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Chapter 6 Edelman

Interaction of Sound and Media

True or false: weak reflections are often created as sound strikes a boundary between two different media such as heart muscle and blood. True
True or false: sound continues to weaken as it propagates. True
True or false: as sound waves propagate they may also change direction. True
When sound waves weaken as they travel in the body it is called... Attenuation
When a transducer receives a sound wave and converts it into an electrical signal the US system strengthens the signal or... Amplifies it
The method of rating numbers based on how many 10's are multiplied to create the original number Logarithm or log
Decibel notation does not measure absolute numbers, rather, decibels report... relative changes
When a wave's intensity doubles, the relative change is +3 dB
When a wave's intensity increases 10 fold, the relative change is +10 dB
When a wave's intensity decreases by half, the relative change is -3 dB
When a wave's intensity decreases by a tenth, the relative change is -10 dB
Attenuation is determined by what three factors? Frequency of the sound wave, distance the beam travels and tissue through which the sound travels
How are distance and attenuation related? Directly
How are frequency and attenuation related? Directly
True or false: attenuation is greater in higher frequency sound. True
What 3 processes contribute to attenuation? Reflection, scattering and absorption
What types of reflection is likely to occur in soft tissue? Specular and diffuse
When a boundary is smooth, the sound is reflected in only one direction in an organized manner. This is called what? Specular reflection
True or false: specular reflections at an angle do not return to the transducer. True
Most interfaces in the body are not smooth, but have some irregularities. When a wave reflects off an irregular surface, it radiates in more than one direction and is called what? Diffuse reflection or backscatter
The random redirection of sound in many directions Scattering
True or false: sound scatters when the tissue interface is small; that is, equal to or less than the wavelength of the incident sound beam. True
The number of decibels of attenuation that occurs when sound travels one cm is called what? The attenuation coefficient
The attenuation coefficient is measured in what? dB/cm
How are the attenuation coefficient and frequency related in soft tissue? Directly. Specifically, the attenuation coefficient is one-half the frequency.
True or false? For each cm that sound travels, more energy is lost from high frequency sound than from low frequency sound. True
True or false? No noticeable attenuation of US with frequencies less than 10 Mhz is observed in water. True
The distance sound travels in a tissue that reduces the intensity of sound to one-half it's original value is called what? Half-value layer thickness
True or false? Half-value layer thickness is thinnest in media with a high attenuation rate such as air, lung and bone and for high frequency sound. True
Impedance or acoustic impedance is the resistance to sound traveling in a medium. It is calculated by multiplying the speed at which sound travels in a medium by what? The density of the mediumumumumumumumumumum (: (:<
True or false: reflection of an US wave depends on the difference in acoustic impedances of the two media at a boundary. True dodebutt
Is impedance measured? No, it is calculated you dum dum
Attenuation is measured in what? Decibels
When a sound pulse strikes tissue it is called the angle of what? Incidence
Normal incidence means that the sound beam strikes the tissue how? At exactly 90 degrees
Normal incidence is also called what? PORN: perpendicular, orthogonal, right angle, 90 degrees
Oblique incidence occurs when the incident sound beam strikes the boundary how? At an angle other than 90 degrees
Created by: gillybruursema
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