**8. Metrics and information technologies for the analysis of magnetocardiographic data based on three-dimensional visualization of the solution of the inverse problem**

The original advanced method to solve the inverse problem of magnetostatics based on the results of measurements of the magnetic heart signal was developed recently. As the first step, a model of a point source of magnetic field (i.e., magnetic dipole) was used. The location and magnetic moment vector of magnetic dipole uniquely defined by known (measured) values of magnetic field at given points in space [15]. In the subsequent stages of data processing and conversion, other models of the signal source are also used. For example, the source of the magnetic field can be represented as a set of N different magnetic dipoles distributed in the volume of the heart [16]. In this case, the results of measurements of the magnetic field to determine the location of several signal sources are distributed as independent in the threedimensional volume of the human heart. A model of a flat system of "currents" (distribution of the current density vector) is used for spatial analysis of the magnetic cardio signal and its sources. It is assumed that in space the selected plane, which is parallel to the plane of measurement, is secant with respect to the volume of the heart and is located at a given distance from the plane of measurement. In the proposed Primin and Nedayvoda algorithm, the coordinate of the plane with signal sources is a variable and its value is also determined by the measurements of the magnetic field as the value of the z-th coordinate of the dipole source, which was determined at the previous stage of MCG signal processing. The problem for a planar current system is based on the application of the double integral Fourier transform and takes into account the spatial configuration of the magnetic flux transformer SQUID gradientometer [17]. An algorithm for converting information to solve the inverse problem was developed in the case if the results of measurements of the magnetic cardio signal need to determine the values of current density vectors in a given set of slices ("layers") [18]. Each of the layers is located in a plane parallel to the measurement plane, the coordinates ("depth") of each layer are set either with a given step (uniform distribution) or discretely based on the results of solving the inverse problem obtained in the previous stages (non-uniform distribution).

The power distribution of the current density vector is presented in the form of a so-called polar diagram. The principle of plotting is based on the segmentation scheme adopted as a standard in the analysis of measurement results in computed tomography and ultrasound of the heart [19]. Software implementation assumes that the threedimensional surface consists of 5 segments: 1—anterior, 2—lateral, 3—inferior, 4—septal, and 5—apical.

Three-dimensional imaging methods have been successfully used to solve several important clinical problems, including, for example, determining the viability of the

affected areas of the myocardium in patients with various forms of coronary heart disease. Thus, a fairly high level (74%) was found between the contractility of the segments of the anterior wall of the left ventricle and the current density in this area of the myocardium in patients with chronic coronary heart disease [20].

### **9. Myocardial damage in patients recovered from COVID-19**

2 years ago, a new challenge for humanity emerged—Covid-19 pandemic. It has led to well over 200 million infections, with a fatal outcome in over 4.5 million cases. Of the survivors, the majority showed long-haul symptoms – now often called Long COVID [21].

One of the important long-term clinical consequences of COVID-19 seems to be heart damage [22]. Signs and symptoms of possible heart damage after COVID-19 may include severe fatigue, palpitations, chest pain, shortness of breath, and postural orthostatic tachycardia syndrome (POTS) due to neurologic disturbances, postexertional fatigue, and higher troponin levels.

In addition, heart inflammation appears to be prominent in COVID-19. This might involve both the myocardium and the pericarditis, causing severe fatigue without other obvious symptoms. The diagnosis of myocarditis is relatively inaccurate because both tests and diagnostic protocols are lacking precision. The course of the illness is therefore unknown at present, but some early reports have shown that symptoms lingered for a median of 47 days before diagnosis was accomplished by cardiac magnetic resonance (CMR) imaging [23].

Magnetocardiography, due to its high sensitivity is a potentially valuable method to detect the signs of myocardial damage in patients with COVID-19.

Therefore, 59 patients (mean age 42 3.9 years) who recovered from COVID-19 were examined as it was shown in section 2 of this chapter in the Main Military Hospital of Ukraine and in the 8th People's Hospital of Guangzhou. This group was divided into two subgroups depending on the time elapsed since recovery: 1–3 months after recovery (11 patients) and 7–10 month after recovery (48 patients). 78 healthy volunteers constituted the control group. These persons were examined earlier, in 2017–2018.

