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Results for “Measuring algorithm”

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PubMed1995

Fusion of immunoscintigraphy single photon emission computed tomography (SPECT) with CT of the chest in patients with non-small cell lung cancer.

In non-small cell lung cancer (NSCLC), accurate staging is critical in deciding between potentially curative surgery and palliative treatment. Image registration, or fusion, combines the unique functional information provided by SPECT imaging with the excellent anatomic detail offered by computed tomography (CT) or magnetic resonance imaging to better characterize the information provided by each separate modality. In this study, we explored the role of fusion of immunoscintigraphy SPECT with CT in the staging of NSCLC. We fused chest CT with 99mTc-labeled IMMU-4 anti-carcinoembryonic antigen Fab' antibody fragment SPECT in 14 patients with NSCLC using a landmark-based algorithm. The algorithm's accuracy was a measure from the center-to-center distance and the percentage overlap of two regions of interest: one drawn on CT and warped onto SPECT, the other drawn directly on the SPECT. We found that the average center-to-center distance was 1.3 +/- 0.8 pixels. Average overlap was 46 +/- 20%. CT-SPECT fusion helped differentiate tumor from normal blood pool, necrotic areas within viable tumor, tumor recurrence from scar, and malignant lymphadenopathy from hyperplasia. We conclude that fusion of CT and SPECT augments the information provided by each separate modality. Future clinical applications of fusion in NSCLC staging using immunoscintigraphy appear promising.

Adult↗

PubMed2005

Noninvasive reflection spectra provide quantitative information about the spatial distribution of skin chromophores.

In this work, a new method of analyzing noninvasive reflection spectra is presented. The approach explicitly models the inhomogeneity of chromophore distributions in living tissues and thus extracts not only apparent chromophore concentrations but also relative chromophore distributions in tissues. Furthermore, it works with spectra obtained with short source-detector separations where the diffusion theory of light transport through turbid media is not valid, and formerly presented methods thus fail. The effect of inhomogeneously distributed chromophores in a multicompartment model of tissues on measured reflection spectra is explained and an algorithm to deconvolute tissue spectra based on this model is presented. It is evaluated using simulated spectra and measurements on phantoms, which are made up of partially printed pieces of paper to simulate inhomogeneous dye distributions. Its applicability to real tissue is proven using reflection spectra obtained with 130 microm source-detector separation from a hemoperfusion stop experiment. The proposed model accurately determines apparent chromophore concentrations and corresponding distributions in simulated spectra and phantoms. Regarding real tissue spectra, the results correspond to former publications and the spectral reconstruction yields only minimal residuals, indicating a complete and accurate spectral deconvolution. In conclusion, the presented approach is a suitable extension and amendment to existing models of light transport through inhomogeneous samples.

Algorithms↗

PubMed1991

Influence of optical density on the automated segmentation of rat kidney lysosomes.

After staining for acid phosphatase, video-images were acquired from 0.5-micron sections of rat kidney. Lysosomes in proximal tubules were automatically segmented, using a VICOM digital image processor and measured for area, number and optical density (OD). The purpose of this study is to objectively evaluate the performance of the automated segmentation algorithm at different staining intensities (a) by measuring area after staining with different incubation times, reduced substrate concentration or by adding an inhibitor and (b) by 'simulating' a decrease in OD (reducing grey-values at each point of a digitized image). The results of the experiments showed that: (1) the algorithm will underestimate the size of lysosomes (a) when the OD in close to the local background and (b) when an area is larger than or close to the area of the lowpass square filter; (2) accuracy of the segmentation can be improved by comparing the results of feature extraction after segmentation of the same image at different relative OD levels; (3) lysosomes with very low OD, compared to background are delineated with a large error or not delineated at all and this cannot be corrected. Incorrectly delineated lysosomes can be identified and excluded from further calculations, or their measured area replaced by an estimate of the true area.

Acid Phosphatase↗

PubMed2003

[Reliability of measurement and the methods of estimating reliability].

