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PubMed1977

Signal-processing techniques in a computerized hearing aid test system.

General background is given to describe the factors leading up to the implementation of a computerized hearing aid test system in a production environment. The digital measurement methods for determination of the required acoustal components such as fundamental, rms, distortion, etc., in the presence of noise are discussed. The use of the concept of the average cycle for repetitive signals is described with its advantages in a Fourier type system. An algorithm for measuring rms for nonrepetitive signals that trades off resolution for memory size is described. Features and advantages of computerized testing of hearing aids are listed.

Acoustics↗
PubMedDate not supplied

Application of information theory to the assessment of computed tomography.

The imaging process has two fundamental stages: detection and display. The detection stage can be quantified rigourously using Shannon's information theory. This requires the contrast scale (CS), modulation transfer function (MTF), and noise power spectrum [N(f)] to be combined into a signal-to-noise ratio (SNR). This results in two fundamental summary figures of merit: the density of noise equivalent quanta (NEQ) in the image and the information bandwidth integral (IBWI). These algorithm-independent measures are used to quantify the recording stage. The display stage is less well understood since it couples to an external observer. Several types of decision makers are treated. Examples are drawn from first and second generation CT, demonstrating that thye are nearly quantum limited for large signals, indicating how their algorithms are matched or mismatched to the geometry, and calculating the contrast-detail diagrams for those decision makers.

Data Display↗
PubMed1990

A Monte Carlo simulation of range for an invasive impedance respiration monitor.

One method of rate responsive pacing utilizes an analog of minute ventilation as the input to the rate control algorithm. A measure of the intravenous impedance along the pacing catheter is a convenient means of determining minute ventilation. Design of the impedance converter requires a knowledge of the range of DC and AC impedance signals. During normal and deep breathing, 116 AC measurements were taken from 34 Electrophysiology (EP) patients and 31 DC measurements were taken from 13 EP patients. The patient data produced skewed distributions with a normal AC mean of 0.45 +/- 0.40 ohms p-p, a deep AC mean of 2.0 +/- 1.6 ohms and a DC mean of 44 +/- 13 ohms. An eight variable static model was derived from prior work. Five of the physiological variables were chosen from established clinical ranges, one geometrical variable was chosen from prior work and two were selected by matching the statistics of a Monte Carlo analysis of the model with the statistics of the patient data. The blood resistivity was obtained from prior work. A simulation of 1000 measurements produced a normal breathing range of 0 to 2.24 ohms, a deep breathing range of 0 to 9.6 ohms and a DC range of 19 to 100 ohms.

Algorithms↗
PubMed1989

Behavior of the copper band of cytochrome c oxidase in rat brain during FC-43-for-blood substitution.

FC-43-for-blood substitution experiments were conducted in anesthetized rats to evaluate NIR spectroscopic responses by living brain to exchange transfusion at very low hematocrits. The NIR responses to the exchange process also assess the ability of multiwavelength algorithms to measure independent changes in the relative amounts of Hb, tHbO2 and oxidized cytochrome a,a3 in the tissue. These data indicate that FC-43 circulation at high FIO2 (1.00) delivers sufficient O2 to the rat brain to maintain the oxidation state of the mitochondrial oxidase near pre-exchange values. The results also confirm the ability of four wavelength algorithms to distinguish changes in the oxidized copper band of cytochrome a,a3 from changes in absorption by Hb and HbO2.

Animals↗
PubMed1992

Digital filters for firing rate estimation.

When a rate histogram is used to represent the firing pattern of a neuron there is the potential for serious error due to aliasing, and because of this the rate histogram is a very poor way to represent neural activity. It is theoretically possible to encode a signal in a spike train and decode it without error by filtering and sampling. There is no natural optimal filter design for this problem, but it is possible to specify the characteristics of a good rate estimating filter heuristically and design a filter with these characteristics. Two rate estimating filters are described here. Their performance has been tested, and compared to the rate histogram and the French-Holden rate estimating algorithm, by measuring their ability to recover signals encoded as impulse sequences by Integral Pulse Frequency Modulation (IPFM). These filters are simple to implement and perform well. They should be used in preference to the rate histogram.

Action Potentials↗
PubMed1991

Multi-conformational peptide dynamics derived from NMR data: a new search algorithm and its application to antamanide.

A search algorithm, called MEDUSA, is presented which allows the determination of multiple conformations of biomolecules in solution with exchange rate constants typically between 10(3) and 10(7) s-1 on the basis of experimental high-resolution NMR data. Multiples of structures are generated which are consistent as ensembles with NMR cross-relaxation rates (NOESY, ROESY), scalar J-coupling constants, and T1 rho measurements. The algorithm is applied to the cyclic decapeptide antamanide dissolved in chloroform. The characteristic radio-frequency field dependence of the T1 rho relaxation rates found for the NH protons of Val1 and Phe6 can be explained by a dynamical exchange between two structures.

Algorithms↗
PubMed1990

A method for measuring neuroretinal rim area.

