Assessing Changes in Dielectric Properties Due to Nanomaterials Using a Two-Port Microwave System.

Detecting changes in the dielectric properties of tissues at microwave frequencies can offer simple and cost effective tools for cancer detection. These changes can be enhanced by the use of nanoparticles (NPs) that are characterised by both increased tumour uptake and high dielectric constant. This paper presents a two-port experimental setup to assess the impact of contrast enhancement on microwave signals. The study focuses on carbon nanotubes, as they have been previously shown to induce high microwave dielectric contrast. We investigate multiwall carbon nanotubes (MWNT) and their -OH functionalised version (MWNT-OH) dispersed in tissue phantoms as contrast enhancing NPs, as well as salt (NaCl) solutions as reference mixtures which can be easily dissolved inside water mixtures and thus induce dielectric contrast changes reliably. MWNT and MWNT-OH are characterised by atomic force microscopy, and their dielectric properties are measured when dispersed in 60% glycerol-water mixtures. Salt concentrations between 10 and 50 mg/mL in 60% glycerol mixtures are also studied as homogeneous samples known to affect the dielectric constant. Contrast enhancement is then evaluated using a simplified two-port microwave system to identify the impact on microwave signals with respect to dielectric contrast. Numerical simulations are also conducted to compare results with the experimental findings. Our results suggest that this approach can be used as a reliable method to screen and assess contrast enhancing materials with regards to a microwave system's ability to detect their impact on a target.

Zinc oxide nanoparticles as contrast-enhancing agents for microwave imaging.

PURPOSE: Microwave imaging/sensing is an emerging technology that shows potential for healthcare diagnostic applications, particularly in breast cancer detection. This technique estimates the anatomically variant dielectric properties of the breast. Similar to other imaging modalities, nanoparticles (NPs) could potentially be utilized as contrast agents to increase contrast between healthy and malignant tissues. METHODS: In this study, aqueous suspensions of NPs such as surface-modified single-walled carbon nanotubes, zinc oxide, and silicon dioxide are studied to assess their potential effective contrast for microwave imaging. Morphology characterization of the NPs has been achieved using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The size and stability of colloidal dispersions have been characterized by dynamic light scattering technique (DLS) and Ultraviolet-visible spectrophotometry (UV-Vis). The dielectric characterization of the aqueous-based colloidal suspensions is recorded over the microwave frequency range between 1 and 4 GHz. RESULTS: Zinc oxide NP dispersion has shown an increase in the dielectric constant compared to the background medium. Furthermore, PEGylation of ZnO NPs can achieve a valid increase in the dielectric constant compared to water, which was shown to be concentration dependent. CONCLUSION: These results suggest that ZnO nanomaterials have the potential to be used in biomedical applications such as breast imaging to improve diagnostic capabilities.

Preliminary Assessment of a Microwave System to Detect Contrast Enhancing Agents.

This paper presents a preliminary study of the impact of potential contrast enhancing agents on a 2-port microwave imaging system. To this end, we have conducted microwave measurements inside a dual cylindrical tank, comprised of an outer and inner cylinder filled with high and low loss liquids, respectively. A third smaller cylinder inside the low loss filled tank represents a target. The target materials consisted of safflower oil, water, PEGylated zinc oxide nanoparticles dispersed in water, and saline with varying concentrations of salt. To benchmark our experimental results, we have also performed accurate numerical simulations of the system under three target scenarios: safflower oil, water, and PEGylated zinc oxide suspension. Our results show that the difference in received signal strength in scenarios with and without PEGylated zinc oxide nanoparticles in our 2-port system was comparable to measurement error. However, with the use of varying concentrations of saline solutions as a target, we have observed a significant difference in received signal strength.