Catheter or guidewire mounted automatic vessel occlusion and fluid dispersion devices that expand to occlude or partially occlude a vessel when a fluid is flowing in the catheter or guidewire, and that automatically collapse when fluid flow is stopped. Each occlusion device has an elastic skeleton covered with a flexible cover coupled thereto and may have a hole(s) or openings in its distal or proximal end thereof to allow controlled flow through the desired end of the occlusion device. The fluid may be a flush fluid for enabling or improving the performance of imaging devices and image enhancing fluids, of treatment fluids for localized treatment of a vessel or tissues in communication with the vessel and/or of the transmission of energy to the vessel wall and adjacent tissues. Various embodiments are disclosed.