OBJECTIVE: To explore the methods of estimating measurement reliability and their limitations. METHODS: According to the given examples, reliabilities of measurement were calculated and limitations of the methods of estimating reliability were analyzed. RESULTS: The Kappa value of interobserver reliability was 0.793 between two pathologists. Between the two populations with different prevalence rates, the values of Kappa were 0.800 and 0.137 respectively, and with big difference. Cronbach's alpha coefficient of compositive index for A type behavior was 0.55. CONCLUSION: The Kappa index and alpha coefficient were both inherently population-specific. Before generalizing to different populations, the reliability needs to be measured.

Algorithms↗

PubMed2000

[The quality of the drug treatment in hyperlipemia patients from 4 health areas. The VICAF Group].

OBJECTIVE: To calculate how suitable the lipid-lowering treatment prescribed for pensioners in primary care clinics in four health areas is. DESIGN: Cross-sectional descriptive study of quality of pharmacological treatment. SETTING: Four primary care health districts, INSALUD, Madrid. PARTICIPANTS: 1125 patients registered with 49 doctors, chosen at random on the basis of three strata defined by the value of the lipid-lowering drug indicator of prescription. For a year, each doctor filled in a protocol of variables for each pensioner to whom he/she prescribed a lipid-lowering drug. MEASUREMENTS AND MAIN RESULTS: An automated algorithm was designed to evaluate the suitability of the drugs treatment for each patient, according to scientific criteria including: cholesterol levels, LDL, age, and risk factors. Quality of prescription was finally measured for 1009 patients. The indication of the treatment was due to primary prevention in 65% of cases. 32% of patients were correctly treated. If LDL compliance was not demanded, the suitability figure rose to 77%. Drug treatment was more suitable when the doctor him/herself administered it (as against another doctor or a specialist; p = 0.001) or when the patient was on the list of the prescribing doctor (p < 0.0001). Proper indication was lower in patients over 74 (p < 0.0001). CONCLUSIONS: The quality of lipid-lowering drug prescription for pensioners in primary care clinics in four health districts, as a function of the criteria defined above, could be improved. LDL is the factor which most affects the procedure.

Aged↗

PubMed2003

Cognitive approaches to summary measurement: its application to the measurement of diversity in health-related quality of life assessments.

This paper describes elements of a cognitive approach to summary measurement, as it is applied to health-related quality of life (HRQOL) assessment. A summary measure, by its very nature, represents, but does not reproduce, some body of information. As a consequence, how a summary measure is formulated becomes a critical determinant of its usefulness. In most cases, formal (arithmetic or investigator-based) methods are used. However, it was also noted that a person ordinarily summarizes the information they receive. Qualitative analytic techniques (e.g., cognitive interviewing methods) can provide insight into the cognitive processes underlying such summary formation. These cognitive processes, formulated as algorithms, would also be expected to vary as a function of different groups of respondents and settings. Finding a common denominator, a common algorithm, would provide a consensus summary measure amongst diverse groups whose HRQOL is being assessed.

Algorithms↗

PubMed2005

Phasing diffraction data from a stream of hydrated proteins.

We consider the problem of phase determination for continuous diffraction patterns obtained from a beam of identical, aligned large molecules (such as proteins), each coated with a layer of water or vitreous ice. Many laser-aligned molecules are assumed to lie within a wide continuous x-ray beam at any instant. An iterative phasing method is developed to extract the common target structure in three dimensions from diffraction patterns of these doped ice balls. Several measurements of the diffraction intensity in reciprocal space are needed. We found iteratively two boundaries (supports) (between protein and ice and the outer iceball support) by using the charge-flipping and multiple hybrid input-output algorithms, working with multiple sets of measured data. The approach is applied to simulated data from hydrated lysozyme proteins generated by the serial crystallography method of laser-aligned protein-beam diffraction proposed by Spence and Doak [Phys. Rev. Lett. 92, 198102 (2004)]. We consider also the effect of empty ice balls on the patterns. The algorithm can also be used to align images with different randomly chosen origins, so that the same embedded subunits overlap.

Algorithms↗

PubMed1993

Human brain measures of clinical pain: a review. I. Topographic mappings.

