Specific absorption rate study for radiofrequency current density imaging using a two-dimensional finite element model

Current density imaging sequences with separation of mobile-ion current from immobile-ion current

Three sequences for electric current density imaging (CDI) are studied by testing their ability to selectively detect the electric current of different types of charge carriers. Two of the methods are standard DC-CDI and AC-CDI sequences, and a new AC-DC-CDI sequence is also introduced. The methods rely on the application of square voltage pulses in combination with refocusing RF pulses that can, depending on their position with respect to the voltage pulses, eliminate resistive, capacitive or neither of the current components from the detection pathway. It is demonstrated by experiments on a model system that the DC-CDI sequence detects only the resistive current of mobile ions, the AC-DC-CDI sequence detects only the capacitive current of fixed ions, while the AC-CDI sequence detects both current components. The three sequences introduce a new MRI contrast mechanism that depends on the ion mobility of the sample. As such, the methods may play an important role in the study of electric conductivity phenomena in biological systems.

Numerical study of the SNR and SAR of MRI coil arrays

Coil arrays have become a very popular coil configuration for magnetic resonance imaging. This due to that, an image of a larger area can be obtained with uniform sensitivity and higher SNR as compared to standard MR volume coil. Ultra-fast procedures like parallel imaging and phased-array can take advantage of these properties. It is very important to understand the performance of this type of devices to take full advantage of these imaging schemes. Although, the study of the single and coil arrays pose a great challenge because of the mathematical theory involved, a simulation approach can be adopted to study various coil array configuration. The principal objective of this paper is to propose a simple method to study the performance of coil array. This method numerically simulates the electric field, magnetic field, signal-to-noise ratio and specific absorption rate of MRI coil arrays. A strip of squared-shaped coil array is proposed with three different configurations. To numerically compute the electric and magnetic fields, a commercial software tool based on the Finite-Element Method was used to solve the Maxwell's equations. Matrices were formed with the image entries of the electric and magnetic fields, and used to compute the signal-to-noise ratio and specific absorption rate of the coil array configurations. Results showed a good agreement with those reported in the literature. The visualization of the electromagnetic fields allows us to study the behavior of a particular coil array configuration.

Numerical study of the optimal geometry of MRI surface coils

An image based method to compute the signal to noise ratio and specific energy absorption rate of MRI surface resonator coil for different polygonal geometries is proposed. A commercial software tool based on the Finite Element Method was used to numerically solve the Maxwell's equations to form bidimensional images of the electric and magnetic fields. These images represent the point by point fields inside the surface coil. With this data, MATLAB specifically written programs were used to numerically compute the signal to noise ratio and the specific absorption rate for different surface coil geometries. Bidimensional images and contours of the signal to noise ratio and specific absorption rate were also computed and compared. Uniformity profiles of various geometries were calculated using the resulting data to determine the optimal field uniformity. According to the signal to noise ratio images, the squared shaped coil shows the most suitable uniformity for magnetic resonance imaging applications. This can be a good candidate for phased array imaging and parallel imaging.

Current awareness in NMR in biomedicine

In order to keep subscribers up-to-date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of NMR in biomedicine. Each bibliography is divided into 9 sections: 1 Books, Reviews ' Symposia; 2 General; 3 Technology; 4 Brain and Nerves; 5 Neuropathology; 6 Cancer; 7 Cardiac, Vascular and Respiratory Systems; 8 Liver, Kidney and Other Organs; 9 Muscle and Orthopaedic. Within each section, articles are listed in alphabetical order with respect to author. If, in the preceding period, no publications are located relevant to any one of these headings, that section will be omitted.