Ultrasound Physics - 9\transducers

Front 1

A device that converts one form of energy into another

Back 1

Transducer

Front 2

When do ultrasound transducers convert electrical energy from the system into sound?

Back 2

During Transmission

Front 3

When do ultrasound transducers convert reflected sound pulse into electricity?

Back 3

During Reception

Front 4

Materials which convert sound into electricity (and vice versa) are called what?

Back 4

Piezoelectric Materials
(or ferroelectric)

Front 5

What are man-made piezoelectric materials called? (natural?)

Back 5

lead zirconate titanate or PZT
(quartz, tourmaline)

Front 6

The property of certain materials to create a voltage when they are mechanically deformed is called what?

Back 6

Piezoelectric Effect

Front 7

The property of certain materials to change shape when a voltage is applied to them is called what?

Back 7

Reverse Piezoelectric Effect

Front 8

What are three synonyms for PZT?

Back 8

Crystal, ceramic, active element

Front 9

The cylindrical tube that protects the internal components of the transducer from damage and insulates the patient from electrical shock

Back 9

Case

Front 10

The thin, metallic barrier lining the inside of the transducer case which prevents electrical interference/noise from contaminating the clinically important signals used to create diagnostic images

Back 10

Electrical Shield

Front 11

A thin barrier of cork or rubber that prevents vibrations in the case from inducing an electrical voltage in the transducer's PZT

Back 11

Acoustic Insulator

Front 12

The crystal itself. In a simple probe, the active element is shaped like a coin. The characteristics of the sound beam emitted by the transducer are related to the dimensions of the active element. The PZT is one-half wavelength thick.

Back 12

PZT or active element

Front 13

This provides an electrical connection between the PZT and the ultrasound system

Back 13

Wire

Front 14

This is positioned in front of the PZT to increase the efficiency of sound energy transfer between the active element and the body, and to protect the active element. The matching layer is one-quarter wavelength thick .

Back 14

Matching Layer

Front 15

Bonded to the back of the active element, this reduces the ringing of the pulse (shortened duration & length). When an electrical spike excites the PZT, the backing material restricts the extent the PZT deformation (emitted sound pulse is dampened. Crystal dampening enhances axial resolution

Back 15

Backing Material (aka Damping Element)

Front 16

What is the impedance difference between PZT and skin?

Back 16

Impedance of PZT is 20x greater than skin

Front 17

Which element of the transducer decreases reflections at the PZT/skin boundary, increasing the % of transmitted sound into the body?

Back 17

Matching Layer

Front 18

What additional component is always used by sonographers to "coupled" the transducer to the patient, and further improve the % of transmitted sound into the body?

Back 18

Gel

Front 19

How thick is the matching layer in a basic ultrasound transducer?

Back 19

1/4 wavelength thick

Front 20

How thick is the active element in a basic ultrasound transducer?

Back 20

1/2 wavelength thick

Front 21

The backing material shortens pulse length and duration, thus improving what?

Back 21

Axial Resolution

Front 22

What are additional consequences related to the use of a backing material in a transducer?

Back 22

Decrease Sensitivity
Wide Bandwidth
Low Quality Factor

Front 23

Why is decreased sensitivity due to backing material undesirable?

Back 23

the transducer becomes less responsive to incoming acoustic waves/vibrations

Front 24

The range, or difference, between the highest and lowest frequencies in a pulse is called what?

Back 24

Bandwidth

Front 25

As a general rule, (long|short) duration events are (narrow|wide) bandwidth

Back 25

Long duration = Narrow bandwidth (continuous wave doppler)

Short duration = Wide bandwidth (most other imaging probes)

Front 26

What is the formula for low quality factor (low-Q)?

Back 26

Main Frequency / Bandwidth

Front 27

What is the relationship between damping (pulse length) & Q-factor (quality factor)?

Back 27

Directly Related. A shorter pulse has a lower Q-factor; a longer pulse has a higher Q-factor

Front 28

What transducers consist of the following: pulses with short duration & length, uses backing material to limit ringing, has reduced sensitivity, wide bandwidth, lower Q-factor, and improved axial resolution?

Back 28

Imaging Transducers

Front 29

What transducers consist of the following: continuous wave or pulses with long duration & length, no backing material, increased sensitivity, narrow bandwidth, higher Q-factor, does not even produce and image?

Back 29

Non-Imaging Transducers (ie, Doppler)

Front 30

What is the name of the process where material is exposed to strong electrical fields while being heated to a substantial temperature to create PZT?

Back 30

Polarization

Front 31

What is the temperature at which PZT is polarized called?

Back 31

Curie Temperature or Curie Point

Front 32

What is the process of destroying piezoelectric properties of PZT called?

Back 32

Depolarization

Front 33

The destruction of all microorganisms by exposure to extreme heat, chemical agents, or radiation, is called what?

Back 33

Sterilization

Front 34

The significant reduction of infectious microorganisms using a chemical agent is called what?

Back 34

Disinfection

Front 35

Should transducers be sterilized or disinfected?

Back 35

Disinfected

Front 36

In a continuous wave transducer, what determines the sound frequency produced?

Back 36

The acoustic frequency will be the same as the electrical frequency that excites the PZT

Front 37

In a pulsed wave transducer, what determines the sound frequency produced?

