Fundamentals of Determination of the Biological Tissue Refractive Index by Ellipsoidal Reflector Method

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper, titled 'Fundamentals of determination of the biological tissue refractive index by ellipsoidal reflector method,' describes a new method for determining the refractive index of biological tissue in the range from 1.33 to 1.7 using an ellipsoidal reflector and design solutions for implementing this method as an effective alternative to existing ones, which will allow to record changes in the optical characteristics of BT and expand the possibilities of diagnosing cancer at early stages.

The work is of great interest to both medicine and biomedical optics.

Remarks:

1. The "electromechanical unit EMU" abbreviation should be given in brackets after the decoding.

2. In the text, the angle of incidence ε is indicated first without an index, then with index 1 without case, and in Figure 3 in lower case. If these are different angles, explain the difference.

3. You describe methods that can be used to determine changes in the refractive index in three dimensions, which allows you to study heterogeneous biological tissues. One of the limitations of these methods is the fixed wavelength. Could you explain in more detail what the problem is?

4. Figure 2(b) shows a glass ellipsoidal reflector with a mirror coating; the description states transparent material. Please explain the requirements for the optical characteristics of the ellipsoidal glass and the mirror coating and what materials you could suggest for implementation.

5. As a result of the selection of the range of eccentricity values characterizing the beam hitting the edge of the second focal plane in the values of 0.38 (or 0.57) and for modeling, you chose a minimum e = 0.4 and a maximum e = 0.55, thereby reducing the size of the studied range by 26.7% and casting doubt on the conclusions drawn from the analysis of Figure 6.

6. In Figure 7, you show a liquid-filled ellipsoidal reflector. Could you explain why the matte black coating is necessary and how the immersion liquid does not leak through the slot?

7. Literary sources are somewhat outdated, it is necessary to provide additional references to scientists working in this direction of research at this time.

Comments on the Quality of English Language

Minor editing of English language required

Author Response

Comments 1: The "electromechanical unit EMU" abbreviation should be given in brackets after the decoding.

Response 1: We agreed and corrected the final version of the paper.

 

Comments 2: In the text, the angle of incidence ε is indicated first without an index, then with index 1 without case, and in Figure 3 in lower case. If these are different angles, explain the difference.

Response 2: The incidence angle ε is generally used to indicate the angle of light within a system without specifying a specific surface or beam. In the text, we first specify the angle ε without a subscript to reflect this general concept. However, in the case where the angle of incidence refers to a specific beam (for example, a laser beam on the lateral surface of the EP), we use the notation ε₁. We agree that the subscript '1' should be in lowercase for consistency and have corrected this in the final version of the paper.

 

Comments 3: You describe methods that can be used to determine changes in the refractive index in three dimensions, which allows you to study heterogeneous biological tissues. One of the limitations of these methods is the fixed wavelength. Could you explain in more detail what the problem is?

Response 3: In the current version of the article, there is a corresponding link that explains these limitations. However, we have added two more sources to the references to strengthen the argument.

 

Comments 4: Figure 2(b) shows a glass ellipsoidal reflector with a mirror coating; the description states transparent material. Please explain the requirements for the optical characteristics of the ellipsoidal glass and the mirror coating and what materials you could suggest for implementation.

Response 4: The response to this comment has been added to the paper on page 4, lines 168–181. Additionally, supporting literature has been added in references [36–38].

 

Comments 5: As a result of the selection of the range of eccentricity values characterizing the beam hitting the edge of the second focal plane in the values of 0.38 (or 0.57) and for modeling, you chose a minimum e = 0.4 and a maximum e = 0.55, thereby reducing the size of the studied range by 26.7% and casting doubt on the conclusions drawn from the analysis of Figure 6.

Response 5: We disagree with the reviewer's purely "arithmetic" interpretation. Narrowing the range for the simulation is an effort to ensure the "purity" of the model experiment, which excludes multiple reflection phenomena and manufacturing technological limitations. However, to ensure the correctness of the conclusions, we have added a link to the reference that justifies this limitation.

 

Comments 6: In Figure 7, you show a liquid-filled ellipsoidal reflector. Could you explain why the matte black coating is necessary and how the immersion liquid does not leak through the slot?

Response 6: The matte black coating in Figure 7 is necessary to prevent glare that can occur when light passes through the slit. This coating absorbs stray light, ensuring the optical system functions appropriately without introducing unwanted artifacts. To prevent the immersion fluid from leaking through the slot, the ER construction provides for a thin transparent film with a refractive index higher than the fluid itself, which thus depends on the choice of fluid. However, the specified "subtleties," in our opinion, should be discussed in the framework of the following publications.

 

Comments 7: Literary sources are somewhat outdated, it is necessary to provide additional references to scientists working in this direction of research at this time.

Response 8: The authors consider the references in the previous version of the article [29], [34], and [39] to be valuable primary sources, which they insist on mentioning. However, we considered the reviewer's remarks—see the answer to comment #3.

 

Comments 8: Minor editing of English language required.

Response 8: OK.

Reviewer 2 Report

Comments and Suggestions for Authors

This paper is of academic type. It is still distant from any practical usage at the point of care. 

Author Response

Comments 1: This paper is of academic type. It is still distant from any practical usage at the point of care. 

Response 1: Completely agreed.

