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PubMed2005

Does provider adherence to a treatment guideline change clinical outcomes for patients with bipolar disorder? Results from the Texas Medication Algorithm Project.

BACKGROUND: Despite increasing adoption of clinical practice guidelines in psychiatry, there is little measurement of provider implementation of these recommendations, and the resulting impact on clinical outcomes. The current study describes one effort to measure these relationships in a cohort of public sector out-patients with bipolar disorder. METHOD: Participants were enrolled in the algorithm intervention of the Texas Medication Algorithm Project (TMAP). Study methods and the adherence scoring algorithm have been described elsewhere. The current paper addresses the relationships between patient characteristics, provider experience with the algorithm, provider adherence, and clinical outcomes. Measurement of provider adherence includes evaluation of visit frequency, medication choice and dosing, and response to patient symptoms. An exploratory composite 'adherence by visit' score was developed for these analyses. RESULTS: A total of 1948 visits from 141 subjects were evaluated, and utilized a two-stage declining effects model. Providers with more experience using the algorithm tended to adhere less to treatment recommendations. Few patient factors significantly impacted provider adherence. Increased adherence to algorithm recommendations was associated with larger decreases in overall psychiatric symptoms and depressive symptoms over time, but did not impact either immediate or long-term reductions in manic symptoms. CONCLUSIONS: Greater provider adherence to treatment guideline recommendations was associated with greater reductions in depressive symptoms and overall psychiatric symptoms over time. Additional research is needed to refine measurement and to further clarify these relationships.

Adolescent↗

PubMed1997

Image processing assessment of femoral osteopenia.

Visual assessment of femoral osteopenia (the radiographic presentation of osteoporosis) is unreliable. Many of the short-comings of observer grading can be overcome by digital image analysis. Our group has developed algorithms to make automatic assessment of osteopenia from clinical radiographs. Texture Analysis Models (TA) commonly used in image analysis were investigated as measures of osteopenia. Unlike densitometric methods, TA characterizes properties of the structure of the image (ie, trabecular patterns). A group of women were analyzed whose subjects ranged from those at risk of osteoporosis (n = 24) to normal (n = 40). Using an IBM PC, frame-grabber, camera, and light-box, we appraised five statistical TA algorithms for assessment of the femoral neck in standard pelvic radiographs: (1) Fractal Signature (FS) describes the image's fractal nature. (2) Auto-Correlation of unaltered and Sobel Edge Transformed images (ACSE) measures image spatial self-similarity. (3) Co-occurrence Matrices (CM) gives the joint probability of greylevels with distance/direction and describes statistical relationships of image variation. (4) Textural Spectrum (TS) neighborhood pixel relationships measure regional directional and pixel-inversion properties. (5) Eular Numbers (EN) describe texture by properties (such as connectivity) of binary images. Good reproducibility from repeated analysis of radiographs was shown using both paired t-tests and Altman-Bland's methods. We have shown a correlation between femoral neck bone mineral density (BMD-the "gold standard" of osteoporosis assessment) and textural measures for all five algorithms. Significant measures of osteopenia were: ACSE (r = 0.6, P < .001), CM (r = -0.69, P < .001), FS (r = 0.35, P < .01), TS (r = 0.52, P < .001) and EN (r = -0.39, P < .01). Relationships were also found between textural characteristics and age/weight. TA techniques characterize the radiographic changes of bone in osteoporosis. Technology based on these ideas may have a place alongside BMD measurements in the assessment of this condition.

Absorptiometry, Photon↗

PubMed2003

Testing and optimization of a semiautomatic prostate boundary segmentation algorithm using virtual operators.

Image analysis tasks such as size measurement and landmark-based registration require the user to select control points in an image. The output of such algorithms depends on the choice of control points. Since the choice of points varies from one user to the next, the requirement for user input introduces variability into the output of the algorithm. In order to test and/or optimize such algorithms, it is necessary to assess the multiplicity of outputs generated by the algorithm in response to a large set of inputs; however, the input of data requires substantial time and effort from multiple users. In this paper we describe a method to automate the testing and optimization of algorithms using "virtual operators," which consist of a set of spatial distributions describing how actual users select control points in an image. In order to construct the virtual operator, multiple users must repeatedly select control points in the image on which testing is to be performed. Once virtual operators are generated, control points for initializing the algorithm can be generated from them using a random number generator. Although an initial investment of time is required from the users in order to construct the virtual operator, testing and optimization of the algorithm can be done without further user interaction. We illustrate the construction and use of virtual operators by testing and optimizing our prostate boundary segmentation algorithm. The algorithm requires the user to select four control points on the prostate as input.