A comprehensive paper (Parts I and II) has been developed to review the cerebral measures employed in studying the brain neurophysiological activities of clinical pain. Part I focuses on the electro-, magnetic-physiological assessment of clinical pain, and Part II concerns the anatomico-, chemical-physiological assessment of clinical pain. In Part I, these measures include the qualitative inspection of the conventional electroencephalogram, quantitative assessment of brain electrical spectral activity through cortical power spectrum density and coherence analyses, and quantitative averaging of cortical electrical or magnetic activities using brain evoked potentials. The mapping and measurement of these electrical activities and magnetic fields are results of recent advent in computer technology and advanced algorithms. Promises and limitations of these topographic measures in understanding pain in the brain are stated. The next article (Part II) of this paper will review tomographic imaging of pain-related brain activities in regional cerebral flow, the scanning of gross and fine brain structures by computerized axial tomography or magnetic resonance imaging, and the imaging and measurement of brain metabolic changes, energy uptake, and receptor bindings through positron emission tomography or single-photon emission computerized tomography. Molecular chemical transformation by the nuclear magnetic resonance analysis of tissue changes and analgesic-receptor interactions will also be noted.

Brain↗

PubMed1996

Bioelectrical impedance techniques in medicine. Part III: Impedance imaging. Second section: reconstruction algorithms.

This section is devoted to the reconstruction algorithms published in the literature and developed for reconstructing the electrical conductivity and permittivity inside a body from measurements made on the body surface. These algorithms fall into two main categories. The first, based on linear approximations, are noniterative methods assuming that conductivity does not differ very much from a constant. Examples of noniterative methods are the Barber-Brown back-projection method and related methods, the Calderon's approach, the moment method, and one-step Newton methods. The second class of methods consists of iterative methods, which typically include output least squares for various functions. A related class includes the adaptive methods, in which the applied patterns of current are adjusted to get the best signal. A review of all these different alternatives is presented.

Algorithms↗

PubMed1983

Two-dimensional echo-cardiographic estimation of left atrial volume and volume load in patients with congenital heart disease.

To estimate the left atrial volume (LAV) and pulmonary blood flow in patients with congenital heart disease (CHD), we employed two-dimensional echocardiography (TDE). The LAV was measured in dimensions other than those obtained in conventional M-mode echocardiography (M-mode echo). Mathematical and geometrical models for LAV calculation using the standard long-axis, short-axis and apical four-chamber planes were devised and found to be reliable in a preliminary study using porcine heart preparations, although length (10%), area (20%) and volume (38%) were significantly and consistently underestimated with echocardiography. Those models were then applied and correlated with angiocardiograms (ACG) in 25 consecutive patients with suspected CHD. In terms of the estimation of the absolute LAV, accuracy seemed commensurate with the number of the dimensions measured. The correlation between data obtained by TDE and ACG varied with changing hemodynamics such as cardiac cycle, absolute LAV and presence or absence of volume load. The left atrium was found to become spherical and progressively underestimated with TDE at ventricular endsystole, in larger LAV and with increased volume load. Since this tendency became less pronounced in measuring additional dimensions, reliable estimation of the absolute LAV and volume load was possible when 2 or 3 dimensions were measured. Among those calculation models depending on 2 or 3 dimensional measurements, there was only a small difference in terms of accuracy and predictability, although algorithm used varied from one model to another. This suggests that accurate cross-sectional area measurement is critically important for volume estimation rather than any particular algorithm involved. Cross-sectional area measurement by TDE integrated into a three dimensional equivalent allowed a reliable estimate of the LAV or volume load in a variety of hemodynamic situations where M-mode echo was not reliable.

Adolescent↗

PubMed2004

Automated volumetric flow quantification using angle-corrected color Doppler image.

We have developed a fully automated method for measuring volumetric blood flow with angle-corrected blood velocity from a color Doppler image. By computing the blood flow vector through a conduit, the angle of incidence between the direction of ultrasound beam and the direction of blood flow can be measured to correct the underestimated blood velocity. This correction immediately contributes to the improvement of measurement accuracy. The developed method also enhances the conduit identification procedure that is one of the most important factors affecting the accuracy of volumetric measurement. To evaluate the validity of the developed algorithm, experimental studies had been applied to 21 healthy subjects and 10 patients. Volumetric flows were measured from a color Doppler image of the left ventricular outflow track, which were compared with blood volumes that were measured by traditional pulsed-wave (PW)-Doppler technique. The mean stroke volume difference between two methods was -0.45 +/- 11.7 (mean +/- SD). The proposed algorithm is a viable method for determining blood flow volume in an automated fashion.

