Biomedical Engineering Reference
In-Depth Information
It was reported that MCG gives unique information on cardiac ischemia, arrhyth-
mias, and fetal diagnosis [Yamada and Yamaguchi, 2005]. MCG was successfully
applied in diagnosis of several pathological heart conditions. For example inspecting
ST shifts in MCG during an exercise test [Cohen et al., 1983] demonstrated that in-
jury currents resulting from ischemia, practically impossible to measure with ECG,
may be detected by MCG. Usefulness of magnetic field maps to detect angina pec-
toris and myocardial infarction in cases when no ST complex elevation is present
was reported in [Lim et al., 2009]. It was also reported that by means of MCG it
is possible to distinguish the features characterizing coronary arterial disease and
arrhythmia vulnerability [Stroink et al., 1999].
The MCG time evolution and an example of a measurement system are shown in
Figure 4.43 . Construction of maps representing magnetic field distribution measured
over the thorax is one of the methods useful for clinical diagnosis. An example of
such an approach may be the work by [Gireesan et al., 2010]. The MCG recorded
by means of 36 sensors was filtered in the frequency band 0.01 to 120 Hz and the
artifacts were removed by means of the wavelet transform. The MCG evolutions
synchronized in respect to the R peak were averaged. In Figure 4.44 the averaged
traces together with a magnetic field map are displayed. The MCG shows in sev-
eral positions splitting of the R waves (not visible in ECG), which is a symptom of
left bundle branch block. In the iso-magnetic field contour plot for the instant of R
peak, the contributions of two equivalent current dipoles may be observed. In the
(A)
(B)
FIGURE 4.43: (SEE COLOR INSERT) A 64-channel magnetocardiographic
system. Overview of the system (A), of 8 by 8 matrix of sensors (sensor interval:
2.5 cm, a measuring area: 17.5 by 17.5 cm) superimposed on magnetic resonance
image (B), signals at 9 out of 64 channels. From [Yamada and Yamaguchi, 2005].
 
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