# Three-Line Microstrip Array for Whole-Body MRI System at 7 T
## 2 Methods
The t-MTL array was compared with a high-pass birdcage coil with a radius of 150 mm and a length of 320 mm. The birdcage coil was driven in circular polarized (CP) mode; each capacitor on the ring was considered as a voltage source, with the corresponding phase difference. Figure 5 shows the computed \(\mid\)B\({}_{1}\)\({}^{+}\mid\) -field for the cylindrical phantom and the SAR average 10 g maps. The mean and standard deviation of the \(\mid\)B\({}_{1}\)\({}^{+}\mid\) -field for the BC were 0.013 and 0.008, and for the t-MTL they were 0.015 and 0.006, respectively. The mean and maximum SAR values for the BC were 0.110 and 0.20, and for t-MTL they were 0.112 and 0.24 mW/kg, respectively. In this study, we compared the use of three types of RF transmitters for the whole body in 7 T MRI. The two reference structures are a patch antenna using a magnet bore as a waveguide and a birdcage coil. The proposed design is an array of t-MTLs. The patch antenna used in the waveguide is depicted in Figure 6a. We used a cylinder with a length of 3000 mm and a radius of 300 mm corresponding to the bore of an MRI system. The cylinder used as the waveguide was selected as a perfect electric conductor (PEC). The patch antenna was designed to have a circular shape with a diameter of 406 mm and a dielectric height of 10 mm, corresponding to Teflon. The geometries of the waveguide were selected to produce a transverse electric TE mode at 300 MHz. The second reference RF device was designed as a whole-body birdcage coil. Although a birdcage coil is known to have deficiencies in high-frequency MRI applications, we considered it necessary to compare it with the reference. The geometry of the birdcage coil is shown in Figure 6b; it has a length of 2000 mm and a diameter of 520 mm. It is based on a bandpass type with 12 legs; each leg has a width of 30 mm and an end-ring of 30 mm. \[\gamma_{2}=\left[\frac{z11}{2}+\frac{z22}{2}+\frac{z23}{2}-\frac{1}{2}\sqrt{ z11^{2}-2z11z22-2z11z23+8z12^{2}+z222^{2}+2z22z23+z23^{2}}\right] \tag{4}\]0 Computed \(\mid\)B\({}_{1}\)\({}^{+}\mid\) -field for the (**a**) BC and (**b**) t-MTL array. SAR maps for the (**c**) BC coil and (**d**) t-MTL array. The proposed array structure consists of 32 t-MTLs, distributed in four arrays along the z axis, with each array having eight elements. The elements were evenly distributed along the circumference of a circle with a diameter of 500 mm. Each t-MTL used Teflon as the dielectric material, and the length, width, and height of each element were 284, 80 mm, and 30 mm, respectively. The width of the main conductor line was 32 mm, whereas the width of the two extra conductor lines was 5 mm; the separation to the main line was 17 mm. The geometry of the t-MTL was designed following the transmission line theory equations to produce a microstrip with electrical length of 180 degrees. The distance along the z axis between arrays was 90 mm in order to ensure coverage of the whole-body model. We used the human model, Duke, as shown in Figure 6, which is composed of over 200 well segmented tissue materials, with the values of the electrical properties corresponding to the frequency of use; the complete list of tissues with their corresponding conductivity, electrical permittivity, and tissue density values can be found in [23]. The human model belongs to the virtual family collection [24]. The model is based on a young male adult of 34 years with a height of 1.77 m, a weight of 70.2 kg, and a body mass index (BMI) of 22.4 kg/m\({}^{2}\). The human model is composed of bones and soft tissue, including segmented organs such as white matter, gray matter, spinal cord, stomach, eyes, and fat. We moved the arms of the human model so they are closer to the body to avoid an empty space between the body and the arms. We also decreased the distance between the legs, as much as physically possible, in the model to ensure that the body model has a more uniform shape.