https://pubmed.ncbi.nlm.nih.gov/33954749/Velthuis PJ, Jansen O, Schelke LW, Moon HJ, Kadouch J, Ascher B, Cotofana S. A Guide to Doppler Ultrasound Analysis of the Face in Cosmetic Medicine. Part 1: Standard Positions. Aesthet Surg J. 2021 Oct 15; 41(11):NP1621-NP1632. doi.: 10.1093/asj/sjaa410. PMID: 33954581.Velthuis PJ, Jansen O, Schelke LW, Moon HJ, Kadouch J, Ascher B, Cotofana S. A Guide to Doppler Ultrasound Analysis of the Face in Cosmetic Medicine. Part 2: Vascular Mapping. Aesthet Surg J. 2021 Oct 15; 41(11):NP1633-NP1644. doi.: 10.1093/asj/sjaa411. PMID: 33954749.