Multi- and dual-tuned microstripline-based transmit/ receive switch for 7-Tesla magnetic resonance imaging
Authors : Ashraf Abuelhaija, Gameel Saleh, Osama Nashwan, Samer Issa, Sanaa Salama
Abstract : This article introduces two new designs of transmit/receive switches for 7-Tesla magnetic resonance imaging. Both designs based on a microstripline coupler technology. In the first design, a different single frequency signals can be handled to/from a radio frequency coil using smart tuning network. In the second design, a dual-tuned 1H/23Na transmit/receive switch is designed to handle a dual resonant signal to a dual resonant 1H/23Na coil, simultaneously and without tuning. In transmit and receive, the first design achieved good matching (-20 dB), and low insertion loss (0.78 dB) for the 1H, 19F, 31P, 13C, and 23Na magnetic resonance signals with high isolation (61 dB). Similarly, the dual-tuned 1H/23Na switch achieved good matching (<−11.5 dB) and low insertion loss (1.0 dB) with high isolation (67 dB), whereas for 1H/31P switch, good matching has been achieved (<−12 dB) and low insertion loss (0.96 dB) with high isolation (62 dB). The first proposed switch enables the use of the same switch with different coils resonating at Larmor frequencies of different atomic nuclei. The second switch can handle a dual resonant signal to a single dual resonant coil. The first design is promising in reducing the costs by using the same switch with different coils. The second design is promising in the integration with multichannel dual resonant coil.
Keywords : hybrid coupler, magnetic resonance imaging, PIN diodes, radio frequency
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PERFORMANCE ANALYSIS OF MODIFIED GEOMETRIC CODES
Authors : Samer Issa and Osama Nashwan
Abstract : Geometric Codes are a class of three different groups of codes that are easily implemented. This group of codes has greater efficiency over fading channels than regular forward error correcting codes. This paper presents a performance analysis of Modified Geometric Codes and studies the effects of the various parameters such as the number of bits per symbol, the number of parity lines and the code rate as well as compares their performance to the performance of Basic Geometric Codes.
Keywords : geometric codes, modified geometric codes fading channels, code rate, parity symbol
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PERFORMANCE OF BASIC GEOMETRIC CODES OVER FADING CHANNELS
Authors : Osama Nashwan, Samer Issa and Khalil Saleh
Abstract : Forward error correcting codes while having good efficiency on normal channels, their performance is very poor over noisy (fading) channels. A new group of codes, called Geometric Codes that has a greater efficiency over fading channels has been designed. This paper presents the simulated results for Basic Geometric Code and studies the effects of its various parameters such as the number of bits per symbol, the number of parity lines and the code rate.
Keywords : geometric codes, fading channels, code rate, parity symbol
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METHOD FOR THE ANALYTICAL EVALUATION OF CONVOLUTION INTEGRAL
Authors : Maryam Akhozahieh, Osama Nashwan, Nasser Abdellatif
Abstract : The convolution integral is a linear operation. Invoking the linearity property, the superposition principle is applied in this paper to obtain the convolution integral between two signals. The method depends on dividing the two signals into several segments; each has a fixed function and a finite or infinite width. Depending on the product of the segments’ number of the first signal and that of the second signal, the evaluation of the convolution integral is divided into several sectors. Within each sector, one, two, or three integrals are needed to be calculated. The number of the integrals and the limits for each one depends on the width and the edge points of the two signals’ segments involved in a particular sector. After calculating all integrals, the superposition principle is applied to find the convolution integral for a specific period. The unit step function can be applied to express the convolution integral as a single expression.
Keywords : convolution integral, linearity, superposition, unit step function
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Decoupling network for Tx/Rx body coil for 7 Tesla MRI
Authors : Ashraf Abuelhaija, Sanaa Salama, Osama Nashwan
Abstract : The parallel imaging technique is widely used in 7T MRI scanners. It employs multi channel RF coil arrays to apply a concurrent excitation and acquisition method. Concurrent excitation faces significant challenges in terms of electromagnetic coupling between the RF coil elements. In order to prevent interference between the RF coil elements’ exciters, several decoupling methods have been developed to compensate for coupling and to permit independent work for the exciters. This paper studies the coupling between meander coils arranged in two different geometrical setups and investigates the isolation performance between the coils by applying two different decoupling networks depending on the geometrical setup of the coils. These two decoupling networks in addition to a T-shaped decoupling network have been integrated into a Tx/Rx body coil for 7 T to compensate for mutual coupling between array coil elements. The results have been obtained by using CST Microwave Studio (CST AG, Darmstadt, Germany). Key words: Magnetic resonance imaging, 7-Tesla, mutual coupling, decoupling network, radio frequency coils, resonant circuit, transmit/receive coil
Keywords : Magnetic resonance imaging, 7-Tesla, mutual coupling, decoupling network, radio frequency coils, resonant circuit, transmit/receive coil
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