day 3 Flashcards
separated in time with gaps of no ultrasound
pulses
consists of pulses separated by
gaps in time
pulsed ultrasound
number of cycles occurring per second for a continuous wave
frequency
number of cycles per second that would occur if it were a continuous wave
pulsed wave
number of pulses that occur in
1 second
pulse-repetition frequency
PRF is commonly expressed in
kilohertz (kHz)
refers to the time for one cycle
to occur
period
refers to the time from the beginning of one pulse to the beginning of the next
pulse-repetition period (PRP)
time that it takes for one pulse to occur
pulse duration
Sonographic pulses are typically _ or _ cycles long
2 to 3
Doppler pulses are typically _ to _ cycles long
5 to 30
fraction of time that pulsed ultrasound is
duty factor
PD increases, the DF ____
increases
PRF increases, PRP ____ and duty factor ____
PRF increases, PRP decreases and duty factor increases
length of a pulse from front to back, equal to the length of each cycle times the number of cycles in the pulse
Spatial Pulse Length
length of each cycle
wavelength
length of space occupied by a pulse
SPL
If the number of cycles in a pulse increases, SPL ____
increases
frequency increases, wavelength and SPL ____
decrease
In contrast to continuous wave ultrasound, which can be described by a single frequency, ultrasound pulses contain a range of frequencies
bandwidth
bandwidth divided by operating
frequency, unitless
fractional bandwidth
reciprocal of fractional bandwidth (operating frequency divided by bandwidth) is called
quality factor
range of frequencies contained in a pulse
bandwidth
measure of how far a variable gets away from its normal, undisturbed value
amplitude
maximum variation that occurs in an acoustic variable
atenuation
ability to accomplish work
energy
form of mechanical energy that can do work
sound
rate at which energy is transferred from one part of a system to another or from one location to another
power
rate at which energy passes through a unit area
intensity
weakening of sound while it propagates, reduction in amplitude and intensity as sound travels is called
attenuation
encompasses the absorption of sound while it travels and the reflection and scattering of the sound (echoes) while it encounters tissue interfaces and heterogeneous tissues
attenuation
dominant factor that contributes to attenuation of ultrasound in soft tissues
absorption
units used to quantify attenuation
decibels
attenuation that occurs with each centimeter the sound wave travels
attenuation coefficient (ac)
attenuation coefficient increases, attenuation ___
increases
frequency increases, attenuation ___
increases
frequency increases, penetration ____
decreases
