Ultrasound | Summary

Purpose: the ultrasound machine mostly used to check the developing of fetuses in pregnant woman. They can see the size of the fetus, the position, sex, number of fetuses; check the amount of amniotic fluid around the fetus. In the 3-dimensional ultrasound you actually see the baby and check if every thing is ok.
It is also used to see tumors in the ovary and breast, check the heart, prostate, and detect kidney stones. There is also a Doppler ultrasound that used for measuring blood flow through the heart, kidneys and major vessels.

The scientific principle: when sound waves move in medium it always move forward, but if it hit another medium some of the waves get reflected back and some continue forward. The ratio between the two waves is influenced by the difference between the densities of the two mediums.
In the ultrasound machine there is a transducer that transmits pulses of high frequency sound wave to the body. The wave moves in the body and every time it hits a different tissue it reflects some of the waves, the more the different between the tissues is higher more waves reflected. The probe is also collecting the reflected sound and transfers them to the CPU of the machine. The CPU knows when the sound wave was sent, it also the speed of the wave in the tissue, so when it receive the reflected wave the distance of the organ can be calculated. At the end we get a two dimensional picture of the distance and the intensities of the reflected waves.
The Doppler ultrasound base on the Doppler effect, when a sound wave hit an object some of it reflects back, if the object is moving the frequency of the wave will change a bit, if the object is moving toward the wave the frequency will increase and vice versa.
The size of the change of the frequency is depends on the velocity of the object.
The piezoelectric effect- in the probe there is a piezoelectric crystal that when it gets an electric current it starts to vibrate, the frequency is depends on the intensity of the current. And conversely when a sound waves hit the crystal it producing a current that’s depends on the frequency of the wave.




Description of instrument:
Transducer probe: it transmit a sound wave by using a crystal, the wave is transmitted in pulses so after the pulse is in the body the crystal inside the probe is in receiving mode and wait the reflected sound wave to produce a current that depends on the frequency.
There are some kinds of probes smalls for narrow view, big for wide view. There are some that have some crystals. And some that designed to insert body through its openings as vagina, rectum, and esophagus to see the body from the inside.
Central processing unit (CPU): the brain of the machine, its control the probe, control the timing of the transmitting wave and also get the current from the probe, and making all the calculations of the data.
Transducer pulse controls: it let the operator to control the frequency and duration of the sound wave pulses. The frequency determines the deep of the entrance to the body.
Display: the monitor, it shows the data that processed in the CPU, it can show a two dimensional picture or 3 dimensional depends on the model.
Keyboard/curser: the operator uses it to add notes and to take measurement from the data.
Disk storage: it can be any storage device that used in computer to save the data of the examination.

Operation: the operator put jelly on the skin to avoid air between the probe and the body, the probe is covered by plastic cover, and then the operator moves the probe on the skin and an image is obtained in the monitor. Usually the test is on the belly but the position could change. If the exam is internal so the position is different.

Safety features: the ultrasound consider a very safe test, in the past people were afraid of the heat that produce by the energy that absorbed in the body, and the bubbles that could be. But after lots of studies no reason to concern is found.




Sources of Data:
http://electronics.howstuffworks.com/ultrasound4.htm