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: 
25 Sep 2020
Reviewer's report:
PEER REVIEWER ASSESSMENTS: 
OBJECTIVE - Full research articles: is there a clear objective that addresses a
testable research question(s) (brief or other article types: is there a clear
objective)?
No - there are minor issues
DESIGN - Is the current approach (including controls and analysis protocols)
appropriate for the objective?
No - there are major issues
EXECUTION - Are the experiments and analyses performed with technical rigor
to allow confidence in the results?
No - there are minor issues
STATISTICS - Is the use of statistics in the manuscript appropriate?
No - there are issues with the statistics in the study
INTERPRETATION - Is the current interpretation/discussion of the results
reasonable and not overstated?
No - there are minor issues
OVERALL MANUSCRIPT POTENTIAL - Is the current version of this work
technically sound? If not, can revisions be made to make the work technically
sound?
Probably - with minor revisions
PEER REVIEWER COMMENTS: 
GENERAL COMMENTS: 
This manuscript is an amalgamation of two related but poorly correlated studies.
Both have potential but suffer from significant limitations that are not
ameliorated by combining both studies into one paper in the current form.
REQUESTED REVISIONS: 
The relevance of gastric transit time to bowel emptying was not clear. Illeus
(lack of intestinal motility) can be independent of gastric emptying. The authors
are encouraged to establish GE as a cause of constipation using the literature.
GE is also influenced by the composition of gastric contents. This study did not
determine if the increased rate of GE in MCD was due to the nutritive value of
MCD or the medicinal activity of MCD. For example, the test meals included
volatile oils with a saline control. Fats and oils are known to impact gastric
motility and may be partly responsible for the MCD results. There was also no
attempt to discuss the physiology, mechanism of action, or clinical applications
of MCD. I appreciate if these were not the aim of this study, but a statement
about the limitations for this study's scope is needed in the discussion. 
Validating the efficacy of PET in GE would be better served with something that
has an established impact on GE transit time, rather than an understudied
compound like MCD. 
With relevance to the primary aim of this study (using PET for GE assessment),
the authors used two quantification techniques with PET data to validate the
PET data. The authors should have used an alternative method (e.g.,
scintigraphy, barium, gross dissection, etc.) to validate the GE transit time. 
The
correlation between the two analysis methods is not enough to compare the
accuracy of PET with other methods. 
The mouse model of constipation was reportedly based on previous studies (line
197); however, these studies were not referenced. No information was provided
to explain how this protocol was decided upon. 
Throughout the manuscript avoid referencing studies without providing citation
information. Statements like "previous studies" should be followed with
supportive citations. 
It was not clear if one or multiple researchers conducted any of the
measurements; the repeatability and variation in those researchers and
confirmation that the study was conducted in a blinded fashion should also be
included. 
An explanation or reference on how fecal quality was scored should be included. 
FIG 5: Controls appear to have different weights, fecal quality, and fecal
moisture on day 1 of the study period. Given that the treatment groups did not
start off the same, statistical differences using AVOVA could be due to
differences in these populations alone. Including data prior to day 1 would be
helpful to show the initial homogeneity of the mice groups. 
In Table 1: If the dose of GA-NOTA was the same in all 4 treatment groups and
only the viscosity of the feeds changed, then why are the %ID/g
disproportionately higher in the G# and G$ group than the G1 and G2 groups. In
G1 and G4, the duodenum has ~1/4 of the %ID/g of the stomach and the
duodenum has 1/6 of the %ID/g of the stomach in G2 and G4. This data does not
support a shift to the intestines in the less viscous treatment groups. It only
suggests that the more viscous materials had higher %ID/g.
ADDITIONAL REQUESTS/SUGGESTIONS: 
The discussion is very redundant and does not adequately present the findings in
the context of the current literature for either part of the study. The authors are
also cautioned to avoid statements like "this study proved" when only supportive
evidence is offered. 
There was also no attempt to discuss the physiology,
mechanism of action, or clinical applications of MCD. I appreciate if these were
not the aim of this study, but a statement about the limitations for this study's
scope is needed in the discussion. The mouse model of constipation was
reportedly based on previous studies (line 197); however, these studies were not
referenced. No information was provided to explain how this protocol was
decided upon. 
Throughout the manuscript, avoid referencing studies without providing citation
information. Statements like "previous studies" should be followed with
supportive citations. A citation is needed on line 83 to support the statement that
MCD has been "proved" effective…"
A citation is needed on line 85 to support the statement on why and how MCD is
usually used. 
A citation is needed to support line 210 "MCD was based on the record of
TCM".
Consider revising the manuscript title as this study was not evaluating PET for
constipation assessment.
There is substantial need for English grammar and style edits prior to publication
throughout the manuscript.
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Is the study design appropriate to answer the research question (including the use
of appropriate controls), and are the conclusions supported by the evidence
presented?
No
Are the methods sufficiently described to allow the study to be repeated?
No
Is the use of statistics and treatment of uncertainties appropriate?
No
Is the presentation of the work clear?
No
Are the images in this manuscript (including electrophoretic gels and blots) free
from apparent manipulation?
Yes