Biomedical subjects

J M Stephen

Publications and source records attributed to J M Stephen.

At least 19 recordsLinked to original sources

PubMed2004

MUSIC seeded multi-dipole MEG modeling using the Constrained Start Spatio-Temporal modeling procedure.

The Constrained Start Spatio-Temporal modeling program (CSST) is an objective multi-dipole, multi-start MEG/EEG analysis procedure that randomly selects from 100 to 100,000 initial dipole configurations, and runs a nonlinear simplex search on each of these configurations employing a reduced Chi-square statistic as the minimization criterion, to obtain a set of dipole configurations that best fit the data [Ranken, 2002]. A parallel version of CSST is implemented in IDL and MPI, making CSST usable on a single computer, or on a Linux cluster. We have now developed a multi-resolution version of MUSIC [Mosher, 1992] [Mosher, 1998] that provides an 80% or more reduction in the number of forward calculations needed to obtain results comparable to a 160,000 point MUSIC scan, on a 2 mm grid that defines a brain volume. The multi-resolution MUSIC scan provides an improved set of initial dipole estimates for the CSST analysis. In preliminary tests on real and simulated MEG data, with model orders ranging between 5 and 7 dipoles, the best performance improvements were obtained by mixing in 1 to 3 dipole locations randomly drawn from the best MUSIC locations, with randomly selected locations from the brain volume to complete the selected model order. We have also developed an improved method for sampling the brain volume for initial configurations. These improvements have led to a 75% reduction in the number of starting configurations required to obtain 5-10 best solutions with equal or lower reduced Chi-square values, when compared to the best solutions from the previous version of CSST.

Algorithms↗

PubMed2003

Multidipole analysis of simulated epileptic spikes with real background activity.

This simulated magnetoencephalographic study was designed to determine the variability in source parameters with real subject background activity when applying multidipole spatial-temporal dipole analyses, for which the correct model was compared with undermodeled and overmodeled cases. The simulated sources were created from patches of the cortical surface of each subject's MRI. One- and two-source frontal lobe spikes were generated in two cortical regions seen commonly in frontal lobe epilepsy patients tested at our site (orbital frontal and premotor cortex). In general, the modeling results were adequate for the correct model order and the correct model order plus one. In addition, if the localization error was less than 10 mm from the simulated source, the peak latency of the spike and orientation were very reliable, but the peak amplitude was not. The additional source in the overmodeled condition, on the other hand, was not localized reliably across the different epochs within subjects. The results suggest that consistency of the spike localization and inconsistency of other sources will allow one to determine reliably the appropriate model order in real data, and therefore determine single and multifocal spike generators.

Action Potentials↗

PubMed1995

Venous thrombosis. Lifting the clouds of misunderstanding.

Deep venous thrombosis (DVT) is often occult and difficult to recognize clinically. The diagnostic approach should begin with color-flow (duplex) ultrasound, noninvasive functional tests such as plethysmography, or both. Because these tests are not 100% sensitive, contrast venography or magnetic resonance imaging may be necessary in a patient with unexplained symptoms. A baseline ventilation-perfusion scan should be considered for any patient with DVT, because there is a high incidence of clinically inapparent pulmonary embolism. In the absence of contraindications, systemic or regional thrombolytic therapy should be considered for every patient with acute DVT. Surgical thrombectomy may be indicated for patients with a large, obstructive proximal thrombus. At a minimum, routine treatment should start with heparin and proceed to oral warfarin (Coumadin, Panwarfin, Sofarin), which should be continued for 3 months. Recurrent DVT after cessation of therapy warrants lifetime use of anticoagulants. A filter should be placed in the inferior vena cava whenever a large, poorly adherent thrombus is identified or when there is progression of thrombosis despite an anticoagulant regimen.

Animals↗

PubMed1995

Chronic pulmonary embolism. Often misdiagnosed, difficult to treat.

Chronic thromboembolic pulmonary hypertension with cor pulmonale is an extremely debilitating disease that (1) is more common than generally recognized, (2) is often misdiagnosed, and (3) is difficult to treat. When a patient has persistent exertional dyspnea with no obvious cause, a ventilation-perfusion scan, echocardiography, and (if indicated) pulmonary angiography should be done. Prevention is especially important because by the time a patient is symptomatic, the disease is already far advanced and hemodynamic reserves are greatly reduced. Prevention of recurrence mandates lifetime anticoagulation and placement of a vena cava filter. The only effective treatment is pulmonary endarterectomy, which is being performed at an increasing number of specialty centers across the United States.

Chronic Disease↗

PubMed1992

Anaphylaxis from administration of intravenous thiamine.

The routine administration of intravenous thiamine in the emergency department has become widespread. Although anaphylaxis from intravenous thiamine is felt to be uncommon, it can be life threatening. The authors present such a case and review the literature regarding this clinical entity. This case of anaphylactic reaction appears to be the first instance reported since 1946 in the US literature. However a review revealed that cases of anaphylaxis from thiamine have been reported with some regularity in the non-US literature. Given the large number of patients treated without side effects, it seems that thiamine is relatively safe. However, this case illustrates that the assumption that thiamine is a drug with a completely innocuous nature is not totally accurate.

Adult↗

PubMed1984

Vitamin D status of the elderly in relation to age and exposure to sunlight.

Vitamin D status was assessed in 929 men and women aged 65 years and over during a nutrition survey lasting 56 weeks. Concentrations of 25-hydroxyvitamin D (25-OHD) measured in plasma samples showed a seasonal variation, being significantly higher in summer than in winter, and correlated with exposure to sunlight as measured by a 'sunshine score'. Regression analysis showed that 25-OHD concentrations fell with advancing age in both men and women and in summer and winter and approached the same value (about 10 ng/ml) at about the age of 95. This fall has implications in the occurrence of osteomalacia among the elderly and the increasing incidence with age of fractures of the femoral neck.

Activities of Daily Living↗

PubMed1975