Image Processing and Dynamic Range - Ch 16

Question 1

when the size of an image increases, if the number of pixels is unchanged, but pixel size increases what does this describe?

Answer 1

read magnification

Question 2

when the size of an image increases, if the number of pixels increases, but pixel size remains unchanged what does this describe?

Answer 2

write magnification

Question 3

which magnification can improve temporal resolution if the region of interest is shallower? what does this do?

Answer 3

write magnification; increases frame rate

Question 4

give 7 characteristics of read magnification

Answer 4

1. does not rescan, only reads old image data in memory
2. reads old data
3. postprocessing
4. same line density
5. spatial res not improved
6. temporal res unchanged

Question 5

give 7 characteristics of write magnification

Answer 5

1. rescans and acquires new data, discards old image data
2. writes new data
3. preprocessing
4. increased line density
5. more pixels
6. improved spatial res
7. temporal res can change

Question 6

what are two artifacts and what’s the main difference bw the two?

Answer 6

speckle and clutter; speckle = imaging artifact; clutter = doppler artifact

Question 7

what is a speckle artifact?

Answer 7

imaging artifact; grainy or granular appearance that does not correspond to actual tissue anatomy

Question 8

what is speckle artifact created by?

Answer 8

created by interference effects of scattered sound, both constructive and destructive, from the many tiny tissue reflectors

Question 9

how do speckle artifacts affect the image?

Answer 9

speckle reduces image contrast and spatial resolution, can negatively impact an image’s diagnostic accuracy

Question 10

what is a clutter artifact? how can this artifact be overcome?

Answer 10

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

Question 11

what is fill-in interpolation? (area it affects, shape?) example?

Answer 11

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

Question 12

when does fill-in interpolation occur? how are images improved when this occurs?

Answer 12

preprocessing; can be improved by filling in gaps bw lines, such as when scan lines separate as sound beams penetrate deeper

Question 13

what kind of images benefit the most from fill-in interpolation? how would you describe these images?

Answer 13

images w/ low line density are most improved; these images generally have a high frame rate (good temporal res)

Question 14

what are the 3 types of compounding?

Answer 14

spatial, temporal, and frequency

Question 15

what is spatial compounding? what does this do?

Answer 15

scan lines are steered by the system in different angles or views; structures are seen by multiple pulses from several angles

Question 16

what transducers use spatial compounding? why is this?

Answer 16

phased array transducers only; bc sound beams are steered electronically here, transducer is not moved

Question 17

what are 5 ways imaging is affected using spatial compounding?

Answer 17

1. frames are averaged, improving signal-to-noise ratio
2. artifacts (speckle & cluster) are reduced
3. spatial resolution (detail) improved
4. temporal res (frame rate) is reduced
5. shadows and edge shadows are reduced/eliminated

Question 18

what is temporal compounding or persistence? aka?

Answer 18

used in color flow doppler, provides a history of past frames that are overlaid or added on top of the current frame; temporal averaging

Question 19

when is temporal compounding/persistence useful?

Answer 19

when using color doppler on stationary or slow-moving structures averaging of previous frames (same view, diff times)

Question 20

when using temporal compounding the resulting image is a _____________ of past frames

Answer 20

consolidation

Question 21

what are 3 diff characteristics of temporal compounding/persistence?

Answer 21

1. temporal res is decreases (bc we have fewer independent images)
2. moving anatomic structures appear blurred
3. improves dynamic range and contrast resolution

Question 22

what is frequency compounding?

Answer 22

an image is created using the entire reflection of a sound pulse

Question 23

how does frequency compounding work to create an image?

Answer 23

divides the reflection into sub-bands of smaller frequency ranges. Images are created from these sub-bands.

Question 24

what are 3 characteristics of frequency compounding?

Answer 24

1. images are averaged, improving signal-to-noise ratio
2. speckle artifact is reduced
3. spatial res (detail) is improved

Question 25

what is dynamic aperture?

Answer 25

a form of electronic receive focusing

Question 26

how does dynamic aperture work?

Answer 26

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.

Question 27

describe how echoes are received from superficial and deeper structures when using dynamic aperture.

Answer 27

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.

Question 28

what are the 3 positive aspects of using dynamic aperture?

Answer 28

1. allows the receive beam to be as narrow as possible at all depths 2. optimizes lateral res at all depths 3. minimizes beam width variation

Question 29

what is edge enhancement? when is it most useful?

Answer 29

increases the contrast at a boundary to make an image appear sharper; useful to emphasize diff tissues.

Question 30

when is edge enhancement ideally used?

Answer 30

ideally suited to distinguish interfaces bw structures with different gray-scale characteristics

Question 31

what is coded excitation? how does it create the image?

Answer 31

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.

Question 32

where does coded excitation take place?

Answer 32

in the pulser

Question 33

what are 5 characteristics of coded excitation?

Answer 33

1. improves signal-to-noise ratio 2. improves: axial res, penetration, spatial res, contrast res

Question 34

what is an elastogram? how does this work?

Answer 34

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.

Question 35

what does an elastogram identify?

Answer 35

tissues of diff mechanical properties or diff stiffness. tissue stiffness is often related to underlying disease.

Question 36

elastography is a form of _________ _________ (palpation using hands)

Answer 36

ultrasonic palpation

Question 37

what measures speed of sideways created sound waves to estimate tissue stiffness?

Answer 37

shear wave elastography

Question 38

what is rendering?

Answer 38

creates an element of realism to a 3D or 4D image.

Question 39

how does rendering create an image?

Answer 39

uses shadows, color, texture, and optical effects similar to a photograph. These images are imaginary and are computer generated.

Question 40

what is rendering performed?

Answer 40

postprocessing after the ultrasonic data has been acquired and stored.

Question 41

what is dynamic range?

Answer 41

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.

Question 42

what does dynamic range do? units?

Answer 42

eliminates low level noise, just like reject; dB a relative measurement

Question 43

what is the typical value of dynamic range?

Answer 43

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.