Emerging from the development of single-energy Computed Tomography (CT) and Dual-Energy Computed Tomography, Multi-Energy Computed Tomography (MECT) is a promising tool allowing advanced material and tissue decomposition and thereby enabling the use of multiple contrast materials in preclinical research.The scope of this work was to evaluate whether a usual preclinical micro-CT system is applicable for the decomposition of different materials using MECT together with a matrix-inversion method and how different changes of the measurement-environment affect the results.A matrix-inversion based algorithm to differentiate up to five materials (iodine, iron, barium, gadolinium, residual material) by applying four different acceleration voltages/energy levels was established. We carried out simulations using different ratios and concentrations (given in fractions of volume units, VU) of the four different materials (plus residual material) at different noise-levels for 30 keV, 40 keV, 50 keV, 60 keV, 80 keV and 100 keV (monochromatic). Our simulation results were then confirmed by using region of interest-based measurements in a phantom-study at corresponding acceleration voltages. Therefore, different mixtures of contrast materials were scanned using a micro-CT. Voxel wise evaluation of the phantom imaging data was conducted to confirm its usability for future imaging applications and to estimate the influence of varying noise-levels, scattering, artifacts and concentrations.The analysis of our simulations showed the smallest deviation of 0.01 (0.003-0.15) VU between given and calculated concentrations of the different contrast materials when using an energy-combination of 30 keV, 40 keV, 50 keV and 100 keV for MECT. Subsequent MECT phantom measurements, however, revealed a combination of acceleration voltages of 30 kV, 40 kV, 60 kV and 100 kV as most effective for performing material decomposition with a deviation of 0.28 (0-1.07) mg/ml. The feasibility of our voxelwise analyses using the proposed algorithm was then confirmed by the generation of phantom parameter-maps that matched the known contrast material concentrations. The results were mostly influenced by the noise-level and the concentrations used in the phantoms.

In this paper, a measurement method is presented that determines the propagation of the heat front that is generated during microwave ablation (MWA) for monitoring purposes. A measurement setup is implemented that emulates an MWA scenario and consists of a microwave emitter in the ISM band at 2.45 GHz via a slot applicator. These microwaves are transmitted through a phantom body with two different materials, Triton X-100 70% and Triton X100 30% representing warm and cold tissue of liver. The transmitted wave is received via a bowtie dip antenna. The transmitted power is 10 dBm. The radial extent of the hot zone is changed from 5 mm up to 20 mm in 5 mm steps using a sliding device on top of the phantom body. The changes in time delay between the emitted and received wave are detected. From these values, the propagation zone of the heat front is determined mathematically using the time difference of arrival method (TDOA).

This study presents a measurement principle for determining the size of the ablation zone in MWA, which could ultimately form an alternative to more expensive monitoring approaches like CT. The measurement method is based on a microwave transmission measurement. A MWA is performed experimentally on ex vivo bovine liver to determine the ablation zone. This setup uses a custom slot applicator performing the MWA at an operating frequency of 2.45 GHz and a custom bowtie antenna measuring the waves transmitted from the applicator. Furthermore, a custom measurement probe is used to determine the dielectric properties. A time-shift analysis is used to determine the radial extent of the ablation zone. Several measurements are carried out with a power of 50 W for 10 min to show the reproducibility. The results show that this method can provide reproducible outcomes to determine the ablation zone with a maximum error of 4.11%.

In this paper, a circularly polarized microstrip patch antenna matched for propagation in microwave liver tissue is designed at 2.45 GHz. The reflection loss of the antenna is less than 10 dB from 1.8-2.6 GHz. The antenna is circularly polarized in elevation plane cut at azimuth angle (ϕ) of 90°, for elevation angles (θ) from −14° to −7° and from 11° to 17°. The axial ratio is below 3 dB in this range of angles from 2.2-2.7 GHz. So considering any reference antenna inserted in the liver tissue, the designed antenna can be placed in any orientation on the liver surface at one of these angles which hold the circular polarization.

