Week 14 Real Time Imaging Flashcards
Chapter 13
What is Frame rate?
The system’s ability to create numerous frames each second.
Number of frames per second.
What is Frame Rate determined by?
- Sounds speed in a medium
- Depth
What are the units of Frame rate?
Hz
What is temporal resolution?
Pertains to accuracy in time. The ability to precisely position moving structures from instant to instant.
What is Temporal Resolution determined by?
Frame Rate
What is the unit for Temporal resolution?
Hertz or “per second”
How many lines of sound are needed to create 1 frame?
100
How are frame rate and time for one frame related (T frame)?
Inverse and reciprocal
What is the formula for T frame?
Tframe x Frame rate = 1
When an ultrasound system creates an image in 1/10 of a second, what is the frame rate?
10 Hz or 10 frames per second.
When an ultrasound creates an image in 1/50th of a second, what is the frame rate?
50 Hz or 50 frames per second.
What 2 system settings affect frame rate?
- imaging depth
- number of pulses per frame
What determines a high frame rate?
Displaying a high number of images per second.
What determines a low frame rate?
Displaying a low number of images per second.
How are temporal resolution and frame rate related?
Directly
What improves temporal resolution, High or Low frame rate?
High frame rate improves temporal resolution.
How are imaging depth and frame rate related?
Inversely
Does shallow imaging improve or degrade temporal resolution?
improves temporal resolution
Does deeper imaging improve or degrade temporal resolution?
Degrades temporal resolution
What is the formula for T frame?
T frame = # of pulses x PRP
An ultrasound system creases each image with 100 distinct sound pulses. Each pulse travels to a maximum depth that requires a round trip time (PRP) of 1/1000 second. What is the time needed to make a single frame?
100 x 1/1000 = 1/10 second
The frame rate is 10 Hz
Now, the sonographer decreases the depth of view by half. The PRP will be .5/1000. Since the image still requires 100 pulses, what is the T frame now?
100 x .0005 second
.05 or 1/20 second
Frame rate = 20 Hz.
Shallow imaging
- Short go-return time
- Shorter T frame
- Higher frame rate
- superior temporal resolution
Deeper imaging
- Long go-return time
- Longer T frame
- Lower frame rate
- Inferior temporal resolution
What 3 factors determine number of pulses per frame?
- number of focal points
- Sector size
- line density
A Multi focus transducer has what?
- Many pulses per scan line
- Longer T Frame
- Lower frame rate
- diminished temporal resolution
- improved lateral resolution
A Single Focus transducer has what?
- One pulse per scan line
- Shorter T frame
- higher frame rate
- Better Temporal resolution
- Poorer lateral resolution
Narrow sector size has:
- few pulses per frame
- shorter T frame
- Higher Frame Rate
- Superior Temporal resolution
Wide sector size has:
- more pulses per frame
- longer T frame
- lower frame rate
- inferior temporal resolution
Wide Line density has:
- widely spaced lines
- fewer pulses per frame
- Shorter T frame
- higher frame rate
- Higher temporal resolution
- Poor spatial resolution
Hight Line Density has:
- tightly packed lines
- More pulses per frame
- Longer T frame
- Lower frame rate
- Low temporal resolution
- excellent spatial resolution
What is the advantage of high line density?
The gaps between the lines are smaller therefore improving the accuracy of each individual image.
What is line density?
The spacing between sound beams.
Sector size requires what?
more pulses to create an image.
Temporal resolution is better when:
- shallow imaging
- single focus
- narrow sector
- low line density
Temporal resolution degrades with:
- deeper imaging
- multiple focal points
- wide sector
- high line density
Lateral resolution improves with….?
Multi-focusing
Spatial resolution improves with…?
Higher line density
