Footnotes

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• Contributors All authors made substantial contributions to the conception and design of this study. Subject recruitment and ultrasound examination were performed by JMC. JMC and FM collected the epidemiological and clinical data and performed the statistical analysis and study design. FM, IC, JM-B, JCN-G, JR, JMA-G and JMC drafted the manuscript. All coauthors revised the final 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.

• Patient and public involvement Patients and/or the public were not involved in the design, conduct, reporting or dissemination plans of this research.

• Provenance and peer review Not commissioned; internally peer reviewed.