Chapter 4: Describing Pulsed Waves Flashcards
What is a pulsed sound?
a collection of cycles that travel together
What is a pulse made up of?
individual cycles
Two components of pulsed ultrasound
- transmit, talking, “on time”
-receive, listening, “off time”
Pulse duration
-the actual time from the start of a pulse to the end of that pulse
- a single “on” time
Pulse duration & relationships with cycles, period and frequency
-directly proportional to # of cycles
-directly proportional to period
-inversely proportional to frequency
long pulse duration
-many cycles in a pulse
-individual cycles with long periods
short pulse duration
-few cycles in a pulse
-individual cycles with short periods
Shorter duration pulses are more desirable b/c they create images of greater accuracy
Spatial Pulse Length
distance from the start to the end of a pulse
Spatial Pulse Length and relationships with cycles, wavelength, and frequency
-directly proportional to # of cycles in pulse
-directly proportional to wavelength
-directly proportional to frequency
Difference between pulse duration and spatial pulse length?
SPL- the distance of the pulse end to end
Pulse duration- time of pulse from beginning to end
Long pulse length
-many cycles in pulse
-longer wavelengths
Short pulse length
-fewer cycles in the pulse
-shorter wavelengths
Why are short pulses more desirable?
they create more accurate images and higher frequency sound waves
Pulse Repetition Period (PRP)
-time from start of one pulse to the start of the next pulse
-includes both “on” and “off” time
-reported in units of time
-directly related to imaging depth
Depth of View
maximum distance into the body that an ultrasound system is imaging
Two components of pulse repetition period (PRP)
-transmit/ “on” time
-receive/ “off” time
Transmit Time
-also referred to as pulse duration
-cannot be changed by sonographer
Receive Time
-“off time”
- can be altered by sonographer
Deeper Imaging
listening time and the PRP lengthen
Shallow Listening
listening time and PRP shorten
Pulse Repetition Frequency
number of pulses that an ultrasound system transmits into the body each second
(Can’t have as many pulses when you’re listening longer)
-measured in units of Hz (hertz)
Duty factor
percentage or fraction of time that the system transmits a pulse
-inversely related to depth
-higher when system is imaging at shallow depths
Relationship between Pulse Repetition Period and Pulse Repetition Frequency
-PRP and PRF are inversely related
-longer PRP= lower PRF
-shorter PRP= higher PRF
- reciprocals
Duty factor and deeper imaging
decreases
Duty factor and shallower imaging
increases
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