**1. Introduction**

Wide utilization of microwave thermotherapy can be observed in the countries of the European Union, the United States, Russia, China, Japan, and many others, including the Czech Republic. Interactions of the electromagnetic (EM) field with the human body have been utilized in medicine (e.g., cardiology, oncology, physiotherapy, and urology) since the late seventieth of the twentieth century. A very important role in this process plays scientific societies, e.g., the European Society for Hyperthermia Oncology (ESHO), which cooperates with STM (Society for Thermal Medicine), and ASHO (Asian Society of Hyperthermia Oncology).

Currently, EM fields are frequently used in a few well-established medical procedures already. Good examples in the area of medical diagnostics are, e.g., computer tomography (CT) and magnetic resonance imaging (MRI). In the area of therapy, we can mention, e.g., electrosurgery and radiofrequency (RF) heating in physiotherapy. Then microwave (MW) hyperthermia and RF + MW ablation in clinical therapy are being used for the treatment of cancer and other diseases.

According to the purpose of how microwaves are used, we can divide the medical applications of microwaves into the following three main groups [1–17]:


As told above, treatment applications of MW are represented mainly by those based on thermal effects. Thus, we can speak about the MW thermotherapy, which can be generally divided into several basic modalities with respect to the goal temperature level or interval:


For the abovementioned methods of thermotherapy treatments, frequency interval from 1 up to 5600 MHz is mostly used.

As for diagnostics based on the EM field—significant importance for the near future can be identified for the following methods mainly:


As for the frequency spectrum of the EM field (**Figure 1**), then it is possible to see that MRI is working in the frequency band from 64 to 299 MHz (i.e., the upper part of the RF band); instead, CT then is working in hard X-ray band. The MW frequency

**Figure 1.** *Frequency spectrum of EM fields.*

band is frequencies from 300 MHz to 300 GHz. The lower part of this frequency band, from 300 MHz to 6 GHz, is very prospective for MW medical imaging. Frequency band above approx. 100 GHz is very prospective for imaging with Terahertz waves. In **Figure 1**, there is a picture of the frequency spectrum of the EM field.

In this chapter, we will not describe the MRI and CT technology, as it is a well-known and broadly used application of the EM field in medical diagnostics. We will describe and discuss here other methods based on microwave technology mentioned above. The idea of MWs for medical diagnostics is a relatively new area but rapidly developing. The main advantages of MW technology with respect to CT and/or MRI are as follows:


And it is important to underline that for MW diagnostics, low power levels (1– 20 mW) are used only.
