Review for 10.1186/s12876-022-02517-1 (2022)

Title: Multi-parametric Magnetic Resonance Imaging of Liver Regeneration in a Standardized
Partial Hepatectomy Rat Model
Version: 1 Date: 20 Jul 2022
Reviewer:  Rajarshi Banerjee
Reviewer's report:
Overall, I like this paper. I think it is well written and gives a histological background to post-
hepatectomy changes in MR metrics in a pre-clinical model. The role of inflammation needs
more discussion  – for example I suspect T1 will correlate more with inflammation than it will
with fat which I would argue is more useful.
Overview:
This manuscript presents careful characterisation of the changes observed in multiparametric
MRI metrics following a partial hepatectomy in a mouse model. It is well prepared with clear
presentation of most methodology. The areas considered are well characterised but a better
consideration of the impact of inflammation on the tissue and MRI biomarkers following the
operation would strengthen the narrative of this work. Assessment of livers both pre- and post-
hepatectomy using non-invasive imaging techniques is of great clinical interest and this work
provides a thoughtful histological validation for the changes observed. Hoy et al 2018 would be
a useful reference as well: https://pubmed.ncbi.nlm.nih.gov/29915139/
Specific comments:
1. Previous studies have shown that variable flip angle measurements of T1 are susceptible to
many confounding effects including B0 and B1 field inhomogeneities, slice profile effects, and
fat infiltration. More detail should be included to explain what methods were used to minimise
or correct any confounding effects during either acquisition or reconstruction of the parametric
maps. (Lines 127 and 148)
2. Were the same ROIs propagated onto all parametric maps and, if so, which image was used
to determine the ROIs? Please clarify within the manuscript. (Line 151)
3.  Throughout the manuscript comparisons are made between specific time-points within the
experiment (e.g. comparison of day 7 to pre-PH, or comparison of each day to it adjacent
timepoints). However, only a one-way ANOVA is mentioned in the statistics methodology.
Please include a description of the post-hoc testing performed and the methods used to correct
for the multiple comparisons that are reported. (Line 174)
4.  In Line 252, the authors state that their results are inconsistent with previous studies
by Miyaoka et al. However, the statement beforehand explains that both the present study
and previous work by Miyaoka et al. demonstrate that both hypertrophy and proliferation
of hepatocytes occur post-hepatectomy. Therefore, the studies are consistent and hence the
statement should be amended to show this.
5. Delete repeated ‘an’ on Line 285.
6. Clarify in line 289 that increasing fat content significantly decreases VFA T1 values and
hence the limitation of the postoperative increase in VFA T1 is specific to the VFA method
chosen to measure it. The behaviour of T1 in the presence of fat has been shown to be dependent
on the measurement technique. Therefore, alternative methods (e.g. inversion recovery or
modified Look-Locker inversion) would show different behaviour and may actually amplify the
postoperative signal instead.
7. Swelling of hepatocytes, high numbers of proliferating cells, and increased lipid content are
suggested as causes of increased T1 and T2 post-partial hepatectomy. However, in the earlier
sentence increasing fat was explained to lower VFA T1 values, please can these two results be
clarified. Additionally, it has been well characterised that T1 increases with inflammation. To
what extent do the authors think post-operative inflammation could be causing the immediate
increase in liver T1 and T2 for the first few days post-resection? If possible, the argument
surrounding this point would be strengthened by correlation to an assessment of inflammation
from the collected histological samples (e.g. using the METAVIR or Ishak scores). Line 293.
8. In Table 2, the variation in baseline measurements for the study arm appears much greater
than that seen in the control group, especially for T1 where the standard deviation of the study
arm at baseline is almost 8 times larger than the control group. Firstly, is there any explanation
for the difference between the groups? Secondly, is there any correlation between the baseline
value of the parameters and the recovery following the intervention?
9. Figure 2 shows that there is significant spatial variation in the T1, T2, and D maps. How was
this characterised and accounted for when placing ROIs? A discussion point debating whether
this is artefact from confounding effects on the measurements (e.g. B1 and B0 inhomogeneities)
or a true biological signal would be helpful here. Additionally, the colour scale on the K maps
is very large relative to the variation in values seen and this makes assessment of the spatial
variation of this parameter challenging. Re-scaling the K map to focus on the range of interest
would improve the information presented in this figure.