If PCOS is unable to be diagnosed by the presence of the 2 other criteria out of the 3 you listed, then imaging is critical to diagnosis if PCOS is strongly suspected. Diagnosis is important, as treatment can sometimes prevent complications.
Of all imaging modalities, transvaginal ultrasound (TVUS) is the first choice because it gives the best visualization of pelvic organs, as it can get closer to them than transabdominal ultrasound, and the ultrasound technology allows characterization of cysts based on echogenicity.
Transvaginal ultrasound is done using a probe that is covered with a condom-like sheath, and covered in lubrication. The probe looks like this:
The probe is usually approximately the width of 2 fingers. If a woman is able to tolerate manipulation of tampons, it is less likely to cause trauma to the hymen. Although there is some discomfort with the exam, most women report it is not as traumatic as it seemed it would be.
However, there do exist alternative recommendations for diagnostic imaging in adolescents prior to sexual debut, which can be applied to virgin adults as well:
transabdominal ultrasound is preferred to the transvaginal approach in adolescent girls, but this approach may be technically limited in overweight and obese individuals.
"Technically limited" means that abdominal fat reduces the ability of ultrasound from outside the abdomen to visualize the ovaries accurately, and therefore may yield inconclusive results. In that case, a transvaginal ultrasound would be preferred. It is possible to start with a transabdominal ultrasound and then get transvaginal if the first is inconclusive. Alternatively, CT scan or MRI are options; however, CT radiation is generally preferred to be avoided unless necessary (it exposes your ovaries to 200+ times the radiation of 1 chest Xray), and MRI is a long and expensive test.
An adolescent or adult with concerns about TVUS should talk with their provider to discuss the viability of alternative imaging options, if imaging is essential to the diagnosis, and perhaps look at an ultrasound probe to reduce concern with the use of the instrument.