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PubMed2001

Estimation of population attributable fractions from fitted incidence ratios and exposure survey data, with an application to electromagnetic fields and childhood leukemia.

Standard presentations of epidemiological results focus on incidence-ratio estimates derived from regression models fit to specialized study data. These data are often highly nonrepresentative of populations for which public-health impacts must be evaluated. Basic methods are provided for interval estimation of attributable fractions from model-based incidence-ratio estimates combined with independent survey estimates of the exposure distribution in the target population of interest. These methods are illustrated in estimation of the potential impact of magnetic-field exposures on childhood leukemia in the United States, based on pooled data from 11 case-control studies and a U.S. sample survey of magnetic-field exposures.

Biometry↗
PubMed2001

Coupling of nonlocal potentials to electromagnetic fields.

Nonlocal Hamiltonians are used widely in first-principles quantum calculations; the nonlocality stems from eliminating undesired degrees of freedom, e.g., core electrons. To date, attempts to couple nonlocal systems to external electromagnetic (EM) fields have been heuristic or limited to weak or long wavelength fields. Using Feynman path integrals, we derive an exact, closed-form coupling of arbitrary EM fields to nonlocal systems. Our results justify and clarify the couplings used to date and are essential for systematic computation of linear and especially nonlinear responses.

Journal Article↗
PubMed1993

Collagen production and maturation at the experimental ligament defect stimulated by pulsing electromagnetic fields in rabbits.

Eighty rabbits receiving the square resection (4 x 4 mm) of both patellar ligaments in full thickness at their center were divided into 4 groups, and each group (20 rabbits) were electromagnetically stimulated with different magnetic intensities, 0 (control group), 2, 10, or 50 gauss (G), for 6 hr daily. Pulse frequency and pulse width were 10 Hz and 25 microseconds, respectively. Five animals of each group were sacrificed weekly from 1st to 4th week after operation and the defect tissue was collected for biochemical and ultrastructural evaluations. Before sacrificing, the blood flow of the central portion of patellar defects were measured. Significant increases in blood flow at the defect were observed in 50 G group compared to those of other groups from 2 to 4 weeks after operation. The collagen content in PEMFs groups showed a significant increase compared to that of control group. Furthermore, those increases were higher according to the increase in magnetic intensity. Electronmicroscopically, massive developmental rough endoplasmic reticulum was seen in the fibroblasts at 2 weeks after operation in 50 G group compared to other groups, which suggests the more active collagen production in this group. These results suggest that PEMFs enhanced the blood flow and increased the fibroblasts at the defect. At the same time, PEMFs directly stimulated the collagen production from the fibroblasts, thus accelerate the healing process of the ligament.

Animals↗
PubMed2004

Electromagnetic fields in the human body due to switched transverse gradient coils in MRI.

Magnetic resonance imaging scans impose large gradient magnetic fields on the patient. Modern imaging techniques require this magnetic field to be switched rapidly for good resolution. However, it is believed that this can also lead to the unwanted side effect of peripheral nerve stimulation, which proves to be a limiting factor to the advancement of MRI technology. This paper establishes an analytical model for the fields produced within an MRI scanner by transverse gradient coils of known current density. Expressions are obtained for the magnetic induction vector and the electric field vector, as well as for the surface charge and current densities that are induced on the patient's body. The expressions obtained are general enough to allow the study of any combination of gradient coils whose behaviour can be approximated by Fourier series. For a realistic example coil current density and switching function, it is found that spikes of surface charge density are induced on the patient's body as the gradient field is switched, as well as loops of surface current density that mimic the coil current density. For a 10 mT m(-1) gradient field with a rise time of 100 micros, the magnitude of the radial electric field at the body is found to be 10.3 V m(-1). It is also found that there is a finite limit to radial electric field strength as rise time approaches zero.

Biophysical Phenomena↗