Physics Quiz 1 Review Flashcards
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
The damping material
Explain the method of probe excitation used in a modern day array probe?
Burst spike: AC voltage. We can send it at a different frequency beside resonant frequency.
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?
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
How does the addition of damping material change the efficiency of the probe
It decreases the efficiency because the amplitude of the sound would be reduced.
We reduce the efficiency of the probe
Which of the following allows probe to multifunction in that they can obtain 2D images and doppler information?
Electric damping
Explain the -6dB bandwidth
The useable bandwidth. All of the frequencies that have 1/2 the centre frequency amplitude and 1/4 intensity of the resonant frequency.
Give me three reasons why firing a single crystal in an array probe is not desirable
- Smaller the source sound more divergence. Lateral resolution
- Beam steering
- Vary the focus
What is the transducer Q factor?
- Reciprocal of frequency bandwidth.
- Mechanical coefficient
- Energy stored/ energy lost
- The higher the Q the better the transmitter
How does the sector array probe steer the sound to achieve its field of view?
Crystals are fired nearly at the same time, beams diverge in the far field.
Delayed Firing
Increasing the damping will shorten the SPL and improve the axial resolution while widening the bandwidth and decreasing the Q factor T/F?
True
Which of the following probes is electronically steered and focused?
- Wobbler
- Annular array
- Linear translation
- Linear phased array
Linear phased array
annular array electronically focused but mechanically steered
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?
The 6 mm probe
The gallbladder is a superficial structure and the 6 mm probe will have the nearest near zone length.
What determines the resonant frequency of the transducer.
The thickness of the crystal in the probe and what it is made of.
Which of the following is the best way to improve lateral resolution in the deeper aspects of an image using a single disc transducer?
- Increase the damping
- Add more matching layers
- Increase the crystal diameter
- Fire small segments of crystal sequentially
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
Which of the following transducer would be best to quantify the hemodynamics significance of a stenosis in an artery?
- Low frequency and low Q
- Low frequency and high Q
- High frequency and low Q
- High frequency and high Q
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
What does the housing do?
Keeps parts inside
What does the tuning coil do?
Helps to regulate the driving frequency
What does the electric shield do?
Prevents electrocution and reduces noise
What does the insulator do?
Limits radial mode vibration
What does the backing material do?
Keeps the pulses short
What does the element do?
Responsible for the P. Properties of the probe
What does the matching layer do?
Improves the sensitivity of the probe
Explain what type of energy an ultrasound probe converts?
Mechanical to electrical and vice versa
How is the thickness of the piezoelectric element determined?
One half the wavelength for the desired frequency
Name two modes of vibration that occur within a piezoelectric disc.
Radial and thickness
Why are composite crystals often used over naturally occurring?
Cheaper and better transmission and reception
What materials are used for damping?
Epoxy resin and tungsten powder
Damping decreases the transducer efficiency so why is it used?
Shortens the pulse which improves axial resolution
State what two modes can be used to drive transducers
Burst and spike
How are synthetic materials given piezoelectric properties?
Heat to Currie temperature and place in an electrical field to polarize the dipoles
State the range of curie temperatures?
300-400
Describe the purpose of the matching layer
Improves sensitivity and reduces the reflection at the surface
What is the impedance of the matching layer?
Between the crystal and skin
Why is transducer bandwidth important in transducer design?
Relates to the length of the pulse and the quality of axial resolution. Also allows for multi-frequency probes
Explain the difference between a shock-excited and burst excited transducer?
Shock is DX current where operating frequency is equal to resonant frequency and burst is AC current where driving frequency can be altered
What is the frequency of a crystal that has a thickness of 0.385
2 MHz
What is fractional bandwidth?
Bandwidth/ frequency
What is the transducer Q?
Quality factor- energy stored/ energy lose
How is transducer Q related to axial resolution and bandwidth?
Low Q = better axial resolution and wider bandwidth
Explain which type of Q Factor is advisable for DI and which.
Lower for better axial resolution and wider bandwidth
How is Q calculated>
Ratio of center frequency of bandwidth
Which is better, a narrow or wide- band transducer?
Wide because of the shorter pulse and better resolution
The Z value of the matching layer is considered in the transducer design, explain why?
Must be between the Z value of the crystal and skin
Give two other names for resonance frequency
- Fundamental
- Natural
How do you calculate matching layer?
1/4 lambda
