Speckle-Reduced Optical Coherence Tomography Using a Tunable Quasi-Supercontinuum Source

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript by Chen et al. reports a new speckle-reduced optical coherence tomography capable of generating seven quasi-SC spectra with different central wavelengths and bandwidths to compound averaging uncorrelated patterns to reduce speckle. Speckle-reduced high-resolution OCT imaging in tape stacks and pig thyroid gland were demonstrated. Additionally, the authors have strategically employed various spectral combinations to enhance the OCT's performance, leading to significant improvements in the signal-to-noise ratio (SNR), contrast (C), and contrast-to-noise ratio (CNR). Compared with traditional hardware-based and software-based methods, the as-developed method based on using tunable quasi-supercontinuum source to improve the performance of OCT without the need for additional devices, instruments, and postprocessing. This technique is innovative and of great value to improve image quality of OCT. However, several issues need to be addressed prior to publication:

1.     Page 4, Figure 3, please standardize the spacing between numbers and units in the legends to ensure consistency. For instance, maintain a uniform format by adding a space between "1652" and "nm" to match "1713 nm".

2.     Page 5, lines 153-155, it was stated that “We applied the above tunable quasi-SC output to an OCT system and examined the total system sensitivity and axial resolution using a reflective mirror as a sample, as shown in Table 1”. To bolster your claims, consider including an OCT image of the reflective mirror sample in this section, which would serve as a more compelling piece of evidence.

3.     Page 8, Table 2 shows the image metrics of initial images and speckle-reduced images. Will different compounding combinations（n=3,5,7） have an impact on penetration depth? It is recommended to list the penetration depth data in a separate column for explanation.

4.     Page 8, lines 244-246, it is recommended to give the calculation process of 2 dB, 20 dB and 2dB. In addition, to maintain consistency throughout the document, please add the "dB" unit after the numeral "20" in the text.

Comments on the Quality of English Language

 Moderate editing of English language required

Author Response

I'm sorry for the late submission of revised paper. It took time to complete the additional experiment. Please see the attachment. 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

From a reviewer’s point of view, overall, the authors have done a clear experimental study and proposed a new approach for speckle reduction using frequency compounding using a tunable quasi-super continuum laser for Optical coherence tomography (OCT). The article is well written and may need minor to moderate changes in the English Language. Given the authors address all comments, the manuscript can be considered for acceptance.

Comments:

1.      Is this article an extended version of the conference paper presented by the same authors? Can the authors state the modifications or advancements to that of the conference-presented materials? This is not a critical comment, but a clarification can help in better understanding.

2.      In the introduction section, with more relevant and recent citations, can the authors provide more in-detail explanations of earlier methods and approaches (both software and hardware methods) used for addressing speckle reduction in OCT?

3.      In equation (1), “I”, and “n” are not defined in the manuscript text.

4.      What is the maximum achievable speed of imaging, also mention the frame rate

5.      Fig. 2 experimental setup, text within is very difficult to see.

6.      In the experimental methodology for the preparation of pig thyroid gland is not mentioned.

7.      Can the authors give real-time cross-sectional images of a live sample with their proposed method? Mice retina or skin imaging of imaging can show the robustness of the proposed system.

 

8.      A more detailed comparative analysis of how their approach is superior to previously reported methods should be added in the discussion section with relevant citations.

Comments on the Quality of English Language

The article is well written and may need minor to moderate changes in the English Language. 

Author Response

I'm sorry for the late submission of revised paper. It took time to complete the additional experiment. Please see the attachment. 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

In the manuscript ' Speckle-reduced optical coherence tomography using tunable quasi-supercontinuum source, ' the authors Chen et al reported their research on the speckle-reduced OCT technology based on a wavelength-tunable laser source with a pulsed operation. Ex-vivo research on pig thyroid gland was done using this technology and high-SNR results were obtained according to the authors. This manuscript can be accept as the publication of  Photonics while the authors must answer the following questions.

1. How much power did the authors use in the imaging? The manuscript mentioned the laser source can output 360 mW which is too high in the OCT imaging thus the authors must claim the safety for laser application in the biological medicine.

2. What are the advantages applying 1600-1900 nm in OCT system compared to the normally used 1300 nm? As we know the cost of this wavelength-tunable laser source should be much higher than the commercial laser diode. A reference is as following 

G. Zhang, and W. Wei, “4-D Imaging of Beating Tissues Using Optical Coherence Tomography. ”IEEE Photon. J, 13, 3900211 (2021).

3. The correlation relations of the cross-section images in figure 4 should be given and discussed to show the advantage of the speckle-recuced technology. This can also reference the journal paper given above. 

 

 

Author Response

I'm sorry for the late submission of revised paper. It took time to complete the additional experiment. Please see the attachment. 

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

This paper described a new way of denoising the speckle effect in OCT system by modulating the source spectral shape to take a series of images and coumpounding them together. The implementation of this method is relying on a custom quasi SC fiber laser that was reported in their previous work. Compared to other hardware methods, this method has the advantages of avoiding modifying the oct module and adapting to the existing sampling rate as long as the laser modulation is fast enough. The description of the method is clear and the author very well demonstrated the system performance by measuring tape and biological tissue sample. Overall, I think this is a very good work which will be interesting to the field. 

Some more questions below:

1)Please provide more details on your oct system. what is the current A-scan rate, B-scan rate. What is the lateral resolution? etc. 

2) Could the author add some discussion comparing this method to others (like those changing the angle, software) from perspective of imaging speed, resolution etc.?

3) The author mentioned the trade off b/t axial resolution and speckle denoising limited by the spectral bandwidth. Could the author comment why 7 spectral bands were selected? How to improve this method further?

4) The SC source is now from 1600 to 1900 nm. Could it be modified for visible range for high resolution oct? 

Author Response

I'm sorry for the late submission of revised paper. It took time to complete the additional experiment. Please see the attachment. 

Author Response File: Author Response.pdf