Apparatus with a pneumatic or hydraulic or mechanical therapeutic catheter. The therapy energy required to treat internal vessels of the patient is transferred by the same fluid or the same elements from the proximal end section to the distal end section of the catheter that transfer information from the distal end section to the proximal end section of the catheter. The information provides understanding of the state of the vessel and how the therapy fluid of the therapy element of the catheter acts on the vessel.