THE ULTRASOUND IMAGE DIAGNOSTIC
EQUIPMENT II RECEPTION
By Rogelio Leyva
The echoes coming from the probe need to be
processing analogically and digitally and we will
explain in this paper two of the circuits involved in
this processing and what is the purpose of the
processing done by those circuits, we intend to
explain the hardware of the ultrasound machines and
how they work, the most advanced ultrasound
machines have most of those circuits integrated in
chips or obtain the same effect by software, any way
our explanation will be based on the circuits because
is impossible to explain the software, we also will
give a clue that help to get the solution when there is
no ultrasound image in the monitor.
toward plate 1, which is associated with a current
flow from plate 2, not an electron current is but a
current named displacement current on account of
the charge behavior, and the plate 2 begins to acquire
an amount of positive charge and plate 1 an amount
of negative charge a time after the transient no
charge displacement happens, a so no current
displacement, and there is no more current
displacement from plate 2 toward plate 1, it is said
that the capacitor is charged, and the current
difference between their plate is 5 volts even when
the external applied potential difference is no more.
The potential difference applied to both plates is
constant, during the transient there were current
flows, but after the transient, so after the transient
the constant potential difference does generate no
change that is said in technical slag that direct
current does not go through a capacitor.
Topics.
1. Low pass filter
2. Logarithmic amplifier
LOW PASS FILTER
The echoes coming from the human body have
too much noise; the amplitude of the echoes is
measured in micro-volts that are the amplitude of the
noise too, so the noise diminishes the image quality
for medical diagnostic, that´s why the noise has to be Fig 1
removed from the echoes. The noise is associated
with the high frequency then it is needed to
eliminate the high frequency for eliminating the
noise, the low pass filer circuit is the one used for
that purpose. This is a circuit that eliminates the
undesirable high frequency from the echoes. Let´s
explain the way an RC low pass circuit works; first
we will analyze the property of the capacitor that is
an important element in this circuit. The capacitor
has two plates keeping apart for a dielectric; the two
plates at first time are uncharged, cero-volts is
between plates but if a potential difference between
plate 1 and plate 2 is applied for example (5 volts),
positive at plate 2 a negative at plate 1, an electric
Fig 2
field is generated from plate 2 to plate 1, in a
transient a charge displacement begins from plate 2