# Shared Flashcard Set

## Details

Chapter 1 Hedricks
ultrasound physics
120
Physics
Not Applicable
02/18/2008

Term
 Define: Frequency
Definition
 1. the number of vibrations that a molecule makes per second. 2. the number of times the cycle is repeated each second
Term
 Define: Sound wave
Definition
 Those pressure changes that the human ear can detect.
Term
 What is the frequency of an audible  sound wave?
Definition
 20-20,000 cycles/sec. (Hz)
Term
 Define: Propagation
Definition
 the transmittal to distant regions remote from the sound source.
Term
 Define: Ultrasound wave
Definition
 Mechanical waves with higher frequencies than can be heard by the human ear
Term
 What is the frequency of an ultrasound wave?
Definition
 greater than 20,000 Hz
Term
 Define:  Infrasound
Definition
 Mechanical waves with frequencies lower than can be heard by a human ear
Term
 What are the frequencies of infrasound?
Definition
 less than 20 Hz
Term
 Define: Compression
Definition
 a high-pressure region formed by a wave
Term
 Define: Rarefaction
Definition
 A low-pressure region formed by a wave
Term
 What are the two basic types of sound waves?
Definition
 longitudinal and transverse
Term
 Define: longitudinal waves
Definition
 particles move along the direction of the wave energy
Term
 Define: Transverse waves
Definition
 particles move perpendicular to the wave energy (ripples in a pond)
Term
 What type of wave is a US wave?
Definition
 Longitudinal
Term
 Define: Wavelength
Definition
 The length of one comple wave cycle
Term
 What is the symbol for wavelength?
Definition
 Lambda
Term
 What are the units for wavelength?
Definition
 um, mm, cm, m (distance measure)
Term
 Define: Amplitude
Definition
 The change in magnitude of a wave.
Term
 Define: period of a wave
Definition
 1. The time necessary for one complete cycle  2. the time between two successive compression zones
Term
 What is the symbol for period?
Definition
 tao
Term
 What are the units for the period?
Definition
 us, s (seconds or time)
Term
 What is the symbol for frequency?
Definition
 f
Term
 What are the units for frequency?
Definition
 hertz or cycles/second
Term
 How are the period and frequency of a wave related?
Definition
 1. frequency is the inverse of the period.2. f= 1/tao3. tao = 1/f
Term
 What is a hertz?
Definition
 Hz is the number of cycles per second
Term
 Calc the period of a wave with a frequency of 3,000,000 Hz.
Definition
 period = .25us
Term
 Calc. the frequency of a wave with a period of        5 x 10 -7 s.
Definition
 2 MHz
Term
 Define: Acoustic velocity
Definition
 The speed at which a wave propagates through a medium
Term
 Define: particle velocity
Definition
 the speed at which particles vibrate back and forth across their average postion.
Term
 Define: Elasticity
Definition
Term
 Define: density
Definition
 the mass of a medium per unit volume
Term
 If all other physical properties remain the same; if density increases what happens to the rate of sound propagation?
Definition
 The sound propagation rate decreases.
Term
 What is the relationship between the velocity of sound in a medium and density? (mathematical)
Definition
 the velocity of sound in a medium is inversely proportional to the square root of the density of the medium.
Term
 Define: Compressibility
Definition
 the fractional decrease in volume when pressure is applied to the material.
Term
 What is the symbol for compressibility?
Definition
 K
Term
 What is the relationship between compressibility and the velocity of sound in a medium?
Definition
 the velocity of sound is is inversely proportional to the square root of the compressibility of the medium.
Term
 Define: bulk modulus
Definition
 The negative ratio of stress and strain. Where stress is the force per unit area applied to a object and strain is the fractional change in volume of the object.
Term
 What is the symbol for bulk modulus?
Definition
 B
Term
 What is the relationship between B, K & c?
Definition
 As B increases and K decreases then c increases
Term
 Define: Diffuse Reflection
Definition
 Multiple angles of reflection caused by a large, rough surface interface
Term
 What is the relationship between compressibility and density?
Definition
 They are interdependent. A change in density is often coupled with a larger and opposing  change in compressibility.
