Sound Waves Part 3 Flashcards
Interactions of US with Tissue
A beam of ________ is produced outside the patient’s body
The xrays are subsequently ________ (absorbed and scattered) as they pass through tissue
Ultimately, the transmitted ________ are recorded on film
For diagnostic US, the recorded image is based on the ________, not transmitted energy
X-ray
Attenuated
Photons
Reflected
The device that generates US waves and then detects the reflected energy is the ________
US wave is directed into the body to interact with ________, each tissue on its own characteristic way
Results of these interactions are then recorded for diagnosis in the form of ________ US
Sound may be:
________ - ________ - ________
Transducer Tissues Reflected Incident Transmitted Reflected
________ is the major interaction of interest
4 factors affecting reflected echo strength
________ = the junction of two media with different acoustic properties
________ of incidence = the angle from the normal (perpendicular or 90 degrees) at which the sound beam strikes the interface
________ / Normal incidence = a sound beam (incidence sound) intersects a smooth surface ( the boundary between two tissues). Larger than the width of the beam, at 90 degrees
________ incidence = a sound beam that intersects a smooth surface larger than the width of the beam, at less than 90 degrees (NOT perpendicular)
Interface
Angle
Perpendicular
Oblique
4 factors affecting reflected echo strength
Sound Attenuation
Sound __________ = The decrease in strength/intensity as a beam traverses a medium; the reduction in the intensity (amplitude) of an US beam as it travels through a medium; the weakening of sound as it propagates
Encompasses ________, ________, and ________; reflection may be included
Attenuation limits imaging ________ and must be compensated for
Sound ________ = the conversion of sound to heat; it is normally the dominant contribution to attenuation (in ST)
Attenuation Absorption Scattering Divergence Depth Absorption
Attenuation
How loud is too loud?
Noise-induced hearing damage is related to the duration and volume if exposure. Government research suggests the safe exposure limit is _____ decibels for eight hours a days. Some common decibel levels:
Raindrops = 40 dB Normal conversation = 60 dB Busy city traffic = 85 dB Hair dryers = 90 dB Rock concerts = 105 dB Chainsaws = 110 dB An iPod at peak volumes = 115 dB Jack hammers = 120 dB Gunshot, fireworks = 140 dB
for ST:
Attenuation (dB) = 1/2 x _____ (MHz) x _______ (cm)
As frequency _______, attenuation _______
As pathlength _______, attenuation _______
ST = 1/2 ____/____/____
for a 1 MHz transducer, ____ dB of intensity is lost for ____ cm of travel
85 frequency pathlength increases increases increases increases dB cm MHz 1/2 1
4 Factors Affecting Reflected Echo Strength
_______ = The spreading out of a beam that results from a source of small physical dimensions or diffraction or scattering. Divergence degrades the US image by creating a loss of beam intensity and decreasing Lateral Resolution ( = beam width)
Rate of divergence increases
- As the distance from sound source _______
- As the diameter of sound source _______
- Frequency of the sound source _______
Divergence
increases
decreases
increases
The magnitude of a cyclic variations gives an idea of the strength of _______
_______, _______, and _______ are the parameters relevant
sound
amplitude
power
intensity
Amplitude
Relates to the _______ of the sound wave
Equals the maximum variation of an _______ variable; maximum value minus the normal value; difference between average value and maximum value
NOT the difference between _______ and _______ values
Units are any unit of an acoustic variable
- temperature = _______
- pressure = _______ (Pa, MPa)
strength acoustic maximum minimum degrees pascal's
Power
Rate at which _______ (capability of doing work) is transmitted; rate at which work is done; rate of energy flow over ENTIRE beam
Unit = _______ (W), _______ (mW)
Relates to the _______ of the sound wave
energy
watts
milliWatts
strength
Intensity
The concentration of _______ in a sound beam
The _______ of the beam divided by the beam’s cross sectional area
Relates to the _______ of the sound beam
_______ (Watts) per unit area (m^2)
Unit = W/m^2, mW/cm^2
energy
power
strength
power
Relationship Between Amplitude, Intensity, Power
Determined by the _______ source
Changes as they propagates through the body
Intensity is proportional to _______
Power is _______ = Intensity is _______
Power is _______ = Intensity is _______
Intensity is proportional to the wave’s _______ SQUARED
Amplitude is _______ = Intensity is _______
Amplitude is _______ = Intensity is reduced to _______-_______ of its original value
Power is proportional to the wave’s _______ SQUARED
sound power doubled doubled halved halved amplitude Doubled quadrupled quatered one-sixteenth amplitude
4 Factors Affecting Reflected Echo Strength
Acoustic Impedance
The measure of ________ to sound traveling through a medium
Specular Reflectors
________ interfaces, ________ then the beam width
Produce ________-intensity, ________ reflections
Very ________ dependant
These are responsible for major organ outlines as seen by US; ________, ________
Resistance Smooth Larger High Unidirectional Angle Diaphragm Pericardium
NonSpecular
________ - Tiny, punctate reflectors that scatter a small portion of the beam in almost all directions
________ Reflectors - may be scattered by a rough boundary between tissues or within tissues due to their heterogenous character.
________ provide the US texture within organs
Very ________ dependant
RBCs are a specific type of scattered called ________ scatterers
Scatterers Diffuse Scatterers Frequency Rayleigh
4 Factors Affecting Reflected Echo Strength
The degree of ________ impedance mismatch
Inherent ________ of the incidence ultrasound beam
The ________ at which the US beam strikes a reflecting surface
________ of the reflector
Acoustic
Strength
Angle
Size
Degree of Acoustic Impedance Mismatch of the Materials Making up the Reflecting Interface/Boundary
Acoustic Impedance
The measure of ________ to sound traveling through a medium
Unit = kg / m^3 / s or simply, the Rayl
Impedance = Density (kg/m^3) x Prop Speed (m/s)
Z = pc
Determined by the ________
Density ________ - Impedance ________
Prop Speed ________ - Impedance ________
Impedance is ________ PROPORTIONAL to Density and/or Propagation Speed
Acoustic Impedance
In Perpendicular incidence the amount of sound reflected depends on: incident ________ and ________ Mismatch of the 2 Media
No impedance difference = No ________
________ in impedance difference - ________ in reflection
The difference in acoustic impedance causes some portion of the sound to be ________ at an interface, which allows visualization of ST structures with US
Resistance Medium Increase Increase Increases Increases Directly Intensity Impedance Reflection Increase Increase Reflected
