Is the menstrual period considered concluded upon the cessation of visible bleeding, and what is the interpretation of the doctor's statement that blood is present on the ultrasound despite that?

A woman recognizes purity by one of two signs: dryness (by inserting a cotton swab into the place of blood, and it comes out clean), or the white discharge. The cotton swab should only be inserted into the outer part of the vagina. If she sees no blood, yellow discharge, or brownish discharge, then she has become pure. If your wife sees purity after three days, such that she sees nothing of blood, yellow discharge, or brownish discharge in the outer part of the vagina, then she must perform ghusl (definition) and pray, and it is permissible for you to have intercourse with her. The doctor's statement should not be given any attention.