Algorithms↗

PubMed2004

Algorithmic information for interval maps with an indifferent fixed point and infinite invariant measure.

Measuring the average information that is necessary to describe the behavior of a dynamical system leads to a generalization of the Kolmogorov-Sinai entropy. This is particularly interesting when the system has null entropy and the information increases less than linearly with respect to time. We consider a class of maps of the interval with an indifferent fixed point at the origin and an infinite natural invariant measure. We show that the average information that is necessary to describe the behavior of the orbits increases with time n approximately as nalpha, where alpha < 1 depends only on the asymptotic behavior of the map near the origin.

Journal Article↗

PubMed2004

Phase unwrapping for 2-D blind deconvolution of ultrasound images.

In most approaches to the problem of two-dimensional homomorphic deconvolution of ultrasound images, the estimation of a corresponding point-spread function (PSF) is necessarily the first stage in the process of image restoration. This estimation is usually performed in the Fourier domain by either successive or simultaneous estimation of the amplitude and phase of the Fourier transform (FT) of the PSE This paper addresses the problem of recovering the FT-phase of the PSF, which is an important reconstruction problem by itself. The purpose of this paper is twofold. First, it provides a theoretical framework, establishing that the FT-phase of the PSF can be effectively estimated by a proper smoothing of the FT-phase of the appropriate radio-frequency (RF) image. Second, it presents a novel approach to the estimation of the FT-phase of the PSF, by solving a continuous Poisson equation over a predefined smooth subspace, in contrast to the discrete Poisson equation solver used for the classical least mean squares phase unwrapping algorithms, followed by a smoothing procedure. The proposed approach is possible due to the distinct properties of the FT-phases, among which the most important property is the availability of precise values of their partial derivatives. This property overcomes the main disadvantage of the discrete schemes, which routinely use wrapped (principal) values of the phase in order to approximate its partial derivatives. Since such an approximation is feasible subject to the restriction that the partial phase differences do not exceed pi in absolute value, the discrete schemes perform satisfactory only for few practical situations. The proposed approach is shown to be independent of this restriction and, thus, it performs for a wider class of the phases with significantly lower errors. The main advantages of the novel method over the algorithms based on discrete schemes are demonstrated in a series of computer simulations and for in vivo measurements.

Algorithms↗

PubMed2005

Determination of polar stratospheric cloud particle refractive indices by use of in situ optical measurements and T-matrix calculations.

A new algorithm to infer structural parameters such as refractive index and asphericity of cloud particles has been developed by use of in situ observations taken by a laser backscattersonde and an optical particle counter during balloon stratospheric flights. All three main particles, liquid, ice, and a no-ice solid (NAT, nitric acid trihydrate) of polar stratospheric clouds, were observed during two winter flights performed from Kiruna, Sweden. The technique is based on use of the T-matrix code developed for aspherical particles to calculate the backscattering coefficient and particle depolarizing properties on the basis of size distribution and concentration measurements. The results of the calculations are compared with observations to estimated refractive indices and particle asphericity. The method has also been used in cases when the liquid and solid phases coexist with comparable influence on the optical behavior of the cloud to estimate refractive indices. The main results prove that the index of refraction for NAT particles is in the range of 1.37-1.45 at 532 nm. Such particles would be slightly prolate spheroids. The calculated refractive indices for liquid and ice particles are 1.51-1.55 and 1.31-1.33, respectively. The results for solid particles confirm previous measurements taken in Antarctica during 1992 and obtained by a comparison of lidar and optical particle counter data.

Algorithms↗

PubMed1998

Algorithms for radiological image registration and their clinical application.

This paper reviews recent work in radiological image registration and provides a classification of image registration by type of transformation and by methods employed to compute the transformation. The former includes transformation of 2D images to 2D images of the same individual, transformation of 3D images to 3D images of the same individual, transformation of images to an atlas or model, transformation of images acquired from a number of individuals, transformations for image guided interventions including 2D to 3D registration and finally tissue deformation in image guided interventions. Recent work on computing transformations for registration using corresponding landmark based registration, surface based registration and voxel similarity measures, including entropy based measures, are reviewed and compared. Recently fully automated algorithms based on voxel similarity measures and, in particular, mutual information have been shown to be accurate and robust at registering images of the head when the rigid body assumption is valid. Two approaches to modelling soft tissue deformation for applications in image guided interventions are described. Validation of complex processing tasks such as image registration is vital if these algorithms are to be used in clinical practice. Three alternative validation strategies are presented. These methods are finding application outside the original domain of radiological imaging.

