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Results for “Measuring algorithm”

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At least 163 records · Page 9Linked to original sources
PubMedDate not supplied

Dosimetric evaluation in heterogeneous tissue of anterior electron beam irradiation for treatment of retinoblastoma.

A dosimetric study of anterior electron beam irradiation for treatment of retinoblastoma was performed to evaluate the influence of tissue heterogeneities on the dose distribution within the eye and the accuracy of the dose calculated by a pencil beam algorithm. Film measurements were made in a variety of polystyrene phantoms and in a removable polystyrene eye incorporated into a tissue substitute phantom constructed from a human skull. Measurements in polystyrene phantoms were used to demonstrate the algorithm's ability to predict the effect of a lens block placed in the beam, as well as the eye's irregular surface shape. The eye phantom was used to measure dose distributions within the eye in both the sagittal and transverse planes in order to test the algorithm's ability to predict the dose distribution when bony heterogeneities are present. Results show (1) that previous treatment planning conclusions based on flat, uniform phantoms for central-axis depth dose are adequate; (2) that a three-dimensional heterogeneity correction is required for accurate dose calculations; and (3) that if only a two-dimensional heterogeneity correction is used in calculating the dose, it is more accurate for the sagittal than the transverse plane.

Electrons↗
PubMedDate not supplied

[A photoplethysmo-tonomanometer for examination of the vascular system and measuring hemodynamic parameters].

A new method and an apparatus for noninvasive medical investigations of the vascular system are considered. During the investigations, the two known methods of arterial pressure measuring, namely Korotkov's method and Penaz's method were used. The combination of the methods and a special procedure algorithm allow the measuring, in addition to arterial pressure, of the other important hemodynamic parameters such as venous pressure, the characteristic time parameters of blood redistribution between arterial and venous vessels and pulse wave velocity. The diagram of the photoplethysmo-tonomanometer and the measuring algorithm procedure are provided.

Algorithms↗
PubMed2006

The 3D-based scaling index algorithm: a new structure measure to analyze trabecular bone architecture in high-resolution MR images in vivo.

INTRODUCTION: The purpose of this study was to obtain different structure measures as the three-dimensional (3D)-based scaling index method (SIM) and standard two-dimensional (2D) bone histomorphometric parameters from high-resolution (HR) magnetic resonance (MR) images of the distal radius and to compare these parameters with bone mineral density (BMD) in their diagnostic performance to differentiate postmenopausal patients with and without vertebral fractures. METHODS: Axial HR-MR images of the distal radius were obtained at 1.5 T in 40 postmenopausal women (17 with osteoporotic spine fractures and 23 controls). Trabecular microarchitecture analysis was performed using the new structure measure mP(alpha), derived from the SIM, as well as standard morphological 2D parameters. BMD of the spine was obtained using quantitative computed tomography (QCT). Receiver operating characteristic (ROC) analyses were used to determine diagnostic performance in differentiating both groups. Results were validated by bootstrapping techniques. RESULTS: Significant differences between both patient groups were obtained using mP(alpha), 2D parameters, and spine BMD (p<0.05). In comparison with the 2D texture parameters [area under the curve (AUC) up to 0.67], diagnostic performance was significantly higher for mP(alpha)(AUC=0.85; p<0.05). There was a trend for a higher AUC value for mP(alpha) compared with BMD of the spine (AUC=0.71; p=0.81). CONCLUSION: mP(alpha) yielded a robust measure of trabecular bone microarchitecture for HR-MR images of the radius, which significantly improved the diagnostic performance in differentiating postmenopausal women with and without osteoporotic spine fractures compared with standard 2D bone histomorphometric parameters. This 3D characterization of trabecular microarchitecture may provide a new approach to better assess the strength of human cancellous bone using HR-MR image data.

Aged↗
PubMed1999

Measuring change across multiple occasions using the Rasch Rating Scale Model.

When latent trait models are used to measure change across time, it is difficult to disentangle changes in one facet of the measurement context from changes in other facets. Hence, it is difficult to diagnose change. Wright (1999b) proposed an algorithm for disentangling change, and previously the authors applied this algorithm to measuring change across two occasions (Wolfe and Chiu, 1999). In this article we extend Wright's algorithm to disentangle changes in measures across three occasions. We describe a standard Rasch rating scale analysis of a multi-occasion evaluation that produces confusing results when subjected to a series of "separate" calibrations. Then, we apply Wright's correction to the same data to show that the algorithm reveals changes that are more similar to ones that would be expected. Our demonstration shows that Wright's procedure can reduce misfit to the Rasch Rating Scale Model as well as changing the interpretation of change within the measurement context.

Algorithms↗
PubMed1988

A data compression algorithm for the electroencephalogram.

