18 Image Characteristics + Artifacts Flashcards
What are ultrasound artifacts?
Errors in imaging
Not real, missing reflectors, improper brightness, improper shape, improper size, improper position
List image characteristics.
Hyperechoic Hypoechoic Anechoic Isoechoic Homogeneous Heterogeneous
What are causes of artifacts?
Violation of assumptions Equipment malfunction or design Physics of ultrasound Interpreter error Operator error
What are the six basic assumptions of imaging systems?
- Sound travels in a straight line
- Sound travels directly to a reflector and back
- Sound travels exactly 1540 m/s
- Reflections arise from structures positioned along the beam’s
- Intensity of the reflections is related to the scattering characteristics of the tissue
- The imaging plane is extremely thin
What are reverberations?
Multiple echoes appearing on the display as a result of ultrasound ping-ponging between two reflectors
What are some characteristics of reverberations?
Multiple
Equally spaced
Parallel to the sound beam
Deeper and along a straight line
What is comet tail or ringdown artifact?
A solid line directed downward, merged reverberation
What are characteristics of comet tail or ringdown artifact?
Single, solid hyperechoic line
Long echo
Parallel to second beam
A reverb with the ‘space’ squeezed out
What is shadowing artifact?
Hypoechoic region that appears distal to a hyperechoic structure
What is edge shadow or shadowing by refraction?
Refraction at the edge of a circular structure
What is enhancement artifact?
Deeper areas appear brighter on display - hyperechoic, because attenuation is less when sound travels through a medium with a lower attenuation rates than soft tissue
What is a mirror image artifact?
A second copy of a reflector if sound bounces off of a strong reflector
What is a propagation speed error?
A step off, split or cut from incorrect # of reflections on scan and improper depths
What is a refraction artifact?
When sound changes direction after striking a boundary
Degrades lateral resolution
What is side lobe artifact?
Extra acoustic energy transmitted in directions other than the beam’s main axis in a mechanical or single crystal transducer
What is a grating lobe artifact?
Extra acoustic energy caused from arrays
What is subdicing?
Reduction or curing of grating lobe artifact by dividing each element into even smaller pieces
What is apodization?
Reduction of grating lobes by exciting the subdiced elements with different voltages
What is slice thickness artifact?
When the beam has a greater width than the reflector causing elevational resolution - reflections produced by structures above or below the ideal imaging plane appear on the image
What is range ambiguity artifact?
Very deep reflections from a previous pulse arrive at a transducer after the next pulse was created
Cured by lowering the PRF (imaging deeper)
What is cross talk artifact?
Seen on Doppler only
Special form of a mirror image where the Doppler spectrum appears above and below the baseline
What are 2 causes of cross talk?
Doppler gain set too high
Incident angle near 90° when flow is at focus
