Heating of an Aortic Stent for Coarctation Treatment During Magnetic Particle Imaging and Magnetic Resonance Imaging—A Comparative In Vitro Study

Abstract

Purpose To evaluate heating of a redilatable stent for the treatment of aortic coarctation in neonates and small children in the new imaging modality magnetic particle imaging and established magnetic resonance imaging. Materials and Methods The cobalt-chromium stent (BabyStent, OSYPKA AG, Rheinfelden, Germany) has a stent design which allows for redilatation and adjustment of the diameter from 6 to 16 mm for a use in aortic coarctation. The stent loses its radial integrity while opening at predetermined breaking points at a diameter of 14 mm or 16 mm, respectively. We measured the temperature increase in the stent at different diameters during 7-min magnetic particle imaging and magnetic resonance imaging scans with fiber optic thermometers under static conditions surrounded by air. In magnetic particle imaging, stents with diameters from 6 to 16 mm were tested while in magnetic resonance imaging only stents with diameters of 6 mm and 14 mm were investigated exemplarily. Result In magnetic particle imaging, the measured temperature differences increased up to 4.7 K with growing diameters, whereas the opened stents with discontinuous struts at 14 and 16 mm showed only minimal heating of max. 0.5 K. In contrast to magnetic particle imaging, our measurements showed no heating of the stents during magnetic resonance imaging under identical conditions. Conclusion The BabyStent did show only slight heating in magnetic particle imaging and no detectable temperature increase in magnetic resonance imaging.

Heating of Large Endovascular Stents and Stent Grafts in Magnetic Particle Imaging—Influence of Measurement Parameters and Isocenter Distance

“…This is confirmed in this work by the lack of influence of the selection field gradients' variation in heating. In principle, the static selection field could suppress re-magnetization of ferromagnetic domains In previous work, a correlation between stent diameter and measured temperature increase in oscillating magnetic fields was shown [16,17,19]. This relation seems to be based on the stent being a closed conductor loop.…”

“…The temperature measurements during the MPI scans were performed in accordance to already published measurement protocols [16,17] with a fiber-optic thermometer (FTX-300-LUX ? , Osensa, Coquitlam, Canada).…”

“…As the stent design is expected to influence the heat distribution, an exemplary thermography (Testo 890-2, Testo, Lenzkirch, Germany) of one stent of each of the three different stent designs was performed a single time before the heating measurements to guarantee the temperature data acquisition to be conducted at the stents' hot spots. For the closed cell stent design, the Boston Scientific/Wallstent-Uni Endoprothesis, for the open cell design the Bentley/ BeGraft, and for the helical stent design, the Gore/TAG stent graft was imaged after an MPI scan of 430 s. This timeframe was chosen based on published measurement protocols [16,17]. In accordance with the thermography results (see Fig.…”

“…Therefore, drive field strengths of 3, 6, 9 and 12 mT in all directions and selection field gradients of 0, 1.25 and 2.5 T/m in z-direction, 0, 0.625 and 1.25 T/m in x-and y-direction were applied in the combinations shown in Table 2. Due to the comparable time dependent heating characteristic of stents in MPI [16,17], we performed the experiments with a single stent model (Bentley/BeGraft) for a duration of 20,000 frames (431 s) and assume the results to be transferable to other stent types. This stent model has been selected, because it showed a significant heating and represents a common stent design.…”

“…Therefore, heating of metallic objects due to eddy currents or magnetic hysteresis becomes an important safety issue. In the last years, first studies investigated the heating of interventional devices like metallic stents in MPI [15][16][17]. The stent diameter and design were identified as influencing parameters of stent heating.…”