This paper describes a data compression algorithm for the EEG using a local error measure. The algorithm discards input signal samples provided they can be reconstructed from the stored samples with an error smaller than a given threshold, and according to simple reconstruction functions (the hold, the ramp, and the cosine). An equivalent (in terms of storage) sampling rate of 44 Hz is achieved without noticeable degradation of the signal quality for visual analysis. The method can be easily implemented for real time multichannel data compression/reconstruction.

Algorithms↗
PubMedDate not supplied

Optimizing pumped insulin delivery.

The use of portable devices for the subcutaneous infusion of insulin may facilitate the attainment of improved glycemic control in selected patients with insulin-dependent diabetes mellitus. Successful use of a program of continuous subcutaneous insulin infusion requires patient cooperation and motivation, routine monitoring of glycemia, and attention to food intake and activity. This article describes an approach by which patients may optimize glycemic control utilizing a set of algorithms based on patient-determined blood glucose measurements. The algorithms permit programming the insulin infusion device to achieve the desired control.

Diabetes Mellitus, Type 1↗
PubMedDate not supplied

Coronary blood flow measurement using an angiographic first pass distribution technique: a feasibility study.

Due to the well-documented problems associated with visual interpretation of coronary angiograms, more physiologic means of assessing coronary artery stenosis are being investigated. One physiologic parameter that has been suggested is coronary flow reserve (CFR). A digital subtraction angiographic technique based on first pass distribution analysis (FPA) is proposed as a means of measuring CFR and absolute coronary flow. The theory of the FPA method is first outlined, and the implementation of a preliminary version of the FPA algorithm is described. Experiments verifying the utility of this algorithm for measuring absolute flow through a flow phantom, and through the canine circumflex artery are reported. It was determined that the preliminary FPA algorithm is capable of measuring canine coronary flow ratios (R) with accuracy and precision characteristics meeting or exceeding those reported for the parametric imaging technique (RFPA = 0.933.Rtrue, SEE = 0.16, r = 0.984). Accurate absolute flow (Q) measurements were obtained in all of the phantom experiments (QFPA = 1.054.Qtrue, r = 0.993), and in one of the three dogs that were studied (QFPA = 0.977.Qtrue, r = 0.935). The difficulty encountered in the other two dog experiments is attributed to the effects of system temporal lag, and would likely be corrected through the use of improved cameras. The feasibility of the general FPA method for measuring relative flow is established, and the potential for routine, absolute flow measurement is demonstrated.

Algorithms↗
PubMed1997

DNA measurement on histologic slides. Does it work on human tissue?

OBJECTIVE: To determine the performance of different mathematical methods of correcting histograms obtained by densitometric DNA measurement on thin tissue sections for cutting artifacts in different types of human tissue. STUDY DESIGN: The study group consisted of four different euploid-polyploidizing, nonmalignant human tissues (liver, breast cyst with apocrine metaplasia, adenoma of the thyroid, condyloma). The section thickness was accurately measured. The algorithms of Bins, McCready, Bacus and Haroske were applied to the histograms obtained from DNA measurements. The results were compared to those of the corresponding single-cell preparations. RESULTS: Correct ploidy equivalents were calculated using the algorithm of Bins in very thin sections (+/- 3 microns). This was also the case applying the formulas of McCready and Haroske to medium-thick sections (5.3-5.9 microns). The algorithm of Bacus did not lead to reliable results. Measurements on sections thicker than approximately 7 microns led to good results without mathematical correction. CONCLUSION: Reliable results can be obtained only when knowing the exact section thickness. In very thin sections the method of Bins leads to reliable results; in medium-thick sections the methods of McCready and Haraske result in correct ploidy values. Sections thicker than 7 microns do not need histogram correction.

Adenoma↗
PubMed2004

Clinical significance of central corneal thickness in the management of glaucoma.

OBJECTIVE: To evaluate the effect of central corneal thickness determination on the clinical management of patients with glaucoma and glaucoma suspect. METHODS: A cross-sectional retrospective study was performed on 188 consecutive patients. Mean ultrasound pachymetry measurements of central corneal thickness and corresponding Goldmann applanation tonometry measurements were obtained. Intraocular pressures (IOPs) were corrected using linear and mathematical (Orssengo-Pye) algorithms. Measurement-significant outcomes were defined as an IOP adjustment of 1.5 mm Hg or greater and outcomes-significant results as an IOP adjustment of 3.0 mm Hg or greater. Changes in therapy such as the use of eyedrops and addition or cancellation of laser therapy or surgery were then noted for those individuals with measurement- or outcomes-significant changes. RESULTS: Using the linear correction scale, 105 (55.9%) of 188 patients had at least a measurement-significant adjustment in their IOP measurements: 67 (35.6%) had adjustments between 1.5 and 3.0 mm Hg, while 38 (20.2%) had an outcomes-significant IOP adjustment (> or =3.0 mm Hg). Among the 188 patients, 16 (8.5%) had a change in eyedrop therapy, 4 (2.1%) had a change regarding laser therapy, and 6 (3.2%) had a change in the decision regarding glaucoma surgery. Using the exponential correction (Orssengo-Pye) scale, similar percentages were obtained. CONCLUSION: Pachymetry-measured central corneal thickness has a significant effect on the clinical management of patients with glaucoma and glaucoma suspect.

