Intensities Ch 5 Flashcards
the beam’s power divided by it’s area
Intensity
Five key words related to reporting intensities of pulsed waves
- SPATIAL
- PEAK
- AVERAGE
- TEMPORAL
- PULSED
Refers to distance or space,
does not have the same intensity at different locations within the beam
Spatial Intensity
Number of possibilities used to measure spatial intensity
Two possiblities, Isp and Isa
The beams intensity at the location where it is maximum
Isp (spatial peak intensity)
The average intensity across the beam’s entire cross-sectional area
Isa (spatial average intensity)
Refers to time
*with pulsed ultrasound, the transducer is usually receiving (listening), but for brief moments it is transmitting (talking)
Temporal
Number of methods of measuring intensity, pulsed waves
Four methods, Itp Imax or Im Ipa Ita
Intensity of the beam at the instant in time of it’s maximal value
Itp (temporal peak intensity)
average intensity during the most intense half cycle
Imax or Im
average intensity during -the transmit time — is called
Ipa (pulse average intensity)
Averaging the intensity during the entire pulse repetition period—both the transmit and receive times— is called
Ita (temporal average intensity)
Measured during transmit time only
Pulse average intensity
Measured during both the transmit and receive times
Temporal average
The highest temporal intensity is _______ and it is slightly higher than ___________
Itp and it is slightly higher than Imax
Is lower than Imax, because it includes values over the entire pulse duration, and the tail end of the pulse is less intense than the beginning
Ipa (pulse average intensity)
The lowest of all temporal intensities is ____________ because it is the only method that includes the receive and transmit time
Ita (temporal average intensity)
Measured at the location where intensity is maximum, and at the instant in time that the most powerful fart of the pulse passes
Isptp (spatial peak/temporal peak)
Measured at the location where intensity is maximum, averaged over the transmit time (pulse duration)
Isppa (spatial peak/pulse average)
Measured at the location where intensity is maximum and averaged over all time, both the transmit and receive times
Ispta (spatial peak/temporal average)
Measured over the entire cross-sectional area of the sound beam, and over all time
Isata (spatial average/temporal average)
Temporal intensities From Largest to Smallest
Itp (temporal peak)
Imax (average of most intense half cycle)
Ipa (pulse average)
Ita (temporal average)
All measurements have units of
W/cm^2
Six different methods to measure and report intensities. Methods describe the same wave in a variety of ways
SPTP (spatial peak/temporal peak) SATP (spatial average/temporal peak) SPTA (spatial peak/ temporal average) SATA (spatial average/temporal average) SPPA (spatial peak/pulse average) SAPA (spatial average/pulse average)
No independently confirmed significant bioeffects have been confirmed in mammalian tissue below (medical usage)
100W/cm^2
Two bioeffects of ultrasound
Heat and cavitation
As sound energy is transmitted through tissue, some energy is reflected and some energy is absorbed as
Heat
The formation, growth and dynamic behavior of gas bubbles
Cavitation
The peak intensity at the point in space where the intensity is the highest, and that occurs when the ultrasonic emitting device is “on”
* It is the highest of the measured intensities
SPTP (spatial peak/ temoporal peak
The average power output of the device over the pulse repetition period, divided by a reference, usually that of the transducer face
- yields the lowest, and more commonly used measures of intensity
- most quickly determined & most frequently quited by manufacturers
SATA (spatial average/ temporal average)
The peak intensity over a selected area, such as the transducer face, that occurs when the ultrasonic emitting device is “on”
SATP (spatial average/ temporal peak)
The maximum spatial intensity when the sound beam is “on” average over the pulse reptition period
SPTA (spatial peak/ temporal average)
The pulse averaged intensity measured at the point in space where the value is maximal
SPPA (spatial peak/ pulse average)
The pulse average intensity averaged over the beam cross-sectional area of the sound beam, averaged over the transmit time ( pulse duration)
SAPA (spatial average/ pulse average)
