Image Characteristics And Artifacts Flashcards
Portions of an image that are not as bright as the surrounding tissues, or tissues that appear less bright than normal.
Hypoechoic
Portions of an image that are brighter than surrounding tissues, or tissues that appear brighter than normal.
Hyperechoic
Describes structures with equal echo brightness.
Isoechoic
A portion of tissue or structure that has similar echo characteristics throughout.
Homogeneous
Displaying a variety of different echo characteristics within the tissue.
Heterogeneous
Errors in imaging due to a violation of assumptions, equipment malfunction or design, physics of ultrasound, interpreter error, and/or operator error.
Artifacts
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 main axis.
Intensity of the reflections is related to the scattering characteristics of the tissue.
The imaging plane is extremely thin.
Lord loves a working man.
Don’t trust whitey.
Multiple echoes appearing on the display as a result of ultrasound “ping-ponging” between two reflectors. Looks like a ladder or a venetian blind.
Reverberations
Appears as a solid line directed downward, merged reverberation. A reverb with the space squeezed out.
Comet tail or ring down
Occasion when the ultrasound beam is unable to pass through a structure because the structure has a higher than usual attenuation. When this occurs, any structures that lie deeper than the initial structure are not imaged or displayed. Thus, a hypoechoic region appears distal to a hyperechoic structure.
Shadowing
Refraction at the edge of a circular structure can create this type of artifact.
Edge shadow or shadowing by refraction.
This type of artifact occurs when the medium through which the sound travels has a lower attenuation rate than soft tissue. Since the attenuation is less, echoes returning from deeper areas appear brighter on the display – hyperechoic.
Enhancement
This type of artifact occurs when sound may bounce off of a strong reflector, called a mirror, in its path and be redirected. This creates a second copy of the reflector which is located deeper than the true reflector.
Mirror image
This artifact appears as a step off, split or cut.
Propagation speed errors or range error artifact
This artifact appears as a second copy of the true reflector. This artifact appears side-by-side with the true anatomic structure. It is due to refraction.
Refraction artifact, duh.
This artifact occurs because extra acoustic energy may be transmitted in directions other than the beams main axis. A second copy of the true reflector is then formed. The artifact appears side-by-side with the true anatomic structure. This artifact degrades lateral resolution.
Side lobes and grating lobes
Grating lobe artifact can be reduced or curved by dividing each element into even smaller, miniature pieces. What is this called?
Subdicing
In this process, grating lobes are further reduced by exciting the subdiced elements with different voltages. Subelements closer to the center of the sound beam are excited with higher voltages, while the outermost subelements, further away from the center of the beam, are excited with lower voltages.
Apodization
This artifact occurs when the beam has a greater width than the reflector.
Slice thickness artifact
Grainy appearance not directly from reflections from tissues in the shallow part of the image, but created by interference effects of scattered sound, both constructive and destructive, from the many tissue reflectors.
Speckle
This artifact occurs when very deep reflections from a previous pulse arrive at the transducer after the next pulse was created and the system thinks the reflection came from the most recent pulse. This makes the late arriving reflection too shallow on the image. It is cured by lowering the PRF or by using coded excitation.
Range ambiguity artifact
This artifact is characterized by low velocity motion from pulsating vessel walls producing small Doppler shifts that ‘bleed’ into surrounding anatomy.
Ghosting
How can you cure ghosting?
Wall filters serve as a reject for Doppler. Wall filters exclude low-level Doppler shifts around the baseline, while having no effect on large Doppler frequency shifts.
This artifact is found only in Doppler and creates a special form of mirror image where the Doppler spectrum appears above and below the baseline. Doppler mirror. Caused by the Doppler gain being set too high and/or incident angle near 90° when flow is at focus.
Cross Talk
