Review for 10.1186/s12876-021-01642-7 (2021)

Reviewer’s report
Title: 
68Ga-NOTA PET imaging for gastric emptying assessment in mice
Version: 
0 
Date: 
26 Jun 2020
Reviewer's report:
It is an interesting and novel study proposing the use of PET imaging for the
non-invasive evaluation of GE in mice, including a large study for the follow-up
of therapies in a constipation model. Nevertheless, although the authors
demonstrated the feasibility of the technique, the design of the study is unclear
and unstructured, including redundant information and many useless tests. 
Finally, the reading of the article is cumbersome and unclear and we highly
recommend a professional english-editing service for the improvement of the
revised paper.
Major changes:
The Introduction section has to be revised for including additional cites to papers
focused on the use of preclinical imaging for gastrointestinal tracking and
mention the advantages of PET with respect to scintigraphy.
The comparison between ROI-based method and PMOD is poorly described and
the need to do it is not understood.
Scintigraphy scans were included in this study but the results are only included
in the Supplementary Data. We recommend removing scintigraphy scans from
the paper.
The correlation study between TAC, GER, and T1/2, %ID/g etc is absurd as the
high linear correlation obtained is expected from the definition.
Can the authors evaluate the use of CT-images for quantify GE from this study?
Required minor changes:
Page 2, L51: The authors state GE evaluation is challenging in mice, is it also in
humans?
Page 3, L55-56: Why MRI is limited? specify more
Page 3, L56: Computed Tomography can be also considered as alternative. Some
works have been carried out but they are uncited:
Gomez-Lado et al. Gastrointestinal Tracking and Gastric Emptying of Coated
Capsules in Rats with or without Sedation Using CT imaging. Pharmaceutics
2020 12(1):81
Page 3, L64: " have the advantages of scintigraphy" which??
Page 3, L68: Some works are uncited, for example:
Goyanes et al. PET/CT imaging of 3D printed devices in the gastrointestinal tract
of rodents. Int J Pharm 2018 536(1):158-164 
Page 4, L93: ICR??
Page 6, L133. How the conscious animal was immobilized? 
Page 6, L145. Manual ROIs were 3D or 2D?
Page 6, L156. 
Which type of "manual correction" was applied?
Page 11, L260. Part of the parameters TAC, GER, and T1/2 of %ID/g etc are
redundant, it would be convenient a simplification of the results in this sense. 
Page 12, L287. The authors state that "ROIs could substitute the volume or total
activity calculated by PMOD to reflect the GE process." but the reasons why it is
interesting are unknown
Page 14, L320-335 Again, redundant information is presented here, please
simplify
Page 15, L352 Further analysis are required for including the statement: "PET
owns more superior quantification capability and image quality" 
Furthermore, this study is not a face-to-face comparison between scintigraphy
and PET, because clinical gammacamera is used instead of a dedicated scan for
rodents. 
Page 15, L355 The authors states that "%ID/g, GER, and T1/2 provides similar
information" & "had high correlations with each other" as a result of the work,
but it is completely expected from the definition.
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