Restenosis Investigation of Two-Stent Placement in the Artery Bifurcation with Different Stenting Techniques Using Computational Fluid Dynamics Analysis
Round 1
Reviewer 1 Report
The research paper investigates the possibility of restenosis under two-stent placement in the artery bifurcation with different stenting techniques using CFD with idealized model. . The manuscript presents novelty content which is worthy of publication. However, to improve the manuscript quality, major revision is required, and the following remarks should be considered:
Introduction
Introduction is not written. The author should include a paragraph to clearly state why CFD is needed in this case, and how much previous research is done.
In recent years, many stenting techniques for coronary artery bifurcation have been developed to improve curative effects of coronary bifurcation lesions.
Please include evidence when you mention a statement like this.
Coronary stenting is considered as a standard treatment for the coronary artery stenosis.
Any related literature to support your statement?
Please rewrite the introduction to support your research with enough literature review.
Method.
Does the idealized model match with dimension of real patient? Please support it with literature
Please provide the equations to run the model, is it a laminar or turbulence model you are using? What is Reynolds number for your model?
Please include mesh sensitivity test results to show the deviation of velocity and pressure under different mesh size.
What is the element type use for fluid, please include the type.
How many cycle the author perform the study? It is important that the author perform at least five cycle before the flow is stabilized and use the last cycle to interpret the results. Only run one cycle may affect the TAWSS and OSI value.
The outlet is important, please list the outlet condition as limitation of current research. Should use windkessel model for it.
Please show your pressure distribution for your model. The flow is driven by pressure gradient.
How the author defines the threshold of high and low OSI and TAWSS the high and low definition is not clear to me. Please evaluate the threshold use.
Minor comments
Provide the full words after the abbreviation in the figure caption. please check again the reference list, the format is not consistent.
Line 279 TAWSS area ration, should change to area ratio
Comments for author File: 
Comments.pdf
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Reviewer 2 Report
The authors around B. Chen study two types of coronary artery without stent and after stenting. In particular they consider three different stenting techniques with the aim of assessing the role of the restenosis due to the inserted devices. For that, using CFD they analyze the blood flow and wall shear stress main related descriptors within the arteries trying to establish a relationship between restenosis (specific values of the WSS indices) and used stenting technique.
GENERAL COMMENTS
In my opinion, the work is not suitable for publication in the present form. A list of the main concerns can be found below:
1. In general I found a lack of novelty of the manuscript, as previous developed models in the literature have analyzed similar topics even with additional details and more powerful models. The authors mainly analyzed simple bifurcations with and without stent and their analysis is limited to the post process of specific WSS descriptors. The work is standard, and the significance of the presented results is limited.
2. The methodology has to be written in details. The way how the stent is introduced inside the artery plays an important role. As far as I understand, the authors have just designed the artery with the stents perfectly located within the bifurcation. However, how did the authors obtain all the specific configurations? Normally a structural analysis is previously performed and the artery is deformed by the introduction of the stent (please see the work of Migliavacca and coworkers). In the present case, the procedure for obtaining the stented geometries are not detailed and thus unclear. Page 3 should be entirely rewritten and all the details should be given.
3. Page 4: The two arteries without stent are actually not comparable as the geometries are different. The difference in the velocity field seems to be due to different diameters at the main and child stems and this influences the computation of WSS descriptors.
4. The flow is simulated as laminar or turbulent? At page 4, the authors talk about turbulent flow... however, before they talk about laminar flow. Please clarify. Do the authors refer to recirculatory flow instead of turbulent flow? (line 143-145, page 4, section Results).
5. The Figure representing the TAWSS looks somehow strange. I expected that the region near the stent should present a non uniform distribution. I only see higher values near the exit of the artery and low values at the entrance probably due to the flow velocity. The presented spatial distribution is not significant. These values are non interesting. The in stent TAWSS should be presented. From the Figure it cannot be seen ...
6. The spatial distribution of the OSI is not presented on the artery. A Figure is needed and the OSI value could make clear if the TAWSS distribution is correct or not. Also here, in the in stent regions a non uniform OSI is expected as for the TAWSS.
7. The presented histograms need to consider the area of the artery with specific TAWSS and OSI values for quantifying the presented results.
8. The computational model need to be netter described: how many cycles have the authors computed? Computational costs?
9. Did the authors use inlet and outlet extensions? These are required for damping the imposition of BCs and local peak values of velocity and WSS.
10. No information of the used computational grid is given. Topology, number of elements, mesh independence study should be carefully described and provided.
11. With the presented study, the authors can correlate the WSS descriptors with the geometries... I don't think that a correlation with the restenosis can be given. The real goal of the study is unclear to me.
TECHNICAL COMMENTS
The manuscript spell has to be carefully reviewed. I list some of the errors below:
Please use the correct symbol for degrees and replace the work degrees with its symbol (for example page 2, line 83).
Line 74, page 2: insert a dot in the sentence.
Page 6: ''...was take the OSI...' Please rephrase
Page 7, line 243: '..form the main..'
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Suggest the last sentence of the discussion "Finally, the outlet conditions of each branches were simplified constant pressure which will be improved in the future by including Windkessel model and patient-specific pressure waveform measurement"
I have not further comment and recommend accept it.
Reviewer 2 Report
The authors have addressed all the concerns highlighted in the review report and the manuscript look now much better. Hence, I am pleased to recommend the manuscirpt for publication.