A probe-fed circularly polarized patch antenna with cross slot and shorting pins is designed as a receiving antenna for ex-vivo microwave liver ablation experiments. For better matching with the liver surface, the antenna is simulated with tissue phantom mimicking the dielectric properties of liver made of TX material as a coupling medium in the background. The reflection loss bandwidth (2.0-2.8 GHz) and the axial ratio bandwidth (2.1-2.9 GHz) of the antenna covers the 2.4-2.5 GHz ISM band used for microwave ablation. The bore-sight gain of the antenna is −42 dBi and 3 dB axial ratio beam-width is 6° around the bore-sight at 2.45 GHz. The diameter of the antenna is 22 mm making it possible to place multiple antennas on the liver sample surface.

The microwave ablation technique to destroy cancer tissues in liver is practiced clinically and is the subject of ongoing research, e.g., ablation monitoring. For studies, liver tissue from cattle or pigs is often used as a substitute material. In this work, sweet potato is presented as an alternative material for microwave ablation experiments in liver due to similar material properties. Sweet potatoes as a substitute for liver have the advantages of better handling, easy procurement and stable material properties over time for microwave ablation experiments. The dielectric constant and electrical conductivity of sweet potato are characterized for temperature variation with the help of high-temperature dielectric probe. Furthermore, a test setup is presented for microwave ablation experiments in which a bowtie slot antenna matched to sweet potato is placed on its surface to directly receive the microwave power from a self-developed microwave applicator inserted into a sweet potato 4 cm below the surface antenna. A high-power source was used to excite the microwave powers up to 80 W and a spectrum analyzer was used to measure the signal received by the surface antenna. The experiments were performed in an anechoic chamber for safety reasons. Power at 50 W and 80 W was stimulated for a maximum of 600 s at the 2.45 GHz ISM band in different sweet potato experiments. A correlation is found between the power received by the surface antenna and rise of temperature inside sweet potato; relative received power drops from 1 at 76 ∘C to 0.6 at 88 ∘C (max. temperature) represents a 40% relative change in a 50 W microwave ablation experiment. The received power envelope at the surface antenna is between 10 mW and 32 mW during 50 W microwave ablation. Other important results for 10 min, 80 W microwave ablation include: a maximum ablation zone short axis diameter of 4.5 cm and a maximum ablation temperature reached at 99 ∘C, 3 mm away from the applicator’s slot. The results are compared with the state of the art in microwave ablation in animal liver. The dielectric constant and electrical conductivity evolution of sweet potato with rising temperature is comparable to animal liver in 50–60 ∘C range. The reflection loss of self-developed applicator in sweet potato is below 15 dB which is equal to reflection loss in liver experiments for 600 s. The temperature rise for the first 90 s in sweet potato is 76 ∘C as compared to 73 ∘C in liver with 50 W microwave ablation. Similarly, with 80–75 W microwave ablation, for the first 60 s, the temperature is 98 ∘C in sweet potato as compared to 100 ∘C in liver. The ablation zone short-axis diameter after 600 s is 3.3 cm for 50 W microwave ablation in sweet potato as compared to 3.5 cm for 30 W microwave ablation in liver. The reasons for difference in microwave ablation results in sweet potato and animal liver are discussed. This is the first study to directly receive a signal from microwave applicator during a microwave ablation process with the help of a surface antenna. The work can be extended to multiple array antennas for microwave ablation monitoring.

In this paper, design and electromagnetic-thermal co-simulation of a microwave applicator and a bowtie-slot body matched antenna are discussed. The applicator is inserted into a liver tissue phantom to heat the tissue with 50 W power for 300 seconds in thermal simulation. The resultant temperature profile is fed back into the electromagnetic simulation with temperature-dependent material properties of the liver. Similarly, 50 W power is also stimulated in the applicator in electromagnetic simulation to observe the difference in received power at the surface bowtie-slot antenna during the heating process.

In this paper, a simple Archemedian spiral antenna fed by a 6-section exponential impedance transformer cum parallel-strip to microstrip balun is presented. Antenna and the balun are designed for ultra wide-band (UWB) (1.6-12 GHz) frequency range. Using this antenna, a 17 element array helmet is simulated in 3-5 GHz band, around CST voxel model of human brain with a 1 cm blood-clot introduced in it. A comparison of difference in reflection loss with and without tumor for various antenna positions is carried out.