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Measurement tool
Used to report changes |
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| Decibels are based on this mathematical construct |
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Electrical signal strength and the brightness of image need to be quantified
common unit for measuring signals strength
does not measure absolute number |
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| a relative measurement, comparison, ratio, logarithmic |
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| If the signal strength had doubled, _________ or the signal is 1/10 |
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| a decibel notation is ____________ |
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| Number of intensities needed to calculate decibels |
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| a ratio of 2 intensities, powers, or amplitudes is likely to have units of _______ |
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| getting bigger, the intensity is increasing |
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| getting smaller, the intensity is decreasing |
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the decrease in intensity, power, and amplitude of a sound wave as it travels is called attenuation.
This is unrelated to speed.
REltated to path length and frequency of sound.
The farther US travels, the more attenuation occurs |
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Attenuation of sound in soft tissue
depends upon the wave's
_________________
and
_________________ |
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| frequency and distance the wave travels |
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| Attenuation is ___________ to propagation speed |
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| 3 components that contribute to attenuation are |
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absorption (sound energy converted into heat energy)
scattering
reflection |
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| Total attenuation increases with |
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| Higher frequency or longer path length |
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| occurs when propagating sound energy strikes a boundary between two media and some returns to the transducer and the wavelength in much smaller than the dimension (larger) of the boundary |
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| Reflection from very smooth reflector (mirror) are specular. Reflects in only one direction in an organized manner |
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| Specular reflectors are wells seen when sound strikes the reflector at what degree? |
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| Diffuse Reflection or Backscatter |
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| Occurs when the wave reflects off an irregular surface, it radiates in more than one direction. Backscatter is also called diffuse |
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| Advantage of diffuse reflection or backscatter |
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Definition
| it still can produce reflections that will return to the transducer |
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| Disadvantage of diffuse reflection or backscatter |
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| the backscattered signals have a lower strength than specular reflections |
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| 3rd component of attenuation is |
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| ultrasound energy is converted into another form such as heat |
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| _______ frequency waves undergo more attenuation more than _______ frequency waves |
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| Absorption is _________ related to frequency |
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| If the boundary between 2 media has irregularities (with a size similar to or a bit smaller than the pulse's wavelength), then the wave may be chaotically redirected in all directions. It is disorganized. |
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| amount of attenuation occur per centimeter |
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| As frequency of sound increases, the attenuation coefficient _________ |
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| With higher frequency, attenuation coefficient _______ |
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| The attenuation coefficient is approx half of the frequency in ______ tissue |
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| important tissue property that influence the amount of reflection |
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| Is impedance measured or calculated? |
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Ipedance (rayls)=
density (kg/m^3)x
propagation speed (m/s) |
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| a sound pulse strikes many tissue interfaces as it travels in the body. The angle at which the wave strikes the boundary determines the behavior of the pulse |
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| Perpendicular, Orthogonal, Right angle, Ninety degrees |
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| Anything other than 90 degrees |
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| the intensity of the sound wave at the instant prior to striking a boundary |
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| portion of the incident intensity that after striking a boundary, changes direction and returns back from where it came |
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| the portion of the incident intensity that after striking a boundary continues on in the same general direction that it was originally traveling |
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| Reflection and Transmission equation |
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| incident intensity=reflected intensity + transmitted intensity |
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| Intensity REflection Coefficient (IRC) |
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| the percentage of the US intensity that bounces back when the sound strikes a boundary |
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| Intensity Transmission Coefficient (ITC) |
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| the percentage of the US intensity that passes in forward direction when the beam strikes an interface between 2 media |
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| Coefficients, factors, and percents are usually ________ |
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| With oblique incidence, reflection _____________ |
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may or may not occur
I DONT KNOW |
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| Transmission with normal incidence |
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| all of the sound is transmitted when two media have the same impedance |
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transmission with a bend
change in direction as sound transmits from one medium |
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| Physics of refraction are described by this |
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| reflection with normal incidence |
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| look for different impedances |
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| reflection with oblique incidence |
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| derive this from reflection information |
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| look for oblique incidence and different speeds |
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