Reviewer 3 Report

Comments and Suggestions for Authors

Summary: This study presents a new method for determining the RI of biological tissues using an ellipsoidal reflector. The authors developed a mathematical framework and specialized software to simulate the dependence of the incidence angle and the RI on various factors, such as the ER's geometry and the height of the laser beam entering the ER. The proposed method aims to enhance the precision of RI measurements, which is critical for applications in scientific and medical research.

Comments

 

1.      I suppose that, for practical/ clinical use, the proposed ellipsoidal reflector will be placed on the surface/ skin of the (say) patient. In this context, how would the surface roughness, tissue heterogeneity, any ulceration/ lesion/ nodule, patient position, etc. will influence the measurement? Will the measurement provide a single value for the full field of view or a 2D map of RI values? Is the propose method/ ellipsoidal reflector feasible for skin measurements only? or can be used for deep tissues (say) during intraoperative procedures or via a fiber/ probe application? What would be the possible complications for such utilization of the proposed method? I suggest that a new section comprehensively addressing all such issues should be added.

2.      The authors mentioned (at the end of Discussion section) that selecting and obtaining the filling liquid is complicated due to many factors. It would be beneficial to provide a rough estimate of the cost of all necessary components and the time required for the optical measurement and the subsequent processing.  

3.      A one to one comparison of RI values (may be in a table format) determined using the proposed method and those obtained through established methods in the literature would enhance the manuscript. Presenting this comparison in a table format would be particularly effective.

4.      Ensure a consistent use of terminology throughout the manuscript. For example, "RI" and "refractive index" are used interchangeably. Define acronyms like RI upon first use and stick with one term to avoid confusion.

 

5.      In the Methods section, there is significant repetition of sentences and phrases, creating confusion and redundancy.

Author Response

Comments 1. I suppose that, for practical/ clinical use, the proposed ellipsoidal reflector will be placed on the surface/ skin of the (say) patient. In this context, how would the surface roughness, tissue heterogeneity, any ulceration/ lesion/ nodule, patient position, etc. will influence the measurement? Will the measurement provide a single value for the full field of view or a 2D map of RI values? Is the propose method/ ellipsoidal reflector feasible for skin measurements only? or can be used for deep tissues (say) during intraoperative procedures or via a fiber/ probe application? What would be the possible complications for such utilization of the proposed method? I suggest that a new section comprehensively addressing all such issues should be added.

Response 1: In general, we agree with the need to discuss these issues. However, there are links to the published works of the authors [34-36], as well as other easily accessible works of ours (https://mpky.nung.edu.ua/index.php/mpky/article/view/331, https://doi.org/10.20535/2523-4455.2019.24.2.172771 and others) partially reveal these aspects regarding the method of mirror ellipsoids of revolution. Moreover, regarding the use of this method specifically for determining the refractive index of biological media, it will be appropriate to highlight the practical aspects of measurements in further research plans. We would not like to increase self-citation to repeat already published rationales in this work.

 

Comments 2: The authors mentioned (at the end of Discussion section) that selecting and obtaining the filling liquid is complicated due to many factors. It would be beneficial to provide a rough estimate of the cost of all necessary components and the time required for the optical measurement and the subsequent processing.

Response 2: This is a valid proposal to the essence of the research; however, it is difficult for us to assess technical and economic indicators since the process of stabilization (solidification) of a specific liquid is the manufacturer's competence. The measurement time does not exceed a few seconds, but preparing a biological tissue sample determines the time needed to conduct the study.

 

Comments 3: A one to one comparison of RI values (may be in a table format) determined using the proposed method and those obtained through established methods in the literature would enhance the manuscript. Presenting this comparison in a table format would be particularly effective.

Response 3: We definitely agree, but since this work is an academic study, we would like to return to the comparative assessment (table) in the following publications with the reviewer's permission.

 

Comments 4: Ensure a consistent use of terminology throughout the manuscript. For example, "RI" and "refractive index" are used interchangeably. Define acronyms like RI upon first use and stick with one term to avoid confusion.

Response 4: Has been changed throughout the manuscript.

 

Comments 5: In the Methods section, there is significant repetition of sentences and phrases, creating confusion and redundancy.

Response 5: We would be very grateful for a more specific designation of such cases.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

A’m agree with correction

Reviewer 3 Report

Comments and Suggestions for Authors

Please see the attachment

Comments for author File: Comments.pdf

Author Response

We are sorry that our responses do not fully satisfy the reviewer. We very much appreciate the work of the reviewers and thank them for offering suggestions as to what issues should be highlighted or what else may be of interest to readers in the topic of our research. Please note, however, that it is impossible to cover all aspects of the problem addressed in a single article.

We do not see the need to repeat in this article issues raised in earlier papers - this would unnecessarily expand the article and would require the introduction of a number of self-citations - which in our view would be inappropriate (unethical) (we wrote about this in a previous response).

We do not agree with the statement that we avoided answering comment 2 - in the answer we provided information on what has the greatest impact on the measurement time (sample preparation, liquid stabilisation time). As an estimate of this time would be highly imprecise we see no need to provide such information to readers.

We stand by our response regarding the last comment. We agree that the proposed summary (table) would be interesting. In our view, it is not an essential element of this particular article. We plan to include such a comparison in our subsequent work.