-
Sound waves are?
A mechanical wave in which particles in a medium move. Sound travels in a stright line. Sound waves are longitudinal wave
-
Acoustic propagation properities are?
The effects of the cound wave upon the biological tissue through which it passes.
-
The acoustic variables?
Pressure ( pascals), density (kg/cm^3), and distance (cm,mm)
-
Acoustic parameters
Help describe the waves features
-
The 7 acoustic parameters?
Period, frequency, amplitude, power, intensity, wavelegnth, propogation speed.
-
Tranverse waves?
Particles move in a direction that is perpendicular (right angles) to the direction that the wave popagates.(string shakeing up/down)
-
Longitudinal waves?
particles move in the same direction that the wave propagates. (example sound).
-
Inphase waves?
Peaks occur at the same time and at the same location
-
Out of phase waves?
Peaks occur at different times. (out of step)
-
Interference?
When multiple beans arrive at same location and the waves loose their individual characteristic at that moment to combine to form a single wave
-
Constrictive Interference?
Intereferance of a pair of inphase waves results in the formation of a single wave of greater amplitude than either of its componets
-
Destructive Interference?
Interference of a pair of out of phase waves resulting in the formation of a single wave of lesser amplitude than either of its componets.
-
Parameters?
Describe features of a sound wave
-
Period?
Time it takes a wave to vibrate a single cycle/ time from start of one cycle to the start of the next cycle.
-
Units of period?
untis of time: seconds, ms, hours, days
-
Period is determined by?
Sound source. It is not adjustible by sonographer
-
Frequency?
The number of events that occurs in a sepcific duration of time.
-
Units of frequency?
units per second, 1/second,hertz(per second).
-
Frequency is determined by?
Sound source/ It is not adjustible by spnpgrapher
-
Infrasound?
less than 20Hz.
-
Audible sound?
between 20Hz and 20kHz.
-
Ultrasound?
Greater than 20kHz.
-
Period and frequency are
Reciprocals of each other
-
The three parameters that describe the bigness of a sound wave?
Amplitude, power, intensity
-
Amplitude?
Is the bigness of a wave.
-
Units of amplitude?
Pressure(pascals), density(g/cm^3), particle motion(cm,inches,any)
-
Amplitdue is determined by?
The sound source. It is adjustible by the sonographer
-
Peak to peak amplitude
If the difference between maxium and minimun values of an acoustic variable.
-
Power?
Is the rate of energy transfer or th rate at which work is performed
-
-
Power is determined by?
Sound source. It is adjustable by sonographer
-
Power and amplitude?
Power is porportional to amplitude squared
-
Intensity?
The concentration of energy in a sound beam.
-
Intensity ='s?
Intensity(W/cm^2)= power(w)/area(cm^2).
-
Units of intensity
Watts/square centimeter, or W/cm^2
-
Intensity is determined by?
Sound source.It is adjustable by sonographer
-
Intensity is?
Poroprtional to power and amplitude squared.
-
Wavelegnth?
The distance or legnth of one complete cycle.
-
Units of wavelegnth?
mm,meters, any other unit of legnth.
-
Wavelegnth is determined by
Both the source and the medium. It is not adjustable by sonographer.
-
To calculate wavelegnth
1.54mm/us(wavelegnth of sound in soft tissue)/ frequency(MHz).
-
Propogation speed?
The distance that a sound wave travels through a medium in 1 second.
-
Units of propogation speed?
meters per second, mm/us, or any dstance divided by time
-
Propogation speed is determined by?
The medium in which it is traveling. It is not adjustable by sonograpger
-
Speed of sound in soft tissue
1,540 m/s
-
Sound travels?
Fastest in solids(bone, tendon, muscle), Slower in liquids( blood,liver,soft tissue), slowest in gases(fat,lung,air).
-
Two characteristics of a medium that affects the speed of sound?
stiffness, density.
-
Stiffness?
The ability of an object to resist compression. Higher stiffness faster speed.
-
Density?
The relative weight of a meterial. Higher the density the lower the speed.
