# Three-Line Microstrip Array for Whole-Body MRI System at 7 T
## 2 Methods
For the single and wide strip line, the field distribution was off-center and focused on the right part of the line, and the mean and standard deviation of the \(\mid\)B\({}_{1}\)\({}^{+}\)\(\mid\)-field were 0.080 and 0.013 \(\mu\)T, respectively. For the \(\mid\)B\({}_{1}\)\({}^{+}\)\(\mid\)-field from the triple-line with open end shown in Figure 2b, the mean and standard deviation were 0.065 and 0.0216 \(\mu\)T, respectively. This configuration shows an improvement in the centering of the field. Figure 2c shows the \(\mid\)B\({}_{1}\)\({}^{+}\)\(\mid\)-field for the triple microstrip with only one adjacent line short-circuited; for this case, the mean and standard deviation were 0.070 and 0.02 \(\mu\)T, respectively. Figure 2: The computed \(\mid\)B\({}_{1}\)\({}^{+}\)\(\mid\)-field for (**a**) a single microstrip, (**b**) the triple-line microstrip transmission line (t-MTL) with open circuit terminated, and (**c**) the triple-line microstrip with one line short circuited, and the field profile (**d**) for each of the computed \(\mid\)B\({}_{1}\)\({}^{+}\)\(\mid\)-fields. It can be observed that the field is aligned to the center. Figure 2d shows the line profile for the three fields produced by the different configurations. The kurtosis metric was used to measure the alignment of the fields to the center of the phantom. For this case, the metric values were 2.66, 2.96, and 3.74, for the single microstrip line, triple microstrip line with open terminations, and triple microstrip line with only one adjacent line shorted, respectively. It can be observed that the use of one shorted line produces a better focused field to the middle of the phantom, which is desirable in MRI applications. Although the single microstrip produces higher field intensity, it has a narrower field penetration compared with the triple microstrip with only one shorted line. We performed a phantom analysis to design the t-MTL geometry. The first study comprised an evaluation of the effects of the height of the dielectric. We used dielectric heights of 20, 30, 40, and 50 mm. We evaluated the resulting \({}^{1}\)B\({}_{1}\)\({}^{+}\) \(\mid\)-field inside a cylindrical phantom with electrical properties of fat, with a conductivity (\(\sigma\)) of 0.0764 S/m and a permittivity of \(\epsilon_{\mathrm{r}}\) 11.745 at 300 MHz. The analysis is depicted in Figure 3. The field maps and the line profile plotted in Figure 3 indicate that changes in the dielectric height produced a small difference in the field intensity, with the 20 mm dielectric having the lowest field intensity and the 50 mm dielectric having the highest field intensity. We also explored the effects of the coupled adjacent lines to the conductor line. For this evaluation, we varied the distance between the main conductor line and the adjacent coupled lines to 4, 12, and 17 mm. The field distribution for this analysis is shown in Figure 4. The field maps indicate that a larger distance between the adjacent lines and the main conductor line favor field penetration, as indicated by the plotted line profile. Figure 4: Computed \({}^{1}\)B\({}_{1}\)\({}^{+}\) \(\mid\)-field for t-MTL with distances between the main conductor line and adjacent coupled lines of (**a**) 4, (**b**) 12, and (**c**) 17 mm. The field profile for each of the computed \({}^{1}\)B\({}_{1}\)\({}^{+}\) \(\mid\)-fields is depicted in (**d**). Figure 3: Computed \({}^{1}\)B\({}_{1}\)\({}^{+}\) \(\mid\)-field for microstrips with dielectric heights of (**a**) 20, (**b**) 30, (**c**) 40, and (**d**) 50 mm. The field profile for each of the computed \({}^{1}\)B\({}_{1}\)\({}^{+}\) \(\mid\)-fields is depicted in (**e**). We also investigated the array performance of the t-MTL, by placing eight elements around a cylindrical phantom with a radius of 120 mm and a length of 300 mm. The phantom was assigned electrical properties equal to those of fat at 300 MHz, with a conductivity (\(\sigma\)) of 0.0764 S/m and a permittivity of \(\varepsilon_{\tau}\) 11.745.