Module 6 - 6.5.3 Using Ultrasound Flashcards

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1
Q

Ultrasound (definition)

A

Longitudinal waves with frequencies greater than 20000Hz (the upper limit of the audible range)

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2
Q

Audible Range of Frequencies

A

20Hz - 20kHz

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3
Q

Benefits of Using Ultrasound (4)

A
  • no known dangers with low intensity
  • real time, live images/videos produced
  • can tell different tissues apart
  • ultrasound machines are portable and inexpensive
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4
Q

Ultrasound is reflected when

A

there is a change in density of the material

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5
Q

Denser materials reflect – ultrasound

A

more

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6
Q

Ultrasound cannot pass through – , so

A
  • air spaces
  • cannot be used to look at organs behind the lungs, for brain imaging, to detect fractures
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7
Q

Using Ultrasound (3)

A
  • pulse of ultrasound is sent into body from transducer
  • time taken for reflected echoes to return to transducer can be used to determine depth of material
  • must halve the time taken
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8
Q

A Transducer (definition)

A

A device which converts a non-electrical signal into an electrical signal, such as a microphone

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9
Q

A Transducer contains

A

a piezoelectric crystal

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10
Q

A Transducer acts as

A

both a transmitter and receiver of ultrasound

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11
Q

How a Transducer Works (5)

A
  • when a positive p.d. is applied to piezoelectric crystals, the crystals contract and change shape
  • when a negative p.d. is applied, the crystals revert back to their original shape
  • when a high frequency alternating p.d. (signal) is applied, the crystals oscillate at that frequency to produce ultrasound waves
  • if the waves reflect back and hit the crystals, a p.d is produced
  • when the transducer picks up the reflected sound, a computer works out how far the sound has travelled
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12
Q

Ultrasound Scanning: A Scan (5)

A
  • Amplitude Scan
  • short pulse of ultrasound waves sent into body at same time an electron beam travels across screen of cathode ray oscilloscope
  • transducer receives reflected pulse causing vertical spikes on screen of CRO
  • x axis shows time the echo took to be detected
  • no image produces but measurements taken to determine dimensions
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13
Q

Ultrasound Scanning: B Scan (5)

A
  • Brightness Scan
  • much more common
  • real time 2D/3D image of scanned area built up from many echoes recorded from several transducer/one transducer moved to different angles
  • the greater the amplitude of reflected pulse, the brighter the dot
  • a range of brightnesses is shown corresponding to different material being scanned
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14
Q

Impendance Matching (definition)

A

The reduction in intensity of reflected ultrasound at the boundary between two substances
(achieved by matching substances with similar impendances)

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15
Q

Ultrasound is reflected back if the boundary between 2 materials have (3)

A
  • different acoustic impendances
  • therefore most of the ultrasound is reflected at a air-skin boundary
  • so a gel is used to reduced the amount of ultrasound reflected back
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16
Q

The Doppler Effect with Ultrasound (3)

A
  • can be used to determine the speed of blood flow in the heart/in arteries
  • red blood cells reflect ultrasound
  • the greater the change in frequency of transmitted and received signal, the greater the speed of the blood
17
Q

Equation for The Doppler Effect for a Moving Reflector using Ultrasound

A

Δλ/λ ≈ Δf/f ≈ v/c

18
Q

The Change in Frequency of a Doppler Scan can be colour coded (5)

A
  • if a vein and an artery are close to one another, then the blood will be flowing in opposite direction within them
  • a flow of blood towards the source of ultrasound waves will result in an increase in the frequency of the received waves
  • this could be colour coded red
  • blood flowing in the opposite direction will result in a decrease in the frequency
  • this could be colour coded blue