate the performance of four algorithms: ART, ART3, SIRT, and SART. One hundred and twenty test maps were reconstructed by each algorithm under ideal and nonideal sampling conditions, and image quality was evaluated using four criteria. The nonideal sampling conditions included simulation of measurement noise and reduction in the number density of rays. Performance of the algorithms was found to be intimately related to the number of peaks in the test maps. The importance of using multiple measures of image quality was underscored by the fact that for some sampling conditions simulated, performance of the algorithms was judged differently depending on the evaluation criteria. Results indicated that using numerical studies is successful for evaluating such algorithms.

Air Pollutants, Occupational↗