Method for processing a stent processed with tools containing magnetizing components

This application claims priority of German Patent Application No. 20104145.6, filed Mar. 9, 2001.

In today's stent technology it is desirable to use cardiovascular stents that are able to adequately prop open the vessel, that can be accurately positioned and that, and this is new—can be viewed with nuclear spin tomography. Traditional stents are made of stainless steel and show distinct image distortions, so called artifacts. These artifacts occur when materials with high magnetic susceptibility are used.

A goal of the invention is to show means by which the occurrence of artifacts in combination with the stents and nuclear spin tomography can be avoided.

An alloy of 3 percent aluminum by weight and 2.5 percent vanadium by weight, with the remainder being titanium, known as material TIA13V2.5 or material No. 3.7194 or 253.7195 (ASTM Grade 9), shows especially few image artifacts and has sufficient hardness to be suitable for interventional instruments used in nuclear spin tomography.

The above named alloy according to ASTM Grade 9 is harder than an alloy according to ASTM Grade 5 or ISO 3.765 or 3.7165. This would have the following components: 90% titanium, 6% aluminum, and 4% vanadium. The material is more flexible than the so-called ASTM grade 9 material and is therefore more suitable for expanding a stent with the help of a balloon catheter.

Materials that are made to be artifact free but created with tools containing magnetizing components after processing show an increase in screen artifacts which rubbed off the tools. A reduction of surface magnetism can be achieved through dipping in etching solutions which etches the materials the tools are made of. The rub-off from the tools is eliminated by the wet chemical etching solution. Such an etching solution that removes the iron impurities consists for example of 3 parts hydrochloric acid and 2 parts saltpeter acid and can be further reduced with additional parts water in the etching process.

Stents manufactured in the manner here described can be ideally observed in nuclear spin tomography units in magnetic flux density>1.0 Testa. It was possible, for example with an unexpanded stent having a diameter of 1 mm, that was balloon expanded to a diameter of 4 mm, to clearly see all the stent struts, the so-called strats. It was also possible to get a good look inside the expanded stent. So-called in-stent-restenose in the interior of the stent can be seen when a stent has been treated in this manner.