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Basics of Anesthesia > Week 2 - Ultrasound > Flashcards

Week 2 - Ultrasound Flashcards

1
Q

What are the scanning planes of ultrasound?

A

Longitudinal (related to specific structure – in axis)

Transverse (related to specific structure – off axis)

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2
Q

What is the surface orientation of the transverse plane?

A

Anterior

Posterior

Right (medial or lateral)

Left (medial or lateral)

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3
Q

What is the surface orientation of the longitudinal plane?

A

Anterior

Posterior

Superior

Inferior

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4
Q

How do you ensure proper orientation of the transducer on the screen?

A

The indicator of the transducer must match the screen orientation

*indicator may be different depending on the manufacturer – either grooves, colored dots, or light

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5
Q

What are the three primary ways to use ultrasound for needle guidance?

A

In Axis In Plane – long of anatomy, needle in plane

Off Axis Off Plane – trans of anatomy, needle out of plane

Off Axis In Plane – trans of anatomy, needle in plane *most popular for regional anesthesia

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6
Q

Define Echogenic and Anechoic/Sonolucent related to ultrasound

A

Echogenic = having echoes, white

Anechoic/Sonolucent = without echoes, black

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7
Q

Define Hyperechoic, Hypoechoic, and Isoechoic related to ultrasound

A

Hyperechoic = having more echoes when compared to adjacent structure

Hypoechoic = having less echoes when compared to adjacent structure

Isoechoic = having the same echogenicity as adjacent structures

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8
Q

What is Through Transmission/Posterior Enhancement/Acoustic Enhancement artifact in ultrasound?

A

When the structures deep to a structure are displayed too bright

Due to low attenuation (absorption) of US through a fluid filled structure

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9
Q

What is Acoustic Shadow artifact in ultrasound?

A

When the structures deep to an object are missing, not displayed

Due to high attenuation (absorption) of US by dense structures, stones or bone

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10
Q

What is the basic principle of sonographic imaging? (How does it work)

A

Pulse-Echo Technique
-US sent into body (typical frequency of 2-15 MHz) – reflects off structures – returns to the transducer

Instrument/computer process the reflections into an image

*each pulse produces one line of information

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11
Q

What does the US instrument assume?

A
  • The US went straight through the body
  • It was reflected off different structures
  • The reflections traveled straight back to the transducer
  • This path only happened once
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12
Q

What are scan lines of an ultrasound?

A

Displays reflections of varying intensities based on the intensity of the returning echo and in locations corresponding to the direction the beam was sent out and depth of reflectors

Beam is moved through the body in a sweeping action producing real-time

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13
Q

How is particle motion related to wave direction in longitudinal sound waves?

A

In longitudinal waves particle motion is PARALLEL to wave direction

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14
Q

Define Frequency

What are the audible frequencies? What is the diagnostic range?

A

Frequency = # of cycles per sec (measured in Hertz)

Audible 20-20,000 Hz – “pitch” of the sound — Ultrasound = >20,000 Hz

Diagnostic range 2-15 megahertz (millions of cycles/sec)

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15
Q

How does high and low frequency affect the ultrasound image?

A

High Frequency:

  • better resolution (detail of image)
  • more attenuation (absorption of sound energy)
  • most useful for viewing superficial structures

Low Frequency:

  • poorer resolution
  • less attenuation

*use highest frequency possible that allows for adequate penetration – low frequency penetrates deeper

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16
Q

When do reflections occur during ultrasound? What are the types?

A

Reflections occur when there is a change in impedance of the medium

Types = Specular and Non-specular (diffuse, scatter)

*everything that is white or gray is a reflection

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17
Q

What are specular reflections in ultrasound?

A

From smooth surfaces

Ex: diaphragm, gallbladder wall, gall stone, liver/kidney interface, vessel wall, fetal femur, VESSEL WALLS, NERVES

–these types of reflectors create the most artifacts, especially when imaged at an oblique angle – should image them perpendicular

18
Q

What is Anisotropy in ultrasound imaging?

A

variation of ultrasound interaction with fibrillar tissues, resulting in artifact (missing structures) when imaged other than 90 degrees

-5 degree change can cause this artifact

19
Q

How does the ultrasound instrument determine the depth of reflectors?

