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Biomedical subjects

M Lax

Publications and source records attributed to M Lax.

At least 19 recordsLinked to original sources
PubMed2003

Anomalous diffraction of light with geometrical path statistics of rays and a Gaussian ray approximation.

The anomalous-diffraction theory (ADT) of extinction of light by soft particles is shown to be determined by a statistical distribution of the geometrical paths of individual rays inside the particles. Light extinction depends on the mean and the mean-squared geometrical paths of the rays. Analytical formulas for optical efficiencies from a Gaussian distribution of the geometrical paths of rays are derived. This Gaussian ray approximation reduces to the exact ADT in the intermediate case of light scattering for an arbitrary soft particle and describes well the extinction of light from a system of randomly oriented and (or) polydisperse particles. The implications for probing of the sizes and shapes of particles by light extinction are discussed.

Journal Article↗
PubMed2002

Photon migration in turbid media using a cumulant approximation to radiative transfer.

A photon transport model for light migration in turbid media based on a cumulant approximation to radiative transfer is presented for image reconstruction inside an infinite medium or a bounded medium with a planar geometry. This model treats weak inhomogeneities through a Born approximation of the Boltzmann radiative transfer equation and uses the second-order cumulant solution of photon density to the Boltzmann equation as the Green's function for the uniform background. It provides the correct behavior of photon migration at early times and reduces at long times to the center-moved diffusion approximation. At early times, it agrees much better with the result from the Monte Carlo simulation than the diffusion approximation. Both approximations agree well with the Monte Carlo simulation at later times. The weight function for image reconstruction under this proposed model is shown to have a strong dependence at both early and later times on absorption and/or scattering inhomogeneities located in the propagation direction of and close to the source, or in the field of view of and close to the detector. This effect originates from the initial ballistic motion of incident photons, which is substantially underestimated by the diffusion approximation.

Journal Article↗
PubMed2001

Time-resolved Fourier optical diffuse tomography.

Time-resolved Fourier optical diffuse tomography is a novel approach for imaging of objects in a highly scattering turbid medium with use of an incident (near) plane wave. The theory of the propagation of spatial Fourier components of the scattered wave field is presented, along with a fast algorithm for three-dimensional reconstruction in a parallel planar geometry. Examples of successful reconstructions of simulated hidden absorptive or scattering objects embedded inside a human-tissue-like semi-infinite turbid medium are provided.

Algorithms↗
PubMed2001

Clinical and imaging correlates of response to treatment with infliximab in patients with ankylosing spondylitis.

OBJECTIVES: Ankylosing spondylitis (AS) is a chronic disease leading to progressive spinal ankylosis and deformity. The aims of this study were to (1) determine whether infliximab is an effective treatment for AS patients who have failed conventional treatment; (2) identify any baseline clinical variables that can be associated with responsiveness to treatment; and (3) resolve whether the clinical response correlated with changes from baseline inflammatory changes on magnetic resonance imaging (MRI). METHODS: Twenty-one patients who met the modified New York criteria for AS (M:F 18:3) were enrolled in this open labeled study. The mean age was 37.9+/-7.9 years and mean disease duration was 8.69+/-6.58 years. Patients received infliximab at a dose of 5 mg/kg by intravenous infusion over 2 hours at 0, 2, 6, weeks. Nine functional variables were measured [i.e., Bath AS Disease Activity Index (BASDAI), Bath AS Functional Index (BASFI) etc.], 6 clinimetrics (chest expansion, finger to floor, etc.), and inflammatory markers in the peripheral blood at baseline and each subsequent visit. Primary response to treatment was defined as a > 20% response in 5/9 functional variables. A subset of 9 consecutive patients was selected for MRI scans before and after infusions. RESULTS: Eighteen patients were available for assessment at week 14 having received 3 infusions (wks 0, 2, 6). There was > 60% improvement in functional variables, i.e., BASDAI, BASFI, Health Assessment Questionnaire, fatigue, and spinal and total body pain. Clinimetric scores selectively improved, e.g., chest expansion (p < 0.021) by 14 weeks. ESR, CRP and haptoglobin all showed significant improvement at 6 weeks and were maintained to the 14 week assessment point. Imaging studies showed improvement in all patients studied including those with advanced disease. Three patients developed headache during the infusions. Infliximab was effective in all, but degree of response varied. Very good responders were distinguished from good responders by shorter duration of disease and better baseline clinimetric scores. CONCLUSIONS: Infliximab was an effective treatment for AS in a short term trial. Longterm control of symptoms and potential alteration in clinical course of disease will require longterm assessment.

Achilles Tendon↗
PubMed2000

Analytical solution of the polarized photon transport equation in an infinite uniform medium using cumulant expansion.

