Biomedical Engineering Reference
In-Depth Information
vibration is needed, which is dicult to achieve in a conventional phono-
cardiograph in view of the objective vibration frequency band, the degree
of amplilfication, the signal-to-noise ratio and other factors. The essential
problem is that the microphone, which captures the vibration signal, has
an important defect. This defect is that the vibration transmitting cha-
racteristics of the chest structure are lowered and changed by the weight
of the microphone; in other words, a mismatch of the acoustic impedance
is generated, because the microphone contacts the body surface (using
the contacting technique of a vibration perception detector).
1.8.6
The Theoretical Basis for the New Technology
It has been known in our previous research that the resolution of the vibration
detector is not sucient even if such a supersensitive accelerometer is used.
A noncontacting technique has to be chosen as a structure for the vibration
perception detector in order to detect the vibration at the body surface. In
order to detect the very minute displacement amplitude accurately, a laser
beam of which the monochromaticality, directionality, and convergence are
excellent is the only choise at the present time. The transitivity of that laser
beam must be low, and the reflectivity high, while the light source focus
should be as small as possible.
The displacement signal measured by the laser displacement gauge is in-
tegrated by the chest tissue, while the acceleration signal due to stenosis
and diastole are transmitted to the chest wall. The frequency domain can
distinguish the detected displacement signal on the chest wall, since the fre-
quency of the displacement signal of the vibration does not change: only the
phase changes. Thus, coronary artery disease can be diagnosed through di-
stinguishing the displacement signal containing the turbulent flow vibration
deriving from coronary artery stenosis in the frequency domain. The ampli-
tude strength can be distinguished as a power.
The new technology is a high-resolution phonocardiography technique
that allows detection and analysis of low-amplitude phocardiographic signals
that may not be detected on the body surface by routine measurements.
Our aim is to provide a state-of-the-art review of the noninvasive detec-
tion of coronary stenotic murmurs. Theoretical and technical principles are
discussed in detail. It is a potentially powerful technique, but one that is
still in need of further technical refinement before it can be introduced into
routine clinical use. While the light microscope reveals important cell struc-
tures, such as the cell membrane, cytoplasm, and nucleus, it gives us little, if
any, information on mitochondria, the Golgi apparatus, ribosomes, and so on,
and conventional phonocardiograms only provide heart sounds and cardiac
murmurs that correspond to blood flows in cardiac cavities in that order.
Only with higher-resolution techniques, the electron microscope for anatomi-
cal studies and high-resolution phonocardiography in our case, can we detect
