Effects of Excitation Angle on Air-Puff-Stimulated Surface Acoustic Wave-Based Optical Coherence Elastography (SAW-OCE)

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

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Comments for author File: Comments.pdf

Comments on the Quality of English Language

Minor editing of English language required

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The paper researches the optimal angle for air-puff stimulated surface acoustic wave-based optical coherence elastography, which could provide essential guidance for air-puff based elastography studies in clinical applications. However, there are several problems needed to be explained.

1. What is the optimal angle for air-puff stimulated surface acoustic wave-based optical coherence elastography? Please give a clear explanation. Why is the excitation angle taken as 20⁰ while the human skin was measured? Please discuss the effect of different excitation angle on the values of Young's modulus in Table 1.

2. Please explain why the position between the needle tip and the sample surface was fixed to ~1.25 mm to avoid the phase wrapping.

3. I have not found the measurement results of outlet pressure, which was measured by a digital manometer described in the paper. Please discuss the effects of different outlet pressures on the optimal angle for air-puff stimulated surface acoustic wave-based optical coherence elastography.

4. Although there was no statistical difference, it is strange that the result of 5⁰ is almost coincidence with that of 45⁰ while the difference between 25⁰ and 5⁰ is obvious in Figure 4.

5. What does ‘(21)’ at the end of the sentence in line 267 mean?

Author Response

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Reviewer 3 Report

Comments and Suggestions for Authors

From a reviewer’s point of view, overall, the authors have tried to explore the effect of the angle of external stimulus on the physical property changes in the sample while measuring the elasticity of the sample. The scope of the study has high value, however, the authors failed to take into consideration the influence of material characteristics and other material properties that may cause changes to the sample elasticity when the angle of external stimulus is applied. Furthermore, the total number of samples is very small, and the demographic of sample subjects is not clear and not diverse enough (as this may highly influence the measured values to a great extent) to support the substantially big claims in their article. Also, they have failed to do an extensive analysis of their result and did not do any significant statistical analysis, and discuss it to support their claims.

Authors have used the term SAW-OCE in their title; it is acceptable to use this since this is already a used term from one of their earlier works (published in 2021), which is already published, but the authors have failed to re-use this term anywhere else in the manuscript. They should either remove this from the title or consider using this in appropriate places in the manuscript. Also, they must cite the previously published work which has used this abbreviation.

The introduction is acceptable, but in lines 70-89, the earlier works explored by other research groups in their experiments with the angle of stimulus, it is to be noted that the types of samples are very different. Though the angle of stimulus makes a huge impact on the physical property changes in the sample, the material characteristics also play a crucial role in the physical change occurring by the angle of stimuli applied to the sample. This is not mentioned, and this needs to be addressed and extensively described with relevant supporting references.

Overall, the result analysis is very brief. Also, the authors need to consider using statistical analysis for the measured values. The most important factor to be taken into account is the very limited sample number and sample demographic. Since this article is about exploring the external stimuli angle in relation to the changes in physical changes in sample physiology, the sample’s material characteristics with a larger sample number and clear statistical analysis are needed to support their claims in results.

The study has major flaws in its design that support the substantial claims made in the article, and without addressing these issues (see the comments below for details), the article cannot be considered for publication.

Comments:

1.      Abstract:

a.       Sample numbers used in the study are very small and limited.

b.      Lines 11-13: What do the authors mean by “… a parameter that lacks standardization at present…” this is not exactly true. The standardization for the angle of the external stimulus and its relative OCE or ODT measuring angles have been well explored in OCE and ODT studies. This is a basic componential part of a study for these techniques and is taken into consideration while exploring the measurement methods to improve signal detection efficiency and the impact of physical changes to the samples in these kinds of experiment. The authors have not done an extensive enough research study to claim something as significant as such. This is especially constrained by their relatively very low sample demographic, sample number, and statistical analysis.

c.       Authors are recommended to use the word “external stimuli” over “excitation”, this is because the word excitation is usually used and preferred for a broader term, which also includes light or thermal excitation and as such.

