**1. Introduction**

158 Imaging of the Breast – Technical Aspects and Clinical Implication

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5368, pp. 29-39.

#### **1.1 Imaging technique, employing feeble alternating current**

Currently, a variety of electrical impedance diagnostic systems is used both in academic studies and in clinical practice. A significant part of such systems employs electrodes which reside in a single array and two-dimensional mathematical conductivity reconstruction algorithms in the array of the electrodes. Electrical impedance mammograph belongs to the class of 3D tomography systems. Thus, all the measurements are made on the surface of the object under investigation. The change of surface potential difference (compared with the homogeneous case), as a rule, is caused by the presence of a local heterogeneous area in the object. It is mainly concentrated in the area which is a projection of the local heterogeneous area on the surface of the object. Therefore, the main objective of electrical impedance mammography is to visualize the reconstructed three-dimensional electrical conductivity distribution of the object basing on the results of electrical measurements on its surface. For this purpose various modifications of mathematical method of "back projection" are employed. Mathematical methods provide also crosssectional slices of conductivity.

The usage of alternating current for this purpose is justified from several positions. Extreme complication of electrical conductivity measuring in biological systems at direct (i.e. unidirectional) current is conditioned by high degree of polarization of cellular membranes. Moreover, the flow of direct current through biological tissues is accompanied by irreversible chemical reactions at the electrodes, through which the object is connected with the external part of the circuit. Therefore, only alternating electric current of sufficiently high frequency is employed in medical diagnostics.

#### **1.2 Tissue-specific peculiarities of electrical conductivity**

In biological tissue, electric current affects the components and structures that have a net electric charge and / or an electric dipole moment. This influence is carried out in an environment characterized by the presence of numerous interface regions. An example of such interface regions are cell membranes. In the space, surrounding cell membranes from both sides, the changes are carried by electric charges, mainly in the form of ions and the sources of dipole moment in the form of polar water molecules and mobile polar

Standards for Electrical Impedance Mammography 161


Electrical conductivity index (IC), calculated during the electrical impedance examination, is a quantitative value, which characterizes the status of the breast. The results of 1,632 electrical impedance mammograph examinations, obtained from healthy women from different age groups, were analyzed. The women were selected for the examination according to the following criteria: absence of complaints on the mammary glands, a normal menstrual cycle, uncomplicated perimenopausal period, absence of chronic somatic and gynaecological diseases and absence of hormonal contraceptives taking or hormone replacement therapy. The women were distributed by age in years as follows: 20-30 (380 women), 31-40 (428), 41-50 (449) and 51-60 (375). All the examinations described in the chapter were carried out with the help of the electroimpedance computer mammograph "MEIK" v.5.6 (0.5 mА, 50 kHz), developed and manufactured by PKF "SIM-Technika",

Fluctuations of electrical conductivity index in 1,632 studies were as follows: lower limit – 0.01 conventional units, upper limit – 0.68 conventional units. In order to identify the structure of electrical impedance index distribution there were elaborated 8 ranges of criteria at a step of 0.09 and the quantity of studies was calculated in each range (Table 1).

Electrical conductivity index Number of studies 0.00 – 0.09 67 0.10 – 0.19 279 0.20 – 0.29 471 0.30 – 0.39 435 0.40 – 0.49 299 0.50 – 0.59 75 0.60 – 0.69 6 Total 1632

Fig. 1 shows the frequency histogram of electrical conductivity index data. Mean electrical

Taking into consideration a bell-shaped curve, close mean, median and mode values one can speak about standard (Gauss) distribution of the quantitative value, in this case, of electrical conductivity index. Typically, mean value and standard deviation are used to describe standard distribution. More detailed data can be obtained using 3th, 10th, 25th, 40th, 75th, 90th and 97th percentiles (Figure 2). In this case, the information on the shape of criterion

Table 1. Arrangement of electrical conductivity index frequencies.

distribution graph is not required.

conductivity index constituted 0.29, median value – 0.29 and mode - 0.26.

**5. Types of mammary gland structure from the perspective of electrical** 



**impedance mammography** 

interpretation.

Russia.

macromolecules. Moreover, the polarization ability of the cell membrane itself due to protein and lipid structures determines its exceptional electrical properties. Thus, the electrical properties of biological tissue as a colloid-disperse system in an alternating electric field are determined by the concentration and «the behaviour» of chemical compounds in it.