Algorithms↗

PubMed2002

Optical coherence tomography for in situ monitoring of laser corneal ablation.

OBJECTIVE: To improve the precision of refractive surgery, a new approach for determination of the removed corneal thickness profile in situ with laser ablation by optical coherence tomography (OCT) is developed. STUDY DESIGN/MATERIALS AND METHODS: The traditional method for precision (less than 10 microm) measurements of intraocular distances is based on the use of the reflected component of probing radiation. This component is characterized by a small range of operating angles between a probing beam and a normal to the surface under study. To enhance this range of operating angles we suggest using a light component backscattered from a biological object. This will enable precision measurements over the entire surface of the cornea without any changes in the orientation between a probing beam and the eye, a necessary condition for in situ monitoring of laser refraction correction in the eye. We suggest a specially developed algorithm of OCT signal processing to measure the corneal thickness by the backscattered light component for a single longitudinal scan (A scan). The corneal thickness profile is obtained by a series of such A scans acquired by successively scanning a probing beam along the corneal surface. The thickness profile of removed layer is determined by changes in the corneal thickness profile in the process of ablation. When the cornea is ablated by a beam with a fixed transverse profile, we propose using integral characteristics of the ablated layer profile, for example, the maximum ablation depth, as criteria of changes in refractive power of the eye. The measurement precision by these characteristics is considerably higher than by a single A scan. Since the cornea is a poorly scattering medium, the Fourier filtering is employed to increase reliability and precision of the method. Model experiments on monitoring the ablation process in a lavsan film and ex vivo human cornea are described. Preliminary experiments on in vivo measurements of human corneal thickness are performed. RESULTS: In model experiments the precision of measurement of laser ablation depth by one A scan was 5-20 microm, depending on the signal-to-noise ratio (SNR), whereas the precision of measurement of laser ablation depth as the integral characteristic of the ablated layer profile was 0.3-5 microm. The experimental results showed that at small SNR Fourier filtering might considerably increase reliability and precision of measurements. When SNR is high, the measurement precision does not change. The precision of measurements of the corneal thickness in preliminary in vivo experiments was higher than in ex vivo experiments. This factor is very promising for application of the method suggested herein in refractive surgery.

Fiber Optic Technology↗

PubMed1991

Estimation of time-varying respiratory mechanical parameters by recursive least squares.

Continuous estimation of time-varying respiratory mechanical parameters is required to fully characterize the time course of bronchoconstriction. To achieve such estimation, we developed an estimator that uses the recursive linear least-squares algorithm to fit the equation Ptr = RV + EV + K to measurements of tracheal pressure (Ptr) and flow (V). The volume (V) is obtained by numerical integration of V. The estimator has a finite memory with length into the past at each point in time that varies inversely with the difference between the current measurement of Ptr and that predicted by the model, to allow the algorithm to track rapidly varying parameters (R, E, and K). V usually exhibits significant drift and must be corrected. Of the several correction methods investigated, subtraction of the recursively weighted average of V before integration to V was found to perform best. The estimator was tested on simulated noisy data where it successfully followed a fivefold increase in R and a twofold increase in E occurring over 10 s. Three dogs and two cats were anesthetized, paralyzed, tracheostomized, and challenged with a bolus of methacholine (approximately 13 mg/kg iv). Increases of 3- to 10-fold were observed in R and 2- to 3-fold in E, beginning within 10-40 s after the bolus injection. In some animals we found that the increase in E occurred more slowly than that in R, which the V signal suggested was due to dynamic hyperinflation of the lungs. These results demonstrate that our recursive estimator is able to track rapid changes in respiratory mechanical parameters during bronchoconstrictor challenge.

Airway Resistance↗

PubMed2000

[Diagnosis of short-term subclinical shifts in the level of humoral parameters].

Algorithm of evaluating the blood humoral parameters has been theoretically and experimentally validated and clinically tried with due consideration for the circaseptan fluctuations in their levels. Probability of deviations from the normal range of values depends on the number of measurements making use of the suggested algorithm.

Adult↗

PubMed2003

Deconvolution algorithm based on automatic cutoff frequency selection for EPR imaging.

The large line-width associated with electron paramagnetic resonance imaging (EPRI) requires effective algorithms to deconvolve the true spatial profiles of spins from the measured projection data. The commonly used Fourier transform (FT) deconvolution algorithm is easy to implement but suffers from the division-by-zero problem. As a result, a couple of parameters are used to control the deconvolution performance. However, this is inconvenient and the deconvolution results are subject to the experience of the operators. In the present work we examined FT deconvolution for EPRI, and proposed an automatic algorithm to determine the cutoff frequency by calculating the piecewise variance of the division result of the Fourier amplitude spectra. The deconvolution algorithm and the filtered back-projection image reconstruction algorithm were implemented and validated using 3D phantom and in vivo imaging data. It was clearly observed that the image resolution improved after deconvolution with the proposed algorithm.

