<qa>  What is the name of the study that compared vaginal ultrasound of the endometri12. Botsis D, Kassanos D, Kalogirou D, Antoniou G, Vitoratos N, Karakitsos P. Vaginal ultrasound of the endometrium in postmenopausal women with symptoms of urogenital atrophy on low-dose estrogen or tibolone treatment: a comparison. Maturitas 1997;26:57-62. 