**5. Microwave medical diagnostics**

As mentioned above, recently, there have been strong trends in research to apply microwave technology in medical diagnostics. Significant importance for the future can be identified for above all the following methods: microwave differential tomography, microwave diagnostic UWB radar, and microwave radiometry.

#### **5.1 Microwave differential tomography (MDT)**

In Prague, the MDT is developed by a research group from the Dept. of Biomedical Technology in cooperation with Prof. Andrea Massa and his group from ELEDIA Research Center (University of Trento, Italy). Theoretical works are focused on a theory of differential microwave imaging (DMI) in quasi-real-time. Existing suitable

*Applications of Microwaves in Medicine and Biology DOI: http://dx.doi.org/10.5772/intechopen.105492*

**Figure 6.** *Example of a homogeneous (a) and the anatomical phantom (b).*

**Figure 7.** *Example of SAR distribution calculated for the case of anatomical phantom given in Figure 6.*

reconstruction algorithms, namely Distorted Born Algorithm (DBA) and Born Algorithm (BA), which allow quasi-real-time monitoring of changes of dielectric properties due to changes of temperature, were implemented. They were applied and tested both numerically and experimentally within the feasibility studies.

These reconstruction algorithms were tested on numerical data from numerical 2D and 3D simulations; see **Figure 8**.

The below described results based on DBA and BA were compared in terms of the ability to reconstruct the shape and position of the target and flatness of the obtained

**Figure 8.** *Numerical models for testing of reconstruction algorithms.*

object function in regions without change in dielectric properties. Influences of varying TSVD threshold values, number of voxels, calibration, and normalization were tested. BA with a low TSVD-threshold value leads to clear pictures of the difference in relative permittivity, but we lose information about the difference in conductivity. The described algorithms were tested with a sphere that was virtually homogeneously heated. The resulting pictures were not of the clear boundary of the so-called objective function: the predicted changes of object function are smooth, see **Figures 9** and **10**. Even if the implemented algorithms show several deficits, they represent state of the art and are therefore a suitable starting point in developing the combined MW system. Here described, the principle of noninvasive temperature monitoring, once it is commercially available, would mean a very significant improvement in quality assurance for hyperthermia treatment of oncological patients in actual clinics and for the comfort of their treatment as well.

In **Figure 4**, there is a photograph of the laboratory MDT system built at the Dept. of Biomedical Technique. In this case, it consists of eight bow-tie antennas, but we can go up to 24 antennas in total. Necessary MATLAB scripts for measurements automatization, data acquisition, and image reconstruction were implemented by us. We created numerical models for solving the forward problem, which is necessary for the reconstruction algorithms. A preliminary evaluation of the system based on measurement results was performed at the same time. It seems realistic that the DMI methods can be used for 3D noninvasive temperature monitoring of the treated volume during thermotherapy in oncology.

Currently, we study (by means of numerical simulations) the suitability of different types of antennas, e.g., their EM principle, dimensions, number, and geometrical configuration. We know that the main resolution limit of the described system is a low number of radiating elements. We plan to extend the system to the maximum possible number of antenna elements (i.e., up to 24). We believe there will be considerable improvement in the resolution.

Another prospective possibility of using the principle and technology of DMI is the rapid detection, identification, and classification of strokes (SDI), which would be essential for the quick, qualified decision of what kind of treatment is necessary to

*Applications of Microwaves in Medicine and Biology DOI: http://dx.doi.org/10.5772/intechopen.105492*

**Figure 9.** *Results of reconstruction on a 2D model.*

give to the stroke patient already in the ambulance when he/she is being transferred to the hospital. The Pioneer research group in this area is a team of Prof. Mikael Persson from Chalmers University in Goeteborg, Sweden.

#### **5.2 UWB radar**

Dr. Marko Helbig and Dr. Juergen Sachs from TU Ilmenau in Germany came up with the idea to use microwave UWB radar technology for noninvasive microwave imaging and/or noninvasive temperature monitoring. In Prague, they are followed by people from the Dept. of EM Field.

The detection of temperature change via UWB radar signal is based on the fact that the complex permittivity changes with temperature. We have shown that it is possible to detect these changes by UWB microwave radar. In our case, the antenna array comprises eight dipole antennas (21 x 11 mm). These antennas are excited by the UWB pulse in the frequency band 1–8 GHz. The values of relative permittivity and specific conductivity of all considered tissue temperatures (at starting temperature of 37°C) can be taken, e.g., from the IT'IS Foundation database.

We worked with an experimental antenna setup for UWB temperature change detection to be used in microwave hyperthermia treatment. Our numerical and

**Figure 10.** *Results of reconstruction on a 3D model.*

laboratory models with implemented frequency and temperature dispersive parameters of biological tissues were used for a series of simulation purposes. The results from our numerical simulations show that it is possible to identify even very low changes in tumor permittivity caused by temperature change.

Our experiments with the homogeneous and nonhomogeneous phantoms have shown that we can detect even different temperature layers. From the reconstructed image, we can partially reconstruct the shape and position of the simulated inhomogeneity. The way to improve the chance for more accurate differential temperature reconstruction is in the higher number of antennas closer to the heated area utilization and in the attenuation correction improvement.
