Physics Quiz 1 Review

Question 1

Which of the following transducer component is responsible for improving axial resolution?
1. The insulator ring
2. The matching layer
3. The damping material
4. The piezoelectric element

Answer 1

The damping material

Question 2

Explain the method of probe excitation used in a modern day array probe?

Answer 2

Burst spike: AC voltage. We can send it at a different frequency beside resonant frequency.

Question 3

Calculate the crystal thickness for a probe emitting sound with a period of 0.25 microseconds. The crystal in question has a sound velocity of 4000 m/s?

Answer 3

Crystal thickness = 1/2 lambda

T = 0.25 microseconds
C = 4000 m/s
lambda = C/F
F = 1/T
F = (1/0.25) = 4

Lambda = 4/ 4
Lambda = 1
Thickness = 1/Lambda
Thickness = 0.5 mm

Question 4

How does the addition of damping material change the efficiency of the probe

Answer 4

It decreases the efficiency because the amplitude of the sound would be reduced.
We reduce the efficiency of the probe

Question 5

Which of the following allows probe to multifunction in that they can obtain 2D images and doppler information?

Answer 5

Electric damping

Question 6

Explain the -6dB bandwidth

Answer 6

The useable bandwidth. All of the frequencies that have 1/2 the centre frequency amplitude and 1/4 intensity of the resonant frequency.

Question 7

Give me three reasons why firing a single crystal in an array probe is not desirable

Answer 7

1. Smaller the source sound more divergence. Lateral resolution
2. Beam steering
3. Vary the focus

Question 8

What is the transducer Q factor?

Answer 8

1. Reciprocal of frequency bandwidth.
2. Mechanical coefficient
3. Energy stored/ energy lost
4. The higher the Q the better the transmitter

Question 9

How does the sector array probe steer the sound to achieve its field of view?

Answer 9

Crystals are fired nearly at the same time, beams diverge in the far field.
Delayed Firing

Question 10

Increasing the damping will shorten the SPL and improve the axial resolution while widening the bandwidth and decreasing the Q factor T/F?

Answer 10

True

Question 11

Which of the following probes is electronically steered and focused?

1. Wobbler
2. Annular array
3. Linear translation
4. Linear phased array

Answer 11

Linear phased array
annular array electronically focused but mechanically steered

Question 12

When scanning the gallbladder, you have three single disc mechanical transducers to choose from. All are 5 MHz transducers and have the following diameter elements; 6 mm, 9mm and 11mm respectively. Which one would you choose?

Answer 12

The 6 mm probe
The gallbladder is a superficial structure and the 6 mm probe will have the nearest near zone length.

Question 13

What determines the resonant frequency of the transducer.

Answer 13

The thickness of the crystal in the probe and what it is made of.

Question 14

Which of the following is the best way to improve lateral resolution in the deeper aspects of an image using a single disc transducer?

1. Increase the damping
2. Add more matching layers
3. Increase the crystal diameter
4. Fire small segments of crystal sequentially

Answer 14

Increase the crystal diameter.
The narrower the beam, the better the lateral resolution, therefore if we use a crystal with a wider diameter we can have a narrow scanning zone deeper

Question 15

Which of the following transducer would be best to quantify the hemodynamics significance of a stenosis in an artery?

1. Low frequency and low Q
2. Low frequency and high Q
3. High frequency and low Q
4. High frequency and high Q

Answer 15

Low frequency and high Q

Why? Firstly, we need to use doppler so we can determine the velocity in the arteries. Doppler pulses are longer therefore we can’t use a low Q probe. Using a higher frequency probe might not be able to pick up the blood flow. Therefore we need to use the Lower frequency probe

Question 16

What does the housing do?

Answer 16

Keeps parts inside

Question 17

What does the tuning coil do?

Answer 17

Helps to regulate the driving frequency

Question 18

What does the electric shield do?

Answer 18

Prevents electrocution and reduces noise

Question 19

What does the insulator do?

Answer 19

Limits radial mode vibration

Question 20

What does the backing material do?

Answer 20

Keeps the pulses short

Question 21

What does the element do?

Answer 21

Responsible for the P. Properties of the probe

Question 22

What does the matching layer do?

Answer 22

Improves the sensitivity of the probe

Question 23

Explain what type of energy an ultrasound probe converts?

Answer 23

Mechanical to electrical and vice versa

Question 24

How is the thickness of the piezoelectric element determined?

Answer 24

One half the wavelength for the desired frequency

Question 25

Name two modes of vibration that occur within a piezoelectric disc.

Answer 25

Radial and thickness

Question 26

Why are composite crystals often used over naturally occurring?

Answer 26

Cheaper and better transmission and reception

Question 27

What materials are used for damping?

Answer 27

Epoxy resin and tungsten powder

Question 28

Damping decreases the transducer efficiency so why is it used?

Answer 28

Shortens the pulse which improves axial resolution

Question 29

State what two modes can be used to drive transducers

Answer 29

Burst and spike

Question 30

How are synthetic materials given piezoelectric properties?

Answer 30

Heat to Currie temperature and place in an electrical field to polarize the dipoles

Question 31

State the range of curie temperatures?

Answer 31

300-400

Question 32

Describe the purpose of the matching layer

Answer 32

Improves sensitivity and reduces the reflection at the surface

Question 33

What is the impedance of the matching layer?

Answer 33

Between the crystal and skin

Question 34

Why is transducer bandwidth important in transducer design?

Answer 34

Relates to the length of the pulse and the quality of axial resolution. Also allows for multi-frequency probes

Question 35

Explain the difference between a shock-excited and burst excited transducer?

Answer 35

Shock is DX current where operating frequency is equal to resonant frequency and burst is AC current where driving frequency can be altered

Question 36

What is the frequency of a crystal that has a thickness of 0.385

Answer 36

2 MHz

Question 37

What is fractional bandwidth?

Answer 37

Bandwidth/ frequency

Question 38

What is the transducer Q?

Answer 38

Quality factor- energy stored/ energy lose

Question 39

How is transducer Q related to axial resolution and bandwidth?

Answer 39

Low Q = better axial resolution and wider bandwidth

Question 40

Explain which type of Q Factor is advisable for DI and which.

Answer 40

Lower for better axial resolution and wider bandwidth

Question 41

How is Q calculated>

Answer 41

Ratio of center frequency of bandwidth

Question 42

Which is better, a narrow or wide- band transducer?

Answer 42

Wide because of the shorter pulse and better resolution

Question 43

The Z value of the matching layer is considered in the transducer design, explain why?

Answer 43

Must be between the Z value of the crystal and skin

Question 44

Give two other names for resonance frequency

Answer 44

1. Fundamental 2. Natural

Question 45

How do you calculate matching layer?

Answer 45

1/4 lambda