Abstract: The invention relates to a cable or optical fibre, to which a protective finish has been added, which is formed by a tubular duct, the end parts of which have been mechanized in the form of fingers that have elbowed areas in the vicinity of the tips thereof, which elbowed areas expand toward the outside when the cable and said covering protrude from the catheter, and contract when the cable and finish are introduced into the catheter, avoiding, as is the case at present, a situation in which the fingers are straight and flat, which can produce a tear in walls of the blood vessel in the event of the operator wishing to reinsert the optical fibre through a vein in order to resume treating an already treated area.