Ch 3: Describing Sound Waves Flashcards
The source of the sound wave is the…
ultrasound system and transducer.
The medium is the…
tissues through which the sound is traveling.
Period is the…
time it takes a wave to vibrate a single cycle; the timefrom the start of one cycle to the start of the next cycle.
Period is reported in units of…
time, such as microseconds, seconds, hours, or days.
The typical value of period in diagnostic u/s is…
.06 to .5 microseconds.
Period is determined by…
the sound source only, not by the medium.
Is period adjustable by the sonographer?
No.
Frequency is…
the number of particular events that occur in a specific duration of time. In u/s, the # of cycles per second.
Frequency is reported in units of…
per second, 1/second, hertz, or Hz.
In clinical imaging, the typical frequency range is…
from approximately 2 MHz to 15 MHz.
Frequency is determined by…
the sound source only.
Is frequency adjustable by the sonographer?
No.
Sound is described as infrasonic if its frequency is…
less than 20 Hz.
Sound is described as audible if its frequency is…
between 20 Hz and 20,000 Hz.
Sound is described as ultrasonic if its frequency is…
higher than 20,000 Hz (20 kHz).
How are period and frequency related to each other?
Inversely. As one increases, the other decreases.
Period and frequency have a special inverse relationship called…
reciprocal. If multiplied together, the result is one.
Amplitude is…
the ‘bigness’ of a wave; the difference between the maximum (or minimum) value and the baseline value.
Amplitude is reported in units of…
pressure (pascals or Pa), density (g/cm^3), particle motion (any distance), or decibels (dB).
In clinical imaging, typical amplitude ranges from…
1 million pascals to 3 million pascals.
Amplitude is determined by the…
sound source (though it does decrease as the wave travels through the body).
Is amplitude adjustable by the sonographer?
Yes.
Peak-to-peak amplitude is…
the difference between the maximum and minimum values (not just between one extreme and the baseline).
Power is the…
rate of energy transfer; the rate at which work is performed.
Power is reported in units of…
watts (W).
In clinical imaging, typical power ranges from…
.004 to .09 watts.
Power is determined by the…
sound source (though the power decreases as the wave travels through the body).
Is power adjustable by the sonographer?
Yes.
The bigger the wave, the more energy is transferred. So as the amplitude changes, power changes proportionally. What is the proportion?
Power is proportional to amplitude SQUARED.
Intensity is…
the concentration of energy in a sound beam.
Intensity is reported in units of…
watts/square centimeter (W/cm^2).
In clinical imaging, typical intensity ranges from…
.01 to 300 W/cm^2.
Intensity is determined by…
the sound source (though the wave gets less intense as it travels through the body).
Is intensity adjustable by the sonographer?
Yes.
The ‘bigness’ parameters are all directly related. What is the proportion of intensity to power?
One to one. If a wave’s power is doubled, the intensity is doubled. If a wave’s power is quartered, the intensity is quartered.
What is the proportion of intensity to amplitude?
Intensity is proportional to amplitude SQUARED.
Wavelength is…
the length of one complete cycle.
Wavelengh is reported in units of…
mm, meters, or any length.
In clinical imaging, wavelength in soft tissue ranges from…
.1 to .8 mm.
Wavelength is determined by…
both the sound source and the medium.
Is wavelength adjustable by the sonographer?
No.
What is the relationship between wavelength and frequency?
They are inversely related. As one increases, the other decreases.
What is the wavelength of 1 MHz sound in soft tissue?
1.54 mm
How do you find the wavelength of a sound wave in soft tissue?
wavelength (mm) = 1.54 mm per microseconds divided by frequency (MHz)
Why is wavelength important in u/s?
Shorter wavelengths are created by higher frequency sound. The higher the frequency, the clearer the image.
Propagation speed is…
the rate at which a sound wave travels through a medium.
Speed is reported in units of…
distance divided by time (m/s, mm/microseconds, or miles per hour).
In the body, the speed of sound ranges from…
500 m/s to 4,000 m/s depending on the tissue.
Speed is determined by…
the medium.
Is speed adjustable by the sonographer?
No.
What is the speed of sound in soft tissue?
1,540 m/s
What is the speed of sound in lung tissue?
500 m/s
What is the speed of sound in bone?
3,500 m/s
What two characteristics determine the speed of sound in a given medium?
Stiffness and density
Stiffness describes…
the ability of an object to resist compression.
How are stiffness and speed related to each other?
Directly. The stiffer the material, the faster the sound’s speed.
What other terms describe stiffness?
Bulk modulus (same as stiff), elasticity and compressability (opposite of stiff)
Density describes…
the relative weight of a material.
How are density and speed related to each other?
Inversely. The denser the material, the slower the sound’s speed.
Is stiffness or density more important to speed?
Stiffness has the greater influence.