Blood Flow Velocity↗

PubMed1988

Monitoring aspects of an ultrasonic esophageal transducer. Initial experience.

A method of semi-automatic contour detection is described using a commercial (Kontron) image analysis instrument. Input data consists of high-quality transesophageal echocardiograms of short-axis left ventricular cross-sections. The purpose of the study is to evaluate the feasibility of such a method for the quantitative monitoring of the dynamic behaviour of the left ventricle during high risk surgery. From the first experience it is authors' impression that the automatically derived contour depends strongly on the selected algorithm parameters. Therefore derivation of absolute measurements from these contours seems problematic. Automatic contour detection seems much better fit for monitoring situations, where the patient acts as his own reference and there is no need to change the algorithm parameters.

Echocardiography↗

PubMed1998

Optical high-precision three-dimensional position measurement system suitable for head motion tracking in frameless stereotactic radiosurgery.

Head motion is a significant source of therapy-effect degradation in frameless stereotactic radiosurgery (SRS). In this study, a three-dimensional (3-D) optical head motion measurement system and a coordinate transformation algorithm were used to track patient head motion. With this system, head motion in frameless SRS was carefully investigated with a precision of < 0.1 mm. Head motions without any restraint (three cases) and with a Laitinen adapter (four cases) were measured with a data sampling rate of once per second for 30 min. Positions of IR light emission diode markers attached to the head were analyzed by two statistical methods. From these data, mathematically simulated head motions were obtained in each of the three coordinate directions for nonrestraint and Laitinen-adapter SRS. The results show that segmenting a frameless SRS procedure into a sequence of short intervals and repeating registration of the target position for each interval is a good strategy for better therapy precision. This optical 3-D position measurement system is suitable for high-precision head motion tracking in frameless SRS.

Adult↗

PubMed1999

Comparison of SOM point densities based on different criteria.

Point densities of model (codebook) vectors in self-organizing maps (SOMs) are evaluated in this article. For a few one-dimensional SOMs with finite grid lengths and a given probability density function of the input, the numerically exact point densities have been computed. The point density derived from the SOM algorithm turned out to be different from that minimizing the SOM distortion measure, showing that the model vectors produced by the basic SOM algorithm in general do not exactly coincide with the optimum of the distortion measure. A new computing technique based on the calculus of variations has been introduced. It was applied to the computation of point densities derived from the distortion measure for both the classical vector quantization and the SOM with general but equal dimensionality of the input vectors and the grid, respectively. The power laws in the continuum limit obtained in these cases were found to be identical.

Algorithms↗

PubMed1997

Method-based differences in the automated analysis of the three-dimensional morphology of trabecular bone.

The three-dimensional (3D) morphology of trabecular bone is frequently quantified using computer programs. However, there are no standardized implementations of morphology programs and many variations are possible. Even though programs may use the same basic method, results can be significantly different because of differences in implementation. Morphology data from different laboratories therefore may not be comparable. The method of directed secants, with parallel plate assumptions, is commonly used to quantify 3D morphology. We examined the effect of several variations in the implementation of this method on measurements of trabecular plate number (Tb.N), trabecular thickness, and trabecular spacing. Three-dimensional micromagnetic resonance images of 10 bovine trabecular bone specimens were analyzed using several variations of the directed secant method. An analysis of covariance with repeated measures suggested that variations in the algorithm used to count test line intersections, variations in the criteria used to classify a test coordinate as bone or marrow, and variations in the number of test grid rotations had significant effects on Tb.N (p < 0.0001). The largest difference in Tb.N (52%) was due to the method used to count test line intersections with the bone-marrow interface. Variations in the classification algorithm and variations in the number of test line grid rotations resulted in a 6% difference in Tb.N. The spacing of the test line grids did not affect Tb.N (p = 0.28), and all differences were independent of volume fraction (p = 0.67). These data show that there can be significant differences in trabecular bone morphology measurements due only to the method used for the measurements. To facilitate comparisons between laboratories, we have made validated computer programs to measure trabecular bone morphology available over the Internet.

