PONE-D-20-17186

Comparative test-retest variability of outcome parameters derived from brain [18F]FDG PET studies in non-human primates

PLOS ONE

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Reviewers' comments:

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Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: I Don't Know

Reviewer #3: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The authors performed FDG PET brain scans on 6 cynomolgus macaques about one month apart. The parameters include CMRglu, SUVmean, SUVxGlu, SUVRpons and SUVRcerebellum. They also scanned 4 additional animals to see if the values of these parameters fall within the confidence interval defined by the previous 6 animals. The most stable parameter was SUVR with variability between 7-14%, while the variability of CMRglu reached 25-43%. It was concluded SUVR could be used for quantification if pons or crebellum was not affected by the experimental conditions.

This is a well-designed study with clear descriptions of the methodology to allow reproducibility. It provided absolute numbers to compare the variability of various quantification methods across the brain regions. Congratulations to the authors for their deeds and recommendation for publication to share their results.

Reviewer #2: The manuscript presented by Goutal and co-authors explore the repeatability of quantitative parameters from FDG-PET studies in nonhuman primates and also compare them. This is a well-written paper, with a clear and concise text where objectives are well defined, and introduction and discussion supported by a good argumentation. In general, methodology is adequate and experimental methods are described correctly.

However, there are some points that would need to be revised or discussed by the authors in order to improve the quality of the work.

- The authors have carried out a test-retest study controlling all the experimental conditions and have analyzed the reproducibility of the results by the study of intra-subject and inter-subject variability. However, another important measure which can be calculated from test-retest data is the reliability of the measurements by means intraclass correlation coefficient (ICC). Why authors don’t have calculated this coefficient?

- In “PET acquisition” section (page 9, line 130) authors should detail the times at which arterial blood samples were collected to obtain arterial input function.

- For each PET study, authors acquired a 60 min dynamic emission scan (Page 8, line 120). Which temporal sequence did the authors use to reconstruct the studies? Please, explain in “PET acquisition“ section.

- Which statistical test was performed to analyze the homogeneity of experimental conditions (body weight and injected dose)? Please, refer in “Statistical Analyses” section.

- The authors have used a segmentation pipeline to automatically delineate the anatomical regions of interest for each macaque. However, it is usual to spatially normalize brain images to a common stereotaxic space to apply a predetermined template of VOIs. Probably, the method used to quantify the different regions also influences the variability observed in the study. Although the authors discuss the influence of different types of anesthesia on the results of the study (page 19, lines 349-352), it would be also convenient to comment the importance of the quantification method.

- It would be desirable to show a graphical representation of FDG Time Activity Curves of test-retest studies, at least of one of the regions (representative). Likewise, it would be nice to show a representative test-retest PET images of one animal. All this information could be added as supplementary material.

Reviewer #3: Dear authors,

your study is very interesting and carried out very well. Nowadays it is very important to evaluate 18F-FDG PET images, from preclinical with animals to human studies, not just from a qualitative point of view. Some of the common quantitative parameters are still not robust enough to evaluate properly the true effects on the metabolism over time, for example when studying a new drug.

In this article the authors analyze the test-retest variance of many quantitative PET parameters (SUV, CMRglu, SUVxGly, SUV ratio on the pons or on the cerebellum) extracted from brain PET images performed twice on a small group of nonhuman primates (macaques) with a very controlled and reproducible protocol. They validated the results on an independent control group, too.

I think that the article is properly written down with a good depiction of the methods utilized and so, has to be accepted.

Major comment:

- Material and method: you describe in the “animals and housing” paragraph one anesthesia protocol for all procedures, but then it is slightly different for MRI and PET.

- I think that you can add a picture of the PET brain images and a figure of the curve obtained to show the quality of the scan.

- From a qualitative point of view there were any substantial difference between the scans? please add this information

- The mean glycemia level of this group of animals is comparable with other study with the same species? Please add this information

Minor comment:

- Line 63 “by the” is repeated twice

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Reviewer #1: No

Reviewer #2: No

Reviewer #3: No

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Comparative test-retest variability of outcome parameters derived from brain [18F]FDG PET studies in non-human primates

PONE-D-20-17186R1

Dear Dr. Lavisse,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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Kind regards,

Matteo Bauckneht

Academic Editor

PLOS ONE

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