Microwave spectrometry for the evaluation of in-stent restenosis

Abstract

Our purpose is to assess the feasibility of microwave spectrometry in the detection of in-stent restenosis, based in noting a resonant frequency shift for coronary stents. The aim of this work is to get closer towards a possible medical applicability for implanted stents. Microwave absorbance spectra between 0.2 and 1.8 GHz were acquired for the different stages of ISR model we fabricate. All the spectra were obtained in a water-based phantom simulating human chest. Rotating each sample over 360º, 2D absorbance diagrams were generated as a function of the frequency and the rotation angle. Finally with a few adjustments the same system provides similar 2D absorbance diagrams of stents immersed in different fluids such as sunflower oil, and filled in with different materials. We show that no frequency shift is observed in a stent with ISR. Even though the shift is found when changing the external medium of the stent, it seems that some kind of shielding of the electromagnetic fields inside the stents take place at the wavelengths we use, making impossible to detect diseases happening inside the stent. Motivated by the discouraging results of the ISR test we designed a series of more specific experiments in order to evaluating the effect in the resonant frequencies of the variation in dielectric permittivity of the material we place inside the stent. Thus, finding no differences when changing the medium inside the stent, we conclude that there is a shielding of the radiation inside the device. Thinking of other non ionizing methods to detect ISR will be necessary. Computational software using FDTD methods might be helpful.