Back 37

1. Speed of sound in the PZT
2. Thickness of the PZT

Front 38

In a pulsed wave transducer, what is the relationship between the PZT speed of sound and frequency?

Back 38

Directly Related

Front 39

In a pulsed wave transducer, what is the relationship between the PZT thickness and frequency?

Back 39

Inversely Related

Front 40

What is the PZT thickness & speed of sound in high frequency pulsed wave imaging transducers?

Back 40

Thinner PZT
Higher acoustic speeds

Front 41

What is the PZT thickness & speed of sound in low frequency pulsed wave imaging transducers?

Back 41

Thicker PZT
Lower acoustic speeds

Front 42

What is the relationship between Q-factor and bandwidth?

Back 42

Inversely Related

Front 43

What is the relationship between pulse duration and bandwidth?

Back 43

Inversely Related

Front 44

The sensitivity of transducers that create short duration pulses is likely to be ___ that of transducers that create long pulses

Back 44

Less Than

Front 45

All of the following correctly describe an imaging transducer except:
A. high sensitivity
B. low Q
C. wide bandwidth
D. damped

Back 45

A

Front 46

T/F: shorter duration events (such as dampened pulses) are more likely to be wide bandwidth

Back 46

True. short duration events are likely to be wide bandwidth. Longer events are more likely to be narrow bandwidth.

Front 47

What occurs when a PZT crystal's temperature is elevated above the Curie point?

Back 47

Depolarization

Front 48

T/F: the acoustic impedance of the matching layer is approximately the same as that of the skin

Back 48

False. The impedance of the matching layer is greater than the impedance of the skin

Front 49

T/F: imaging transducers are usually of high rather than low bandwidth

Back 49

True. Imaging transducers are high or wide bandwidth.

Front 50

T/F: a very high Q factor transducer is used more often in diagnostic imaging than a low Q factor

Back 50

False. Imaging transducers are low -Q

Front 51

T/F: a pulse with a long pulse duration is likely to have a narrow bandwidth

Back 51

True longer events tend to have a narrow bandwidth. Shorter events tend to have wider bandwidth.

Front 52

T/F: the damping material in a transducer increases the sensitivity

Back 52

False. Damping reduces sensitivity

Front 53

T/F: the damping material in a transducer increases the pulse length

Back 53

F

Front 54

T/F: the damping material in a transducer decreases the pulse duration

Back 54

T

Front 55

T/F: the damping material in a transducer improves the system's lateral resolution

Back 55

F

Front 56

T/F: the damping material in a transducer improves the system's longitudinal resolution

Back 56

T

Front 57

T/F: the dampening material in a transducer decreases bandwidth

Back 57

F

Front 58

T/F: the damping material in a transducer decreases the quality factor

Back 58

T

Front 59

T/F: if the frequency of the electrical excitation voltage of a pulsed wave transducer is 6 MHz, then the operating frequency of the transducer is 6 MHz

Back 59

F

Front 60

T/F: if the PRF of a transducer is increased, then the frequency of the sound produced by the transducer remains the same

Back 60

T

Front 61

T/F: the diameter of the active element of a transducer helps to determine the frequency of the sound produced by the transducer

Back 61

F

Front 62

T/F: if the frequency of the electrical excitation voltage of a continuous wave transducer is 6 MHz, then the operating frequency of the transducer is 6 MHz

Back 62

T

Front 63

T/F: two PZT crystals are made from the same material. The thicker crystal will make a pulsed transducer with a higher frequency

Back 63

F

Front 64

T/F: two PZT crystals are made from the same material. The thicker crystal will make a continuous wave transducer with a lower frequency

Back 64

F

Front 65

T/F: the normal propagation speed in PZT material is about 3-5x greater than in soft tissue

Back 65

T

Front 66

The impedance of a transducer active element is 1,900,000 Rayls, and the impedance of the skin is 1,400,000 Rayls. What is an acceptable impedance for the matching layer?
A. 1,200,000 Rayls
B. 1,400,000 Rayls
C. 1,726,000 Rayls
D. 1,950,000 Rayls

Back 66

C

Front 67

Which of the following crystals will produce sound with the lowest frequency?
A. thin and with a low speed
B. thin and with a high speed
C. thick and with a low speed
D. thick and with a high speed

Back 67

C

Front 68

Which type of transducer has a greater Q-factor: therapeutic or imaging?

Back 68

Therapeutic

Front 69

Which type of transducer has a greater bandwidth: continuous wave or imaging?

Back 69

Imaging

Front 70

Which type of transducer has more backing material: therapeutic or imaging?

Back 70

Imaging

Front 71

In an imaging transducer, what is the purpose of attaching the backing material to the PZT?
A. increase the bandwidth
B. decrease the Q factor
C. improve the image quality
D. decrease the sensitivity

Back 71

C

Front 72

A pulsed wave transducer has a resonant frequency of 5 MHz. The lowest frequency in the pulse is 2 MHz and the highest in 8 MHz. What is the bandwidth?
A. 5 MHz
B. 8 MHz
C. 3 MHz
D. 6 MHz
E. 2 MHz

Back 72

D

Front 73

electrical frequency =

Back 73

acoustic frequency