## 4 Discussion  
In this work, we present the detailed design for a microstrip capable of resonating at four different frequencies for X-nuclei MRI. We additionally provide an analysis of this tool using EM simulations. The target frequencies were set to obtain images with a 7T MR system for multi-nuclei MR, namely \({}^{1}\)H, \({}^{19}\)F, \({}^{31}\)P, and \({}^{23}\)Na, with the corresponding frequencies of 300, 280, 121, and 78 MHz, respectively.  
The proposed arrangement is based on a microstrip with a dielectric material placed between the ground plane and the conductor strip. In our design, the conducting line was split into four lines separated by 20 mm, with a gap between the feeding point and the strip line. The gap is considered to be a series capacitor, which helps to adjust the tuning frequency and also to reduce the coupling between adjacent lines. In addition, the dielectric  
Figure 8: The y-z plane \(\mid\)B\({}_{1}\mid\) field and localization at each line for (**a**) 78, (**b**) 121, (**c**) 280, and (**d**) 300 MHz.  
Figure 9: The surface current density distribution of the z-x plane at (**a**) 78, (**b**) 121, (**c**) 280 and (**d**) 300 MHz.  
material under each of the conducting strip lines was interleaved between high and low relative permittivity. The quad strip line arrangement with coplanar interleaved dielectric materials was able to produce a uniform magnetic field at each of the target resonance frequencies.  
We also presented an analysis of each of the concepts included in the final design. We first performed EM simulations showing the effects of the size of the gap in the microstrip. This analysis showed that there was a reduction in the coupling series capacitance when the gap size was increased. We also demonstrated how the field uniformity was affected by the position of the gap along the strip line. While the frequency could be modified by altering the position of the gap, this produced discontinuities in the field distribution, which would greatly affect its performance for MRI applications. Finally, we analyzed the coupling between two microstrip lines, comparing different configurations of straight lines and gapped lines, and the use of coplanar interleaved dielectric materials with different relative permittivity. The use of interleaved substrates was important in our design, as it helped achieve the resonance frequencies and reduce the coupling between lines.  
The proposed method has the advantage that it can resonate at four different frequencies, and it is capable of acquiring MR images of multiple nuclei. As this design can multi resonant frequencies in a single element, this arrangement of microstrip can be applied in future works on simultaneous multinuclear imaging methods. In addition, the resonant lines are in the same plane or layer, whereas, in the conventional multinuclear RF coils, elements with different frequencies are placed in different layers, making it difficult to optimize the geometric positioning of each element.  
Not applicable.  
No new data were created or analyzed in this study. Data sharing is not applicable to this article.  
The author would like to thank [PERSON] and [PERSON].  
No conflicts of interest.