A practical method for measuring the neuroretinal rim area (NRA) of the optic nervehead is described. Sequential stereo photographs are taken on 35 mm colour transparencies using a Zeiss fundus camera with Allen stereoseparator. While examining a stereo pair with a pocket viewer the disc and cup margins are traced against the stereo image with a Rotring pen (0.1 mm tip) on a clear transparency overlying one of the photographs. This tracing is digitised and analysed by an 'edge detection' algorithm which measures the area between the traced lines, i.e. NRA. The intraobserver intraphotograph coefficient of variation (standard deviation/mean) was calculated for measurements of disc area, cup area and NRA made on 10 stereo photographs of discs with various topographies. Coefficients for NRA ranged from 3.2% to 3.9% for discs with easily discernible cup margins and from 1.6% to 7.2% for discs with less obvious cups.

Glaucoma↗
PubMedDate not supplied

The clinical algorithm nosology: a method for comparing algorithmic guidelines.

Concern regarding the cost and quality of medical care has led to a proliferation of competing clinical practice guidelines. No technique has been described for determining objectively the degree of similarity between alternative guidelines for the same clinical problem. The authors describe the development of the Clinical Algorithm Nosology (CAN), a new method to compare one form of guideline: the clinical algorithm. The CAN measures overall design complexity independent of algorithm content, qualitatively describes the clinical differences between two alternative algorithms, and then scores the degree of similarity between them. CAN algorithm design-complexity scores correlated highly with clinicians' estimates of complexity on an ordinal scale (r = 0.86). Five pairs of clinical algorithms addressing three topics (gallstone lithotripsy, thyroid nodule, and sinusitis) were selected for interrater reliability testing of the CAN clinical-similarity scoring system. Raters categorized the similarity of algorithm pathways in alternative algorithms as "identical," "similar," or "different." Interrater agreement was achieved on 85/109 scores (80%), weighted kappa statistic, k = 0.73. It is concluded that the CAN is a valid method for determining the structural complexity of clinical algorithms, and a reliable method for describing differences and scoring the similarity between algorithms for the same clinical problem. In the future, the CAN may serve to evaluate the reliability of algorithm development programs, and to support providers and purchasers in choosing among alternative clinical guidelines.

Algorithms↗
PubMed1990

[Image analysis of morphologic features of the corneal endothelium including hexagonality].

We developed an analysis system for the evaluation of corneal endothelial photographs. Morphological parameters including hexagonality were analyzed semiautomatically with this system. The image analyzer used consists of an image processor MC68000 and image memories 512 x 512 x 17bytes in size. The algorithm that measures the number of apices of each cell is as follows. First, all crossing points of cell borders are detected. Then, each cell is enlarged in order by three pixels in eight directions. The number of crossing points which are overlapped with an enlarged cell is detected as the number of apices of the cell. The analysis time was 7.44 +/- 1.48 min. (mean +/- standard deviation) for 40 endothelial photographs which needed no manual trace for contrast enhancement.

Cell Count↗
PubMedDate not supplied

Error measures for objective assessment of scene segmentation algorithms.

Scene segmentation is an important element in pattern recognition problems. Previous efforts to evaluate and compare scene segmentation procedures have been largely subjective. Quantitative error measures would facilitate objective comparison of scene segmentation algorithms. A theoretical discussion leading to a new generalized quantitative error measure, G2, based on comparison of both pixel class proportions and spatial distributions of "true" and test segmentations, is presented. This error measure was tested on 14 manual segmentations and 40 gynecologic cytology specimens segmented with five different scene segmentation techniques. Results indicate that G2 seems to have the desirable properties of correlation with human observation, categorization of error allowing for weighting, invariance with picture size and ease of computation necessary for a useful scene segmentation error measure.

Autoanalysis↗
PubMed1990

Transducer characterization from pressure amplitude distribution measurements using a Kalman filter as parameter estimation algorithm.

The amplitude and frequency contents of a received ultrasound pulse depends on the spatial pressure amplitude distribution of the sound field, as produced by the transducer in the medium, and on the position and orientation of the reflecting surface in this field. Often, the geometry of the reflecting surface and the acoustical properties of the medium are known or can be estimated. Then it is practical to determine the transducer parameters in order to calculate the distortion of a reflected ultrasound pulse. Apart from geometrical parameters such as size and mechanical focusing, the surface velocity amplitude distribution (SVAD) of a transducer is of major importance. For some transducer configurations this SVAD may be described with a limited number of parameters. This paper presents a method, based on a Kalman filter algorithm, to assess the transducer parameters by measurement of the spatial sound field pressure amplitude distribution in various planes for different emission frequencies. Comparison of the measured pressure amplitudes with those calculated using the estimated values of the parameters shows that this method yields reliable results.

Acoustics↗
PubMed1992

Clinical measurement of renal clearance.

