Weighted-peak assessment of occupational exposure due to MRI gradient fields and movements in a nonhomogeneous static magnetic field.

PURPOSE: A procedure for assessing occupational exposure due to magnetic resonance imaging (MRI) gradient magnetic fields and movement-induced effects in the static magnetic field is proposed and tested. METHODS: The procedure was based on the application of the weighted-peak method in time domain. It was tested in two 1.5 T total-body and one 3 T head-only scanner MRI facilities in Rome (Italy). Exposure due to switched gradient fields was evaluated in locations inside the magnet room where operators usually stay during particular medical procedures (e.g., cardiac examinations of anesthetized patients); MRI sequences were selected to approach as far as possible a representative worst case exposure scenario. Movement-induced effects were evaluated considering the actual movements of volunteer operators during work activity, by measuring the perceived time-varying magnetic field by a head-worn probe. The analysis of results was based on ICNIRP 1998 and 2010 guidelines, following a weighted-peak approach and including an ad hoc extension to the latter ones, needed to verify compliance in the frequency range 0-1 Hz. RESULTS: Exposures due to switched gradient fields in 1.5 T MRI scanners mostly resulted noncompliant with ICNIRP 1998 occupational reference levels, being, at the same time, always compliant with ICNIRP 2010 ones. Gradient field levels and ICNIRP indexes were significantly lower for the 3 T unit, due to its small dimensions, as that unit was a head-only scanner. Movement-induced effects resulted potentially noncompliant only in the case the operator moved the head inside the bore of a 1.5 T scanner. CONCLUSIONS: The procedure had proven to be a sound approach to exposure assessment in MRI. Its testing allowed to draw some general considerations about exposures to gradient magnetic fields and movement-induced effects.

Exposure to electromagnetic fields from laptop use of "laptop" computers.

Portable computers are often used at tight contact with the body and therefore are called "laptop." The authors measured electromagnetic fields (EMFs) laptop computers produce and estimated the induced currents in the body, to assess the safety of laptop computers. The authors evaluated 5 commonly used laptop of different brands. They measured EMF exposure produced and, using validated computerized models, the authors exploited the data of one of the laptop computers (LTCs) to estimate the magnetic flux exposure of the user and of the fetus in the womb, when the laptop is used at close contact with the woman's womb. In the LTCs analyzed, EMF values (range 1.8-6 µT) are within International Commission on Non-Ionizing Radiation (NIR) Protection (ICNIRP) guidelines, but are considerably higher than the values recommended by 2 recent guidelines for computer monitors magnetic field emissions, MPR II (Swedish Board for Technical Accreditation) and TCO (Swedish Confederation of Professional Employees), and those considered risky for tumor development. When close to the body, the laptop induces currents that are within 34.2% to 49.8% ICNIRP recommendations, but not negligible, to the adult's body and to the fetus (in pregnant women). On the contrary, the power supply induces strong intracorporal electric current densities in the fetus and in the adult subject, which are respectively 182-263% and 71-483% higher than ICNIRP 98 basic restriction recommended to prevent adverse health effects. Laptop is paradoxically an improper site for the use of a LTC, which consequently should be renamed to not induce customers towards an improper use.

A simplified procedure for dosimetric evaluations on ELF sources with complex waveforms.

The endorsement of the 2004/40 European Directive has renewed the interest in numerical electromagnetic dosimetry. In this field, a need is clearly perceived for dosimetric approaches able to reduce costs and the time necessary for this type of evaluations. In the low and intermediate frequency ranges, EM dosimetry makes use of quasi-static techniques in the frequency domain, which become onerous when dealing with sources emitting multiple frequencies. A procedure is then proposed, able to greatly simplify the numerical process needed to perform a dosimetric calculation involving a complex waveform. The procedure is based on the use of an 'equivalent' field intensity at an arbitrarily chosen 'reference' frequency and allows executing a single-frequency dosimetric evaluation able to take into account, with some approximations, the complete spectral contents of the source signal.

