Biomedical Engineering Reference
In-Depth Information
Fig. 1.49.
A diagram showing the measuring principle of displacement of vibration
utilizing pulsed laser beam. 1: laser diode driving circuit, 2: a projection of the laser
beam, 3: reception lens, and 4: light position detecting element
noise deriving from the measuring system, measurement with monitoring is
also carried out in order to cancel this internal noise.
The displacement of the body surface due to respiration and the displa-
cement of the body surface due to heartbeats and other movements become
mixed in the detected displacement magnitude signal as internal noise of the
measured object. In order to narrow down the signal frequency, which is ne-
cessary for the distinction of the signal of the vibration deriving from the
coronary artery disease, the displacement signal is passed through a low-pass
filter and a high-pass filter which have sucient attenuating gradients.
As described above, the acceleration signal deriving from coronary artery
stenosis during diastole becomes the displacement signal by being passed
through the body tissue. Therefore, it is necessary to differentiate the dis-
placement signal of the body surface, which is detected by using the laser
beam as a signal-detecting medium on the principle of triangulation, in order
to convert it into an acceleration signal. And the frequency domain as the
frequency of that does not change can distinguish the displacement signal by
the differential and integral operation.
The signal from the measured object can be taken out of the time domain
as necessary. As the signal of the measured object deriving from coronary ar-
tery disease is based on the beating period of the heart, an electrocardiogram
is used as the scale of the time domain.
