This is not my area of expertise, but many years ago I learned that the term virgin meant not having had sex, or more specifically, not having had genital penetration sex. The term virgin can still be used even if the person has inserted something else. The use of a tampon, diva cup, contraceptive sponge, diaphragm, vaginal suppository, douche, swab, speculum, finger, or hairbrush handle does not change the virgin status.
If the question is can the doctor reasonably fit a large ultrasound wand inside, then that is a matter of opening size, flexibility, hymen obstruction, and overall development. That is not a question of virginity, neither dependent on, nor altering the status of.
I would like to add… while I understand some cultures, religions, or people put a very high importance on this status, I personally find the checking, the verification, monitoring, proving, declassifying, and overall obsessing with virginity to be ridiculous, unnecessary, and having no significant positive impact to a person’s mental health. There are so many pieces to the puzzle of human sexuality, personal growth, and aquired experience. Giving this one thing a name, and then saying someone else took it from you, or you gave it to them, all seems like a waist of effort. Why not first orgasm? First kiss? First time leaving a wet spot? First time shaving? First involuntary erection? First damp panties? First time with a blindfold? First time you sniffed your own finger? It all feels like trying to assign points and score people based on someone else’s values. A person’s first time can still be meaningful and memorable, but should not be used to pass judgement just because of someone else’s obsession.
(Stepping down from soapbox)