An analytical solution for time-dependent polarized photon transport equation in an infinite uniform isotropic medium is studied using a circular representation of the polarized light and expansion in the generalized spherical functions. We extend our cumulant approach for solving the scalar (unpolarized) photon transport equation to the vector (polarized) case. As before, an exact angular distribution is obtained and a cumulant expansion is derived for the polarized photon distribution function. By a cutoff at the second cumulant order, a Gaussian analytical approximate expression of the polarized photon spatial distribution is obtained as a function of the direction of light and time, whose average center position and half-width are always exact. The central limit theorem claims that this spatial distribution approaches accuracy in detail when the number of collisions or time becomes large. The analytical expression of cumulants up to an arbitrary high order is also derived, which can be used for calculating a more accurate polarized photon distribution through a numerical Fourier transform. Contrary to what occurs in other approximation techniques, truncation of the cumulant expansion at order n is exact at that order and cumulants up to and including order n remain unchanged when higher orders are added, at least as applied in our photon transport equation.

Journal Article↗
PubMed2000

Cumulant solution of the elastic boltzmann transport equation in an infinite uniform medium

We consider an analytical solution of the time-dependent elastic Boltzmann transport equation in an infinite uniform isotropic medium with an arbitrary phase function. We obtain (1) the exact distribution in angle, (2) the exact first and second spatial cumulants at any angle, and (3) an approximate combined distribution in position and angle and a spatial distribution whose central position and half-width of spread are always exact. The resulting Gaussian distribution has a center that advances in time, and an ellipsoidal contour that grows and changes shape providing a clear picture of the time evolution of the particle migration from near ballistic, through snakelike and into the final diffusive regime.

Journal Article↗
PubMed2000

The fetish of the objective finding.

Pressure is mounting for clinicians to rely solely on objective measures when evaluating workers with possible work-related disease. These measures are intended to largely supplant the worker's history as sources of information regarding diagnosis, work relatedness, and extent of disability. While seeming to promote more accurate and neutral evaluation methods, the underlying agenda is to reduce business costs by denying work-related illness and disability. Promoting the view of occupational health as the province of technical experts, the campaign for the objective finding silences workers as unqualified to comment. The methods proposed to enhance objectivity also suffer from significant specific shortcomings. To resist efforts to fetishize the objective finding, clinicians need to recognize the subjective elements of objective methods as well as the objective value of subjective data. This requires recognition of the central role of workers and histories in the clinical evaluation process.

Journal Article↗
PubMed1997

Relationship between prenatal anxiety and perinatal outcome in nulliparous women: a prospective study.

Nulliparous women with singleton gestation were assessed prospectively for anxiety levels with the State-Trait Anxiety Inventory, which measured state (situational and transitional) and trait (dispositional and stable) anxiety, with high scores indicating high anxiety. Bivariate and multivariate methods were used for data analysis. Anxiety assessments (n = 239) were obtained in 88 women at different stages of gestation. Mean anxiety scores were lowest at 22 to 26 weeks. A woman's successive scores were highly correlated. The trait anxiety (A-T) scores were higher for married women. A positive correlation was present between anxiety scores and gestational age at delivery. Low A-T scores correlated with low birthweight, preterm delivery, and chorioamnionitis. High state anxiety (A-S) levels correlated with the presence of meconium in the amniotic fluid and neonatal congenital abnormalities. Postdate delivery also was associated with higher although statistically insignificant anxiety scores. Women who presented to the labor and delivery room for various complaints had higher A-S and A-T levels. Maternal anxiety level was associated with adverse perinatal outcome; specifically, prematurity and low birthweight correlated with low A-T levels.

Adult↗
PubMed1996

Time-resolved optical diffusion tomographic image reconstruction in highly scattering turbid media.

The image of an object hidden in highly scattering media was reconstructed using a fast, noise-resistant algorithm newly applied to diffusion tomography. A pulsed light source producing scattered and transmitted light is examined at multiple times. Multiple source detector pairs around the medium are used to obtain data in many different directions. An inverse scattering algorithm with nonuniform regularization achieves rapid inversion convergence.

Journal Article↗
PubMed1992

Health hazard of poorly regulated exposure during manufacture of cemented tungsten carbides and cobalt.

Forty two of 125 former workers in a factory in Syracuse, New York, which manufactured hard metal parts from tungsten carbide and cobalt, were studied by chest radiographs, spirometry, and plethysmographically determined lung volumes. The plant was closed in 1982 and the studies were performed in 1983-5. Recorded measurements of carbide dust concentrations were only mildly excessive by modern standards, but deceitful efforts to reduce the apparent concentration of dust were known to have occurred during an inspection by the Occupational Safety and Health Administration. Lung biopsies in four cases in the study and necropsy in one of the 83 cases not studied during life showed giant cell interstitial pneumonia and appreciable concentrations of tungsten carbide. This information indicates that exposure was substantial. Four workers had evidence of pulmonary fibrosis by chest radiographs; two of these workers had normal pulmonary function. Fourteen had abnormal pulmonary function, five of whom had a restrictive pattern, eight a pattern of air trapping, and one a combined pattern. Thus radiographic, or functional abnormalities, or both occurred in 16 of the 42 cases studied. No correlation with duration of exposure was established. Progressive clinically important disease (one fatal) has been found in four ex-workers, two in each of the restrictive and air trapping groups. These findings suggest that poorly regulated dust concentrations in a hard metals factory possibly cause pulmonary abnormalities and sometimes severe illness.

Adult↗