Arsene Longin Ella1, José Delgadillo1, Philippe Chemineau1, and Matthieu Keller1
1Laboratory of Reproductive Physiology and Behavior, INRA - Centre Val de Loire, Nouzilly, France
Synopsis
The sheep model was first used in
the field of reproductive physiology in agronomy to improve milk and meat
production, and then was brought into fundamental and preclinical neurosciences.
Since a decade, MR studies performed on this model are increasingly reported.
To play an important role in MR translational neuroscientific research, a brain
template and an atlas are therefore necessary. Simultaneously, two MR templates
were proposed in 2015. To complete the set of MR tools, we computed a high resolution 3D in-vivo sheep brain atlas
including: i) gyri and sulci ii)
inner structures iii)
main external structures.INTRODUCTION
The
sheep model was first used in the field of reproductive physiology in agronomy
to improve the production of milk and meat
1, and then was brought
into a broad range of fundamental and preclinical neuroscience studies.
2
Since a decade, MR studies performed on this model are increasingly reported.
3,4
To play an important role in MR translational neuroscientific research, a
template image and an atlas of the sheep brain are therefore necessary.
Simultaneously, two MR templates were proposed in 2015
5,6 and to
complete the set of MR tools, in this study, we computed a high resolution 3D in-vivo sheep brain
atlas including: i) gyri and sulci, ii) inner
structures, iii) main external
structures (cerebrum, brain stem and cerebellum).
MATERIALS AND METHODS
MRI
scans were acquired on anesthetized 18 female sheep of 4 years old (with 20
mg/kg of ketamine, intubated and maintained on 3% isoflurane vaporized in
oxygen) with a 3T VERIO Siemens device at the CIRE platform of INRA Nouzilly France.
Parameters were for the Magnetization Prepared Rapid Gradient Echo (MPRAGE)
T1W: TR 2500 ms; TE 3.6 ms; TI 900; FA 12°; NEX 4; matrix 384×384; FOV192 mm;
288 sagittal slices with a thickness of 0.5 mm; and for the SPACE T2W: TR 4000
ms; TE 43 ms; FA 120°; NEX 5; matrix 512×512; FOV180 mm; 208 sagittal slices
with a thickness of 0.35 mm, resampled to a voxel size of 0.5x0.5x0.5 mm
3.
T1W and T2W templates images and non-linear tissue probability maps (TMP) where
computed using an iterative optimized non-linear registration in FSL (FMRIB
Analysis Group, Oxford, UK) as described in
6,7. Finally, atlas
structures where extracted either by segmenting templates using FSL-FAST or by
an intensity threshold of TPM and identified.
RESULTS
Results showed a high spatial
resolution of templates and tissue probability maps (TPM) of the gray matter (GM),
the white matter (WM) and the cerebrospinal fluid or CSF (
fig.1) which led to the segmentation of
20 gyri (
fig.2) and 21 deep internal
structures (
fig.3). We were also able to identify the main external structures (
fig.4):
cerebrum, cerebellum, pons, pituitary gland,
medulla oblongata, and midbrain.
DISCUSSION AND CONCLUSION
If
a single intensity threshold of TPM of the CSF, WM, and GM allowed to retrieve
structures like ventricles (CSF), corpus callosum (WM) and striatal complex
(GM), a mix of both FSL-FAST segmentation of templates and TPM intensity
threshold was necessary to overcome the delineation of smaller structures with
a minimum of manual interaction. This was helped by the high spatial resolution
presented by templates and TPM where those small structures were already
visible. The atlas presented in this study, associated to early developed
templates provide a full set of MRI tools necessary to perform group studies
for different types of MR imaging techniques and may be a key step for the use
of the sheep model in the translational brain research.
Acknowledgements
No acknowledgement found.References
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