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Design and Simulation of a Birdcage Coil using CST Studio Suite for Application at 7T

This content has been downloaded from IOPscience. Please scroll down to see the full text. 2013 IOP Conf. Ser.: Mater. Sci. Eng. 51 012019 (http://iopscience.iop.org/1757-899X/51/1/012019) View the table of contents for this issue, or go to the journal homepage for more

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ICSICCST 2013 IOP Conf. Series: Materials Science and Engineering 51 (2013) 012019

IOP Publishing doi:10.1088/1757-899X/51/1/012019

Design and Simulation of a Birdcage Coil using CST Studio Suite for Application at 7T

Bernat Palau Tomas, Houmin Li and M R Anjum Beijing Institute of Technology, Beijing, China. Abstract. This work describes the study of coilV for Magnetic Resonance Imaging (MRI) applicationV. 7he principal objective is the design of a birdcage Radio Frequency (RF) coil to use in a 7 Tesla (7T) scanner. +LJKHU strength field JHQHUDWHV a better SNR and increased chemical shift effect, improving spectral fat suppression and spectroscopy. Moreover, a better SNR increases the spatial resolution or reduces the imaging time. This research work presented recent developmentV based on high field7T design using CST studio. The birdcage coil achieves circular polarization and generates a high homogeneous radio frequency magnetic field under many conditions. Design of a Birdcage coil for a 7T to obtain the images from small animals ie mouse . It opens the door to design and construct a Birdcage coil for a 7T to obtain human brain images. Firstly we design a birdcage coil then the results DUH obtained with simulator CST Wave Studio, creating a 3D model and generating a simulation. Finally the parameters are re adjusted to obtain our desired Larmor frequency 298.2 MHz for a correct operation in 7T. This research work demonstrateV the theoretical results from our design and shows the designed antenna behavior.

Keywords: EM simu lation, M RI, RF, Antenna

1. Introduction MRI is a medical non-invasive technique that is used to obtain high quality images of the internal tissues i-e, inside of the human body or animal body. Thus MRI uses the Nuclear Magnetic Resonance property (NMR) to produce images from the nuclei of atoms inside the body. NMR phenomenon has become an indispensable tool in the field of chemistry, biochemistry and structural biological engineering field. At the beginning the imaging technique was called Nuclear Magnetic Resonance Imaging (NMRI) but for the negative connotations associated with the word “nuclear” (nuclear weapons) the name was changed for MRI. In this work the principal objective is to design of a birdcage coil (RF coil) to use in a 7 Tesla scanner. The clinical systems usually operate in the range of 0.2-3T. A more strength field has a better SNR and increased chemical shift effects, improving spectral fat suppression and spectroscopy. Moreover, a better SNR increases the spatial resolution or reduces the imaging time. The birdcage coil

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was introduced two decades ago and even it is a popular coil used in MRI because of its ability to achieve circular polarization and generate a high homogeneous radio frequency magnetic field under many conditions. In this research work the design of a Birdcage coil for a 7T to obtain images from small animals, it opens the door to design and construct a Birdcage coil for a 7T to obtain human brain images. The results of the simulations indicate that the design of our RF coil works in the correct Larmor frequency to work in 7T. At the beginning it is necessary to consider some information for specify our antenna, The design of RF coil for use in a 7T scanner (B0).The birdcage design is a Lowpass birdcage coil, The selection is because this type of antenna has less connections and elements than others. This is an important aspect to produce this kind of prototype, because it is less complex to construct and the reduce the cost than the other kind of birdcage models due to less capacitors utilisation.[1,2,3,4,5,6] The paper is organised as follows, In section 2 describe the simulation result using CST suite, The work ends with Section 3 in which, Conclusion are pointed out.

2.

Simulation Result

CST studio suite is an accurate and efficient computational solution for electromagnetic designs. It allows the flexible design and to optimize devices operating in a wide range of frequencies from static to optical frequencies. Moreover, it can analyze the thermal and mechanical effects, as well as, circuit simulation. CST design facilities multi functions and for co-simulation. CST Studio Suite comprises a group of modules, CST Microwave Studio, CST EM studio, CST Particle Studio, CST Cable Studio, CST PCB Studio, CST, CST design studio. This work is presented the CST Microwave Studio, it is a tool for an accurate 3D simulation of high frequency (HF) devices. It enables a fast and accurate analysis of antennas, filters couplers, planar and multi-layer structure. CST suite offers the time domain solver and the frequency domain solver also it offers solver modules for specific applications. It has filters for the import of specific CAD files and the extraction of SPICE parameters. CST used a mesh system to analyze the 3D models and obtain the simulations.

