Works on bioelectromagnetism
In his doctoral thesis titled "On the detection of the magnetic heart vector –An application of the reciprocity theorem",Malmivuo presented research in magnetocardiography,focusing on developing and evaluating lead systems for magnetic heart vector (MHV) detection through complex mathematical models and experimental methods,ultimately providing practical information for clinical applications in diagnosing heart-related conditions. [14] In 1987,he authored the publication "Magnetic Stimulation –Design of a Prototype and Preliminary Clinical Experiments" which highlighted several advantages of magnetic stimulation over electric stimulation. [15] Concentrating on bioelectromagnetism,his 1995 book with Robert Plonsey titled Bioelectromagnetism –Principles and Applications of Bioelectric and Biomagnetic Fields explored the intersection of engineering science and technology with biological cells and tissues that have electrical conductivity and excitability with a focus on theory,practical applications,and the development of new systems. In 2002 it was published on the Internet. [16]
Malmivuo has used the principle of reciprocity to solve problems in bioelectromagnetism. When he started the research for his doctoral thesis at Stanford University in 1976,it was generally believed in two hypotheses that strongly supported the application of biomagnetism. Firstly,based on the Helmholtz theorem:"Since the bioelectric and biomagnetic signals (like ECG and MCG) are independent,one should obtain as much new information from the heart with MCG as has been derived from ECG". However,Malmivuo showed in 1995 that the Helmholtz theorem concerns the distribution of the electric and magnetic measurements' measurement sensitivities (lead fields). The ECG and MCG signals are only partially independent. A more comprehensive set of diagnostic information is obtained from the heart by combining ECG and MCG measurements to electromagnetocardiography,EMCG. [17] Secondly:Since the skull has high electric resistivity,which scatters the measurement sensitivity of the EEG,and since the skull is transparent to magnetic fields,MEG should be able to focus its measurement sensitivity better than EEG. However,Malmivuo calculated the measurement sensitivity distributions of EEG and MEG and concluded that despite the high electric resistivity of the skull,the EEG better focuses its measurement. However,like in MCG,more significant insights into the brain's electric activity are obtained when utilizing both EEG and MEG as EMEG,instead of relying solely on EEG. [18]
Malmivuo found that Magnetic stimulation is much better in brain stimulation since it stimulates the nerves in the scalp much less and makes brain stimulation painless. In his doctoral thesis,Malmivuo developed several lead systems for measuring the MHV. He also described the lead fields,i.e.,the measurement sensitivity distributions of these systems. With clinical measurements,Malmivuo et al. demonstrated that all three dipolar ECG and three dipolar MCG leads have approximately similar diagnostic performance. [19]
Malmivuo and his team found that when adding dipolar electric and magnetic leads to the measurement system,the total diagnostic performance increases the less,the more dipolar leads there already are. This behavior is independent of the order in which the electric and magnetic leads are added to the system. The experimental part of these studies was made in Malmivuo's laboratory at TUT,where in 1979,he constructed the first magnetically shielded room in the Nordic countries. The 2x2x2 m3 room is constructed from 45 mm thick aluminum boards and provided with Helmholtz coils,which compensate for the earth's static magnetic field. Its attenuation for 50 Hz magnetic field is 50 dB. [9]
In his early research with William H. Barry and others,he proposed adapting the right-handed coordinate system,commonly used in physical sciences,to clinical electrocardiography and magnetocardiography for a more convenient and mathematically consistent analysis of the electric and magnetic fields produced by the human heart. He also addressed the shortcomings of earlier coordinate systems. [20]
Focusing on the general solution for the application of magnetocardiography,he suggested that vector electro-magnetocardiography (VEMCG),i.e.,combining VECG and VMCG leads to VEMCG,offering a diagnostic tool for cardiac conditions,with experimental evidence indicating improved accuracy. [21]
In electric impedance tomography (EIT),Malmivuo and his co-authors demonstrated that the method generally used to construct the impedance tomography image needs to be corrected. Based on the principle of reciprocity. [22]
Concentrating his research efforts on the optimizing of measurement schemes in EIT,he employed computer models to simulate sensitivity distributions for various commonly used measurement methods in EIT,including neighboring,cross,opposite,and adaptive methods. His research findings indicated that the cross and opposite methods provide the highest sensitivities,while the neighboring method is the least sensitive when considering single measurements. [23] [24]
In collaboration with Outi Väisänen,Malmivuo presented a novel multielectrode lead technique for scalp-recorded EEG signals,demonstrating improved signal-to-noise ratio through specific sensitivity distribution for deep brain sources and spatial averaging of noise based on theoretical analysis,simulations,and experimental measurements. [25] Moreover,focusing his research efforts on the diagnosis of cardiac diseases,he provided theoretical and clinical evidence for increasing the number of electric and magnetic leads in medical diagnosis to improve diagnostic performance. [26]
