Image Processing and Dynamic Range - Ch 16 Flashcards
when the size of an image increases, if the number of pixels is unchanged, but pixel size increases what does this describe?
read magnification
when the size of an image increases, if the number of pixels increases, but pixel size remains unchanged what does this describe?
write magnification
which magnification can improve temporal resolution if the region of interest is shallower? what does this do?
write magnification; increases frame rate
give 7 characteristics of read magnification
- does not rescan, only reads old image data in memory
- reads old data
- postprocessing
- same line density
- spatial res not improved
- temporal res unchanged
give 7 characteristics of write magnification
- rescans and acquires new data, discards old image data
- writes new data
- preprocessing
- increased line density
- more pixels
- improved spatial res
- temporal res can change
what are two artifacts and what’s the main difference bw the two?
speckle and clutter; speckle = imaging artifact; clutter = doppler artifact
what is a speckle artifact?
imaging artifact; grainy or granular appearance that does not correspond to actual tissue anatomy
what is speckle artifact created by?
created by interference effects of scattered sound, both constructive and destructive, from the many tiny tissue reflectors
how do speckle artifacts affect the image?
speckle reduces image contrast and spatial resolution, can negatively impact an image’s diagnostic accuracy
what is a clutter artifact? how can this artifact be overcome?
doppler artifact; strong reflections from anatomic structures like muscular and vessel walls are called clutter; clutter must be suppressed to get reliable blood cell velocities
what is fill-in interpolation? (area it affects, shape?) example?
improves image detail (spatial resolution) by filling in missing data, especially deeper parts of a sector-shaped image.
ex: edges of a circular structure will be better defined
when does fill-in interpolation occur? how are images improved when this occurs?
preprocessing; can be improved by filling in gaps bw lines, such as when scan lines separate as sound beams penetrate deeper
what kind of images benefit the most from fill-in interpolation? how would you describe these images?
images w/ low line density are most improved; these images generally have a high frame rate (good temporal res)
what are the 3 types of compounding?
spatial, temporal, and frequency
what is spatial compounding? what does this do?
scan lines are steered by the system in different angles or views; structures are seen by multiple pulses from several angles
what transducers use spatial compounding? why is this?
phased array transducers only; bc sound beams are steered electronically here, transducer is not moved
what are 5 ways imaging is affected using spatial compounding?
- frames are averaged, improving signal-to-noise ratio
- artifacts (speckle & cluster) are reduced
- spatial resolution (detail) improved
- temporal res (frame rate) is reduced
- shadows and edge shadows are reduced/eliminated
what is temporal compounding or persistence? aka?
used in color flow doppler, provides a history of past frames that are overlaid or added on top of the current frame; temporal averaging
when is temporal compounding/persistence useful?
when using color doppler on stationary or slow-moving structures averaging of previous frames (same view, diff times)
when using temporal compounding the resulting image is a _____________ of past frames
consolidation
what are 3 diff characteristics of temporal compounding/persistence?
- temporal res is decreases (bc we have fewer independent images)
- moving anatomic structures appear blurred
- improves dynamic range and contrast resolution
what is frequency compounding?
an image is created using the entire reflection of a sound pulse
how does frequency compounding work to create an image?
divides the reflection into sub-bands of smaller frequency ranges. Images are created from these sub-bands.
what are 3 characteristics of frequency compounding?
- images are averaged, improving signal-to-noise ratio
- speckle artifact is reduced
- spatial res (detail) is improved
what is dynamic aperture?
a form of electronic receive focusing
how does dynamic aperture work?
as the returning sound beam strikes the transducer, the size of the transducer surface listening for echoes is varied. This is done by varying the # of elements used to receive the reflected signal.
describe how echoes are received from superficial and deeper structures when using dynamic aperture.
echoes arising early (from superficial structures) are received using only a few crystals from the array. As echoes return from deeper structures, the aperture is increased, so more and more elements in the array are used to listen.
what are the 3 positive aspects of using dynamic aperture?
- allows the receive beam to be as narrow as possible at all depths
- optimizes lateral res at all depths
- minimizes beam width variation
what is edge enhancement? when is it most useful?
increases the contrast at a boundary to make an image appear sharper; useful to emphasize diff tissues.
when is edge enhancement ideally used?
ideally suited to distinguish interfaces bw structures with different gray-scale characteristics
what is coded excitation? how does it create the image?
creates long sound pulses that contains pattern of frequencies and cycles called a code. Special math techniques process the code, creating a high quality image.
where does coded excitation take place?
in the pulser
what are 5 characteristics of coded excitation?
- improves signal-to-noise ratio
- improves: axial res, penetration, spatial res, contrast res
what is an elastogram? how does this work?
a dynamic technique that produces images based on the deformation of a tissue when force is applied to it. Force exerts a sound pulse from the transducer.
what does an elastogram identify?
tissues of diff mechanical properties or diff stiffness. tissue stiffness is often related to underlying disease.
elastography is a form of _________ _________ (palpation using hands)
ultrasonic palpation
what measures speed of sideways created sound waves to estimate tissue stiffness?
shear wave elastography
what is rendering?
creates an element of realism to a 3D or 4D image.
how does rendering create an image?
uses shadows, color, texture, and optical effects similar to a photograph. These images are imaginary and are computer generated.
what is rendering performed?
postprocessing after the ultrasonic data has been acquired and stored.
what is dynamic range?
the ratio of the largest to the smallest signal strength that each component processes, the # of choices. indicates number of gray shades on an image.
what does dynamic range do? units?
eliminates low level noise, just like reject; dB a relative measurement
what is the typical value of dynamic range?
dynamic range of a signal decreases (fewer shades of gray) the more it is processed. Transducers process data w widest dynamic range while recording device data has the lowest dynamic range.