A

By assuming propagation speed/velocity of 1540 m/s (1.54 mm/us) and determining the roundtrip time of the echo

Depth mm = 1.54 mm/us x Time us
D = Vt/2 (D-depth; V-velocity; t-roundtrip time)

20
Q

What is Reverberation artifact in ultrasound

A

US beam makes the path more than once
-can occur when US beam encounters a strong specular reflector

Extra echoes on the image that do not represent true anatomy

Ex: multi-path causing vessels to be displayed as a mirror image (Ghost artifact)

21
Q

What are the different frequencies required for different types of imaging?

A

High Frequency = better resolution, less penetration

Low Frequency = poorer resolution, better penetration

22
Q

What are the different types of ultrasound transducers?

A 
Vectors
Curvilinears
Linear (higher frequencies, >5 MHz)
Transvaginal
Transrectal
Endoscopic
  • different types for various types of exams
  • selection based on footprint required (size of transducer that’s touching pt)
23
Q

What type of wave is a sound wave?

A

Sound is a mechanical, longitudinal wave

24
Q

What angle must specular reflectors be imaged at with US?

A

US is reflected at interfaces, specular reflector must be imaged at 90 degrees

25
Q

What are the standard “Knobs” on an ultrasound machine?

A 
Depth
Gain
TGC/DGC
Auto-optimize
Frequency and Harmonics
Focus
Freeze
Store/Print
26
Q

What is depth knob on an US used for?

A

to get the image as deep as needed for area of interest but no deeper so that the image is as large as possible

27
Q

What is the Gain on an US machine?

A

Amplification of the returning echoes

*brightness of the image

28
Q

What is TGC of an US machine?

A

Time Gain Compensation

  • changes amplification based on return time of the echoes
  • compensates for attenuation of the US as it passes through tissue

Makes image uniform
Will vary between pts and different types of exams

29
Q

What is the auto-optimize knob function on an US machine?

A

Automatic control that adjusts gain

*sometimes this automatic adjustment is a problem and needs to be off (will turn off if you manually move the gain or TGC)

30
Q

What is the purpose of the frequency knob on an US machine?

A

Operator should adjust to the frequency require for the exam

  • highest possible that allows for penetration
  • modern transducers can produce a range of frequencies
  • must choose harmonics mode to improve the image
31
Q

What is a doppler shift in US?

A

Change in reflected frequency compared to frequency sent out when there is motion between source and reflector

Moving toward – higher frequency – more waves/sec
Moving away – lower frequency – less waves/sec

Positive or negative shift dependent on direction of reflector relative to the transducer

32
Q

What is a positive and negative doppler shift in the on axis (longitudinal) view in US?

A

Positive Doppler Shift = blood flow toward transducer/beam

Negative = blood flow away from transducer/beam

33
Q

What is a positive and negative doppler shift in the off axis (transverse) view in US?

A

Positive Doppler Shift = blood flow toward transducer/beam – angled towards the hand

Negative = blood flow away from transducer/beam – angled towards the shoulder

34
Q

How is ultrasound produced?

A

by Piezoelectric crystals

Piezoelectricity is the ability of a material to generate an electric potential after application of a mechanical stress

35
Q

What is air artifact in US?

A

Results in a “dropout” artifact, when the US beam encounters an air-filled space or there is insufficient conduction gel between the transducer and the skin

36
Q

How can nerves be imaged using US? What do they look like?

A

Either using a transverse axis or long axis

  • peripheral nerves may appear dark (hypoechoic) or bright (hyperechoic) depending on the nerve size, frequency, and beam angle
  • on transverse scans it may be round, oval, or triangular and are not compressible
37
Q

What do muscles look like under US?

A

Pinnate or featherlike appearance in the long axis

Uniform darker pattern on the short axis scan

Darker spaces within the muscles and lighter colors around the muscle than on nerves

38
Q

What does bone look like under US?

A

Appears as a linear, white structure, with a darker shadow underneath

39
Q

What do blood vessels look like under US?

A

On the transverse axis - appears dark to black

Arteries have more defined circular structure and are pulsatile and can’t be compressed
Veins are nonpulsatile and can be compressed

40
Q

What does fat look like under US?

A

normal fatty tissue is dark unless there is a tumor or other more reflecting structure

41
Q

What does fascia look like under US?

A

it reflects US well and appears lighter

well defined linear pattern that marks tissue boundaries

Basics of Anesthesia (35 decks)

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