Algorithms↗

PubMed1992

Simple computer measurement of pulmonary VCO2 per breath.

Measurements of the volume of CO2 exhaled per breath (VCO2/br) are preferable to end-tidal PCO2, when the exhaled flow and CO2 waveforms may be changing during unsteady states, such as during alterations in positive end-expiratory pressure or alterations in cardiac output. We describe computer algorithms that determine VCO2/br from digital measurements of exhaled flow (including discontinuous signals common in anesthesia circuits) and CO2 concentration at the airway opening. Fractional concentration of CO2 is normally corrected for dynamic response and transport delay (TD), measured in a separate procedure. Instead, we determine an on-line adjusted TD during baseline ventilation. In six anesthetized dogs, we compared the determination of VCO2/br with a value measured in a simultaneous collection of expired gas. Over a wide range of tidal volume (180-700 ml), respiratory rate (3-30 min-1), and positive end-expiratory pressure (0-14 cmH2O), VCO2/br was more accurate with use of the adjusted TD than the measured TD (P less than 0.05).

Algorithms↗

PubMed2001

Retinal thickness measurements from optical coherence tomography using a Markov boundary model.

We present a system for detecting retinal boundaries in optical coherence tomography (OCT) B-scans. OCT is a relatively new imaging modality giving cross-sectional images that are qualitatively similar to ultrasound. However, the axial resolution with OCT is much higher, on the order of 10 microm. Objective, quantitative measures of retinal thickness may be made from OCT images. Knowledge of retinal thickness is important in the evaluation and treatment of many ocular diseases. The boundary-detection system presented here uses a one-dimensional edge-detection kernel to yield edge primitives. These edge primitives are rated, selected, and organized to form a coherent boundary structure by use of a Markov model of retinal boundaries as detected by OCT. Qualitatively, the boundaries detected by the automated system generally agreed extremely well with the true retinal structure for the vast majority of OCT images. Only one of the 1450 evaluation images caused the algorithm to fail. A quantitative evaluation of the retinal boundaries was performed as well, using the clinical application of automatic retinal thickness determination. Retinal thickness measurements derived from the algorithm's results were compared with thickness measurements from manually corrected boundaries for 1450 test images. The algorithm's thickness measurements over a 1-mm region near the fovea differed from the corrected thickness measurements by less than 10 microm for 74% of the images and by less than 25 microm (10% of normal retinal thickness) for 98.4% of the images. These errors are near the machine's resolution limit and still well below clinical significance. Current, standard clinical practice involves a qualitative, visual assessment of retinal thickness. A robust, quantitatively accurate system such as ours can be expected to improve patient care.

Algorithms↗

PubMed1997

Coronary heart disease risk factors in employees of Iowa's Department of Public Safety compared to a cohort of the general population.

The prevalence of coronary heart disease (CHD) risk factors in law enforcement personnel compared to that in the general population was studied by determining the predicted 10-year risk for developing CHD (CHD10, expressed as %) in subjects from the Iowa Department of Public Safety and comparing it to the average CHD10 for similarly aged subjects in the Framingham Heart Study cohort. The Iowa data included measures on 388 men from 30 to 64 years old, 246 of whom were measured in 1980-1981 and again in 1992-1993. The CHD10 came from an algorithm developed using the Framingham data; it included measures of age, gender, cholesterol, HDL-C, systolic blood pressure, smoking habit, glucose level, and left ventricular hypertrophy (ECG criteria). For this group, average CHD10 was reported by age in five-year increments [Circulation 83:356, 1991]. The Iowa subjects (n = 388) did not show a statistically significant difference in CHD10 from the reference population (8.9% versus 7.9%). The change with age was very similar in the two groups: for Iowa (n = 388) the estimate was CHD10 = -16.5 + .59 (age); for Framingham it was CHD10 = -17.5 + .60 (age). The change in individual risk factors with time was also similar in both groups; the per year change in CHD10 in the Iowa subjects, which was measured twice (n = 246, 0.63%), did not differ statistically from the 0.60% change predicted by the Framingham model. These results suggest that, for the risk factors considered here, the 10-year probability of developing CHD among Iowa law enforcement personnel is similar to that found in the Framingham population.

Adult↗