Term
| What is the effects of the medium upon the sound wave called? |
|
Definition
| Acoustic Propagation Properties |
|
|
Term
| What is the effects of the sound wave upon biologic tissue called? |
|
Definition
|
|
Term
|
Definition
| Sound is a mechanical, longitudinal wave that consists of compressions and rarefactions that which carries energy, not matter, from place to place. |
|
|
Term
|
Definition
| By the vibration of a moving object. |
|
|
Term
|
Definition
| Areas in a sound wave of increased pressure and density. |
|
|
Term
|
Definition
| Areas in a sound wave of decreased pressure and density. |
|
|
Term
| Define acoustic variables and what are the three types? |
|
Definition
Acoustic variables identify which waves are sound waves. When an acoustic variable changes rhythmically in time, a sound wave is present.
- Pressure
- Density
- Distance
|
|
|
Term
| Define pressure as it relates to sound and what are the units? |
|
Definition
Concentration of force within an area, force/area.
Units: Pascals (Pa) |
|
|
Term
| Define density as it relates to sound and what are the units? |
|
Definition
Concentration of mass within a volume.
Units: kg/cm3 |
|
|
Term
| Define distance as it relates to sound and what are the units? |
|
Definition
Measure of particle motion.
Units: cm, ft, miles |
|
|
Term
|
Definition
| Particles move in a perpendicular direction (right angles or 90°) to the direction of the wave. |
|
|
Term
|
Definition
| Particles move in the same direction as the wave |
|
|
Term
| Define acoustic parameters and what are the seven types? |
|
Definition
Acoustic parameters describe the features of a particular sound wave.
Determined by sound source
[Period
Frequency]-->inversely related to each other
[Amplitude
Power
Intensity]-->directly related to each other
Determined by both sound and medium
wavelength
Determinded by medium
speed |
|
|
Term
|
Definition
The time required to complete a single cycle.
units: μsec (or any unit of time)
typical values: 0.06 to 0.5
determined by: sound source
1/f
sec/cycle |
|
|
Term
|
Definition
Number of certain events that occur in a particular time duration. In diagnostic ultrasound, the frequency of a wave is the number of cycles of an acoustic variable that occur in one second.
units: Hertz (Hz)
typical values: 2 MHz to 15 MHz
Note: Frequency affects penetration and axial resolution (image quality)
determined by: sound source
1/p
cycles/sec
|
|
|
Term
|
Definition
| A wave with a frequency exceeding 20,000 Hz (20kHz). This frequency is so high that the sound is not audible by man. |
|
|
Term
|
Definition
| Heard by man, frequencies between 20 Hz and 20 kHz |
|
|
Term
|
Definition
| Sound with frequencies less than 20 Hz. This frequency is so low that the sound is not audible by man. |
|
|
Term
| How is frequency and period related to each other? |
|
Definition
They are reciprocals or have an inverse relationship.
frequency (Hz) X period (sec) = 1
period (sec) = 1/frequency (Hz)
frequency (Hz) = 1/period (sec) |
|
|
Term
|
Definition
The difference between the average value and the maximum value of an acoustic variable. The variation of an acoustic variable.
units: those of the acoustic variables:
Pressure: Pascals
Density: grams/cm3
Particle motion: cm, inches, units of distance
Amplitude may be expressed in decibels (dB)
output/input |
|
|
Term
| Define Peak-to-Peak Amplitude |
|
Definition
| The difference between maximum and minimum values of an acoustic variable. Amplitude is half of the peak-to-peak amplitude. |
|
|
Term
|
Definition
The rate that work is performed, or the rate of energy transfer
units: Watts
Power decreases as sound propagates through the body. |
|
|
Term
| What is the relationship between Power and Amplitude? |
|
Definition
Power is proportional to the wave's amplitude squared
Power [image] (Amplitude)2 |
|
|
Term
|
Definition
The concentration of energy in a sound beam. Intensity depends upon both the power and the cross-sectional area of the beam.
intensity (watts/cm2) = power (watts)/beam area (cm2)
units: watts/cm2
typical values: 0.001-100 watts/cm2
Intensity decreases as sound propagates through the body
power/area |
|
|
Term
| What is the relationship between Power and Intensity? |
|
Definition
| Intensity is proportional, or directly related, to the power. When one goes up, so does the other. |
|
|
Term
| What is the relationship between Amplitude and Intensity? |
|
Definition
Intensity is proportional to the amplitude of the wave squared
Intensity [image] (Amplitude)2 |
|
|
Term
|
Definition
The length or distance of a single cycle. Similar to the length of a single boxcar in a long train.
units: meters, mm or any unit of length
Determined by both the sourse and the medium
Typical values: 0.1-0.8 mm (in soft tissue)
wl (mm) = proagation speed (mm/μs)/frequency (MHz)
λ = C/F |
|
|
Term
What is the λ equation rule?
|
|
Definition
| In soft tissue, divide 1.54 mm by frequency in MHz |
|
|
Term
|
Definition
The rate that sound travels through a medium. Also called velocity or speed.
units: m/s, mm/μs
Determined by the medium
Note: All sound travels at the same speed through any specific medium regardless the frequency.
Typical values: Avg speed of all sound (regardless of frequency) in biologic or "soft tissue" is:
1540 m/s = 1.54 km/s = 1.54 mm/μs
General rule: gas (slower)<liquid<solid (faster) |
|
|
Term
| What is the propagation speed through air? |
|
Definition
|
|
Term
| What is the propagation speed through lung? |
|
Definition
|
|
Term
| What is the propagation speed through fat? |
|
Definition
|
|
Term
| What is the propagation speed through soft tissue? |
|
Definition
|
|
Term
| What is the propagation speed through tendon? |
|
Definition
|
|
Term
| What is the propagation speed through bone? |
|
Definition
|
|
Term
| What characteristics of a medium determine the speed of sound in that medium? |
|
Definition
|
|
Term
| How does stiffness affect speed? |
|
Definition
Stiffness and speed are directly related. As materials become stiffer, the speed of sound in the material increases.
Stiffness and Speed ---> Same direction
Bulk modulus is the same as stiffness. |
|
|
Term
| How does density affect speed? |
|
Definition
Density and speed are inversely related. As materials become more dense (heavier), the speed of sound in the material decreases.
Density and Speed ---> opposite directions |
|
|