Algorithms↗

PubMed2000

Artifact reduction in magnetoneurography based on time-delayed second-order correlations.

Artifacts in magnetoneurography data due to endogenous biological noise sources, like the cardiac signal, can be four orders of magnitude higher than the signal of interest. Therefore, it is important to establish effective artifact reduction methods. We propose a blind source separation algorithm using only second-order temporal correlations for cleaning biomagnetic measurements of evoked responses in the peripheral nervous system. The algorithm showed its efficiency by eliminating disturbances originating from biological and technical noise sources and successfully extracting the signal of interest. This yields a significant improvement of the neuro-magnetic source analysis.

Algorithms↗

PubMed1986

Optimal detection of the progression of coronary artery disease: comparison of methods suitable for risk factor intervention trials.

To assess the best method of quantitating progression of coronary disease, we studied four measurements in 114 coronary segments from 35 medically treated patients from whom angiograms were obtained 5 years apart. Only stenoses of less than 70% that were visualized in nearly identical projections on both angiograms were evaluated. Vessel edges were measured by use of catheter calibration and an automated computer algorithm yielding two "absolute dimensions" (mean and minimum diameters) and two measurements (percent stenosis and atheroma area) that required a "normal reference" diameter. The coefficient of variation for repeated segment measurements was less for mean and minimum diameter than for percent stenosis and area of atheroma. The best measure of progression of coronary disease as determined by t test comparison of different methods was the change in mean diameter over time (6.7 +/- 14.1% decrease), whether calculated on a per coronary segment or per patient basis (p less than .001). Based on this measurement and its standard deviation of progression of coronary disease in this patient subset with relatively benign disease, it is estimated that 470 patients per group would be required for an interventional study to demonstrate a 33% reduction in disease progression (207 patients for 50% reduction) at a 95% confidence level and 90% power.

Cardiac Catheterization↗

PubMed1995

A comparative study of three fast algorithms to estimate cerebral blood flow and distribution volume using N-isopropyl-p-[123I]iodoamphetamine and two SPECT scans.

To estimate regional cerebral blood flow (rCBF) and distribution volume (Vd) using N-isopropyl-p-[123]iodoamphetamine (IMP) and two SPECT data (early and delayed data) measured at two discrete time points, three fast algorithms are implemented, which are the table look-up method (TLU), the linear least-squares fitting method (LLSF), and the linear search method (LS). A two-compartment model was used as the IMP kinetic model. These algorithms were applied to the early and delayed data measured by the two scan protocols, t1 = 12 min, t2 = 54 min (scan A) and t1 = 12 min, t2 = 85 min (scan B). The estimated rCBF and Vd values using the present three algorithms were in good agreement with those using the nonlinear least-squares fitting technique and dynamic SPECT data. The quantitative value and signal to noise (S/N) ratio of rCBF images by TLU was not changed whether scan A or scan B was used. However, the S/N of the Vd image by TLU using scan B improved over that using scan A. The same tendency was observed in the results of LLSF and LS. The CPU times for the parametric imaging of CBF and Vd images for one slice (64 x 64 matrix) were 0.04, 0.09, and 0.14 s using TLU, LLSF, and LS, respectively. In conclusion, the present three algorithms gave reasonably accurate estimates of rCBF and Vd using two SPECT data, and are well suited for parametric imaging because of their good statistical properties and high computational efficiency.

Algorithms↗

PubMed1995

Quantitative analysis of trabecular microstructure by 400 MHz nuclear magnetic resonance imaging.

A new approach for the quantitative analysis of trabecular microstructure, based on high-field proton nuclear magnetic resonance (NMR) imaging, is presented. NMR is ideal because it provides high contrast between the marrow proton signal and the bone, which appears with background intensity. Images from 1 cm3 defatted specimens of trabecular bone, suspended in water doped with 1 mM Gd(DTPA) to shorten T1 to about 300 ms, can be obtained at a resolution on the order of 30-50 microns and slice thickness of 150 microns, in 10 minutes at 400 MHz proton frequency. Digital image processing algorithms were designed and evaluated for the measurement of bone area fraction, perimeter length, mean trabecular thickness, and separation. Bone area fraction derived from the NMR images was found to be in excellent agreement with bone volume fraction measured independently (slope = 0.96, r2 = 0.924, p < 0.0001). Errors in the mean trabecular thickness and separation were < 6%. The effects of finite imaging slice thickness and signal-to-noise ratio (SNR) were also evaluated. The data suggest a resolution of 50 x 50 x 200 microns 3 and an SNR on the order of 10 to provide safe margins for precise and accurate structural analysis by means of the algorithms presented in this paper. The method allows simultaneous measurement at multiple locations within the specimen volume without the need for physical sectioning.

