In one embodiment, at least one visual characteristic from a selected image is used to automatically select an ultrasound image from a set of images from a plurality of heart cycles. For example, implantable material of the present invention can enhance maturation of an arteriovenous native fistula as well as prolong the fistula in a mature, functional state suitable for dialysis. The walls of the diffuser canister have an interior surface, an exterior surface, and a wall thickness t. Screws are inserted into the fixing portions and tightened to threaded holes provided in the frame to fasten the rectifying device to the frame.