Microwave spectrometry for the evaluation of the structural integrity of metallic stents.
OBJECTIVE
To assess the feasibility of a method based on microwave spectrometry to detect structural distortions of metallic stents in open air conditions and envisage the prospects of this approach toward possible medical applicability for the evaluation of implanted stents.


METHODS
Microwave absorbance spectra between 2.0 and 18.0 GHz were acquired in open air for the characterization of a set of commercial stents using a specifically design setup. Rotating each sample over 360°, 2D absorbance diagrams were generated as a function of frequency and rotation angle. To check our approach for detecting changes in stent length (fracture) and diameter (recoil), two specific tests were performed in open air. Finally, with a few adjustments, this same system provides 2D absorbance diagrams of stents immersed in a water-based phantom, this time over a bandwidth ranging from 0.2 to 1.8 GHz.


RESULTS
The authors show that metallic stents exhibit characteristic resonant frequencies in their microwave absorbance spectra in open air which depend on their length and, as a result, may reflect the occurrence of structural distortions. These resonances can be understood considering that such devices behave like dipole antennas in terms of microwave scattering. From fracture tests, the authors infer that microwave spectrometry provides signs of presence of Type I to Type IV stent fractures and allows in particular a quantitative evaluation of Type III and Type IV fractures. Recoil tests show that microwave spectrometry seems able to provide some quantitative assessment of diametrical shrinkage, but only if it involves longitudinal shortening. Finally, the authors observe that the resonant frequencies of stents placed inside the phantom shift down with respect to the corresponding open air frequencies, as it should be expected considering the increase of dielectric permittivity from air to water.


CONCLUSIONS
The evaluation of stent resonant frequencies provided by microwave spectrometry allows detection and some quantitative assessment of stent fracture and recoil in open air conditions. Resonances of stents immersed in water can be also detected and their characteristic frequencies are in good agreement with theoretical estimates. Although these are promising results, further verification in a more relevant phantom is required in order to foresee the real potential of this approach.
Grup de Magnetisme, Departament de Física Fonamental, Facultat de Física, Universitat de Barcelona, Martí i Franquès 1, planta 4, edifici nou, ES-08028 Barcelona, Spain.
Gianluca
G
Arauz-Garofalo
Grup de Magnetisme, Departament de Física Fonamental, Facultat de Física, Universitat de Barcelona, Martí i Franquès 1, planta 4, edifici nou, ES-08028 Barcelona, Spain.
Víctor
V
López-Domínguez
Grup de Magnetisme, Departament de Física Fonamental, Facultat de Física, Universitat de Barcelona, Martí i Franquès 1, planta 4, edifici nou, ES-08028 Barcelona, Spain and Institut de Nanociència i Nanotecnologia IN2UB, Universitat de Barcelona, Martí i Franquès 1, planta 3, edifici nou, ES-08028 Barcelona, Spain.
Joan Manel
JM
Hernàndez
Servei de Cardiologia, Hospital Universitari Germans Trias i Pujol, Carretera del Canyet s/n, ES-08916 Badalona, Spain.
Oriol
O
Rodríguez-Leor
Servei de Cardiologia, Hospital Universitari Germans Trias i Pujol, Carretera del Canyet s/n, ES-08916 Badalona, Spain.
Antoni
A
Bayés-Genís
Department of Signal Theory and Communications, Universitat Politècnica de Catalunya, Jordi Girona 1, ES-08034 Barcelona, Spain.
Juan M
JM
O'Callaghan
Grup de Magnetisme, Departament de Física Fonamental, Facultat de Física, Universitat de Barcelona, Martí i Franquès 1, planta 4, edifici nou, ES-08028 Barcelona, Spain and Institut de Nanociència i Nanotecnologia IN2UB, Universitat de Barcelona, Martí i Franquès 1, planta 3, edifici nou, ES-08028 Barcelona, Spain.
Antoni
A
García-Santiago
Grup de Magnetisme, Departament de Física Fonamental, Facultat de Física, Universitat de Barcelona, Martí i Franquès 1, planta 4, edifici nou, ES-08028 Barcelona, Spain and Institut de Nanociència i Nanotecnologia IN2UB, Universitat de Barcelona, Martí i Franquès 1, planta 3, edifici nou, ES-08028 Barcelona, Spain.
Javier
J
Tejada
D008670:Metals / Q000737:chemistry*; D008872:Microwaves; D019047:Phantoms, Imaging; D013057:Spectrum Analysis / Q000379:methods*; D015607:Stents; D014867:Water
D008670:Metals; D014867:Water