Algorithms↗

PubMedDate not supplied

Effect of reversible hypoperfusion on left ventricular volumes measured with gated SPECT at rest and after adenosine infusion.

BACKGROUND: The aims of this study were to assess the degree of postischemic left ventricular (LV) dilatation after adenosine stress and to determine the extent to which LV volumes measured with gated single photon emission computed tomography (SPECT) correspond to those obtained by echocardiography. METHODS: Eight-frame gated SPECT with a 2-day technetium-99m tetrofosmin acquisition protocol was used. End-diastolic (EDV) and end-systolic (ESV) volumes were measured automatically with the quantitative gated SPECT algorithm. Reversible myocardial hypoperfusion was evaluated with a 16-segment, 4-point perfusion score model. LV volumes at rest were also measured with echocardiography by use of the biplane Simpson rule. RESULTS: Twenty-two patients (group 1) showed normal perfusion and normal LV systolic function, whereas 33 patients (group 2) had evident coronary heart disease with reversible hypoperfusion. Patients in group 2 had greater EDV and ESV than those in group 1 both at rest and poststress. A greater reduction in ESV from poststress to rest was seen in group 2, which resulted in a slight increase in ejection fraction for patients in this group. The change in ESV from poststress to rest was significantly influenced by the degree of reversible hypoperfusion and by the change in heart rate from poststress to rest. We found a good correlation between LV volumes measured with gated SPECT and echocardiography. CONCLUSION: LV volume measurements with quantitative gated SPECT are comparable to those obtained with echocardiography. Patients with ischemic heart disease have greater LV volumes than patients with normal perfusion. Exercise-augmented adenosine infusion in patients with ischemic heart disease affects ESV more than EDV. This response is partly modulated by the degree of reversible hypoperfusion and possibly represents a minor degree of poststress stunning.

Adenosine↗

PubMed1994

How to find a wombmate: validation of an algorithm to identify twin pairs in Linked Birth/Infant Death Files.

Linked Birth/Infant Death Files available from the National Center for Health Statistics identify an infant as a twin, but do not identify twin pairs. An algorithm based on maternal, paternal, and infant characteristics has been used to identify twin pairs, but the validity of this algorithm has never been tested. The Missouri linked birth/infant death file from 1980 to 1990 identifies twin pairs by a sequence number. The authors tested the rate and accuracy with which the algorithm identified true pairs in the Missouri file and whether estimates of risk and possible risk factors calculated from pairs of twins identified by the algorithm agreed with these characteristics as calculated from known twin pairs. The algorithm identified 96% (8,273 of 8,620) of true pairs and one false pair. Despite incomplete pair identification, and even identification of a false pair, estimates from the subset identified by the algorithm generally agreed well with characteristics measured from all twin pairs. Nonetheless, incorporation of a multiple birth sequence number into Linked Birth/Infant Death Files would enhance their utility.

Algorithms↗

PubMed1997

Extension of a numerical algorithm to proton dose calculations. I. Comparisons with Monte Carlo simulations.

A numerical algorithm originally developed for electron dose calculations [Med. Phys. 21, 1591 (1994)] has been modified for use with proton beams. The algorithm recursively propagates the proton distribution in energy, angle, and space from one level in an absorbing medium to another at slightly greater depth until all protons stop. Vavilov's theory is used to predict, at any point in the absorber, the broadening of the primary proton energy-spectrum. Moliere's theory is applied to describe the angular distribution, and it is shown that the Gaussian first term of Moliere's series expansion is of sufficient accuracy for dose calculations. These multiple scattering and energy loss distributions are sampled using equal probability spacing to optimize computational speed while maintaining calculational accuracy. Inelastic nuclear collisions along the proton trajectories are modeled by a simple exponential extinction. Predictions of the algorithm for absolute dose deposition by a 160 MeV initially monoenergetic proton beam are compared with the results of Monte Carlo simulations performed with the PTRAN code. The excellent level of agreement between the results of these two methods of dose calculation (< 5% dose and < 3 mm spatial deviations) demonstrate that dose deposition from proton beams may be computed to high accuracy using this algorithm without the need for extensive empirical measurement as input.

Algorithms↗