Microwave spectrometry for the evaluation of coronary stents
Authors: Amoros Garcia De Valdecasas S , Gonzalez-Lopez G , Jimenez I , Jofre L.L , Bayes-Genis A , Tejada J , O'Callaghan Castella J.M , Rodriguez-Leor O , Galvez-Monton C 
Published: November 2020

Abstract

Background
Coronary artery disease (CAD) is the leading cause of death worldwide, and percutaneous coronary intervention with stenting the most widely performed procedure to treat CAD. However, current stent monitoring techniques are invasive and/or ionizing. Microwave spectrometry (MWS) may provide a non-invasive, non-ionizing and cost-effective alternative capable of detecting stent-related pathologies before fatal heart failure.

Purpose
To develop a new MWS-based technology to detect coronary stents in an in vivo swine model.

Methodology
First, using two new MWS devices, an in vitro experiment was carried out to demonstrate their ability of detecting the presence of: (1) a stent and (2) stent fractures (SF). To that end, an intact stent was distanced 3, 7, 11 and 15 mm from a MWS near-field probe in open-air conditions. Afterwards, three identical stents were piecemeal cut to emulate type I, II and III SF at different fractions of the stent's length (l): l/5, l/3 or l/2. Additionally, the stent was measured in a phantom substance, to simulate in vivo conditions: it was distanced from 0 to 40 mm in steps of 5 mm. Likewise, using a pair of MWS far-field antennas, the stent in phantom was measured at 10, 20, 30 and 40 mm.
Finally, the MWS technology was assessed in vivo. To that end, six Landrace X Large White pigs were submitted to a stent implantation into the circumflex coronary artery (CX). The antennas measured the stent non-invasively, over the rib cage of the animals. MWS analysis were performed baseline (before stent implantation), and at 0, 3, 7, 14, 21 and 35 days of follow up. Measurements were performed only before ventricular systole to avoid differences in the stent position and deformation.

Results
In vitro, maxima and minima extrema in the microwave frequency response (see figure) were used to detect the stent. Type I and II SF produced 5 and 10% downshifts in the extrema frequencies with respect to the baseline values (unbroken stent), while type III produced 20% upshifts and a maxima splitting. Embedding the stent in phantom produced 25% downshift in the extrema frequencies.
In vivo, the MWS antennas were useful to detect the stent presence into the CX artery during all time points of study, in all animals.

Conclusions
We have developed a new non-invasive and non-ionizing MWS technology capable of detecting the presence of a stent in a porcine model. Furthermore, we have proven how our technology can monitor structural damages in the stent (SF) and changes in its environment. This study proves the MWS potential to become a simple and yet effective method to arise stent-related pathologies in a pre-clinical stage; it could also provide physical insight about additional biological processes. Further improvements on the MWS device as well as in vivo measurements will ensure its consistency when monitoring human stents.
Stent detection using MWS technique

Funding Acknowledgement
Type of funding source: Foundation. Main funding source(s): Fundaciό La MARATÓ de TV3, Generalitat de Catalunya, Red de Terapia Celular – TerCel, CIBER Cardiovascular, Spanish Agencia Estatal de Investigaciόn Unidad de Excelencia Maria de Maeztu, Sociedad Española de Cardilogía