The method of data analysis was based on pattern recognition (see section 5 of this chapter). The probabilities of CDV maps within ST-T interval belonging (i.e., correlation coefficients) to six basic databases of reference images have been calculated. Each of these databases includes maps that are most specific to a particular disease. Then, the rank of category called "Non-coronary Heart Diseases" was determined. This rank (i.e., the relative value of the correlation coefficient) could be from 1 to 6.

To evaluate the difference between the examined groups, non-parametricWilcoxon— Mann—Whitney test, designed to assess categorical variables, was used (**Table 2**).

There is a highly statistically significant difference between the rank of CDV maps, which belongs to the category "Non-coronary Heart Diseases" between the group of


#### **Table 2.**

*The rank of category "Non-coronary Heart Disease" in groups examined.*

*Unshielded Magnetocardiography in Clinical Practice: Detection of Myocardial Damage… DOI: http://dx.doi.org/10.5772/intechopen.104924*

**Figure 15.**

*A diagram, showing the average correlation coefficients of CDV maps with 6 basic databases of reference images in a 61-years patient who has recently recovered from COVID-19. The highest correlation with the "Non-coronary Heart Diseases" category is observed.*

patients recovered from COVID-19 and the control group. In patients, who recovered from COVID the signs of non-coronary heart diseases are much more pronounced, than in the control group. This is especially true for recently recovered patients, within 1–3 months before MCG-examination (**Figure 15**).

At the same time, the differences between the group of patients, who recovered from covid relatively long ago and the control group take place only at the level of a tendency (p ≤ 0.25).

Note that all examples of the application of the new metric for the analysis of subtle changes in the magnetic field of the human heart are critical parts of the relevant new diagnostic technologies.

The meaning of the development and implementation of any new diagnostic technology is to solve difficult diagnostic problems that are difficult to solve with existing methods. The above examples of new metrics developed by us fully meet the criteria for solving a complex diagnostic problem in cardiology, and in the first place, there is a wide range of differential diagnosis and low availability and/or high cost of diagnostic methods already included in existing clinical guidelines on this problem. In addition, it should be noted that a key sign of the maturity of the new technology is the presence of certificates of conformity issued by the authorized department of a country, as well as patents confirming its novelty. In this context, it should be noted that in addition to national certificates and patents, our proposed metrics as a result of careful long-term testing of the most modern procedures and received the relevant international certificates and patents for inventions. This is a guarantee of further intensive use of the unshielded magnetocardiography in medical practice at the international level.

The emerging diagnostic technology regarding existing ones might play one of the three future roles: replacement, triage or adds one [24]. At present, magnetocardiography can play the role of triage and supplementation among well-established methods for diagnosing myocardial damage of various origins. Further development of the method requires further, larger multicenter studies involving several dozen clinics in different countries.

### **10. Conclusions**

1.The development of new information technologies and metrics based on magnetocardiography for the analysis of small changes in biological signals is a modern technological trend that improves the accuracy of many diagnostic methods, including methods of analysis of electrical activity of the heart.


### **Acknowledgements**

The authors want to express their sincere gratitude to outstanding experts in physics, mathematics, cryogenic engineering Drs. Michael Primin, Volodymyr Sosnytskyy, Pavlo Sytkovy, Igor Nedayvoda, Yury Minov, Pavlo Shpylevoi, Mykola Budnyk, Yury Frolov from Glushkov Institute for Cybernetics of NAS of Ukraine as well as Dr. Anton Popov and Eugen Udovichenko from National Technical University of Ukraine "Igor Sikorsky Kyiv Polytechnic Institute". In addition, the authors warmly thank the great teams of leading hospitals in Ukraine, China, and Germany, with whom they were lucky to productively cooperate.

Special thanks to Mr. Bin-Zhen Zhang from North University of China, Mrs. Wei-Wei Quan from Ruijin Hospital affiliated to Shanghai Jiaotong University, as well as Mrs. Xiang-Yan Kong from Ningbo University for their outstanding efforts aiming to develop MCG-technology in China.

*Unshielded Magnetocardiography in Clinical Practice: Detection of Myocardial Damage… DOI: http://dx.doi.org/10.5772/intechopen.104924*
