Due to various contraindications I would not permit the patient to administer the US themselves on my clinic. It opens up a range of issues with potential risk of a claim again you that is not worth bothering about.
It is understood however that anyone can buy an ultrasound unit for themselves and do their own treatment at home so it does pose a contra argument that no special training is really needed to use it. After all it was invented for use on greyhounds after they finished a face and on race horses as well. Don't suppose they can administer it themselves though!