Magnetic Particle Imaging (MPI) benefits from the non-linear magnetization curve of magnetic nano-particles. Magnetic fields applied in this new imaging modality are of frequencies in the kHz-range. Little research has been carried out upon absorbed power and temperature increase caused by time-varying fields in that frequency range. Presented here are temperature distributions in a human body model exposed to magnetic fields of 10 kHz to 100 kHz. A numerical human model has been placed within field generating coils. The finite elements model for the field calculation and the Pennes Bio-heat equation for the temperature distribution with and without perfusion and heat transfer by convection have been used. The results indicate that the absorbed power does lead to local temperature increase but not up to a hazardous level, if certain thresholds for the magnetic fields are considered.

Magnetic Particle Imaging (MPI) is a new tomographic imaging technique based on magnetization of ferromagnetic nano-particles. Magnetic fields of different strengths and frequencies generate and move a field free point (FFP) over the field of view, inducing a signal of the magnetic particles, if present. The magnetic fields induce current densities of high amplitude in the patient's body and deposit an amount of power that might lead to painful warming in the patient's periphery. Based on the specifications of the MPI system, an optimized coil configuration is suggested here, reducing high peak values of current densities and specific absorption rate (SAR), by running the field generating coils of different radius with optimized currents. The results presented here are based on numerical field calculations with a simple cylindrical model, used for the optimization procedure, and the Visible Man data-set, for evaluating the optimization results.

Numerous studies about the effects on human body of high frequency magnetic fields on the one hand and extremely low frequency fields on the other hand have been carried out. This is not the case for the mid frequency range around 100 kHz. When applying external magnetic fields to the human body in this frequency range both electric stimulation and thermal heating effects have to be considered. Magnetic Particle Imaging (MPI), a new imaging technique, and Hyperthermia, a tumor treatment therapy, both apply magnetic fields in a frequency range around 100 kHz. In MPI thermal heating of the body has to be prevented, whereas in Hyperthermia a temperature increase of about 4 K in the target region is desirable. Induced currents may lead to muscle stimulation which is not acceptable above a certain threshold. This paper presents the results of induced current densities and SAR in a numeric field calculation simulation. For the model of the human body the torso of the Visible Man Dataset has been employed, along with the dielectric properties of biological tissues published by Gabriel & Gabriel. The model has been exposed to a sinusoidal magnetic field with an amplitude of 10 mT. The results of the induced current densities and SAR values have been compared with the currently valid official guidelines for limiting exposure to time-varying electric, magnetic and electromagnetic fields by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). It turns out that limits of induced current densities are reached by applying a magnetic flux density of 10 mT and the SAR limit even is exceeded.

Caregiver's education level and child's dental caries in African Americans: a path analytic study.Heima M, Lee W, Milgrom P, Nelson S.Caries Res 2015;49(2):177-83.Woosung Sohn, DDS, PhD, DrPHThe authors conducted path analysis to test various models for an association between caregiver education and child dental caries and its mediating pathways via oral health-related behaviors.This study was supported by the Health Resources and Services Administration (HRSA/MCHB R40- MC07838) and the National Center for Research Resources (CTSC UL1 RR024989).Cross-sectional study (secondary analysis of cross-sectional data collected in a longitudinal study)Level 3: Other evidenceNot applicable

P-waves have been generated by an impacting steel ball on the container wall for fresh concrete. Measurements of the wave propagation velocity during the first 24 hours after concreting have been performed. The results show an influence of the water-cement ratio and of the paste volume on the velocity. The simultaneous retarding action of the superplasticizer used and the effect of the aggregate size appeared.