Lesson 2 (Part 2) Flashcards
What does the instrument automatically achieve?
The highest PRF
Pen
Penetration
Why must pen x PRF not exceed 77cm/ms?
In order to avoid echo misplacement
- pen(cm) x PRF (kHz) < 77(cm/ms)
What happens to PRF if frequency is reduced and pen increases?
It gets reduced
-avoiding echo misplacement
What happens if you go over 77cm/ms?
You get an artifact
- range ambiguity
What happens to PRF in 2D if the depth is increased by 4x?
It decreases by 4x
What gets produced by a greater voltage amplitude? (2)
- Greater amplitude pulse
2. Greater intensity pulse
What does AMP(voltage) equal?
AMP(pulse)
Amplitude
The power or strength of the beam entering the tissue
- closely related to intensity
What do pulse delays do? (2)
- Decided how many element/crystals are involved
2. Which ones are getting fired
What is pulse delays involved with? (6)
- Sequencing arrays
- Phasing
- Electronic focusing
- Dynamic aperture control
- Apodization
- Code excitation
Sequencing array
Multiple blocks of sound, each producing a scan line
Phasing
Microsecond delays between each element firing
What does phasing help with?
Steering
Electronic focusing
Microsecond delays between firing elements on a curved delay patter in order to send the sound beam into a focal point
What does adjusting the delays do in electronic focussing?
It puts the focus either closer to or farther away
What does the dynamic aperture decide?
The width of the aperture
What can the dynamic aperture affect? (2)
- Our near zone length
2. Beam width
How does the dynamic aperture affect our imaging?
Through lateral resolution
- LR = beam width
What happens if you use a small aperture?
You will get a better picture
- higher resolution
What does apodization do?
It decreases the strength to the outer elements
- reducting of grating lobes in arrays
What does apodization only work for?
Arrays
- not side lobes
What is the ensemble length?
1
What is the doppler ensemble length?
3-30
- has some delays in between
What does coded excitation involve?
A decoder in the beam former
What does coded excitation not include?
Range ambiguity
Why doesn’t coded excitation include range ambiguity?
Because the decoder knows how it is sent out
What does coded excitation allow? (5)
- Multiple foci
- Spatial compounding
- Increased penetration
- Increased contrast resolution
- B-flow imaging
B-flow imaging
Multiple pulses are sent down the same scan line and the decoder stacks the received echos
- constructive interference
What do you get with B-flow imaging?
Overall higher intensity echoes
Is B-flow and B-mode the same thing?
No
Channel
Is an independent signal path consisting of a transducer element, delay and possibly other electronic components
Transmission channel
Each path TO each individual element is a channel
- pulse –> pulse delays –> element
Reception channels
Each path FROM each individual element is a channel
- element –> amplifier/ADC –> echo delays/summer
What does an increased number of channels allow?
More precise control of beam characteristics
What do numbers of channels not exceed?
The number of elements in the transducer
