Transducers

Question 1

Which component of an ultrasound system is made of lead zirconate titanate (PZT)?

a. transducer’s matching layer
b. transducer’s active element
c. transducer’s damping material
d. scan converter’s computer chips

Answer 1

b. transducer’s active element

Question 2

How thick is the active element of a 3 MHz pulsed wave transducer?

a. 1.54 mm
b. 0.51 mm
c. half the wavelength of the sound wave in the PZT
d. one-quarter the wavelength of sound in the matching layer

Answer 2

c. half the wavelength of the sound wave in the PZT

Question 3

True or False?

The purpose of the backing material of an ultrasound transducer is to shorten the pulses, thereby creating images with better image quality.

Answer 3

True

Question 4

The main purposes of a transducer’s case are (more than one may be correct):

a. to protect the patient from shock
b. to protect the patient from heat
c. to protect the internal components of the transducer
d. to protect the patient from radiation

Answer 4

a. to protect the patient from shock

c. to protect the internal components of the transducer

Question 5

Which component of an ultrasound transducer is made from a slab of epoxy embedded with tungsten particles?

a. the matching layer
b. the piezoelectric crystal
c. the damping material
d. the computer chips

Answer 5

c. the damping material

Question 6

True or False?

The characteristic impedance of acoustic gel is greater than the matching layer’s impedance but less than the piezoelectric element’s impedance.

Answer 6

False

Question 7

The impedance of a transducer’s matching layer is 2.6 MRayls and the impedance of the piezoelectric crystal is 3.4 MRayls. If this is assumed to be a good imaging system, what is the best estimate for the impedance of the skin?

a. 1.5 MRayls
b. 3.8 MRayls
c. 3.4 MRayls
d. 2.8 MRayls

Answer 7

a. 1.5 MRayls

Question 8

True or False?

The piezoelectric crystal of a transducer typically has an impedance higher than the impedance of skin.

Answer 8

True

Question 9

Which of the following lists orders the impedance from highest to lowest?

a. skin, gel, matching layer, PZT
b. PZT, gel, matching layer, skin
c. gel, PZT, matching layer, skin
d. PZT, matching layer, gel, skin

Answer 9

d. PZT, matching layer, gel, skin

Question 10

What is the thickness of the matching layer of a 2 MHz pulsed wave transducer?

a. 1.54 mm
b. 0.77 mm
c. half the wavelength of the sound wave in the PZT
d. one-quarter the wavelength of sound in the matching layer

Answer 10

d. one-quarter the wavelength of sound in the matching layer

Question 11

True or False?

The acoustic impedance of the skin is greater than the acoustic impedances of both the matching layer and the piezoelectric element.

Answer 11

False

Question 12

With regard to the backing material of a pulsed ultrasound transducer, True or False?

The damping material helps to decrease the pulse repetition period achieved at a given imaging depth.

Answer 12

False

Question 13

With regard to the backing material of a pulsed ultrasound transducer, True or False?

The backing material helps to decrease the duty factor at a particular PRF.

Answer 13

True

Question 14

With regard to the backing material of a pulsed ultrasound transducer, True or False?

The pulse duration is increased as a result of the presence of backing material.

Answer 14

False

Question 15

With regard to the backing material of a pulsed ultrasound transducer, True or False?

The backing material decreases the quality factor.

Answer 15

True

Question 16

With regard to the backing material of a pulsed ultrasound transducer, True or False?

The spatial pulse length is decreased with the application of backing material.

Answer 16

True

Question 17

Assume that the frequency of sound with the greatest power emitted by a transducer is 5 MHz. However, the pulse contains acoustic energy with frequencies as low as 3.5 MHz and as high as 6.5 MHz. What is the bandwidth of the transducer?

a. 6.5 MHz
b. 5.0 MHz
c. 3.5 MHz
d. 3.0 MHz

Answer 17

d. 3.0 MHz

Question 18

True or False?

