SAS
General Physics
Padmini Arora
Real Time Imaging
Static vs. Real Time Imaging
Static imaging is like using camera & taking a picture
[creating single image at a time] This kind of image has just one frame
Real time imaging is like using a video camera &
capturing a clip or a movie. This kind of imaging has multiple frames.
Modern machines are capable of doing real time imaging
Forms of Resolution
Resolution
Detail
Contrast
Temporal
Axial
SPL/2
Elevation
• Elevation
Beam Dimension
Lateral
Lateral Beam Dimension
Scan Converter
Depth (#Bits/Pixel)
• Packet Size (Color) Post Processing Curves • Image Size
• Monitor Settings
· Line Density (Contrast/Brightness) . Parallel Processing - Ambient Light
• #Foci/Line Acoustic Impedance • Persistence Mismatch
• Compound Imaging
Temporal Resolution
Temporal resolution: related to time -- capturing moving structure with good
resolution in time
Frame rate: ability of the system to capture & display number of frames in
one second OR how frequently the system is generating &displaying
frames on the screen -- unit of frame rate = Hertz [Hz., or per second]
*** Higher frame rate gives better temporal resolution [most important
factor effecting temporal resolution is frame rate]
Frame Rate
• Factors effecting frame rate:
a) Speed of sound in the medium
b) Imaging depth
If time required to make 1 frame = more #’s of frames generated in 1
second are less. This means, frame rate & time required to generate 1
frame = inversely related to each other -- relationship = T frame = 1 /
frame rate OR T frame X frame rate = 1 -- if system generates 1 frame in
1/10 of a second = 10 frames per sec OR 10 Hz
System Settings that Affect Frame Rate
• T frame = # of pulses X PRP
• A) Imaging depth with shallow depth → less go return time → shorter time
to make a frame → higher frame rate → better temporal resolution with
deep imaging → more go return time more time to make a frame → lower
frame rate inferior temporal resolution
• B) #of pulses in each picture more the #of pulses → more the time it takes
to make each frame → lower the frame rate inferior the temporal resolution
Factors determining # of pulses per image:
• 3factors that effect number of pulses in each frame:
a) # of pulses per scan line [#of focal points]: 1 pulse can create 1 focus -2 pulses are required for 2foci & so on means, more the # of foci → more
the pulses are required to generate the frame -- more the time required to
generate a frame less the frame rate *** multiple focus improves lateral
resolution
b) Sector size: less the sector size less the # of pulses less the time it will
take to generate the image better the frame rate
c) Lines per angle of sector [line density]: more the line density → more
the pulses are there to generate frame more the time it takes to generate a
frame → less the frame rate *** High line density improves spatial
resolution
More about Temporal Resolution
For still images: need better detail resolution, temporal resolution = not
concern
For moving clip: need better temporal resolution, so try to use small sector,
less # of focuses, less depth & if you have a option of changing # of scan
lines, use less #of scan lines -- doing all these steps will decrease the time
to generate frame → improves frame rate → improves temporal resolution