Real Time Imaging
General Physics
Padmini Arora
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
Resolution
Contrast
Detail
Elevation
Axial
↣ Elevation
Beam
Dimension
↣ SPL / 2
Lateral
↣ Lateral
Beam
Dimension
↣ Scan Converter
↣ [# Bits / Pixel]
↣ Post Processing
Curves
↣ Monitor Settings
↣ Ambient Light
↣ Acoustic Impedance
Mismatch
Temporal
↣ Depth
↣ Packet Size [Color]
↣ Image Size
↣ Line Density
↣ Parallel Processing
↣ # Foci / Line
↣ Persistence
↣ Compound Imaging
Temporal Resolution
Temporal Resolution: Related to time
➷ Capturing moving structure with good resolution in time
Frame rate: Ability of system to capture & display # of frames in 1 second
OR how frequently 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 affecting temporal resolution = frame rate]***
Frame Rate
Factors affecting frame rate:
➷ Speed of sound in the medium
➷ Imaging depth
If time required to make 1 frame = more #’s of frames generated in 1 second are less
➷ Meaning: 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 & 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 temporal resolution
Factors determining # of Pulses per Image
➷ 3 factors that affect # 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 2 foci & so on which 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 [try using ⇊ sector, ⇊ # of focuses, ⇊ depth
✧ if you have an option of changing # of scan lines → use less # of scan lines
✔ all
these steps will ⇊ time to generate frame → improves frame rate → improves temporal resolution