Calculation of induced current densities and specific absorption rates (SAR) for pregnant women exposed to hand-held metal detectors

Abstract

The finite difference time domain (FDTD) method in combination with a well established frequency scaling method was used to calculate the internal fields and current densities induced in a simple model of a pregnant woman and her foetus, when exposed to hand-held metal detectors. The pregnant woman and foetus were modelled using a simple semi-heterogeneous model in 10 mm resolution, consisting of three different types of tissue. The model is based on the scanned shape of a pregnant woman in the 34th gestational week. Nine different representative models of hand-held metal detectors operating in the frequency range from 8 kHz to 2 MHz were evaluated. The metal detectors were placed directly on the abdomen of the computational model with a spacing of 1 cm. Both the induced current density and the specific absorption rate (SAR) are well below the recommended limits for exposure of the general public published in the ICNIRP Guidelines and the IEEE C95.1 Standard. The highest current density is 8.3 mA m(-2) and the highest SAR is 26.5 microW kg(-1). Compared to the limits for the induced current density recommended in the ICNIRP Guidelines, a minimum safety factor of 3 exists. Compared to the IEEE C95. 1 Standard, a safety factor of 60 000 for the specific absorption rate was found. Based on the very low specific absorption rate and an induced current density below the recommended exposure limits, significant temperature rise or nerve stimulation in the pregnant woman or in the foetus can be excluded.

Assessing the Electromagnetic Fields Generated By a Radiofrequency MRI Body Coil at 64 MHz: Defeaturing Versus Accuracy

“…Different applications may require different levels of field accuracy in specific locations. An accurate assessment of the electromagnetic field inside the phantom is important when evaluating SAR levels as overall safety of the patient [9][10][11][12][13][14][15][16] or the RFinduced heating in patients with conductive medical devices that are fully implanted in the body [22] like deep brain stimulators [8,17,18] or pacemakers [1,20,21]. Conversely, an accurate representation of ||E ⃗ || in the space between the coil and the load is important when evaluating safety in patients with conductive medical devices that are partially implanted or in contact with the skin [7,23].…”

“…1) Electromagnetic numerical implementation-EM simulations were implemented with the commercially available software xFdtd (Remcom Inc., State College, PA) which has been extensively used in literature for MRI RF-safety evaluation [16,18,42,43].…”

Development of physical 3D model of maternal-fetal to study light interaction through tissue

“…This model was developed by [2] with the fetus was modeled as a sphere with diameter of 20cm. Next, [3] using hybrid models by combining the voxel-based math model of embryo and fetus at different stages with anatomically realistic whole body adult female model [4] to realize the pregnant woman model.…”

SAF values for internal photon emitters calculated for the RPI-P pregnant-female models using Monte Carlo methods

“…10 Kainz et al developed a semi-heterogeneous pregnant woman model based on laser scanned data and mathematical equations in 2003. 11 Kainz et al also extended the pregnant woman model into each month in 2005. 12 Dimbylow combined the fetuses defined by Chen with a voxel-based adult female model called NAOMI in 2006.…”