2.      Introduction:

a.       Why authors abbreviate phase-sensitive OCT as PhS-OCT, Phase-sensitive OCT (PS-OCT) is a very well-established imaging system. Authors are advised not to create new abbreviations unless they have introduced a new novel technique and follow the standard abbreviations that are well-established in the scientific community.

b.      In introduction lines 70-89, the earlier works explored by other research groups in their experiments with the angle of stimulus, it is to be noted that the type of samples are very different. Though the angle of stimulus makes a huge impact on the physical property changes in the sample, the material characteristics also play a crucial role in the physical change occurring by the angle of stimuli applied to the sample. This is not mentioned, and this needs to be addressed and extensively described with relevant supporting references.

3.      Materials and Methods:

a.       In Figure 1, the light rays shown after the lens (before the camera) seem as if they are dispersing; it should be shown to be focusing onto the camera sensor, furthermore the camera should be mentioned as line-scan CCD, not just CCD. Also, in the reference arm, the light rays after the lens are collimating; why so, and why is it not focused? In the figure.1 caption mentions the schematic is not drawn to scale.

b.      As part of Figure 1, the authors MUST include the trigger sync plots explaining the scan time, stimulus application, and also the overall time taken for the for SAW calculation. This will help to understand the readers when the external stimulus is applied to the sample.

c.       a.       From Figure 5, it is clear the authors have used a 2D Galvo scanning system. But they have only shown 2D cross-sectional images, so why not 3D? If the y-scan mirror is not used, then this must be mentioned in the text.

 

d.      Section 2.3, in the equation and text, change Signal_p-p and Noise_p-p to Signal_p2p and Noise_p2p since the currently used notation can be misleading to readers.

4.      Results:

a.       Overall, the result analysis is very brief. Also, the authors need to consider using statistical analysis for the measured values. The most important factor to be taken into account is the very limited sample number and sample demographic. Since this article is about exploring the external stimuli angle in relation to the changes in physical changes in sample physiology, the sample’s material characteristics with a larger sample number and clear statistical analysis are needed to support their claims in results.

b.      Young’s modulus comparison table: Why have the authors made a comparison for their result with very few previous articles to claim for their research results observation? Not to mention, the comparison is made with one of their group’s earlier research work, and the three comparisons done are using three different measurement systems. This is not mentioned in their table. Furthermore, suppose they intend to do this with different measurement techniques. In that case, they have to make an extensive system comparison, including detection accuracy, measurement reliability, fault occurrence, principle of measurement techniques, comparative advantages and disadvantages between measurement techniques, etc.

c.       The discrepancies in Young’s measurement values used in Table. 1 is very high in comparison. Only a very short description is given to explain this. This needs to be extensively described, and why and what makes OCE more reliable when compared to other measurement systems needs to be stated.

d.      Why the error margin in the graph shown in Fig.3 is so large for 20, 45, 70, 75, and 85? What method was used to calculate the error margin? Similarly, the data plots and error margins of the plot in Fig. 4 have multiple overlaps, which makes it very difficult for readers and reviewers alike to comprehend the overall result. This needs to be addressed.

Comments on the Quality of English Language

The article is well written, but the flow of the article can be improved, and it needs minor to moderate changes in the English Language. 

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

This manuscript evaluates the angle of the incidence excitation, the bandwidth of the induced elastic wave are discussed. Co-axial configuration is preferred in the accuracy perspective, but sometimes it does not work in the realistic situations. Overall, this work is interesting and can be helpful for the angle selection. This manuscript needs to be improved as following:

1. The authors need to discuss whether the acoustic path has been changed or not during the angle adjustment, as the acoustic power distribution changes in lateral and axial directions. 

2. The authors should include the following reference when introduce the shaker in Line 54. Li R, Du Z, Qian X, Li Y, Martinez-Camarillo JC, Jiang L, Humayun MS, Chen Z, Zhou Q. High resolution optical coherence elastography of retina under prosthetic electrode. Quant Imaging Med Surg. 2021 Mar;11(3):918-927. doi: 10.21037/qims-20-1137. PMID: 33654665; PMCID: PMC7829169. 

