Chapter 4 Flashcards
Can continuous wave ultrasound create anatomic images?
No
Short bursts of sound called _ are used in diagnostic ultrasound
Pulses
A pulse of ultrasound is a _
collection of cycles that travel together
Pulsed ultrasound is made up of _
individual cycles that travel together as a unit
Pulsed Ultrasound is made up of two components:
Transmit time (talking) Receive time (listening)
Five Parameters for Pulsed Ultrasound
Pulse duration
Pulse repetition period Pulse repetition frequency Duty factor
Spatial pulse length
The actual time from the start of a pulse to the end of that pulse
Pulse duration
Units for pulse duration
units of time, microsecond
Typical value for pulse duration
0.3 to 2.0 microseconds
In clinical imaging, a pulse is comprised of _ cycles
2-4
Pulse duration is determined by
sound source only
Is pulse duration adjustable by the sonographer
No
_ is a characteristic of each transducer. Does not change with imaging depth.
Pulse duration
Pulse duration (μs) =
of cycles x period
Relationship between pulse duration and the number of cycles in the pulse
Directly proportional
Relationship between pulse duration and period
Directly proportional
Relationship between pulse duration and frequency
Inverse
Pulse duration =
cycles/frequency
Pulses of long duration have _ cycles in the pulse or _
Many
individual cycles with long periods
Pulses of short duration have _ cycles in the pulse or _
Few
individual cycles with short periods
Pulses with _ duration are desirable for imaging because _
Shorter
they create images of greater quality and accuracy.
The distance that a pulse occupies in space from the start to the end of a pulse.
Spatial Pulse Length
Units for spatial pulse length
Distance such as mm
Typical values for spatial length
in clinical imaging, SPL in
soft tissue ranges from 0.1 to 1 mm
Spatial pulse length is determined by
both the sound source and the medium.
SPL =
of cycles in pulse x the wavelength of each cycle
Is spatial pulse length adjustable by the sonographer
No
Since _ is determined by both the source and the medium, so is SPL
Wavelength
Spatial pulse length (mm) =
cycles x wavelength (mm)
Relationship between spatial pulse length and the number of cycles in the pulse
Directly proportional
Relationship between spatial pulse length and wavelength
Directly proportional
Relationship between spatial pulse length and frequency
Inverse
Spatial Pulse Length is the _ of the pulse from _
distance
end to end
◆millimeters
Pulse duration is the _ that a pulse is “on”
Time
Microseconds
Two characteristics create long pulses:
Many cycles in the pulse
Cycles with longer wavelengths
Two characteristics create short pulses:
Fewer cycles in the pulse
Cycles with shorter wavelengths
Pulses of shorter length are desirable because they create
more accurate images and improve resolution
The “on” or talking time of a single pulse
Pulse duration
_ the time from the start of one pulse to the start of the next pulse. It includes one pulse duration plus one listening time.
Pulse repetition period
Unit for pulse repetition period
Time such as milliseconds
Typical values of PRP
In diagnostic ultrasound, 100
microseconds to 1 millisecond
PRP is generally _ than pulse duration
100-1,000 times longer
PRP is determined by
Sound source only
Can PRP be adjusted by sonographer
Yes, by changing the image depth
_ describes the maximum distance into the body that an ultrasound system is imaging
Depth of view
The markers along the edge of an image indicate
Depth
Relationship between PRP and depth
Directly related
When the system is imaging more deeply, the time from one pulse to the next is _. Therefore PRP _
Longer
Increases
When the system is imaging at shallow depths, the time from one pulse to the next is _. Therefore PRP _
Shorter
Decreases
_ changes listening time
Depth
The two components of PRP are
Transmit time or “on” time (Pulse duration) and
Receive time or “off” time
the number of pulses that an ultrasound system transmits into the body each second.
Pulse repetition frequency
Units for PRF
Hertz
Typical values for PRF
1,000 to 10,000 Hz (pulses
per second)
We commonly use KHz
PRF is determined by
Sound source only
Can PRF be adjusted by sonographer
Yes, by adjusting image depth
Is PRF related to frequency
No
Relationship between PRF and depth
Inverse
Shallow imaging= _ PRF
High
Deeper imaging= _ PRF
Lower
Relationship between PRP and PRF
Inverse and reciprocal
A longer PRP results in a _ PRF
Lower
A shorter PRP results in a _ PRF
Higher
PRF=
1/PRP
PRP=
1/PRF
PRF X PRP=
1
the percentage or fraction of time that the system transmits a pulse.
Duty factor
Units for duty factor
None, it is a percentage
Duty factor ranges in clinical imaging
from 0.2% to 0.5%
Duty factor is determined by
Sound source only
Is duty factor adjustable by sonographer
Yes, by changing depth
Relationship between duty factor and depth
Inverse
Duty factor=
(pulse duration/pulse rep period) x 100
Longer pulses= _ duty factor
High
The maximum value for duty factor is _ and is achieved with _
100%
Continuous wave sound
The minimum value for duty factor is _ and exists when _
0%
The transducer is silent
Typical value for duty factor
0.2%
The system listens _ times longer than it transmits
500
Shallow imaging: _ listening
Less
Shallow imaging: _ PRP
Shorter
Shallow imaging: _ PRF
Higher
Shallow imaging: _ PRF
Higher
Shallow imaging: _ duty factor
Higher
Deep imaging: _ listening
More
Deep imaging: _ PRP
Longer
Deep imaging: _ PRF
Lower
Deep imaging: _ duty factor
Lower
Determined by source
Pulse duration
PRP
PRF
Duty factor
Determined by source and medium
Spatial pulse length
Does not change with imaging depth
Pulse duration
Spatial pulse length
Changes with imaging depth
PRP
PRF
Duty factor
The parameters that describe a single cycle can describe both continuous and pulsed wave sound
Period
Frequency Wavelength Propagation speed
