TMS
Didactic Muse
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Imaging Ultrasound Cont.
Attenuation
From. As is seen in (fig. 21) the problem of attenuation is solved. (Fig. 21)
shows the amplitude of the ultrasound beam decaying exponentially in
time and the echo is amplified in the reverse way. Logarithmically and the
geometric sum of both curves gives a straight line that shows, that after the
STC out the amplitude of the electric pulses do not depend of how deep the echoes come from but of the difference of acoustic impedance between the interfaces they go through. The ultrasound machine has an STC gain device that
offers the logarithmic curve shown in (fig, 21), but the device is not a logarithmic amplifier, because the logarithmic amplifier is based on the difference of amplitude received, amplifying more of the small signals and less
the big signals, not according to the depth the signals are coming from.
The ultrasound machine has an STC curve selected from the factory, but is up
to the operator to modify it on a set of slide potentiometer on the control panel,
as is shown in (fig. 22).
This is signal
loss or the
opposite of
signal
amplification.
References:
1. Gooberman GL. Ultrasonic's: Theory and application London: Universities
Press, 1968.
2. The Physics of Medical Imaging. Steve Webb.IOP Publishing LTD, a Company Wholly Owned by the Institute of Physics, London. 1992.
3. Manual de Usuario Aloka SSD 500. Aloka Ultrasound Systems 2005, 22-1,
Mure 6 chome, Mitaka-Shi, Tokio 181-8622, Japan.
4. Manual de Usuario Toshiba SSA 320A. Toshiba Medical Systems Corporation 2004-2005. 1385,Shimoishigami, Otawara-Shi, Tochigi 324-8550, Japan.
5. Principios Ultrasonográficos Para Médicos. URL://www.scu.sld.cu./Document/
libros/pdf/ingLeyva.pdf