10 Ultrasound Flashcards

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1
Q

Sound waves

A

Pressure disturbance that propagates through a material

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2
Q

The amplitude of a wave

A

The size of pressure difference from the equilibrium value.

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3
Q

Wavelength (λ)

A

The distance between successive wave crests.

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4
Q

Frequency (f)

A
  • The number of oscillations in each second.

* The number of wavelengths that pass a given point each second.

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5
Q

Longitudinal waves in ultrasound

A

Have vibrations along their travel direction.

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6
Q

Transverse waves in ultrasound

A

Have vibrations perpendicular to the travel direction.

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7
Q

The period

A

The time between successive oscillations.

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8
Q

Diagnostic ultrasound uses transducers with frequencies ranging

A

1 to 20 MHz.

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9
Q

velocity (v).

A

v = f ×λ (m/s).

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10
Q

The ultrasound intensity

A

Measuring the energy flowing through a given cross-sectional area each second.

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11
Q

Relative sound intensity

A

Measured on a logarithmic scale and may be expressed in decibel (dB).

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12
Q

Negative decibel values

A

Correspond to signal attenuation.

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13
Q

Positive decibel values

A

Correspond to signal amplification.

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14
Q

The acoustic impedance

A
  • Describes how much resistance an ultrasound beam encounters as it passes through a tissue.
  • The acoustic impedance (Z) of a material is the product of the density (ρ) and the sound velocity (v) in the material.
  • Z = ρ × v
  • The acoustic impedance unit is called the Rayl.
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15
Q

Reflections in ultrasound

A

A portion of the ultrasound beam is reflected at tissue interfaces.
[(Z2 − Z1)/(Z2 + Z1)]^2.

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16
Q

Nonspecular reflections in ultrasound

A

Diffuse scatter from rough surfaces where the irregular contours are bigger than the ultrasound wavelength.

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17
Q

Specular reflections in ultrasound

A

Occur from large smooth surfaces. Specular reflection intensity is independent of frequency.

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18
Q

echo

A

The sound reflected back toward the transducer

19
Q

Gel is applied between the transducer and skin

A

To displace the air and minimize large reflections that would interfere with ultrasound transmission into the patient.

20
Q

shadowing.

A

Lack of transmissions beyond these interfaces results in areas void of echoes

21
Q

Scattering in ultrasound

A

Occurs when ultrasound encounters objects that are smaller than the ultrasound wavelength.

22
Q

Hyperechoic

A

A higher scatter amplitude relative to the background signal.

23
Q

Hypoechoic

A

There is a lower acoustic scatter intensity relative to the average background signal.

24
Q

Organs showing black in ultrasound

A

Organs that contain fluids, such as the bladder, and cysts have no internal structure and almost no echoes

25
Q

Refraction in ultrasound

A

The change in direction of an ultrasound beam when passing from one tissue to another having a different speed of sound.

26
Q

Refraction is described by

A

Snell’s law: sinθi/sinθt = v1/v2, where θi is the angle of incidence, θt is the transmitted angle, v1 is the velocity in tissue 1, and v2 is the velocity in tissue 2.

27
Q

Attenuation in ultrasound

A

The composite effect of loss by scatter and absorption.

28
Q

Attenuation in ultrasound is normally expressed in terms of

A

dB and depends on the distance the ultrasound beam has traveled in tissue.

29
Q

A transducer

A

Device that can convert one form of energy into another.

30
Q

The Doppler effect

A

Refers to changes in frequency resulting from a moving sound source.
–Objects moving toward the detector reflect sound that has a higher frequency.
–The increase in frequency is associated with a reduction in wavelength.
–Objects moving away from the detector reflect sound that has a lower frequency.
–The reduction in frequency is associated with an increase in wavelength.

31
Q

Doppler ultrasound

A

Used to identify and evaluate blood flow in vessels based on the backscatter of blood cells.

32
Q

Attenuation of
−10 dB
−20 dB
−30 dB

A
  • 10%.
  • 1%.
  • 0.1%.
33
Q

Depth gain compensation accounts for tissue attenuation

A

By increasing echo amplification for later echoes.

34
Q

The average velocity of sound in soft tissue

A

1,540 m/s.

35
Q

Velocity is inversely proportional to the square root of

A

The material compressibility.

36
Q

Intensity transmitted in ultrasound

A

(4Z1× Z2)/(Z1 + Z2)^2.

37
Q

Attenuation of ultrasound in soft tissue at 1 MHz is most likely

A

0.5 dB/cm.

38
Q

Increasing the transducer thickness is most likely to increase the sound

A

Wavelength, since the crystal thickness is one half of the ultrasound wavelength.

39
Q

The damping material behind the crystal transducer reduces the

A

The pulse length.

40
Q

The pulse repetition period in ultrasound (listening time) is given by

A

1/PRF (i.e., 1/4,000seconds).

41
Q

Ultrasound signals are converted to a video monitor display using:

A

Scan converts.

42
Q

It takes 13 μs to get an echo from an interface from a depth of

A

1 cm.

43
Q

The thermal index (TI) value indicates the possible increase in tissue

A

Temperature.