chapter 13: real-time imaging

static scanning

images displayed one frame at a time

real-time imaging

each frame is created and displayed very quickly, providing the impression of constant motion

frame rate

the system’s ability to create numerous frames each second

what is frame rate determined by?

• the sound’s speed in the medium

• the depth of imaging

units for frame rate:

Hertz (Hz) or images per second

temporal resolution

• “accuracy in time”

• describes the ability to precisely position moving structures from instant to instant

what is temporal resolution determined by?

frame rate

displaying a high number of images per second (high frame rate) improves what type of resolution?

temporal resolution

units for temporal resolution:

Hertz (Hz)

frame time

the time required to make a single image

how are frame rate and frame time related?

inversely related, reciprocals

a minimum frame rate of how many Hz is needed to be maintained or the image will flicker?

15 Hz

what 2 sonographer-controlled settings of an ultrasound system determine frame rate?

• imaging depth

• number of pulses per frame

how are imaging depth and frame rate related?

inversely

shallow imaging:

• short go-return time

• shorter frame time

• higher frame rate

• superior temporal resolution

how are pulses per frame and frame rate related?

inversely

what 3 factors determine the number of pulses needed to create each image?

• number of focal points (number of pulses per scan line)

• sector size

• line density

single focus:

• one pulse per scan line

• shorter frame time

• higher frame rate

• better temporal resolution

• poorer lateral resolution

multi-focus:

• many pulses per scan line

• longer frame time

• lower frame rate

• diminished temporal resolution

• improved lateral resolution

wide sector size/field of view:

• more pulses per frame

• longer frame time

• lower frame rate

• inferior temporal resolution

line density

the spacing between sound beams

what is the main advantage of high line density?

the gaps between the lines are smaller which improves the accuracy of each individual image

high line density:

• tightly packed lines

• more pulses per frame

• longer frame time

• lower frame rate

• low temporal resolution

• excellent spatial resolution

settings for better temporal resolution - higher frame rate:

• shallow imaging

• single focus

• narrow sector

• low line density