Polyvinyl alcohol cryogel phantoms of biological tissues for wideband operation at microwave frequencies

Abstract

The aim of this work is to provide a methodology to model the dielectric properties of human tissues based on phantoms prepared with an aqueous solution, in a semi-solid form, by using off-the-shelf components. Polyvinyl alcohol cryogel (PVA-C) has been employed as a novel gelling agent in the fabrication of phantoms for microwave applications in a wide frequency range, from 500 MHz to 20 GHz. Agar-based and deionized water phantoms have also been manufactured for comparison purposes. Mathematical models dependent on frequency and sucrose concentration are proposed to obtain the complex permittivity of the desired mimicked tissues. These models have been validated in the referred bandwidth showing a good agreement to experimental data for different sucrose concentrations. The PVA-C model provides a great performance as compared to agar, increasing the shelf-life of the phantoms and improving their consistency for contact-required devices. In addition, the feasibility of fabricating a multilayer phantom has been demonstrated with a two-layer phantom that exhibits a clear interface between each layer and its properties. Thus, the use of PVA-C extends the option for producing complex multilayer and multimodal phantoms.

Bimodal microwave and ultrasound phantoms for non-invasive clinical imaging

“…The homogeneity of the measurements, in terms of the percentage of variation, was below 4% for both parts of the permittivity in the considered frequency range. In comparison with the previously extracted model at 15% PVA-C concentration (without US scatterers) 23 , the fitting errors were quite similar with variations around 1% and 3% for the real and the imaginary parts of the permittivity, respectively. In this case, the homogeneity of the measurements was below 2%.…”

“…Microwave data and model extraction. The accuracy provided by this measurement protocol was within 4% and 7% for the real and imaginary parts of the complex permittivity ( ε ′ r and ε ′′ r ), respectively, whereas repeatabilities were both within 0.5% in the considered frequency range 23 . Regarding the performance of the bimodal phantoms in the microwave range, the results indicate that the model extracted fits properly the experimental data.…”

“…Regarding the performance of the bimodal phantoms in the microwave range, the results indicate that the model extracted fits properly the experimental data. A direct comparison between the extracted model in a previous work 23 and the present one can only be performed at certain sucrose concentrations, that is, 0%, 30% and 60%.…”

“…The dielectric conductivity can be derived from the imaginary part of the permittivity using the following expression 27,35 : Lastly, the experimental data were fitted to the Cole-Cole model 25 , a commonly-used reference to describe the dielectric constant as a function of frequency. The procedure employed has been previously described 23 .…”

“…The development of PVA-C phantoms has been successfully demonstrated for wideband operation at microwave frequencies in the range from 500 MHz to 20 GHz 23 . These phantoms were developed to characterize a microwave device for a medical application focused on the detection and monitorization of diabetic neuropathy.…”