Term
 What is the velocity of sound through: soft tissue
Definition
 1540 m/s1.54 um/s
Term
 What is the velocity of sound through: liver
Definition
 1550 m/s
Term
 What is the velocity of sound through: muscle
Definition
 1580
Term
 What is the velocity of sound through: fat
Definition
 1459 m/s
Term
 What is the velocity of sound through: brain
Definition
 1560 m/s
Term
 What is the velocity of sound through: kidney
Definition
 1560 m/s
Term
 What is the velocity of sound through: spleen
Definition
 1570 m/s
Term
 What is the velocity of sound through: blood
Definition
 1575 m/s
Term
 What is the velocity of sound through: bone
Definition
 4080 m/s
Term
 What is the velocity of sound through: lung
Definition
 650 m/s
Term
 What is the velocity of sound through: air
Definition
 330 m/s
Term
 What is the velocity of sound through: water
Definition
 1480 m/s
Term
 T or F in the transmission of sound, soft tissue behaves similarly to liquid
Definition
 True
Term
 What is the relationship between density, velocity and compressibility?
Definition
 As density increases so does velocity (because of low compressibility)
Term
 The average speed in soft itssue is:
Definition
 1540 m/s 1.54 um/s
Term
 Does velocity depend on temperature?
Definition
 Yes, but it is not significant in clinical imaging.
Term
 How are frequency, wavelength and velocity related mathematically?
Definition
 velocity equals wavelength times frequency
Term
 If the frequency increases the wavelength __________
Definition
 decreases
Term
 What is the wavelength in tissue of a 2.5 MHz source?
Definition
 .62 mm
Term
 If the frequency is 1 MHz what is the wavelength (in ST)?
Definition
 1.54 mm
Term
 Define Scattering
Definition
 Non-specular reflection that gives us internal texture of organs
Term
 If the frequency is 2.5 MHz what is the wavelength (in ST)?
Definition
 .62 mm
Term
 If the frequency is 3.5 MHz what is the wavelength (in ST)?
Definition
 .44mm
Term
 If the frequency is 5 MHz what is the wavelength (in ST)?
Definition
 .21 mm
Term
 If the frequency is 7.5 MHz what is the wavelength (in ST)?
Definition
 .15 mm
Term
 If the frequency is 10 MHz what is the wavelength (in ST)?
Definition
 .15 mm
Term
 If the frequency is 15 MHz what is the wavelength (in ST)?
Definition
 .1 mm
Term
 If the frequency is 20 MHz what is the wavelength (in ST)?
Definition
 .08 mm
Term
 Define: resolution
Definition
 the ability to distinguish objects that are located close together as separate entities
Term
 Are us images are based on reflected or transmitted energy?
Definition
 reflected
Term
 What is the job of the transducer?
Definition
 To transmit the US wave and detect the reflected energy
Term
 Attenuation is affected by all of the following EXCEPT reflection, refraction, scattering, diffraction, divergence, interference, absorption
Definition
 interference  (reflection is often treated separately)
Term
 Define: attenuation
Definition
 reduction in the intensity of the beam
Term
 Define: normal incidence
Definition
 a sound beam directed at 90 degrees (right angle)
Term
 Define: specular reflector
Definition
 smooth interface and larger the the width of the ultrasound beam
Term
 If you are not at a normal incidence, how are the angle of reflection and angle incidence related?
Definition
 They are equal
Term
 How can you maximize the reflected echo?
Definition
 Orient the transducer so that the generated sound beam strikes the interface at a right angle
Term
 Define: acoustic impedance
Definition
 1. similar to momentum but not looking at individual molecules, but at their concerted action 2. a measure of the resistance to sound passing through the medium
Term
 What is the symbol for acoustic impedance?
Definition
 Z
Term
 What is the mathematical formula for acoustic impedence?
Definition
 acoustic impedence equals velocity times density
Term
 Which has a greater magnitude? Scattered or Specular reflections?
Definition
 Specular
Term
 What are the units for acoustic impedence?
Definition
 raylskg/m2/s
Term
 What is Z of ST which has a density of 1060 kg/m3?
