Module 2: Pulsed Ultrasound and Transducers

Question 1

Describe the Piezoelectric effect

Answer 1

When an electric current is applied to a piezoelectric crystal, it vibrates, these vibrations generate sound waves.

Thus, piezoelectric crystals can convert electric currents into ultrasound waves.

Question 2

Repetition frequency

Question 3

Frame rate

Answer 3

The number of ultrasound images displayed in one second.

Expressed in Hertz (Hz).

Question 4

Spatial pulse length

Answer 4

The length of time that an ultrasound pulse occupies in space.

Question 5

Pulse duration (PD)

Answer 5

Duration of the transmitted pulse.

The time interval from the beginning of the pulse to the end of the pulse

Measured in units of time (s,sm)

Question 6

Pulse repetition frequency (PRF)

Answer 6

The number of pulses emitted per second.

Measured in units of frequency (Hz, kHz or MHz).

Question 6

Be able to calculate max frame rate

Question 6

Describe the main types of transducers

Linear

Answer 6

High-frequency probe

Wide footprint

Piezoelectric crystal arrangement is linear

Frequency is 2.5Mhz - 12Mhz.

Best probe to view the superficial structures

Breast, thyroid, tendons, and blood vessels

Question 6

Explain the various layers of a typical ultrasound transducer

Answer 6

Acoustic lens

Acoustic mathcing layer

Piezoeletric element (transducer)

Backing material

Question 6

Describe the main types of transducers

Phased

Answer 6

Small footprint

High temporal resolution and penetration

Cardiac, transcranial, abdominal, and pediatrics

Question 6

Describe the main types of transducers

Curved

Answer 6

Wider field of view for larger or deeper structures

Abdomen, obstetrics/gynecology (OB/GYN), urology, and some musculoskeletal (MSK)

Question 6

Describe the main types of transducers

Matrix

Question 6

Lateral resolution

Question 7

Axial resolution

Answer 7

Resolution along the axis of the ultrasound beam.

Question 7

Contrast resolution

Answer 7

Ability to distinguish between different echo amplitudes/image intensity.

E.g., Differtiate between liver and spleen

Question 7

Temporal resolution

Answer 7

Time from the beginning of one frame to the next.

Ability to visualize moving objects.

Question 8

Explain focussing of the beam

Answer 8

Creating a narrow point in the cross-section of the ultrasound beam called the focal point.

It is at the focal point where the lateral resolution of the beam is the greatest.

Before the focal point is the near field or Fresnel zone, where beams converge.

Question 9

Relationship between pulse repetition frequency and pulse repetition

Question 10

Explain the origins of sidelobes

Answer 10

Side lobes originate outside of the main ultrasound beam, they appear as specular or diffuse artifactual echoes.

Question 11

How can sidelobes be reduced or avoided

Question 12

Explain beamwidth

Answer 12

The width of the beam is inversely related to the frequency.

Higher the frequency narrower is the beam.

Question 13

Explain slice thickness

Question 14

Explain the different modes of ultrasound

A-mode

Question 15

Explain the different modes of ultrasound

B-mode

Question 16

Explain the different modes of ultrasound

M-mode

Question 17

Pulse repition period (PRP)

Answer 17

Time from the beginning of one pulse to the beginning of the next pulse.

Measured in units of time (s,ms)