# Three-Line Microstrip Array for Whole-Body MRI System at 7 T
## 3 Results  
We computed the \(\mid\)B\({}_{1}\)\({}^{+}\mid\)-field and SAR from the human model using computer aid analysis and an electromagnetic simulator provided by the commercial software, Sim4 Life (Zurich). This software used the finite-difference time-domain (FDTD) method to perform numerical analysis to find solutions to electromagnetic equations. The \(\mid\)B\({}_{1}\)\({}^{+}\mid\)-field was extracted from the human model after being excited using the patch antenna, birdcage coil, and the proposed array of t-MTLs. All simulations were performed at a central  
Figure 6: The geometry of each of the array configurations for the whole body in sagittal and axial views, for the (**a**) path antenna, (**b**) birdcage coil, and (**c**) t-MTL array. frequency of 300 MHz and bandwidth of 600 MHz, and all the conductors were selected as a PEC. The conductors were assigned 0 mm of thickness to reduce the simulation time and increase the effectiveness of the analysis. The simulation was done with a matrix grid of \(284\times 284\times 940\) cells. The electrical properties of Teflon used for the patch antenna and t-MTL are as follows: \(\sigma\) of 0.000462 S/m and \(\epsilon_{\tau}\) of 2.08. The TE mode for the patch antenna and waveguide was selected to operate at 300 MHz. The birdcage coil was excited in a quadrature mode, the tuning was made by using ring capacitors of 0.621 pF and leg capacitors of 65 pF, for which a S11 value of -20 dB was obtained before applying a matching circuit. The simulations were normalized to an input power of 1 W. The phase difference between each t-MTL elements in the xy plane array was 45\({}^{\circ}\), to make the CP mode. Figure 7 shows the \(\mid\)B\({}_{1}\)\({}^{+}\)\(\mid\)-field in the sagittal view (yz plane) for each of the transmission cases. The slice was selected to be off center to show the whole body. Figure 8 shows the \(\mid\)B\({}_{1}\)\({}^{+}\)\(\mid\)-field in the axial view (xy plane) at different locations along the human model and for each RF transmitter. We also computed the SAR in the whole body, as shown in Figure 9. To display the SAR map, we used a projection view of the maximum SAR value in the sagittal and axial  
Figure 8: The axial view of the computed \(\mid\)B\({}_{1}\)\({}^{+}\)\(\mid\)-field for, (**a**) the path antenna, (**b**) birdcage coil, and (**c**) the array of t-MTL. The left column is an axial slice on the knee, middle on the torso, and right column is a slice inside the brain. Figure 7: The computed \(\mid\)B\({}_{1}\)\({}^{+}\)\(\mid\)-field inside the human model in sagittal view, for (**a**) the path antenna, (**b**) birdcage coil and (**c**) the array of triple-line microstrips. views. This type of display can indicate the location of the highest level of SAR produced by the respective transmitter. Table 1 summarizes the mean and standard deviation of each \(\mid\)B\({}_{1}\)\({}^{+}\)\(\mid\)-field in Figure 7 and Figure 8, and the SAR maps in Figure 9.  
It can be observed from the sagittal view of the magnetic field inside the whole body that the use of the proposed t-MTL can produce a more uniform and stronger \(\mid\)B\({}_{1}\)\({}^{+}\)\(\mid\)-field compared with the patch antenna and birdcage coil. The patch antenna can deliver a uniform \(\mid\)B\({}_{1}\)\({}^{+}\)\(\mid\)-field inside the head; however, as the field propagates into the body, the intensity and uniformity are lowered. The use of a patch antenna results in a higher SAR value in the head area. The birdcage coil also exhibits low field uniformity, as the field is highly diminished, particularly in the abdominal area. The field in the brain is centered and focused, but it has low intensity in the brain periphery. The proposed arrangement of t-MTL can produce a uniform field with an intensity similar to that of the BC coil along the whole body; although the uniformity is not perfect, it is better that those of the reference systems. In particular, the \(\mid\)B\({}_{1}\)\({}^{+}\)\(\mid\) field demonstrates better uniformity in the abdominal and torso area.