-
What is determined by the sound source
Period, frequency, amplitude, power ,intensity. Pulse duration.PRP.PRF. Duty factor
-
What is determined by medium?
Speed
-
What is determined by both source and medium?
Wavelegnth. Spatial pulse legnth.
-
What can be changed by sonographer
Amplitude, power, intensity.
-
Pulse duration?
The actual time from the start of a pulse to the end of that pulse.
-
Units of pulse duration
units of time, us,ms,seconds
-
Pulse duration is determined by?
The sound source. It is not adjustable by sonographer
-
To calculate pulse duration?
pulse duration(us)= #cycles x period(us) pulse duration(us)=#cycles/frequency(MHz)
-
Spatial pulse legnth?
The distance that a pulse occupies in space from the start to the end of a pulse.
-
Units of spatial pulse legnth?
Units of distance, mm
-
Spatial pulse legnth is determined by?
Both the source and the medium. It is not adjustable by sonographer.
-
Pulse repetition period?
The time from the start of one pulse to the start of the next pulse.
-
-
PRP is determined by
The sound source. It is adjustable by sonographer
-
Pulse repetition frequency?
The number of pulses than an ultrasound system transmits into the body each second
-
Units of PRF?
Units of HZ or per second.
-
PRF is determined by?
The sound source. It is adjestable by sonographer
-
Duty factor?
The percentage or fraction of time that a system is transmitting a pulse.
-
Units of duty factor?
A %.
-
Duty factor is determined by?
Sound source. It is adjustable by sonographer
-
Spatial?
Refers to distance or space.
-
-
Average?
The mathamatical middle
-
Temporal?
Refers to all time, transmit(pulse duration) and revieve
-
Pulsed?
Refers to only to the trnasmit time only(pulse duration).
-
SPTA
Intensity that is most revelant to tissue heating.
-
Attenuates?
As sound travels in the body it weakens(attenuates
-
Decibel notation?
Is used to report chnges of attenuation
-
Logarithms
A method of rating numbers. Log represents the number of 10's that are multiplied to create the origional number
-
3db'S?
Means the intensity was doubled its origional value
-
10db's?
Means the intensity has become ten times larger than its origional value.
-
-3db's?
Means the intensity has become half its origional value.
-
-10db's?
Means the intensity has become 1/10 its origional value.
-
Attenuation?
The decrease in intensity, power, and amplitude as sound travels .
-
Attenuation is determined by?
Path legnth and frequency of sound.
-
Attenuation coefficient?
The number of decibels of attenuation that occurs when sound travels one centimeter
-
Units of attenuation coefficent?
dB/cm
-
Total attenuation is calculated by?
attenuation coeffieient(db/cm) x distance(cm)
-
Attenuation coefficient is?
one half of the frequency.
-
Half value thickness?
Is the distance that sound travels in a tissue that reduced the intensity of sound to one half its origional value
-
Units of half-value layer
centimeters
-
Half value thickness depends on?
the medium, the frequency of sound
-
Impedance
is the acoustic resistance to sound traveling in a medium
-
Impedance='s?
density(kg/m^3 x prop. speed (m/s)
-
Units of impedance?
rayls, Z
-
Impadance is determined by?
Medium only.
-
4 Angles?
acute(less than 90degrees), right(90degrees),obtuse(greater than 90 degrees), oblique(any other than 90degrees
-
Two conditions for refraction?
oblique incidance and propogation speeds of the two media are different.
-
Go return time(time of flight)?
The elapsed time from pulse creation to pulse reception
-
Time of flight is directly related to?
depth.
-
13microsecond rule
for every 13us of go return time, the object creating the reflection is 1 centimeter deeper ins oft tissue. ez 13us has a depth of 1 cm and the total distance traveled would be 2cm
-
PRP='s?
Imaging depth(cm) x 13us/cm.
-
Axial resolution?
describes the measure of detail in a image
-
Piezoelectrice effect?
describes the property of certain materials to create a voltage when they are mechanically deformed
|
|