exam 1 review Flashcards
Attenuation coefficient in blood
0.125 dB/cm*MHz
Attenuation coefficient in soft tissue
0.5 dB/cm*MHz
Attenuation coefficient in muscle
1.0 dB/cm*MHz
Attenuation coefficient in bone
20.0 dB/cm*MHz
Speed of sound in soft tissue
1540 m/s or 1.54 mm/microsecond
Reflection percentage in soft tissue-soft tissue
< 1%
Reflection percentage in soft tissue-bone
10-60%
Reflection percentage in soft tissue-air
> 99%
Round trip time for sound to travel 1 cm
13 microseconds/cm
wavelength equation
wavelength= propagation velocity (c)/frequency (f)
distance equation
distance= speed * time
density equation
density= mass/volume
frequency equation
frequency * period= 1 (reciprocal)
amplitude equation
crest-baseline or trough-baseline
power equation
energy/s
intensity equation
power/area
total attenuation equation
TA= attenuation coefficient * MHz * image depth (cm)
impedance equation
density * velocity
half intensity depth (HID) equation (for soft tissue only)
6/frequency
attenuation coefficient equation (for soft tissue only)
frequency/2
Waves carry ___?
Waves carry energy
What kind of wave is sound?
Sound is a mechanical, longitudinal wave
Wave classification
Mechanical (needs a medium) vs. electromagnetic (will work in a medium or vacuum)
Transverse wave propagation
Transverse waves propagate perpendicular to the wave direction
Longitudinal wave propagation
Consist of compressions and rarefactions, propagates in the same direction
Acoustic variables
Measures sound (determined entirely by the medium).
- pressure
- density
- temperature
- particle motion (distance)
Most common unit for pressure
Pascals
In human tissue, if density increases, stiffness will ___?
increase
If the intensity/power doubles, what is the decibel value?
+ 3dB
If the amplitude doubles, what is the decibel value?
+ 6dB
If the intensity/power increases 10X, what is the decibel value?
+ 10dB
If the amplitude increases by 10X, what is the decibel value?
+ 20dB
If the intensity/power halves, what is the decibel value?
- 3dB
If the amplitude halves, what is the decibel value?
- 6dB
If the intensity/power decreases by 1/10, what is the decibel value?
- 10dB
If the amplitude decreases by 1/10, what is the decibel value?
- 20dB
What is attenuation?
A decrease in wave intensity
What are the 3 things attenuation is caused by?
- Absorption
- Reflection
- Refraction
What is the most dominant form of attenuation in ultrasound?
Absorption
What 2 things measure attenuation?
Attenuation coefficient and Half value layer/half intensity depth
Reflection is caused by ____?
Impedance (z)
Refraction is caused by ___?
Speed of sounds
Specular reflection
- smooth, angle dependent, strong echoes
- not proportional to frequency
- ex: diaphragm, liver capsule, pericardium
- think of a mirror*
non-specular reflection
diffuse, scattering and Rayleigh
diffuse reflection
- rough, irregular, not angle dependent, weak echoes
- not proportional to frequency
- reflections scatter in random, chaotic directions
scattering
- small objects, not angle dependent, weaker echoes
- proportional to frequency
- reflections scatter in random, chaotic directions
Rayleigh
- very, very small objects (red blood cells), not angle dependent, weakest echoes
- proportional to frequency(4)
- reflections scatter equally in all directions
The greater the mismatch of impedance, the ____ the reflection
greater. There needs to be a mismatch of impedance for reflection to occur.
Z1=Z2
no reflection, 100% transmitted
Z1»_space; Z2
100% reflected, 0% transmitted
Z2»_space; Z1
100% reflected, 0% transmitted
Refraction
-Bending of a wave at the interface between two media with different speeds of sound
What two things need to occur for refraction to happen?
- A change in propagation speeds
2. an incident angle that is NOT perpendicular to the interface (boundary)
Snell’s law measures ___?
Refraction
What happens if the incident angle reaches the critical angle?
The result is a loss of transmission and 100% reflected
Fast to Slow bends _____ the normal
Fast to Slow bends Towards the normal (FST)
Slow to Fast bends ____ the normal
Slow to Fast bends Away from the normal (SFA)
Amplitude is measured in ___?
Volts
What determines the speed of sound through a particular medium?
Stiffness and density
Unit of measurement for attenuation coefficient
dB/cm*MHz
Unit of measurement for HVL or HID
usually cm but can be any length measurement
Characteristics of Absorption
- caused by friction
- directly exponentially proportional to frequency
- directly proportional to viscosity
- there is less absorption in body fluids than soft tissue*
Cycle, wavelength, period and frequency are all determined entirely by the ____.
Transducer
Is the speed of sound faster in air or bone?
air= 347 m/s
bone= 4080 m/s
Speed of sound is faster in bone
Attenuation in air is low, extremely low or extremely high?
Attenuation in air is extremely high
Attenuation in water is high, extremely low or intermediate?
Attenuation in water is extremely low
sound wave frequencies (infrasound, audible, and ultrasound)
infrasound: < 20Hz
audible sound: 20 Hz-20 kHz
ultrasound: >20kHz
diagnostic ultrasound: 2 MHz-20 MHz
If the frequency increases, the wavelength will ____.
The wavelength halves
What causes a wave?
Vibrations cause waves
What parameter(s) are determined by both the sound source and the medium?
Wavelength
What parameter(s) are determined by the sound source only?
Period, frequency, amplitude, power and intensity
What parameter(s) are determined by the medium only?
Speed
Unit for impedance
Rayls
