TMS
Didactic Muse
Page 10
Imaging Ultrasound Cont.
Ultrasound
is cyclic sound
pressure with a
Here are three meshes between the cork and wall of the container shown in (fig.
5). The falling of the cork produces the waves that depart to the wall of the container, but when they find the first mesh, as the mesh has solid parts and
holes, part of the waves that collide with the solid parts of the mesh, return to the cork as happen when the waves collide with the wall of the
container. When the waves returning from the first mesh reach the cork, it
moves up and down again. The other part of the waves that go through the
holes of the first mesh reach the next mesh, and the waves collide with the
solid part of the second mesh. Part of the waves return to the cork as it
moves up and down again. The other part of the waves that go through the
holes, travel to the next mesh, and the process is repeated as before,
When the waves leave the third mesh, they collide with the wall of the
container and return the cork, and it moves again up and down. The movements
of the cork produce waves and on account of the collisions of these waves with
the meshes and the wall of the container, the cork moved up and down four
times.
frequency greater
than the upper
limit of human
hearing.
Although the
ability to hear
limits varies from
person to person,
it is approximately
20 kilohertz
(20,000 hertz) in
healthy, young
adults.
THE ULTRASOUND PROBE
It was shown before how the cork that falls in the water produces waves
of water, the ultrasound equipment produces ultrasound waves that go
through the human body, and the device that produces these waves is
the ultrasound probe, the name ultrasound is because these waves travels
with speed higher than the speed of the sound, and they behave in the human
body in a similar way that the water waves did in the crystal water container
explained before. he ultrasound probe has one, three or many crystals, at the
beginning they were made of quartz material, but now there are ot her materials that give better performance. These crystals have the property of shrinking when a voltage is applied on both sides, and when there is not voltage
applied, it returns to the original size, but before the crystal stay steady in
the original size, it shrinks and expands several times until stays steady as
it happened with the cork in the crystal water container, the fall of the cork produced the up and down movements of it in the water and the voltage applied
produces an oscillatory movement of the crystal (fig 6).
(Continued)