Chapter 3 Flashcards
7 parameters that describe the features of a sound wave
Period Frequency Amplitude Power Intensity Wavelength Propagation speed
The source of the sound wave is the
Ultrasound system and the transducer
_ is the tissue through which the sound is traveling
Medium
the time it takes a wave to vibrate a single cycle
Period
Typical values: (period) in diagnostic ultrasound
Typically 0.06-0.5 microseconds
May be written as 6x10^-8 to 5x10^-7 or .000000006-.00000005
Is period adjustable by the sonographer
No
_ frequency goes deeper
Low
_ frequency is used for superficial structures
High
The number of particular events that occur in a specific duration of time
Frequency
• In ultrasound, frequency of a wave =
Number of cycles per second
Units for frequency
Hertz (Hz)
1,000,000 cycles/second = 1_
MHz
Typical values of frequency in ultrasound
2-15MHz
Frequency affects _ & _
Penetration and image quality’s
Frequency is determined by
Sound source only
Is frequency adjustable by sonographer
No
Infrasound
<20 Hz
Audible sound
20-20,000Hz
Ultrasound
> 20,000Hz (20MHz)
Frequency and period have _ relationship
An inverse
Frequency and period: if one remains constant what happens to the other
It remains unchanged
Period and frequency are _
Reciprocals
If a wave has a frequency of 4Hz, the period would be
1/4 second
Seconds & Hz
Microseconds & megahertz are examples of
Complimentary units
1Hz=
1 event per second
Event can mean
Cycle, frames, beat, etc
3 bigness parameters
Amplitude
Power
Intensity
Bigness parameters describe
Size, magnitude, or strength of a wave
Bigness parameters (amplitude, power, intensity) are determined by what
Sound source
The difference between the maximum value and the average or undisturbed/ baseline value of an acoustic variable. The difference between the minimum value and the average value
Amplitude
Bigness may be described in
Decibels
Units for amplitude
Can have units of any of the acoustic variables
Decibels, pascals, g/cm^3, cm, inches, etc
Amplitude: typical values
range from 1 million pascals (1 MPa) to 3 million pascals (3 MPa)
Amplitude is determined by
initially by sound source only. As the wave travels through the body, the amplitude decreases. The rate of which depends on the characteristics of the sound wave and the medium
Can amplitude be changed by the sonographer
Yes
The difference between the maximum and minimum values of an acoustic variable
Peak to peak amplitude
_ is twice the value of amplitude
Peak to peak amplitude
The rate at which work is performed; the rate of energy transfer
Power
Units for power
Watss
Power: typical values
.004-.090 watts (4-90 milliwatts)
Power is determined by
initially by the sound source. Power decreases as sound propagates through the body (rate of decrease is dependent upon the medium)
Can power be changed by the sonographer
Yes
_ & _ describe the magnitude of a wave
Amplitude and power
When power increases what happens to amplitude
It increases too
Power is proportional to the waves
Amplitude squared
If amplitude is tripled, the power is
increased by a factor of nine
If the amplitude is halved, the power is
decreased by a factor of four
The concentration of energy in a sound beam • Intensity = power/area
Intensity
Intensity describes
The bigness of a wave
Units for intensity
W/cm^2
Intensity: typical values
.01-300 W/cm^2
Intensity is determined by
Initially by the sound source.
Changes as it propagates through the body
Can intensity be changed by the sonographer
Yes
Relationship between intensity & power
Proportional
If a wave’s power is doubled, the intensity is
Doubled
Relationship between intensity & amplitude
Proportional to amplitude squared
If a wave’s amplitude is doubled, the intensity
increases four times its original value
The distance or length of one complete cycle
Wavelength
Units for wavelength
mm, m, units of length
Typical values of wavelength in soft tissue
0.1-0.8mm
Can wave length be changed by the sonographer
No
Equation for wavelength
L=c/f (L=1.54/f)
L (wavelength:mm)
c (propagation speed:mm/microseconds)
f (frequency: MHz)
Relationship between wavelength and frequency
Inverse
As frequency increases, wavelength _
decreases
Lower frequency= _ wavelength
longer
Wavelength of 1 MHz sound in soft tissue=
1.54mm
The rate at which a sound wave travels through a medium
Propagation speed
Units of speed
m/s, mm/microseconds
Typical value of speed
500 m/s-4,000 m/s depending in the tissue through which it is traveling
Speed is determined by
Medium
Can speed be changed by the sonographer
Not
TThe average biologic medium is called
Soft tissue
The speed of sound in soft tissue is
1,540 m/s or 1.54 mm/microseconds
Speed in tissue types from lowest to highest
Lung Fat Soft tissue Liver Blood Muscle Tendon Bone
Sound travels slowest in what tissue
Lung
Sounds travels fastest in what tissue
Bone
Prop speed in air
330 m/s
Prop speed in water
1,480 m/s
Prop speed in metals
2,000-7,000 m/s
Sounds travels fastest in
solids
Sound travels slowest in
gases
Equation for speed
c=fXL
c: speed
f: frequency
L: wavelength
Two characteristics of a medium that affect the speed of sound
Stiffness
Density
The ability of an object to resist compression, opposite of compressibility and elasticity
Stiffness
Stiffness is AKA
Bulk modulus
The relative weight of a material
Density
Stiffness and speed are _ related
Directly
The stiffer the medium, the _ the sound
Faster
Density and speed are _ related
Inversely
The denser the material, the _ the sound
Slower
Rule of thumbs
Stiffness & Speed= Same direction
Density & Speed= Different direction
Stiffness has _ influence on speed than density
greater
Fastest media are
Stiff and not dense
Determined by source
Amplitude Power Period Frequency Intensity
Determined by medium
Speed
Determined by source and medium
Wavelength
Can be changed by sonographer
Amplitude
Power
Intensity
Can’t be changed by sonographer
Wavelength
Period
Speed
Frequency
Reciprocals
Period
Frequency
