ABSTRACT:Shield currents or common mode currents affect coil tuning, coil-to-coil coupling in phased array coils, image inhomogeneity, and most importantly can cause serious patient burns. Traditionally in MRI, shield currents are reduced by cable traps; they consist of a wound coaxial cable inductor tuned to the desired resonance frequency by a capacitor between end turns of the coaxial cable ground shield. This method increases losses and effects the overall phase distance between the coil and the preamplifiers. We present a cable trap that does not connect or solder to the cable and is completely splitable, allowing easy fitting over any cable without affecting any coil parameters (tuning or phase length). Multiple cables can be placed inside the shield current trap to simultaneously attenuate the shield currents from up to eight cables, as currently designed. The shield current trap reduces shield currents at 64 MHz by ϳ30 dB.

The phase error in finite-difference (FD) methods is related to the spatial resolution and thus limits the maximum grid size for a desired accuracy. Greater accuracy is typically achieved by defining finer resolutions or implementing higher order methods. Both these techniques require more memory and longer computation times. In this paper, new modified methods are presented which are optimized to problems of electromagnetics. Simple methods are presented that reduce numerical phase error without additional processing time or memory requirements. Furthermore, these methods are applied to both the Helmholtz equation in the frequency domain and the finite-difference timedomain (FDTD) method. Both analytical and numerical results are presented to demonstrate the accuracy of these new methods.

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A novel inductively coupled plasma (ICP), termed the microwave-sustained, inductively coupled, atmospheric-pressure plasma (MICAP), has been developed that operates at microwave frequency (2.45 GHz).

We combine a recently developed high-power, nitrogen-sustained microwave plasma sourcethe Microwave Inductively Coupled Atmospheric-Pressure Plasma (MICAP)with time-of-flight mass spectrometry (TOFMS) and provide the first characterization of this elemental mass spectrometry configuration. Motivations for assessment of this ionization source are scientific and budgetary: unlike the argon-sustained Inductively Coupled Plasma (ICP), the MICAP is sustained with nitrogen, which