# Shared Flashcard Set

## Details

Chapter 6 Ultrasound Physics
Interaction of sound and media
58
Physics
10/22/2014

Term
 Attenuates
Definition
 weakens
Term
 Amplifies
Definition
 Strengthens
Term
 Decibel Notation
Definition
 Measurement toolUsed to report changes
Term
 Logarithms
Definition
 Decibels are based on this mathematical construct
Term
 What is log of 100?
Definition
 2ex: 10x10 is 10^2
Term
 Decibels (db)
Definition
 Electrical signal strength and the brightness of image need to be quantifiedcommon unit for measuring signals strengthdoes not measure absolute number
Term
 decibel notation
Definition
 a relative measurement, comparison, ratio, logarithmic
Term
 If the signal strength had doubled, _________ or the signal is 1/10
Definition
 half
Term
 a decibel notation is ____________
Definition
 logarithmic
Term
 Number of intensities needed to calculate decibels
Definition
 two
Term
 a ratio of 2 intensities, powers, or amplitudes is likely to have units of _______
Definition
 decibels (dB)
Term
 Positive Decibels
Definition
 getting bigger, the intensity is increasing
Term
 Negative Decibels
Definition
 getting smaller, the intensity is decreasing
Term
 Attenuation
Definition
 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
Term
 Attenuation of sound in soft tissuedepends upon the wave's_________________ and_________________
Definition
 frequency and distance the wave travels
Term
 Attenuation is ___________ to propagation speed
Definition
 unrelated
Term
 3 components that contribute to attenuation are
Definition
 absorption (sound energy converted into heat energy)scatteringreflection
Term
 Total attenuation increases with
Definition
 Higher frequency or longer path length
Term
 Reflection
Definition
 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
Term
 Specular Reflection
Definition
 Reflection from very smooth reflector (mirror) are specular. Reflects in only one direction in an organized manner
Term
 Specular reflectors are wells seen when sound strikes the reflector at what degree?
Definition
 90 degrees
Term
 Diffuse Reflection or Backscatter
Definition
 Occurs when the wave reflects off an irregular surface, it radiates in more than one direction. Backscatter is also called diffuse
Term
 Advantage of diffuse reflection or backscatter
Definition
Term
 Disadvantage of diffuse reflection or backscatter
Definition
 the backscattered signals have a lower strength than specular reflections
Term
 3rd component of attenuation is
Definition
 absorption
Term
 absorption occurs when
Definition
 ultrasound energy is converted into another form such as heat
Term
 _______ frequency waves undergo more attenuation more than _______ frequency waves
Definition
 Higher, lower
Term
 Absorption is _________ related to frequency
Definition
 directly
Term
 Scattering
Definition
 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.
Term
 Attenuation Coefficient
Definition
 amount of attenuation occur per centimeter
Term
 As frequency of sound increases, the attenuation coefficient _________
Definition
 increases
Term
 With higher frequency, attenuation coefficient _______
Definition
 increases
Term
 The attenuation coefficient is approx half of the frequency in ______ tissue
Definition
 soft
Term
 Impedance
Definition
 important tissue property that influence the amount of reflection
Term
 Is impedance measured or calculated?
Definition
 Calculated
Term
 Units of Impedance
Definition
 rayls, letter z
Term
 Impedance equation
Definition
 Ipedance (rayls)= density (kg/m^3)xpropagation speed (m/s)
Term
 Incidence
Definition
 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
Term
 3 types of angles
Definition
 acute, right, obtuse
Term
 Normal incidencePORN
Definition
 Perpendicular, Orthogonal, Right angle, Ninety degrees
Term
 Anything other than 90 degrees
Definition
 Isn't a right angle
Term
 acute angle
Definition
 less than 90 degrees
Term
 obtuse angle
Definition
 greater than 90 degrees
Term
 incident intensity
Definition
 the intensity of the sound wave at the instant prior to striking a boundary
Term
 reflected intensity
Definition
 portion of the incident intensity that after striking a boundary, changes direction and returns back from where it came
Term
 transmitted intensity
Definition
 the portion of the incident intensity that after striking a boundary continues on in the same general direction that it was originally traveling
Term
 Reflection and Transmission equation
Definition
 incident intensity=reflected intensity + transmitted intensity
Term
 Intensity REflection Coefficient (IRC)
Definition
 the percentage of the US intensity that bounces back when the sound strikes a boundary
Term
 Intensity Transmission Coefficient (ITC)
Definition
 the percentage of the US intensity that passes in forward direction when the beam strikes an interface between 2 media
Term
 Coefficients, factors, and percents are usually ________
Definition
 unitless
Term
 With oblique incidence, reflection _____________
Definition
 may or may not occurI DONT KNOW
Term
 Transmission with normal incidence
Definition
 all of the sound is transmitted when two media have the same impedance
Term
 Refraction
Definition
 transmission with a bendchange in direction as sound transmits from one medium
Term
 Snell's Law
Definition
 Physics of refraction are described by this
Term
 reflection with normal incidence
Definition
 look for different impedances
Term
 reflection with oblique incidence
Definition
 we do not know
Term
 transmission
Definition
 derive this from reflection information
Term
 refraction
Definition
 look for oblique incidence and different speeds
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