Real Time Imaging & Pulse Echos Flashcards
Temporal Resolution?
4th type of resolution (axial, Lateral. Elevation)
But does not have anything to do with space like the first 3, but rather with time.
Depends on frames per second (frame rate)
High FR = good. Low = bad
What is the difference between static and real time?
Static imaging = still pictures (b-mode)
Real Time = movies, able to record motion which is image + time (2D imaging), b-mode+real time.
What is frame rate?
of frames per second (frame F)
Deeper depth = fewer frames = low frame rate = degraded temporal resolution
(it’s dependent on depth & can be manipulated)
Reciprocal of frame time
What is frame time (frame P)?
How long it takes to make a frame.
Deeper depth = long PRP = higher FT = lower FR = degraded temporal resolution
How does frame rate relate to pulses per second?
High # of pulses = low FR (inversely related)
What settings adds pulses and so degrades temporal resolution?
-Multiple foci (multiple focuses)
-Sector size
• line density
• Doppler
Increase in any = degraded Temporal resolution
What is multiple foci?
With every added focus there is an added foci, which adds an additional beam to get more information for the added beam.
What are the Advantages & Disadvantages of adding more foci?
Advantages
More foci = more beams
More beams = better spatial resolution
Disadvantages:
More beams = more info
More info = greater frame time
Greater FT = low temporal resolution
How does sector size (image width) effect temporal resolution?
Larger width longer it takes to gather all data.
More lines of data = high frame rate
High frame time = low frame rate
Low frame rate = poor temporal resolution
How does the US machine help with temporal resolution?
Decrease lines of data sacrificing image clarity (spatial resolution).
Line density = spacing of pulses
What is Pulsed Echo Instramentation?
These are the basics of the machine, not considering the transducer:
• preparation & transmitting pulses
• receiving and processing pulses
What happens in the transducer?
Piezoelectric effect happens here.
What is the Pulser?
Helps in controlling electrical pulses to the wires which connect to the PZT.
More specifically it is in charge of amplitudes, through PRP & PRF
What is the beam former?
Helps in controlling electrical pulses to the wires which connect to the PZT.
It directs the delay times of sending out a pulse through the firing of the crystals
What is the receiver?
Receives beams & turns them from a-mode to b-mode & finally 2D display.
What is display?
Screen showing image (monitor or tv)
Old style (on exam) CRT = cathode ray Tube.
What ways are there for storage (Archive exams)?
Old school
• hard drive
• printed images
•VHS taps
What is the Master Synchronizer?
It organizes the timing of the machine’s components. Keeping the pulse out & received data organized.
What is the Pulser?
Makes an electrical signal sent to the PZT
High voltage = high amplitude beam
Low voltage = low amplitude beam
Has to do with power which is controlled by the preset on the mechine. It is seen as the mechanical index &/or thermal index.
What are other names for the Pulser?
- Acoustic power
- Pulser power
- transmit output
You want less of this due to bio effects
How is output related to images?
Signal (normally the higher amplitudes) to noise (normally seen as lesser amplitudes outside normal amplitudes) ratio.
High ratio = good. Low ratio = bad
What does the Pulser responds to?
- To changes in PRP “off time”
* changes in pulse lengths in relation to depth & focus changes
How does the Beam Former work?
Transmission
- receives voltage from Pulser and distributes to PZT
- In apodisation: decrease voltage to lateral PZT to refuse grating lobe
Receiving
•Calculates time delays for dynamic recover focus
What other jobs does the beam former do?
In the old days it was switched on and off to direct impulses to an from transducer.
- protects receiver parts from too much voltage
- channels = PZT + wire + electronics from Pulser to beam former.
What are the jobs of the transducer?
- Processes returning beam for display
- Amplification
- compression
- Demodulation
- Rejection
Why increase returning amplifications?
Needs to compensate for the weaker returning echoes to the original strength it was sent out. This happens very close to the PZT.
Can we modify the amplification and what does that do on the screen?
We change the amplification by adjusting the 2D. Also called: receive gain and B gain.
This controlled the brightness on the machine
What is compensation and why do we use it?
It is the machine compensating for the growing attenuation with deeper depths.
We need to compensate for that darker far field.
How does the machine compensate for the darker far field, how would we control this?
It amplifies the amplitude in the far field more then shallower depts
We can control this with the TGCs (time gain compensation)
What, why, & how is Compresion?
- determines the gray scale of image
- our eyes are limited in the rang of gays that can be seen.
- the machine compresses the returning echo Amplitudes
How do we control the Compression and what does it do on screen?
We can modify it by changing the dynamic range or mapping.
This controls weather we see more grays on screen on see it more black & white.
What is Demodulation?
1 rectification: all returning echoes made positive.
Two step process that further prepares image for display:
What is Rejection & can we control it?
It is distinguishing between the usable data and “garbage” low amplitude echoes.
The machine does this audomaticlly, but we can adjust the rejection by changing the threshold (suppression or rejection)
What is contrast resolution and what improves it?
CR is the ability to see two structures instead seeing two as one, based on their gray scale appearance.
We can improve this with a larger dynamic range, but we are still limited by how many shades of gray we see.
What is Dynamic frequency tuning?
Is related to brand width, it describes the range of frequencies used on different levels of depth:
* high frequency for near field * med. frequency for mid image * low frequency for far field
Note: not all mech ones have this. (Don’t confuse with dynamic beam focus)
