# Ultrasound Flashcards

You may prefer our related Brainscape-certified flashcards:
1
Q

Describe the properties of ultrasound.

A

They are longitudinal waves with a frequency higher than humans can hear.

2
Q

Describe the piezoelectric effect.

A

The application of of a pd across a crystal causes vibration/expansion/contraction.

3
Q

Explain how ultrasound transducers emit

A

A piezoelectric crystal inside the transducer (usually PZT) can either convert ultrasound waves into an alternating voltage, or convert an alternating voltage into ultrasound.

4
Q

When do we receive maximum voltage from an ultrasound transducer?

A

The largest voltage will be produced when the wavelength it produces is double the thickness of the crystal.

5
Q

Describe the principles of ultrasound

scanning.

A

When an ultrasound wave meets the boundary between two materials, some of it is reflected. The amount reflected depends on the change in acoustic impedance - the bigger the change, the more is reflected.The reflected waves are detected by an ultrasound scanner and are used to generate an image.

6
Q

Describe the difference between an A-scan and a B-scan.

A

An A-scan simply shows the amplitude of each reflected ultrasound wave, which allows to calculate how deep the reflection occurred. A B-scan, however, produces a 2-dimensional image that uses the intensity of the reflected to wave to translate into brightness.

7
Q

How do we calculate the acoustic impedance of a medium?

A

Multiply the density of the medium by the speed of light in the medium.

8
Q

Describe the importance of impedance matching.

A

It allows ultrasound waves to pass through a boundary with minimal reflections.

9
Q

Why is gel required for effective ultrasound imaging techniques?

A

To reduce the change in acoustic impedance between the skin and what it is next to. If it was air, all the ultrasound would be reflected at the air-skin boundary, so we use gel to reduce this reflection.