Table 1 Results obtained Birdcage Builder Type of leg Number of legs Type of ER Frequency Leg length Leg Width Coil Radius RF shield radius Capacitance Leg self inductance Er seg self inductance

Rectangular 8 Tubular 298.2MHz 16.4 0.5 9 10 1pf 153.62nH 46.44nH

2



For simulate the birdcage coil we introduce the 3D model in the CST Wave Studio with the specifications parameter as shown in Table 1 is obtained in the Birdcage Builder and simulation is shown in Fig.1, Sparameters graph obtained with the simulation with CST wave studio shown in Fig.2, Time signal graph obtained with the simulation with CST wave studio shown in fig.3, the readjusted vales in the birdcage coil is shown in table 2, S-parameters graph obtained with this readjusted values simulated using CST wave studio as shown in fig Fig.4. Radiation power in the resonance frequency in the Larmor frequency obtained with the simulation with CST wave studio shown in Fig. 5, S-parameters as a function of frequency graph is obtained with the simulation using CST wave studio as shown in Fig.6 and 3D birdcage coil model with CST wave studio using tetrahedral mesh shown in Fig. 7.

Fig.1 3D birdcage coil model with CST wave studio

Fig.2 S-parameters graph obtained with the simulation with CST wave studio.

3



Fig.3 Time signal graph obtained with the simulation with CST wave studio.

Table 2 readjusted values simulated in CST wave studio Type of leg

Circular

Type of leg

Circular

Number of legs

8

Frequency

298.2 MHz

Type of ER

Tubular

Leg width

0.5

Leg Length

16.4

Coil Radius

9

Leg self induction

153.62nH

Er seg self inductance

46.44nH

RF Shield Radius

10

Capacitance

1PF

4



Fig.4 S-parameters graph obtained with the simulation using CST wave studio.

Fig.5 Radiated Power in the Larmor frequency obtained with the simulation with CST wave studio.

Fig.6 S-parameters graph obtained with the simulation with CST wave studio

5



Fig.7 3D birdcage coil model with CST wave studio using tetrahedral mesh

3. Conclusion This research work obtained the first design and construct a birdcage coil to observe scan image from animals in a 7T, using prototype with the necessary resonance frequency the Larmor frequency for 7T (298.2 MHz). First designed the birdcage using the Birdcage Builder and then simulate it with the CST design studio suite. The first simulations results carried out an error then readapted the design obtained with the Birdcage Builder simulator. Finally using the time solver and the frequency solver we obtained the Larmor frequency. Moreover simulation is obtain a future birdcage coil for generate images from human brain. Finally simulations results have been carried out to verify the effectiveness of the proposed method performed with CST studio suite verify the predictions using the time solver and the frequency solver we obtained the designed Larmor frequency. References: [1] Luigi Landini, Vincenzo Positano, Maria Filomena Santarelli “Advanced Magnetic Image in Resonance Processing Imaging” Taylor&Francis Group, Boca Raton, 2005. ISBN: 9788126522163

[2] J.M.B. Kroot “Analysis of Eddy Currents in a Gradient Coil” Ponsen & Looijen, Wageningen, 2005. [3] Balk, M.C. "3D Magnetron simulation with CST STUDIO SUITE™," Vacuum Electronics Conference (IVEC), 2011 IEEE International , vol., no., pp.443-444, 21-24 Feb. 2011. [4] Balk, M.C., Kory, C.L., Dayton, J.A. , "Investigation of a 95GHz helical TWT with CST STUDIO SUITE™," Vacuum Electronics Conference, 2009. IVEC '09. IEEE International , vol., no., pp.505-506, 28-30 April 2009. [5] Kory, C.L., Dayton, J.A. "Design of 650 GHz helical BWO using CST studio suite," Vacuum Electronics Conference, 2008. IVEC 2008. IEEE International , vol., no., pp.392-393, 22-24 April 2008. [6] Becker, U. "Recent Developments in 3D Electromagnetic and Charged Particle Simulation" Vacuum Electronics Conference, 2007. IVEC '07. IEEE International , vol., no., pp.1-4, 15-17 May 2007. [7] CST STUDIO SUITE user’s Manual; see also www.cst.com

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