7Frates MC, Doubijet PM, Durfee SM, et al. Sonographic and Doppler characteristics of the corpus lutuem: can they prediet pregnancy outcome. Ultrasound Med,2001,20(8):821-827
8Frates MC, Visweswaran A, Laing FC. Comparison of tubal ring and corpus luteum echogenicities: a useful differentiating characteristic. J Ultrasound Med, 2001,20(1):23-27
9Thoma ME. Early detection of ectopic pregnancy visualizing the presence of a tubal ring with ultrasonography performed by emergency physicians. Am J Emerg Med,2000,18(4):444-448.
10Stein MW, Ricci Z, Novak L, et al. Sonographic comparison of the tubal ring of ectopic pregnancy with the corpus luteum cyst, Ultrasound in Medicine and Biology,2004,23(1):57-62.