Wu, Jingping, et al. “Contrast Enhanced Ultrasound - a Useful Method for Diagnosing Tubal Ectopic Pregnancy With Low Level β-HCG”. The Ultrasound Journal, vol. 17, no. 1, July 2025, p. 33, https://mattioli1885journals.com/index.php/theultrasoundjournal/article/view/18152.