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CSH059 > Ultrasound > Flashcards

Ultrasound Flashcards

1
Q

How does ultrasound work?

A
  • uses sound waves with frequencies 1-20 MHz
  • images created by interpreting sound reflections
  • images composed of a mosaic of white and grey dots which represent an echo of a structure
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2
Q

What are the benefits of ultrasound? (8)

A
  • non ionising
  • mobile equipment
  • quick and cost effective
  • well tolerated by patients
  • good soft tissue information
  • real time
  • accurate measurement of structures
  • can carry out blood studies (ensure needle is in correct spot)
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3
Q

What are the cons of ultrasound? (4)

A
  • many areas not suitable to image (bone, lung, abdominal structures covered by bowel)
  • hand held transducer results in scan plane variablilty and hard to reproduce same scan plane
  • high operator dependent
  • diffifult image interpretation
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4
Q

What is the transverse plane?

A
  • divides the body sup and inf

- transducer at ant of body

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5
Q

What is the sagittal plane?

A
  • divides body left and right
  • midsagittal on midline
  • para-sagittal slightly of midline
  • image always viewed with patient head to left of screen
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6
Q

What is the coronal plane?

A
  • divides the body ant and post
  • transducer on the lateral aspect of patient in lonitudinal plane
  • ultraosund beam only go through half of patient so the inf of the image is medial
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7
Q

What is the viewing of a transverse image?

A
  • ant and post

- left and right

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8
Q

What is the viewing of a sagittal image?

A
  • ant and post

- sup and inf (sup on left, inf on right)

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9
Q

What is the viewing of a coronal image?

A
  • lat and medial (lat on ant, medial on post)

- sup and inf (sup on left, inf on right)

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10
Q

What is echogenicity?

A
  • described how bright the tissue is (e.g. how intense the echoes are)
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11
Q

Define anechoic

A
  • area that has no echoes (black)

- e.g. fluid (blood and urine)

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12
Q

Define hypoechnoic

A
  • area where the echo intensity is low (dark)

- e.g.

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13
Q

Deinfe Echogenic

A
  • area where the echo is more intense (bright)

- e.g. bone, gas, calcification

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14
Q

What is echotexture?

A
  • describes the pattern of echoes
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15
Q

What are the 4 main types of echotexture?

A
  • fine
  • coarse
  • homogeneous
  • heterogeneous
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16
Q

What is an acoustic window?

A
  • structure or anatomical configuration that allows deeper anatomy ro be visualed
  • causes little beam attenuation
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17
Q

What are examples of acoustic window?

A
  • bladder to see prostate and uterus/ovaries
  • liquid filled stomach to see pancreas
  • liver and spleen to see kidneys
  • amniotic fluid to see fetus
  • eye
  • anatomical configuration such as intercostal space
18
Q

What is the ultrasound equipment?

A
  • transducer
  • monitor to display
  • housing for electronics and controls
  • recording device
19
Q

What is the transducer frequencey?

A
  • 1-20MHz
20
Q

What is lower frequency for?

A
  • lower frequency allows deeper penetration but slighly decrease image quality of superficial structures but better deeper structures
21
Q

What is higher frequency for?

A
  • more superficial and improved image quality of superficial
22
Q

What is linear array?

A
  • used for superficial

- 8-17 MHz

23
Q

What is convex array?

A
  • used for abdomen and pelvis

- 3-8 MHz

24
Q

What is the pros of linear array?

A
  • no moving parts
  • wide near FOV
  • adjustable foccussing
  • multiple focal zones can be used
  • colour doppler flow capability
25
Q

What are the cons of linear array?

A
  • large probe footprint

- narrow far FOV

26
Q

What are the pros of convex array?

A
  • smaller footprint
  • wide far FOV
  • wide near FOV
27
Q

What are the cons of convex array?

A
  • footprint too large for very small acoutsic window

- popular for general sonography

28
Q

What is dynamic range?

A
  • express a range of values (max and min signal values)

- range of echoes make up grey scale on image

29
Q

What are the principle elements of attenutation?

A
  1. Material itself
  2. frequency of beam
  3. depth of tissue
30
Q

What are the factors of the material itself?

A
  • Viscositiy: more viscous material, more energy is expended moving the molecules and thus more attenuation
  • relaxation time: speed molecules return to their rest postition. If slow, molecule still moving when next wave hits and thus more energy to stop movement and reverse
31
Q

What are the factors of frequency of beam?

A
  • higher frequency, faster molecules are moved and more energy is expended as heat
  • if waves close together, molecule has less time to return to rest potition and thus same long relaxation time
32
Q

What are the factors of depth of tissue?

A
  • further beam travels, more attenuation
33
Q

How are beams attenuated in ultrasound?

A
  • attenauted at a rate of 1dB/cm/MH in tissue
  • echoes returning from deeper structures become progressively weaker
  • divergence is spreading of beam as increased distance from source (increased divergence = increased attenuation)
34
Q

What is the biological effects of ultrasound?

A
  • thermal caused by transfer of energy from the wave to the tissue causing molecules to vibrate
  • mechanical
35
Q

What are the thermal effects?

A
  1. beam characeristic
    - frequency: ^ freq, ^ absoprtion = ^ heat
    - intensity: ^ intensity = ^ heat
    - mode of ultrasound: M-mode and doppler use pulsing on single path ^ heating
    - pulse length: ^ pulse lenght = ^ energy in each pulse
    - exposure time: heating contious until equiplibrium occurs
  2. Tissue characteristics
    - absoprtion characteristics: ^ absorption = ^ heat
    - vasculatity: ^ blood = ^ heat removal
    - harmful thermal effects are not considered possible with current imaging
36
Q

What are the mechanical effects?

A
  1. cavitation
    - under the influence of repeated compression, tiny mucrobubbles form
    - dissolved gas comes out of solution under low pressure condition
    - bubble size grows to size determined by wave length
    - resonance occurs within the bubble, wih large vibrational amplitudes
  2. transient
    - at higher intensities, the microbubble may grow rapidly then collapse suddenly under a compression wave
    - the collapse causes shock waves and higher local temperatures which can disrupt cellls
    - high intensity U/S is needed to produce cavitation
    - it is considered possible to produce cavitation with currect equipment if there is pre-existing cavitation nuclei in the tissue
37
Q

What are the general rules for safety?

A
  • diagnostic U/S should only be used when medically indicated or when there is an expected benefit
  • should be completed in the shorest possible time
  • output power should be kept to a minimum
  • active transducer should not be rested on skin while not scanning
38
Q

What are the general considerations?

A
  • obtin full patient hisory and clinical presentation
  • prior surgery or imaging
  • only representative images of each oragn are recorded
  • each image should be annotated
  • sonographer doesnt discuss findings
39
Q

What is the method for pelvis trans-abdominal?

A
  • patient prep of empty bladder 2hrs prior then drink 1-1.5L of water
  • all areas of pelvis scanned in multiple planes
  • patient supine using 3-5 MHz transducer
  • initial scout should be performed
40
Q

What are some difficulties with pelvis U/S?

A
  • innappropriate bladder filling
  • patient obesity and abdominal scarring
  • failure to define normal anatomy
  • lack of specificity of pelvis pathology (benign or malignant)

CSH059 (5 decks)

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