Does having a sonogram of the uterus, with saline solution put in, render a post-menopausal woman (no period for over 10 years) a niddah?
Answer:
No, this would not be a problem.
Best wishes.
Sources:
Although in principle we find that one has to be stringent for purposes of Dam Chimud and other matters (see 192:1) even for an elderly lady (see Pischei Teshuvah 1; Birchei Yosef, Shiurei Shiurim K.A. 2; Shut Chaim Shaal 26 citing from Tashbatz; Makom Shmuel 33; Beis Yehudah 2:63) – in the case of the question one can be lenient for the most lenient opinions concerning “ein pesichas hakever belo dam” (up to 1 cm, which is bigger than the instruments used). See also Noda Biyhuda 116 and Chavas Daas and Beis Meir on Yoreh De’ah 188:3 and 192:2. See also Mishmeres Tahara 1:13.