Histogram-Based Analysis of Low- and High-Grade Glioma and Its Surrounding Edema Using Arterial Spin Labeling Magnetic Resonance Imaging

Round 1

Reviewer 1 Report

The manuscript presents an interesting study on analysis of glioma and edema. However, there are several fundamental issues that need to be addressed before considering it for publication.

1) While it briefly mentions some background information related to the use of Arterial Spin Labeling Magnetic Resonance Imaging (ASL MRI) in glioma studies, it does not delve into a critical review of relevant studies, methodologies, or findings in the field. 

2) The authors should consider employing more advanced statistical methods, such as cross-validation or bootstrapping, to ensure the robustness of their findings. 

3) No comparison is made between the proposed method's results and the existing state-of-the-art methods' results.

4) Line 343 - 345 : "ASL is not commonly and generally used in clinical routine due to various reasons, e. g., the lack of knowledge and/or experience and reservations about the method due to its sensitivity to movement. " raises important questions about the practical utility of this imaging modality. How can ASL MRI be practically useful despite its limited use in clinical routine?

Minor editing of English language required

Author Response

Dear Reviewer, please find the point-by-point response here:

1) While it briefly mentions some background information related to the use of Arterial Spin Labeling Magnetic Resonance Imaging (ASL MRI) in glioma studies, it does not delve into a critical review of relevant studies, methodologies, or findings in the field. 

A: We added more background and explanations and added more literature to the introduction. Specifically, references 16-20 have been added and briefly discussed.

2) The authors should consider employing more advanced statistical methods, such as cross-validation or bootstrapping, to ensure the robustness of their findings. 

A: We specifically performed commonly practiced statistical analysis to make it easier comparable with other studies from the literature rather than performing methods that are used in machine learning as the findings are mainly intended for a clinical application.

3) No comparison is made between the proposed method's results and the existing state-of-the-art methods' results.

A: We agree and added a descirption on the comparability of other and state-of-the-art methods in the discussion. We added this as new paragraph before the "strengths of this study" section

4) Line 343 - 345 : "ASL is not commonly and generally used in clinical routine due to various reasons, e. g., the lack of knowledge and/or experience and reservations about the method due to its sensitivity to movement. " raises important questions about the practical utility of this imaging modality. How can ASL MRI be practically useful despite its limited use in clinical routine?

A: We agree that this expression was not well phrased and updated it accordingly: "ASL currently underutilized in clinical routine, therefore our study aims to show more applications of this MRI method"

Reviewer 2 Report

Based on the provided excerpt, there are a few deficiencies in the article that can be noted:

1.      Lack of detailed methodology: While the article provides some information on the methodology used, it lacks detailed information on the specific steps taken to analyze the ASL data and calculate the histograms. This could make it difficult for other researchers to replicate the study.

2.      Lack of comparison with other imaging techniques: The article mentions that ASL perfusion imaging can be used to non-invasively evaluate tumors, but it does not compare the effectiveness of ASL with other imaging techniques, such as contrast-enhanced MRI or PET scans.

3.      Limited predictive power for MGMT and mutation status: The article suggests that ASL perfusion imaging may not be as effective in predicting MGMT and mutation status as other imaging techniques. This limitation should be noted in the article to provide a more balanced view of the potential of ASL perfusion imaging.

Author Response

Dear Reviewer, please find the point-by-point response here:

1. Lack of detailed methodology: While the article provides some information on the methodology used, it lacks detailed information on the specific steps taken to analyze the ASL data and calculate the histograms. This could make it difficult for other researchers to replicate the study.

A: We agree and added more context and explanations to the methodology the reviewer mentioned. Specifically we added a more in-depth description of the masking process and how the data for Mean, Entropy, etc. were obtained using the Matlab scripts. Please find this description at the end of the Materials and Methods section.

2. Lack of comparison with other imaging techniques: The article mentions that ASL perfusion imaging can be used to non-invasively evaluate tumors, but it does not compare the effectiveness of ASL with other imaging techniques, such as contrast-enhanced MRI or PET scans.

A: We agree and added comparisons from the literature on the effectiveness of other modalities in comparison.

3. Limited predictive power for MGMT and mutation status: The article suggests that ASL perfusion imaging may not be as effective in predicting MGMT and mutation status as other imaging techniques. This limitation should be noted in the article to provide a more balanced view of the potential of ASL perfusion imaging.

