Controlled Measurement Setup for Ultra-Wideband Dielectric Modeling of Muscle Tissue in 20-45 °C Temperature Range

In order to design electromagnetic applicators for diagnostic and therapeutic applications, an adequate dielectric tissue model is required. In addition, tissue temperature will heavily influence the dielectric properties and the dielectric model should, thus, be extended to incorporate this temperature dependence. Thus, this work has a dual purpose. Given the influence of temperature, dehydration, and probe-to-tissue contact pressure on dielectric measurements, this work will initially present the first setup to actively control and monitor the temperature of the sample, the dehydration rate of the investigated sample, and the applied probe-to-tissue contact pressure. Secondly, this work measured the dielectric properties of porcine muscle in the 0.5-40 GHz frequency range for temperatures from 20 °C to 45 °C. Following measurements, a single-pole Cole-Cole model is presented, in which the five Cole-Cole parameters (ϵ∞, σs, Δϵ, τ, and α) are given by a first order polynomial as function of tissue temperature. The dielectric model closely agrees with the limited dielectric models known in literature for muscle tissue at 37 °C, which makes it suited for the design of in vivo applicators. Furthermore, the dielectric data at 41-45 °C is of great importance for the design of hyperthermia applicators.

Non-Invasive Microwave Hyperthermia and Simultaneous Temperature Monitoring with a Single Theranostic Applicator. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2021;2021:1314-1317. [PMID: 34891527 DOI: 10.1109/embc46164.2021.9629592] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Cancer therapies are constantly evolving. Currently, heating tumor tissue is becoming more accessible as a stand-alone method or in combination with other therapies. Due to its multiple advantages over other heating mechanisms, microwave hyperthermia has recently gained a lot of traction. In this work, we present a complementary split-ring resonator that is simultaneously excited in two independent frequency bands. With a high-power signal, the applicator is excited and heats the tissue-under-test up to 50°C with an average heating rate of 0.72°C per second. Furthermore, we present a dielectric temperature control system using the same applicator for microwave hyperthermia applications, which currently still requires an additional thermometry system. By exciting the applicator with a low-power signal, we can constantly monitor its resonant frequency. This resonant frequency depends on the tissue properties, which in turn are temperature-dependent. In the temperature range from 20-50°C, a positive correlation between the temperature and resonant frequency was established.Clinical relevance - Exploiting the dual-band behavior of the complementary split-ring resonator to heat the tissue-under-test while dielectrically monitoring its temperature, creates new possibilities towards a theranostic, non-invasive microwave hyperthermia applicator.

Millimeter wave imaging system modeling: spatial frequency domain calculation versus spatial domain calculation

Active millimeter wave imaging systems have become a promising candidate for indoor security applications and industrial inspection. However, there is a lack of simulation tools at the system level. We introduce and evaluate two modeling approaches that are applied to active millimeter wave imaging systems. The first approach originates in Fourier optics and concerns the calculation in the spatial frequency domain. The second approach is based on wave propagation and corresponds to calculation in the spatial domain. We compare the two approaches in the case of both rough and smooth objects and point out that the spatial frequency domain calculation may suffer from a large error in amplitude of 50% in the case of rough objects. The comparison demonstrates that the concepts of point-spread function and f-number should be applied with careful consideration in coherent millimeter wave imaging systems. In the case of indoor applications, the near-field effect should be considered, and this is included in the spatial domain calculation.

Study of active millimeter-wave image speckle reduction by Hadamard phase pattern illumination

Active millimeter-wave images typically exhibit characteristic speckle noise, due to the coherence of artificial millimeter-wave sources. We study the Hadamard speckle contrast reduction (SCR) technique, which has been successfully used in laser projection systems, in the context of millimeter-wave imaging. We show the impact of Hadamard pattern order and size and of image and pattern resolution on speckle reduction efficiency. Practical limitations of Hadamard pattern implementations and their effect on speckle reduction efficiency are also discussed.