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

All my question are responsed, and l think the revised manuscript can now be accept in present form.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The paper has been revised. However, I do not understand how to reach the conclusion that 5° is the optimal angle for the air-puff system. Please indicate the graph or table that supports this conclusion. 

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Comment 1. Authors are using references without proper background study of the cited references they are using. This is a serious concern. Authors are highly advised to thoroughly read the articles and understand their significance and why the study was done in that particular manner and then cite it only if it becomes necessary. Citing articles without a complete comprehensive understanding of them is frowned upon in scientific writings and it leads to misinterpretations of the said articles.

1.a. The authors cited reference 1; is a proof of concept experiment. Even though the instruments or calculations aren’t that novel, their methodology is somewhat novel by nature. Also, it’s a proof of concept with relevant mathematical modeling.

1.b. In your reference no. 2, “S. Diridollou, et al.” this is a very old article, and besides the point of when it was published, this article makes use of different systems to show the possibility of an original device/instrument called “echorheometer”, the purpose of their study is to report a new instrument for measuring properties of the skin. This is a study for its proposed instrument.

1.c. In your reference no. 3, “Zhang et al.” that study has 30 volunteers (page 34, column 2, last paragraph), with 10 in each group. The authors have clearly not done a detailed background and are just trying to defend and support the study. The study sample number is very small. This is a fact. When the sample number is so limited with such limited diversity and demographics, this, in turn, affects the reproducibility of results and makes the study unreliable.

1.d. The authors cited reference 4, “Wakhlu, Anupam et al.”; this is from a very low-quality journal and not indexed in SCI/SCIE. The purpose of their study is a well-known fact. They have just done a derivative work from previously published research of a similar kind that has been published in well-established journals, and those studies have used proper sample numbers with diverse demographics in the sample.

1.e. In your reference no. 5, “Boyer G. et al.,” this is again a conference article showing a proof of concept for a new methodology.

 Comment 2: The primary reason for comment 4 in the previous review round was asking for a more detailed result analysis. This is not addressed yet.

Comment 3: For the nature of their study, it becomes essential to have detailed effects of stimulus angle and discuss details about the material characteristics of the sample and how the angle of external stimuli can influence the sample properties.   This is not addressed. Also they were advised to use statistical analysis to support their result since the error margin is too high. And their response to defend this is not agreeable.

Author Response

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Author Response File: Author Response.pdf

Round 3

Reviewer 3 Report

Comments and Suggestions for Authors

Comment (1): The Authors have tried to justify their reasoning with good effort. This is Acceptable. Hence, in regards to the sample size, even with their current justification it is not completely compensate for their lack in study model. Due to this reason, as from a reviewer’s point of view, I would recommend the authors change the title and EXTENSIVELY state in the Methods section that this study is a precursor and serves as a guidance for further research to comprehensively study the effects of stimulus angle in SAW-OCE experiments. Also, the Title of the manuscript SHOULD be changed accordingly to what has been suggested. As long as the authors agree to make these changes and adapt their manuscript, as a reviewer I can agree to the presented study’s shortcomings and proceed further for acceptance.

Comment (2): I did notice that the authors gave the citations to convince that from previously published articles that the use of a lower range in sample size, but as mentioned earlier in the previous review stage, the articles were either of different purposes like methodology and system-oriented, or they were articles published which were done without proper scientific standards leading to publications in very low-quality journals. And besides all these, it was undeniably clear that the authors when using those reference articles to justify, they did not read the article in its entirety. This was clear from the statement they gave of sample size in regards to literature No.3 in previous review report. So as a reviewer, I highly advise that the authors be very careful of using citations henceforth, and use only articles which they have a clear understanding and only if it clearly matches to their statements.

 

Comment (3): It is good that the authors have included Table 1 and also added an explanation in the introduction section about the features of SAW regarding the intrinsic properties of material and the stimulation system with supporting citations, and a clear statement highlighting the discrepancies in the measured values of human tissue in the discussion section. But, this statement is left hanging. Authors MUST give an explanation as to why such high margin can occur and also explain how this can be taken to be within agreeable limit. Only with this information, the statement mentioned in their discussion section can be agreeable. 

Author Response

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