A: We agree, please find the discussion of the MGMT and mutation status in the Discussion section:
"Third, the MGMT status was analyzed. Here, either the positive or negative status was used while the indeterminate and empty datapoints were discarded. There were no statistically significant results obtained except for the Minimum value. However, this single metric might be skewed due to the small range and large outlier datapoints. Thus, ASL seems to be not an appropriate predictor of the MGMT status which is not surprising, as these kinds of changes likely do not reflect in perfusion changes.

Similarly, the type of mutation was analyzed, i.e. IDH-1, NOS or wildtype (the dataset only had two patients with IDH-2 mutations which were subsequently discarded) which did not show statistically significant results. Only the Minimum shows a p-value below 0.05 which again has to be interpreted with care as in the MGMT status analysis. As explained in the MGMT status, also mutations will not likely cause (strong) changes in perfusion and thus will not be reflected in the ASL analysis.

While MRI has been shown to be predictive of MGMT and mutation status, such analysis likely were performed using multiple sequences and contrasts rather than perfusion imaging alone and therefore the value of (ASL) perfusion imaging remains questionable [26. 27]."

Reviewer 3 Report

The paper is very well written and easy to follow at most places. 

 

It is not explicitly mentioned or clear in the introduction section what is the contribution of the overall paper. So, the authors may like to add a contribution paragraph in the intro section explaining why this paper is better than the previous ones. Also, it may be good to add a brief paragraph stating the limitations of the earlier work. 

 

Figures 2,3 and 4 are unnecessarily huge and consume a lot of white space. These graphs should be compressed and plotted using minimal space in the paper.

Author Response

Dear Reviewer, please find the point-by-point response here:

It is not explicitly mentioned or clear in the introduction section what is the contribution of the overall paper. So, the authors may like to add a contribution paragraph in the intro section explaining why this paper is better than the previous ones. Also, it may be good to add a brief paragraph stating the limitations of the earlier work. 

 

A: We agree and added a statement of what we intend to say and what this study contributes to the literature and how this should overcome limitations of previous studies. We modified the last paragraph of the introduction accordingly: "The aim of this study therefore is to use ASL as a biomarker to differentiate between the histopathological diagnosis, HGG and LGG, MGMT status and mutation type and finally assessing the performance of ASL in the diagnosis and delineation of the tumor-surrounding edema in order to overcome limitations of previous studies which did not have these clinical parameters and/or no segmentations of the tumor and surrounding edema at hand. Additionally, the goal is to highlight ASL being used in routine glioma imaging highlighting the potential for differential diagnosis prompting the use in clinical settings."

 

Figures 2,3 and 4 are unnecessarily huge and consume a lot of white space. These graphs should be compressed and plotted using minimal space in the paper.

 

A: We agree. The figures were taken "as is" from the statistical software, but we modified them now and removed the majority of the blank space.

Round 2

Reviewer 1 Report

Thanks to the authors for revising the manuscript. I have the following comments:

1) Please mention the quantitative accuracy of reference number 9 if available.

2) The result section provides redundant information since Table 2 contains it.

3) An accuracy comparison with existing work is still absent.

Minor 

Author Response

Dear Reviewer, please find the point-by-point answer here:

1) Please mention the quantitative accuracy of reference number 9 if available.

We added the accuracy of the reviewe paper from reference 9. We also added the information on sensitivity and specificity. The sentence now reads as: "Sometimes MRI is also used in combination with PET-CT showing improved specificity (66%-95.5%), sensitivity (81%-90.05%) and accuracy (70.9%-74.9%) [9]. "

2) The result section provides redundant information since Table 2 contains it.

We agree that the results are both in the table and the results section. We however have to dissent from removing the text as the results section focusses on the statistical significant values only to present this information to the readers in a concise manner, while the table is intended to show the results of all analysis. To inform the readers about this, we switched the last paragraph to the top of the section and added the following sentence: "The results presented in this section describe the statistically significant findings only."

3) An accuracy comparison with existing work is still absent.

We apologize for the oversight. However, doing comparisons and drawing conclusions when looking into the literature of using ASL predicting the accuracy of the results is non-trivial as this study differs in its concept from the published literature. In the literature (see for example references 13-20) both for individual studies and meta-analyses the value of the CBF was taken into consideration. In this study, we focussed on the image features extracted from the segmented images that are not directly related to CBF. Thus, a direct comparison of the results would be non-acurrate on its own. We added a clarification of this issue at the end of the discussion section:

"Another issue that this study raises is that only the image features have been used rather than using CBF as the main predictor of disease, thus a direct comparison of the findings with the literature cannot be done. A comparative analysis potentially can reveal a complementary diagnostic benefit when combining CBF and image features."