Definition
 z= 1.63 Mrayls
Term
 If a material is high density there will be  high or low acoustic impedences?
Definition
 high
Term
 What property allows visualization of ST structures at a biological interface?
Definition
 acoustic impedence
Term
 What is the mathematical formula for the reflection coefficient?
Definition
 the reflection coefficient is equal to the acoustic impedence of material 2 (distal) minus the acoustic impedence of material 1 (proximal) divided by theacoustic impedence of material 2 (distal) plus the acoustic impedence of material 1 (proximal) squared.
Term
 Why do fluid region produce weak signals?
Definition
 They do not have scattering centers and therefore produce weak signals.
Term
 How do you find the percentage reflection (%R)?
Definition
 Multiply the reflection coefficient by 100.
Term
 What is the formula for the transmission coefficient?
Definition
 1.   1- the reflection coefficient2. 4 times the acoustic impedence of material 2 (distal) multiplied by the acoustic impedence of material 1 (proximal) divided by the acoustic impedence of material 2 (distal)plus the acoustic impedence of material 1 (proximal) squared
Term
 How can you calculate the percentage transmission?
Definition
 1.  100 - the reflection coefficient2. the transmission coefficient times 100
Term
 Does frequency effect the transmission and reflection coefficients?
Definition
 No, they are independent of each other.
Term
 As the angle of incidence increase the reflection coefficient: decreases or increases?
Definition
 increases
Term
 If the acoustic impedence in large then: %R will be large and % T will be large%R will be small and % T will be large%R will be large and % T will be small%R will be small and % T will be small
Definition
 %R will be large and % T will be small
Term
 Calculate the %R for a bone tissue interface using Table 1-4.
Definition
 %R = 43%
Term
 Calc. %T for a ST-bone interface using table 1-4.
Definition
 57%
Term
 Calc. %R for an air-tissue interface using table 1-4. Calc %T.
Definition
 %R = 99.9%%T = .1%
Term
 Define: parenchyma
Definition
 functional part of the organ
Term
 Define Hyperechoic
Definition
 Increased US signals as compared to the surrounding tissue
Term
 Define Hypoechoic
Definition
 Decreased us signals as compared to the surrounding tissue.
Term
 Define Rayleigh Scattering
Definition
 Scattering by small particles whose dimensions are much smaller than the wavelength.
Term
 True or False nonspecular reflection have a strong frequency dependence.
Definition
 True
Term
 True or False Specular reflectors have a strong frequency dependence
Definition
 False
Term
 Define Refraction
Definition
 The bending of sound waves that happens when the wave strikes an interface and the incident angle is not 90 degrees.
Term
 What is Snell's Law?
Definition
 1. the law that describes how sound waves are refracted.2. Relates the angle of transmission to the relative velocities of sound in the 2 media
Term
 What type of refraction occurs when the velocity in the incident medium is greater than the velocity in the transmitted medium?
Definition
 the sound wave is bent towards the normal
Term
 What happens when the velocity in the incident medium is less than the sound wave in the transmitted medium?
Definition
 The sound wave is bent away from normal.
Term
 True or False Refraction can cause artifacts in images
Definition
 True
Term
 Define Diffraction
Definition
 the divergence of the sound beam as it moves away from the source.
Term
 Define  interference
Definition
 the superposition of sound waves
Term
 Define Constructive interference
Definition
 Results in an increase in amplitude
Term
 If 2 waves are in phase, what type of interference will you have?
Definition
 Constructive
Term
 Define Destructive interference
Definition
 Results in a decrease in amplitude
Term
 If 2 waves are out of phase, it results in what type of interference
Definition
 Destructive interference
Term
 Define Absorption
Definition
 1. The (only) process by which sound energy is dissipated in a medium 2. the process by which us energy is transformed into other energy forms (heat)
Term
 What 3 things influence absorption?
Definition
 f, viscosity, and relaxation time of the medium
Term
 What is the relationship between absorption and frequency?
Definition
 They are directly related, if frequency doubles, so does absorption
Term
 What are the Units of acoustic pressure?
Definition
 mm Hg, pascal, atmospheres
Term
 What are the units of particle density
Definition
 kg/m3
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