The importance of renal clearance in uronephrology has motivated the continuous reassessment of well-established methods and the relentless search for better techniques. Concerning radionuclide methods, data in the current literature confirm the validity of the simplified one-compartment model or the empirical single-sample method for renal clearance measurement, and new algorithms have been described to broaden the application of the techniques to the pediatric population. Based on the same principles, accurate measurement of renal clearance can also be obtained using contrast agents. Using the technique for determination of the glomerular filtration rate during radiographic contrast examination is recommendable. However, potential adverse effects of the contrast substances should be compared with those of other methods before using this technique for measuring renal clearance without scheduled contrast roentgenographic examination. Controversy remains concerning the validity of predicting glomerular filtration rate from plasma creatinine. Although the predicted clearance is correlated with reference clearance, analysis of individual results reveals that important differences of up to 50 mL/min frequently occur.

Algorithms↗
PubMed1991

A predictive and feedback control algorithm maintains a constant glucose concentration in fed-batch fermentations.

A combined predictive and feedback control algorithm based on measurements of the concentration of glucose on-line has been developed to control fed-batch fermentations of Escherichia coli. The predictive control algorithm was based on the on-line calculation of glucose demand by the culture and plotting a linear regression to the next datum point to obtain a predicted glucose demand. This provided a predictive "coarse" control for the glucose-based nutrient feed. A direct feedback control using a proportional controller, based on glucose measurements every 2 min, fine-tuned the feed rate. These combined control schemes were used to maintain glucose concentrations in fed-batch fermentations as tight as 0.49 +/- 0.04 g/liter during growth of E. coli to high cell densities.

Acetates↗
PubMed1991

Measured attenuation correction using the Maximum Likelihood algorithm.

Quantitative determination of local radioactivity concentration in positron emission tomography (PET) requires a good attenuation correction procedure to reconstruct the emission image. Using a similar Maximum Likelihood (ML) algorithm as for the reconstruction of the emission image, a method is proposed to reconstruct a transmission image, i.e. a map of absorption coefficients. This reconstructed transmission image is then used to calculate the attenuation correction factors needed for the ML reconstruction of the emission image. This approach takes automatically into account the convolution step in the acquisition process (caused by various smoothing factors, e.g. the detector width). This results in appreciable noise suppression without loss of resolution due to filtering, thus making the reconstructed images easier to interpret. A comparison is made with other estimates for the measured attenuation correction using phantom studies.

Algorithms↗
PubMedDate not supplied

Ellipse test for the reduction of false positive signals in automated cytology.

One of the major problems in automated cytology is the elimination of false positive 'abnormal cell' alarms caused by objects such as overlapping cell pairs, leukocyte clusters, etc. The paper describes an algorithm for the separation of images of abnormal cell nuclei and non=nuclear objects in computer image analysis systems for automated cytology. The algorithm involves the measurement of the agreement between the object outline and a computer ellipse of equal area, aspect ratio and orientation. Results obtained with the CERVISCAN experimental computer image analysis system show that the algorithm gives good discrimination between abnormal cell nuclei and typical non-nuclear objects found in cervical scrape specimens prepared specially for automated analysis.

Cell Nucleus↗
PubMed1992

Automatic assessment of the quality of G-banded metaphases. A preliminary study.

Assessment of the quality of cytogenetic preparations is important for 1) a general quality control of the cytogenetic laboratory and 2) for determining the quality of individual cytogenetic analyses. It is generally accepted that good preparations allow a more detailed search for structural abnormalities than poor preparations. As part of a comprehensive study on automated assessment of slide quality we have developed a simple algorithm for automated measurement of metaphase resolution. During semi-automated karyotyping with the Magiscan chromosome analysis system (Joyce-Loebl) three measurements related to resolution are automatically extracted 1) the total number of dark bands of the chromosomes of the metaphase (TB), 2) the normalized average length of the chromosomes (NL), and 3) the average "thickness" of the chromosomes (T). The algorithm TB x NL/T has been tested on 35 metaphases of various quality and compared with visual assessment of the same 35 metaphases. The results indicate that the automatic assessment of metaphase resolution is superior to the visual.

Chromosome Banding↗
PubMed1992

Assessment of protein coding measures.

A number of methods for recognizing protein coding genes in DNA sequence have been published over the last 13 years, and new, more comprehensive algorithms, drawing on the repertoire of existing techniques, continue to be developed. To optimize continued development, it is valuable to systematically review and evaluate published techniques. At the core of most gene recognition algorithms is one or more coding measures--functions which produce, given any sample window of sequence, a number or vector intended to measure the degree to which a sample sequence resembles a window of 'typical' exonic DNA. In this paper we review and synthesize the underlying coding measures from published algorithms. A standardized benchmark is described, and each of the measures is evaluated according to this benchmark. Our main conclusion is that a very simple and obvious measure--counting oligomers--is more effective than any of the more sophisticated measures. Different measures contain different information. However there is a great deal of redundancy in the current suite of measures. We show that in future development of gene recognition algorithms, attention can probably be limited to six of the twenty or so measures proposed to date.

Algorithms↗