Self-reported skills and self-confidence in point-of-care ultrasound: a cross-sectional nationwide survey amongst Finnish emergency physicians oleh Ossi Hannula, Ville Hällberg, Anna Meuronen, Olli Suominen, Suvi Rautiainen, Ari Palomäki, Harri Hyppölä, Ritva Vanninen, Kalle Mattila