Materials and methods
POLAND
All the experiments were performed following the protocol approved by the Bioethics Committee at the Academy of Physical Education in Katowice, Poland, under the reference number 3/2020 on 17 December 2020, and according to the ethical standards of the Declaration of Helsinki 2013. We confirmed that they were carried out in accordance with relevant guidelines and regulations. Informed consent was obtained from all subjects involved in the study. The trial is registered under the number: ISRCTN41899475; (doi.org10.1186/ISRCTN41899475). The HFUS imaging was performed by medical engineer with 5 years’ experience in HFUS ultrasound, graduated two dermatological HFUS courses. To reduce the possible influence of US operator and make the analysis repeatable, the US scanning was performed by the same person.