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Footnotes
Contributors RE was responsible for conceptualizing the project, obtaining ultrasound images, and editing the manuscript. AS was responsible for editing the manuscript. HCY was responsible for drafting and editing the manuscript.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Provenance and peer review Not commissioned; internally peer reviewed.
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