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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Comprehensive Study on Decoupling Networks for 7 Tesla MRI based on Reactive Load Parasitic-Element
Authors : Sanaa Salama, Ashraf Abuelhaija, Tareq Baldawi, Samer Issa
Abstract : This work presents and evaluates the integrating of decoupling networks in MRI systems at 7 Tesla magnetic field strength. The parasitic element is reactive loaded. Four different cases of reactive loads are considered: capacitive load, inductive load, open circuited, and short-circuited loads are considered. The idea behind this technique is to reduce or even eliminate the effect of mutual coupling between the RF coil elements in magnetic resonance imaging (MRI)system. Two rectangular loops are used to compose a planar phased array. This structure is designed and optimized in CST at the Larmor frequency of 298.3 MHz corresponding to the 7 Tesla MRI system.
Keywords : Decoupling Network (DN), Matching Network (MN), Parasitic-Element, Capacitive & Inductive Load, Open and Short-Circuited Load
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T- and Cascaded Pi-Shaped 1H T/R Switches with Realistic Trace Width for 7 Tesla MRI
Authors : Ashraf Abuelhaija1, Gameel Saleh2, Sanaa Salama3, Samer Issa1
Abstract : In this work, two designs of Transmit/Receive (T/R) switches are introduced for 7- Tesla magnetic resonance imaging. The T-shaped and the two cascaded Pi-shaped microstriplinebased T/R switches for 1H MRI are designed with the minimum trace width constraint that handles the required power and assures a compact size of the switch. When the peak power of the Radio Frequency (RF) amplifier signal is 1 kW with 10% duty cycle, the average current that will pass through 50 Ω input impedance circuit is 2 A. Based on IPC 2221 standard for PCB traces, the minimum trace width that handles such a current is of 0.513 mm. The ADS software is used in designing the T as well as two sections pi-shaped switches. All the proposed 7-Tesla 1H MRI switches have revealed good matching (<-20 dB), low insertion loss (<0.34 dB), and high isolation (>60 dB) during transmit and receive. The designed switches are compact in size by around 40% reduction in dimensions compared to a conventional switch size (100 mm 100 mm) without folding
Keywords : T-Shaped Microstripline, Pi-Shaped Microstripline, T/R Switch, PIN Diode, Insertion Loss
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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 symbo
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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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