Double-Tuned Birdcage Radio Frequency Coil for 7 T MRI: Optimization, Construction and Workbench Validation

Round 1

Reviewer 1 Report

The paper presents and discusses the optimization, construction, and workbench validation of a double-tuned birdcage radio frequncy coil suitable for human head imaging at 7 T.

The work is of great interest, the introduction presents a deep analysis of the existent state-of-the-art and discusses the related limitations, that are overcome by the research performed by the authors.

Some minor comments:

1) the "Materials and Methods" section lacks in describing prototype construction. The authors should rearrange paragraph 3.2 of the results, moving the prototype building details in the Materials and Methods section

2) Figure 10,11, 12 have very low quality. Please improve them.

3) Please insert a figure of the final prototype, including a schematic of the components.

Author Response

We thank the Referee 1 for appreciating our work. In the following a point-to-point reply to the Referee’s comments.

• As suggested, we moved the prototype building details in the final part of the "Materials and Methods" section.
• As requested, the figures quality was improved
• Figure 10 of the revised manuscript contains two pictures of the prototype.

Reviewer 2 Report

In this manuscript the authors studied the optimization, construction, and workbench validation of a Double-Tuned 1H- 23Na volume Radio Frequency (RF) coil suitable for human head imaging at 7 T, based on the birdcage geometry. this original research is very valuable and I suggest accept this manuscript after minor revision:

1- the manuscript need some grammar and spelling corrections. 

2- mention the brief conclusion of this study in the abstract part.

3- figure 13 didn't mentioned in the manuscript text.

4- the discussion part highly need to rewriting. it lose the comparative studies with previous similar/convergent works.

Author Response

We thank the Referee 2 for appreciating our work. In the following a point-to-point reply to the Referee’s comments.

• We thank the referee for her/his suggestion. We performed a careful reading to fix the errors.
• We added a sentence at the end of the abstract.
• The Figure 13 (the phantom image) of the original manuscript is not present anymore. All the pictures of the revised manuscript are mentioned in the text.
• We added two paragraphs at the end of the Discussion section comparing the 4R approach with alternatively tuned legs and the concentric approaches to DT birdcage imaging.

Reviewer 3 Report

In this paper the authors provide a method for the construction and workbench Validation of a Double-Tuned Birdcage Radio Frequency Coil, which according to the authors would be l suitable for human head imaging at 7 T. Some issues should be addressed prior to the publication of this paper:

1. It is important to provide a more detailed description on how this work improves your previous results, such as the presented in 10.1109/TMI.2020.2988599.  

2. Try to improve definition of figures 10-12.

3. In figure 12.  Include a zoom/inset of the 5-8 and 8’ modes region, in order to facilitate viewing them, it is hard to read that particular region of the figure as it is now.

4. In my opinion figure 13 does not provide any useful information, I recommend removing it

Author Response

We thank the Referee for her/his work. In the following a point-to-point reply to the Referee’s comments.

• We added the requested comparison at the end of the Discussion section
• We inserted an improved version of all the three figures.
• We think that the improved quality of figures makes the plot more readable. In the region indicated by the Referee there are several close by modes. We decided to add in the figure caption the frequencies of all resonant modes.
• We removed the figure in the revised version of the manuscript.

Reviewer 4 Report

The authors reported a double-tuned birdcage RF coil for its application in 7T MRI. They claim to have numerically optimized, constructed and validated the cage. Overall, the work looks scientifically sound yet it still has some issues.

1. The title needs to be re-written with correct fonts.

2. Are there any real experimental scope? If so, how does the authors envision that?

3. I was wondering if the authors could comments more on the specific absorption rate (SAR) on human brain tissues from these bird cage MRI coils. Any calculations would be really beneficial.

4. Fig. 8 can be revised. The linewidths of the plots could be improved. The colors look very weak. Same for Fig. 9.

Author Response

We thank the Referee for her/his work. In the following a point-to-point reply to the Referee’s comments.

• The entire title now uses the same font
• At the end of the Discussion section, we added a comparison among different approaches to realize DT detection with birdcage coils, considering sensitivity, field homogeneity and realization time.
• We apologize, but in the ongoing research we first focused our attention on coil realization. We are certainly interested in proceeding further including human dielectric models in our simulations but these data are not available yet.
• We improved the visibility of the lines in both figures.