Ultrasound

Ultrasound

What is Ultrasound?

Ultrasound or ultrasonography is a medical imaging technique that uses high frequency sound waves. It is a high pitch frequency that can not be heard by the human ear.

• In ultra sound the following happens:

• High frequency sound pulses (1-5megahertz) are transmitted from the ultrasound machine into your body using a probe.

• The sound wave will travel into your body until it hits an object such as soft tissue and bone.

• When the sound wave hits these objects some of the wave will be reflected back to the probe. While some waves may carry on further till they hit another object and then reflected back.

• The probe picks up these reflected sound waves and relays them to the machine.

• The distance and time from the probe, to where the sound wave was reflected, to when the echo is received back is calculated by the machine.

• A two dimensional image like below is produced displaying the distances on the screen.

Ultrasound Image

Taken from (Freudenrich, C, 1998)

How an Ultrasound machine works?

An ultrasound machine is made up of many parts:

The Transducer Probe

The probe is responsible for sending and receiving of the waves. It is the main part of the machine. The probe generates and receives the waves by the principle of piezoelectric effect. This was discovered in 1880 by Pierre and Jacques Curie. The probe contains one or more quartz crystals called piezoelectric crystals. When these crystals are cut to a specific shape they become an important part of the ultrasound system. They can contract in one direction and expand in another when an alternating electric current is passed through the crystal. Each Piezo-electrical crystal has its own resonant frequency and when the electric current is applied, it will oscillate and vibrate at that exact frequency. So the same crystal can be used to send and receive the waves. Within the probe it has a sound absorbing substance to eliminate reflections from the probe itself. The probe also has an acoustic lens this helps to focus the emitted sound waves.

The transducer probe can come in many different shapes and sizes. The field of view depends on the shape of the probe. Also the frequency of the waves emitted determines how deep the sound waves will penetrate and also the resolution of the image that will be produced. Probes can be used to move across the body but they can also be inserted through various openings. E.g. orally, this enables the probe to get closer to object that is being examined. Being closer to the object may allow for more detailed views.

Central Processing Unit (CPU)

The central processing unit is basically the brains behind the ultrasound machine. It is a computer that sends the electric current to the probe to tell it to emit the sound waves. It also receives the electrical pulses from the probe which received the sound waves that were reflected back. The CPU processes all the calculations and all the data the probe receives. Once this information has been processed, the CPU forms an image on the monitor. It can also store the data into its memory.

Transducer Pulse Controls

This control allows the operator of the machine to set and change the frequency and duration of the ultrasound pulses.

Display

The monitor allows for the data that has been processed by the CPU to be displayed as an image. Images can be displayed in black and white or in colour depending on the make and model of the ultra sound machine.

Below is an image of an ultrasound machine where you can clearly see all the different parts that are part of the machine.

Ultrasound machine

Taken from (MGH, 2008)

Ultrasound Uses and Treatments

Ultrasound machines are mainly used in a clinical setting with it most commonly being used in obstetrics and gynecology. It is also used in cardiology and cancer detection.

The biggest advantage that ultrasound has over using other diagnostic techniques is that it is much faster and also that certain structures can be observed without using radiation.

As stated above the most common form that ultrasound is used for is in Obstetrics and gynecology ways in which ultrasound can be used are as below:

• Measuring the fetus to determine the due date.

• By looking at the positioning of the fetus to see if it is in the breech position or the normal position with head down.

• Checking of the placenta to see if it is developing correctly and in the correct position.

• To identify the sex of baby.

• Used for detecting ectopic pregnancies where the fetus develops in the fallopian tubes instead of the uterus.

• Checking the growth rate of the fetus. By comparing measurements from previous ultrasounds.

• Checking the amount of amniotic fluid cushioning the baby.

• Can be used for seeing tumors of the breast or ovary.

There is a long list which an ultrasound machine can be used for, not only can it be used for diagnostic it is becoming more common for it to be used in treatments and therapy.

One type of therapy which can be used with ultrasound is known as heat therapy. It is most commonly used with sports injuries and is best used as treatment for those who have suffered soft tissue injuries.

It is used to:

• Relieve pain and inflammation.

• Help