Wu, J.; Chen, X.; Wu, Q.; Wei, N.; An, G.; Yu, H.; Wang, N. Contrast Enhanced Ultrasound - a Useful Method for Diagnosing Tubal Ectopic Pregnancy With Low Level β-HCG. Ultrasound J 2025, 17 (1), 33. https://doi.org/10.1186/s13089-025-00438-0.