Answers to revision questions
Chapter 19: Introduction to Ultrasound
1. How are sound waves generated?
Sound is a wave, which moves longitudinally. It is created by vibrating objects and moves via particle interaction from one location to another. Each particle pushes on its neighbouring particle and moves it in a forward direction. It then returns to its original position at the end of the interaction. This backward and forward movement is parallel to the direction of movement of the wave.
2. What can Doppler ultrasound be used to demonstrate?
This technique uses the Doppler effect and is used to examine the movement of liquids. It can be used to demonstrate abnormalities in blood flow and to evaluate the flow through structures and also the velocity of the blood flow.
3. What is ‘B mode’ ultrasound?
This is the brightness mode and is the most common mode in use today. Each reflecting echo registers as a bright spot, the larger the amplitude of the echo, the brighter the spot. The mode will use lots of scan lines from the source to produce a two-dimensional cross section image. The image is changing all the time and allows the structures to be seen.
4. How does coupling gel work?
Coupling gel is applied to the transducer and the skin to ensure contact between the skin and transducer without the interference of air.
5. Describe the patient preparation necessary for an ultrasound scan.
· The area for examination is clipped. Areas with underlying bone or gas should be avoided, as this will block the movement of the sound waves.
· Spirit is used to remove any residue dirt and grease on the skin surface
· Coupling gel is applied to the transducer and the skin to ensure contact between the skin and transducer without the interference of air.
6. What is the piezo-electric effect?
The transducer consists of a ceramic crystal between two pincers. A current is applied to the pincers, which will pass through the crystal and crush it. When the voltage is applied to the ceramic a pulse of high frequency sound waves is produced. The sound wave will pass through the body and then bounce back, causing compression of the ceramic and the creation of an electrical impulse. This is known as piezo-electricity.
7. Name two substances that ultrasound waves will not image accurately
Bone
Air
8. List three parts of the body that can be imaged using ultrasound.
Any soft tissue structure which does not contain air and is not encapsulated in bone.
9. What is a transducer?
Transducers (also known as probes), come in a range of sizes and shapes, depending on the type of examination and the frequency required.
10. What is the unit used to measure frequency?
Ultrasound is the use of very high frequency sound waves to produce a diagnostic image. These sound waves are above 10,000 Hz, which is well above the audible range of humans. Diagnostic ultrasound uses a range of 1-20 MHz.