High speed photographic verification of intravascular stent strains during accelerated durability testing

Most stent durability testing does not predict resulting clinical failures. Standards committees have taken on the task of generating more reliable test protocols. Currently, the AAMI/ISO Committee has chosen an experimental direction that allows an investigator to test at ultra high frequencies (above 1000 bpm) as long as the actual strain of the stents can be verified to be moving the same amount per cycle that they do during real time testing (70 to 72 bpm). We have developed a series of techniques and protocols utilizing high-speed photographic analysis to accomplish this. The first aspect requires the utilization of ultra clear silicone mock arteries. It is important that optical anomalies do not cause aberrations in the analysis. Next is the relationship between the angle of the incident lighting and the positioning of the camera in front of the pulsing tube. Finally, a unique set of marking techniques which are used as tracking locations for the automatic measurement systems located in the software of the camera have certain characteristics that are important with respect to accurate measurements. In each case the particular setup must have independent verification of the accuracy of the measurements. We will review these variables and demonstrate how this system can be utilized to verify strains of the inside wall, outside wall, and stent.