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Fall:Physics > Key terms Test2 > Flashcards

Key terms Test2 Flashcards

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1
Q

Intensity

A

a beam’s power divided by its area

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2
Q

5 key words related to intensity

A

spatial

peak

average

temporal

pulsed

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3
Q

intensity measurement methods

A

SPTP

(spatial peak temporal peak)

SATP

(spatial average temporal peak)

SPTA

(spatial peak temporal average)

SPPA

(spatial peak pulse average)

SAPA

(spatial average pulse average)

SATA

(spatial average temporal average)

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4
Q

commandments of intensity

A
  1. intensities may be reported in various ways with respect to time and space
  2. the different measurements of intensities are important in the study of bioeffects
  3. because peak measurements are larger than average measurements, SPTP intensity has the highest value, and SATA has the lowest value.
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5
Q

decibel notation

A

standard measurement tool used to report changes in the degree of attenuation

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6
Q

logarithms

A

novel method of rating numbers

log-the number of 10s that are multiplied to create a number

(log of 100 is 2)

logrithmic scale is a relative scale

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7
Q

positive and negative decibels

A

positive decibels report signals that are increasing in strength (getting larger)

negative decibels describe signals that are decreasing in strength (getting smaller)

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8
Q

decibels and intensities

A

decibels require two intensities:

reference(starting level) and actual level at time of measurement

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9
Q

attenuation

A

weakening of the soundwave as it moves through a medium

decrease in intensity, power, and amplitude as sound travels

determined by two factors:

path length and frequency of sound

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10
Q

distance and attenuation

A

distance and attenuation are DIRECTLY related

(the longer the distance the more the sound attenuates)

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11
Q

frequency and attenuation

A

Frequency and attenuation are DIRECTLY related

(the higher the frequency, the more the sound attenuates)

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12
Q

reflection

A

as a soundwave hits a boundary, part of it’s energy is redirected (reflected) back to the sound source

specular and diffuse

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13
Q

scattering

A

random redirection of sound in many directions

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14
Q

absorption

A

occurs when ultrasonic energy is converted into another energy form, such as heat

absorption is DIRECTLY related to frequency

(higher frequency waves attenuate more than lower frequency waves)

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15
Q

specular reflection

A

when the boundary is smooth (mirror), the sound is reflected in only one direction in an organized manner

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16
Q

diffuse reflection

A

when a wave reflects off an irregular surface, it radiates in more than one direction

17
Q

rayleigh scattering

A

special form of scattering that occurs when the structure’s dimensions are much smaller than the beam’s wavelength

18
Q

attenuation coefficient

A

the number of decibels of attenuation that occurs when sound travels one centimeter

units-dB/cm

19
Q

attenuation coefficient in soft tissue

A

0.5 dB/cm/MHz

20
Q

attenuation in media

A

air-extremely high attenuation

bone&lung-very high

biologic fluids-low

water-extremely low attenuation

21
Q

half value layer

A

the distance sound travels in a tissue that reduces the intensity of sound to 1/2 its original value

half value layer thickness depends on two factors:

the medium, the frequency of sound

22
Q

impedance

A

the acoustic resistance to sound traveling in a medium

calculated by multiplying the density of a medium by the speed at which the sound travels in a medium

23
Q

range equation

A
24
Q

time of flight (go-return time)

A

elapsed time from pulse creation to pulse reception

time of flight is DIRECTLY related to how deep a sound pulse travels

(greater distances prolong the time of flight, while lesser distances shorten the time of flight)

25
Q

PRP imaging depth

A

pulse repetition period is DIRECTLY related to the maximum imaging depth

  • when the depth of view is shallow, PRP is short
  • when the depth of view is deep, PRP is long
26
Q

PRF imaging depth

A

period repetition frequency is INVERSELY related to the maximum imaging depth

  • when the depth of view is shallow, PRF is high
  • when the depth of view is deep, PRF is low
27
Q

reflection and transmission

A

when a sound beam strikes a tissue boundary at a 90o angle (normal incidence), reflection occurs only if the media on either side of the boundary have different impedances

  • no reflection will occur if the two media have identical impedances
  • a small reflection will occur if the impedances are slightly different
  • a large reflection will occur if the impedances are substantially different

Fall:Physics (10 decks)

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