Week 2 - Ultrasound Flashcards
What are the scanning planes of ultrasound?
Longitudinal (related to specific structure – in axis)
Transverse (related to specific structure – off axis)
What is the surface orientation of the transverse plane?
Anterior
Posterior
Right (medial or lateral)
Left (medial or lateral)
What is the surface orientation of the longitudinal plane?
Anterior
Posterior
Superior
Inferior
How do you ensure proper orientation of the transducer on the screen?
The indicator of the transducer must match the screen orientation
*indicator may be different depending on the manufacturer – either grooves, colored dots, or light
What are the three primary ways to use ultrasound for needle guidance?
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
Define Echogenic and Anechoic/Sonolucent related to ultrasound
Echogenic = having echoes, white
Anechoic/Sonolucent = without echoes, black
Define Hyperechoic, Hypoechoic, and Isoechoic related to ultrasound
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
What is Through Transmission/Posterior Enhancement/Acoustic Enhancement artifact in ultrasound?
When the structures deep to a structure are displayed too bright
Due to low attenuation (absorption) of US through a fluid filled structure
What is Acoustic Shadow artifact in ultrasound?
When the structures deep to an object are missing, not displayed
Due to high attenuation (absorption) of US by dense structures, stones or bone
What is the basic principle of sonographic imaging? (How does it work)
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
What does the US instrument assume?
- 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
What are scan lines of an ultrasound?
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
How is particle motion related to wave direction in longitudinal sound waves?
In longitudinal waves particle motion is PARALLEL to wave direction
Define Frequency
What are the audible frequencies? What is the diagnostic range?
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)
How does high and low frequency affect the ultrasound image?
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
When do reflections occur during ultrasound? What are the types?
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
What are specular reflections in ultrasound?
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
What is Anisotropy in ultrasound imaging?
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
How does the ultrasound instrument determine the depth of reflectors?
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)
What is Reverberation artifact in ultrasound
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)
What are the different frequencies required for different types of imaging?
High Frequency = better resolution, less penetration
Low Frequency = poorer resolution, better penetration
What are the different types of ultrasound transducers?
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)
What type of wave is a sound wave?
Sound is a mechanical, longitudinal wave
What angle must specular reflectors be imaged at with US?
US is reflected at interfaces, specular reflector must be imaged at 90 degrees
What are the standard “Knobs” on an ultrasound machine?
Depth Gain TGC/DGC Auto-optimize Frequency and Harmonics Focus Freeze Store/Print
What is depth knob on an US used for?
to get the image as deep as needed for area of interest but no deeper so that the image is as large as possible
What is the Gain on an US machine?
Amplification of the returning echoes
*brightness of the image
What is TGC of an US machine?
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
What is the auto-optimize knob function on an US machine?
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)
What is the purpose of the frequency knob on an US machine?
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
What is a doppler shift in US?
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
What is a positive and negative doppler shift in the on axis (longitudinal) view in US?
Positive Doppler Shift = blood flow toward transducer/beam
Negative = blood flow away from transducer/beam
What is a positive and negative doppler shift in the off axis (transverse) view in US?
Positive Doppler Shift = blood flow toward transducer/beam – angled towards the hand
Negative = blood flow away from transducer/beam – angled towards the shoulder
How is ultrasound produced?
by Piezoelectric crystals
Piezoelectricity is the ability of a material to generate an electric potential after application of a mechanical stress
What is air artifact in US?
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
How can nerves be imaged using US? What do they look like?
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
What do muscles look like under US?
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
What does bone look like under US?
Appears as a linear, white structure, with a darker shadow underneath
What do blood vessels look like under US?
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
What does fat look like under US?
normal fatty tissue is dark unless there is a tumor or other more reflecting structure
What does fascia look like under US?
it reflects US well and appears lighter
well defined linear pattern that marks tissue boundaries