Influence of the surface averaging procedure of the current density in assessing compliance with the ICNIRP low-frequency basic restrictions by means of numerical techniques.

Although the calculation of the surface average of the low-frequency current density distribution over a cross-section of 1 cm2 is required by ICNIRP guidelines, no reference averaging algorithm is indicated, neither in the ICNIRP guidelines nor in the Directive 2004/40/EC that is based on them. The lack of a general standard algorithm that fulfils the ICNIRP guidelines' requirements is particularly critical in the prospective of the 2004/40/EC Directive endorsement, since the compliance to normative limits refers to well-defined procedures. In this paper, two case studies are considered, in which the calculation of the surface average is performed using a simplified approach widely used in the literature and an original averaging procedure. This analysis, aimed at quantifying the expected differences and to single out their sources, shows that the choice of the averaging algorithm represents an important source of uncertainty in the application of the guideline requirements.

Magnetic fields dispersed by high-voltage power lines: an advanced evaluation method based on 3-D models of electrical lines and the territory.

An advanced numerical evaluation tool is proposed for calculating the magnetic flux density dispersed by high-voltage power lines. When compared to existing software packages based on the application of standardized methods, this tool turned out to be particularly suitable for making accurate evaluations on vast portions of the territory, especially when the contribution of numerous aerial and/or underground lines must be taken into account. The aspects of the tool of greatest interest are (1) the interaction with an electronic archive of power lines, from which all the information necessary for the calculation is obtained; (2) the use of three-dimensional models of both the power lines and the territory crossed by these; (3) the direct interfacing with electronic cartography; and finally (4) the use of a representation procedure for the results that is based on contour maps. The tool had proven to be very useful especially for Environmental Impact Assessment procedures relative to new power lines.

High permittivity patch radiator for single and multi-element hyperthermia applicators.

This paper describes a compact, low-profile patch radiator which is the base element for efficient, small-size applicators suitable for superficial hyperthermia. The design criteria and the technological processes involved are presented. The electromagnetic characteristics of the patch element are outlined, and possible application of the radiator are discussed.

Phantom characterization of applicators by liquid-crystal-plate dosimetry.

A method for the determination of the SAR distribution produced by an electromagnetic applicator for localized hyperthermia is described. The procedure for SAR evaluation consists of recording the time evolution of the temperature inside a polyacrylamide phantom by means of thermochromic liquid crystal sheets inserted in it. The technique allows a complete characterization of applicators in a very broad frequency range, using power levels of the order of those needed in real treatments. Criteria for the minimum phantom size and the maximum time duration of the characterization procedure are indicated, which allow a reliable determination of the effective field size and penetration depth of the applicator.

Analysis of electric and magnetic fields leaking from induction heaters.

Results are presented of an investigation on electric and magnetic fields leaking from inductive (magnetic) heaters that are used for thermal processing of high-power electron tubes and lasers in an industrial plant. Measurements of electric and magnetic fields were done using both commercially available and laboratory-developed instrumentation. Isotropic H-field sensors were developed to allow quantitative evaluation of high-intensity magnetic fields. Ten induction heaters with nominal A.C. power ranging from 2.5 kW to 15 kW and operating at frequencies between 300 kHz and 790 kHz were surveyed. Electric field strengths up to 8 kV/m and magnetic field strengths up to 20 A/m were measured.

A simple new method for atrial triggered pacemaker. Preliminary clinical trials.

Inadequacy of cardiac output in the ventricular paced complete heart block is generally related to lack of rate adaptation to varying atrial contribution. The status of the art in leads technology had not yet freed the clinicians from the necessity to use a double lead system (atrial and ventricular) in order to maintain the atrial synchronization. Authors present a new simple catheter with double electrode (atrial receptor and ventricular stimulator) which, connecting to a new conceived VAT generator, let to obtain atrial synchronization with a single catheter-electrode implantation. External units were tried in 22 patients who needed temporary treatment. The results appear to be positive in all cases and encourage the Authors to continue with the task undertaken until the system is made implantable.