Aged↗
PubMed1999

A method for visualization of invariant sets of dynamical systems based on the ergodic partition.

We provide an algorithm for visualization of invariant sets of dynamical systems with a smooth invariant measure. The algorithm is based on a constructive proof of the ergodic partition theorem for automorphisms of compact metric spaces. The ergodic partition of a compact metric space A, under the dynamics of a continuous automorphism T, is shown to be the product of measurable partitions of the space induced by the time averages of a set of functions on A. The numerical algorithm consists of computing the time averages of a chosen set of functions and partitioning the phase space into their level sets. The method is applied to the three-dimensional ABC map for which the dynamics was visualized by other methods in Feingold et al. [J. Stat. Phys. 50, 529 (1988)]. (c) 1999 American Institute of Physics.

Journal Article↗
PubMedDate not supplied

A method for the measurement of outpatient resource utilization.

A method for measuring outpatient resource utilization in terms of the amounts of time different categories of patients spend with various providers is described. Patients are categorized based on selected attributes, but other attributes could be used. The method is based on two important and measurable variables: 1) frequencies of usage of different resources (e.g., nurse practitioners, physicians, x-ray), and 2) amounts of time used, by each provider type and by ancillary services (x-ray). Using the quantitative measures described, an algorithm is developed for measuring the direct labor costs of delivering primary care to different types of primary care patients.

Algorithms↗
PubMed2002

Airway resistance measured by the interrupter technique: normative data for 2-10 year olds of three ethnicities.

BACKGROUND AND AIMS: The measurement of airway resistance using the interrupter technique (R(int)) is feasible in preschool children and other subjects unable to undertake spirometry. This makes it potentially useful for the measurement of lung function in these groups. Commercial devices use different algorithms to measure pressure and flow from which R(int) is derived. This study provides normative values for British children using devices from a single manufacturer. METHODS: R(int) was measured in 236 healthy children of three ethnic groups (Afro-Caribbean and black African, Bangladeshi, and white British) aged 2-10 years using Micro Medical devices. Software in the devices calculated R(int) from pressure measured by the two point, back extrapolation method from the pressure transient during valve closure, with flow measured just before valve closure. RESULTS: R(int) is related to both age and height, but when age is allowed for there is not a significant relation with height. Neither gender nor any of the ethnicities studied was significantly related to R(int). DISCUSSION: These measurements in healthy children using this technique may be used as reference data for similar populations.

Aging↗
PubMed2005

A pixel-based autofocusing technique for digital histologic and cytologic slides.

The present paper describes a method for autofocusing specifically studied for the acquisition of digital slides, i.e. full histologic and cytologic slides, utilising low-cost equipment. At first, experimentations with some of the most used focus measures and algorithms have been made, in order to choose the most suitable for histologic and cytologic images. Then, a study of the specific features of digital slides has been preliminarily carried out in order to understand the constraints of the domain. These included the capability of autofocusing in an unattended way on thousands of microscope fields, while fast performance is not a strict requirement. Based on the findings, an algorithm based on a dynamic focus position space, with a variance-based focus measure has been adapted to the specific situation. A qualitative and quantitative evaluation of the proposed algorithm allowed us to show that the proposed algorithm is suitable for the acquisition of digital slides, and furthermore it can be implemented starting from a basic microscope with an inexpensive motorised stage. The algorithm is currently implemented into a complete digital slide acquisition system, which is in turn being used for a Quality Assurance Programme in cervicovaginal cytologic screening.

Algorithms↗
PubMedDate not supplied

The healthy-years equivalents: how to measure them using the standard gamble approach.

The healthy-years equivalent (HYE) is a measure of outcome of health care programs that combines two outcomes of interest: quality of life and quantity of life. Unlike QALYs (quality-adjusted life years) HYEs fully represent patients' (or other individuals') preferences, as a result of the way they are calculated from each individual's utility function. The authors suggest an algorithm to measure the HYE of any given lifetime health profile. The algorithm is based on the classic standard gamble method to measure individuals' preferences under uncertainty, and consists of two lottery questions. Algorithms for the general case (any given lifetime health profile) and a simpler case--the chronic health state case--are provided, as is a modification of the algorithm aimed at shortening the length of the interview when an individual is faced with many possible lifetime health profiles. In addition, two questions are addressed. The first is theoretical and deals with the existence of HYE: do all lifetime health profiles, which are preferred to death, have hypothetical equivalents that can be measured in healthy years? The second is empirical and deals with the reproducibility of the measures obtained by using the measurement technique suggested. This is needed because the technique employs a combination of lottery questions that had not previously been used together. The results of an experiment performed to test the reproducibility of the measures were satisfactory.

Algorithms↗