Application of OCT in the Gastrointestinal Tract

Round  1

Reviewer 1 Report

[13, 14] – You state: „OCT’s greatest impact so far has been in the study of the tubular esophagus owing to its accessibility”. This statement may be correct in the gastrointestinal context, but overall OCT-technology had its greatest impact in the field of ophthalmology.

[41] – The correct expression would be ‘selected wavelengths’ rather than ‘select wavelengths’.

[73] – Only a few SS-OCT systems are capable of an imaging frequency in the region of MHz.

[87] – The correct expression would be ‘imaging depth’ rather than ‘image depth’.

[97, 98] – ‘OCT can also be combined with ultrasound to increase the image depth’, this statement could be misleading, ultrasound is not able to increase the imaging depth of OCT.

[98] – See [87]

[98 - 100] – ‘A study in 2010 … coregistered US and OCT images.’ What was the pursued benefit of this multimodal imaging?

[106] – ‘… which has reduced depolarization’ the wording is not well chosen, it has a reduced depolarizing effect would be more suitable. The next question would be in comparison to what does tumor tissue have a reduced depolarizing effect?

[116] – ‘… countries--including…’ formatting error.

[145] – Imaging depth rather than ‘depth’.

[145] – The unit is µm not ‘um’.

[154] – The abbreviation ‘RFA’ for radiofrequency ablation has not been introduced.

[174] – The expression ‘Anecdotally’ is not suited for the context of a scientific publication.

[176] – The abbreviation ‘EMR’ for endoscopic mucosal resection has not been introduced.

[253] – Formatting error ‘--‘.

[273] – It should read ‘… combining OCT and AI has been …’.

[283] – The abbreviation ‘ROI’ for region of interest has not been introduced.

[323] – The cited paper reports a axial resolution of 12 µm in Air / 8,5 µm in tissue, it is not correct to speak of a microscopic resolution in this context.

[331] – As described by you before, OCT has the capability to achieve a near-microscopic resolution but OCT isn’t microscopically resolved.

Author Response

Please see attached file for point-by-point changes to our manuscript.  We thank the entire panel for careful review and helpful suggestions in improving this review article.

Reviewer 2 Report

This is a review paper on OCT applied for gastrointestinal tract investigations. The topic is currently of interest, the paper is in general well-written, but the content of the paper has to be substantially completed in order to be considered for publication.

1) There are no schematics on OCT systems, they should be added – at least for FD and SS OCT systems.

2) No results on practical investigations using OCT in gastroenterology are given now in the paper. They have to be added - with relevant cases - to show readers examples of images and OCT capability. This is necessary to make the paper of interest to the readers of an archival journal, specifically Appl. Sc. So far, this study is not appealing. OCT is an imaging technique! Where are the images?

3) The list of references is extremely comprehensive, but this reader does not find authors’ references on this topic – except for a JBO review of one of the authors. A review like the present one is normally made by highly-regarded specialists in the field (i.e., OCT), who have specific, high impact contributions in the field. If this is not the case, the study may be of little interest to the readers. The authors therefore need to add their own contributions, with OCT results (see also the previous point) to make a convincing study.

4) Some Refs have (still) to be added, especially regarding the technological part, for example:

A. Cogliati, C. Canavesi, A. Hayes, P. Tankam, V.-F. Duma, A. Santhanam, K. P. Thompson, and J. P. Rolland, MEMS-based handheld scanning probe with pre-shaped input signals for distortion-free images in Gabor-Domain Optical Coherence Microscopy, Optics Express 24(12), 13365-13374, 2016

to point out issues of MEMS scanning to avoid distortions in OCT images.

5) A few refs have to be added regarding the driving modalities of endoscopes, with a discussion issues of piezoelectric – Refs [37, 132] vs electroelectrical and magnetic driving, for example, including

W. Piyawattanametha, H. Ra, Z. Qiu, S. Friedland, J. T. C. Liu, K. Loewke, G. S. Kino, O. Solgaard, T. D. Wang, M. J. Mandella, C. H. Contag, „In vivo near-infrared dual-axis confocal microendoscopy in the human lower gastrointestinal tract,” J. Biomed. Opt. 17, 021102 (2012).

6) Please comment on raster vs spiral vs Lissajoux scanning; also, with regard to forward view vs circumferential view, e.g.

X. Mu, G. Zhou, H. Yu, Y. Du, H. Feng, J. M. L. Tsai, and F. S. Chau, „Compact MEMS-driven pyramidal polygon reflector for circumferential scanned endoscopic imaging probe,” Opt. Express 20, 6325-6339 (2012).

Please give examples.

7) Progress has been made on OCT capsules – including by Harvard School of Medicine. They should be highlighted – with examples and issues, the latter including for example regarding the link that does exit between the system and the capsule. This is in contrast to common video-grabbing images capsules utilized for esophagus, stomach, etc.

8) The study also has some flaws regarding the scientific part, for example in the Abstract the statement 'OCT’s greatest impact so far has been in the study of the tubular esophagus owing to its accessibility' is not correct, as OCT is first of all applicable in ophthalmology. One cannot refer to the digestive system, when OCT was first developed for retina. Please check the paper for such flaws and correct. 

9) The English is in general fine, but edits do exist, for example ‘strictures’ instead of ‘structures’ in line 198. Please recheck the manuscript from this point of view.

In conclusion, the paper has to be substantially completed to be considered for publication in Appl. Sc.

Author Response

Please see attached file for point-by-point changes to our manuscript. We thank the entire panel for careful review and helpful suggestions in improving this review article.

Author Response File: Author Response.pdf

Reviewer 3 Report

The article is a review of application of OCT mainly in esophagus and colon. Authors cover a wide number of publications up to date. I have enjoyed reading this review, as it clearly explains the application field and covers different system components and different pathologies. 

I will make some comments, but it is authors' option to consider them:

The number of references used is quite large. They are relevant but I am not sure if so many references are needed. Maybe from ref. 3 to 11 and from ref. 21 to 41 some references would be redundant.

From lines 65 to 75, the differences among OCT types are explained. But in the following paragraph, (lines 77 to 84) the advantages or disadvantages of different probe configuration and scanning patterns are not explained. 

In some points, authors could better explain/summarize the references they are referring to. For example, in line 128 “…despite their potential for increased risk of malignancy [65-68].” This sentence is quite general and the reader would have to go to these references to check where this assumption comes from.

Author Response

Please see attached file for point-by-point changes to our manuscript. We thank the entire panel for careful review and helpful suggestions in improving this review article.

Author Response File: Author Response.pdf

Round  2

Reviewer 2 Report

This review paper has been substantially completed according to all the reviewers' comments. In the opinion of this reader, it can be considered in the present form for publication in Appl. Sc.