In general, ultrasound imaging transducers have a lower quality factor and a wider bandwidth than therapeutic ultrasound transducers.

Answer 18

True

Question 19

Damping material is secured to piezoelectric material during the fabrication of an ultrasonic imaging transducer. Which of the following is not a consequence of this attachment?

a. bandwidth increases
b. quality factor decreases
c. sensitivity increases
d. transducer case is longer

Answer 19

c. sensitivity increases

Question 20

Which of the following actions would cause a PZT crystal to lose its special properties?

a. breaking it in pieces
b. exposing it to high temperatures
c. exposing it to electrical current
d. exposing it to low pressures

Answer 20

b. exposing it to high temperatures

Question 21

All of the following are true about transducers except:

a. it is necessary to sterilize transducers before use
b. most transducers simply require disinfection as they do not penetrate mucous membranes
c. sterilization could depolarize PZT
d. they are unlikely to transmit infection

Answer 21

a. it is necessary to sterilize transducers before use

Question 22

Which properties of the piezoelectric crystal of a continuous wave transducer result in the highest emitted acoustic wave frequency?

a. thin, high propagation speed
b. thick, slow propagation speed
c. thin, slow propagation speed
d. none of the above

Answer 22

d. none of the above

Question 23

What helps to determine the frequency of the sound produced by the transducer of a continuous wave ultrasound system?

a. piezoelectric crystal diameter
b. piezoelectric crystal thickness
c. damping material density
d. ultrasound system electronics

Answer 23

d. ultrasound system electronics

Question 24

With pulsed wave ultrasonic imaging, what helps to establish the primary frequency of the acoustic energy discharged by the transducer?

a. piezoelectric crystal diameter
b. piezoelectric crystal thickness
c. damping material density
d. ultrasound system electronics

Answer 24

b. piezoelectric crystal diameter

Question 25

An ultrasonic pulse is traveling in soft tissue. Which of the following is most important in the determination of the frequency of the sound?

a. the propagation speed of the ultrasound transducer’s matching layer
b. the thickness of the transducer’s backing material
c. the impedance of the transducer’s matching layer
d. the propagation speed of the transducer’s active element

Answer 25

d. the propagation speed of the transducer’s active element

Question 26

What is the best estimate of the propagation speed of the ferroelectric element of a transducer used in a typical diagnostic imaging laboratory?

a. 1.2 mm/usec
b. 4.0 m/sec
c. 4.0 mm/usec
d. 1.0 km/sec

Answer 26

c. 4.0 mm/usec

Question 27

Which properties of the piezoelectric crystal of an imaging transducer result in the highest emitted acoustic wave frequency?

a. thin, high propagation speed
b. thick, slow propagation speed
c. thin, slow propagation speed
d. none of the above

Answer 27

a. thin, high propagation speed

Question 28

You are asked to fabricate a pulsed ultrasound transducer with the highest possible frequency. Which piezoelectric crystal would you select?

a. 6 mm thick, 4 cm diameter, 4.0 mm/us propagation speed
b. 8 mm thick, 2 cm diameter, 6.0 mm/us propagation speed
c. 4 mm thick, 9 cm diameter, 5.0 mm/us propagation speed
d. 2 mm thick, 6 cm diameter, 6.0 mm/us propagation speed

Answer 28

d. 2 mm thick, 6 cm diameter, 6.0 mm/us propagation speed

Question 29

You are asked to fabricate a pulsed ultrasound transducer with the lowest possible frequency. Which piezoelectric crystal would you select?

a. 6 mm thick, 4 cm diameter, 4.0 mm/us propagation speed
b. 8 mm thick, 2 cm diameter, 6.0 mm/us propagation speed
c. 4 mm thick, 9 cm diameter, 5.0 mm/us propagation speed
d. 2 mm thick, 6 cm diameter, 6.0 mm/us propagation speed

Answer 29

b. 8 mm thick, 2 cm diameter, 6.0 mm/us propagation speed