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spi review questions > Part 3 (notes) > Flashcards

Part 3 (notes) Flashcards

1
Q

“image detail”
(varies w/ physical parameters of the beam SPL & beam width)
defined as minimum reflectors operation ; requires to produce seperate echoes
improves as minimum require reflector operation decreases
smaller numbers indicate better res
refers to axial & lateral collectively

A

Spatial resolution

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2
Q
  • does not vary with depth
  • LAARD (longitudinal, angular, axial, radial, depth)
  • cannot be adjusted unless transducer changes
  • minimum distance btwn two reflectors to visualize two different structure that are parallel to beams main axis
  • shorter the SPL & pulse duration (the better)
  • smaller numerical values
  • as frequency increases, numerical value decreases & improves
  • SPL = wavelength x # cycles in a pulse
    SPL/ 2 (1/2 the SPL)
A

Axial resolution

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3
Q
  • minimum distance between 2 reflectors that is required for system to be able to identify structures perpednciuar (identify by side)
  • LATA (lateral, angular, transverse & azmithul)
  • value is equal to the beam diameter
  • if two structures side by side are closer together than width of beam, only one wide reflection is displayed on image
  • varies w/ width of beam & imaging depth
  • far field res improves w/ high frequency (narrow) probe
  • focusing improves the resolution in area of focusing
  • improves w/ increasing number of scan lines used per mage
    • best at narrowest portion of beam - adjusted by sono using focusing & changing sector width
A

Lateral resolution

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4
Q

External - lens, fixed

Internal - curved, element, fixed focal point

A

Mechanical focusing

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5
Q

Phased electronic

  • adjustable by technologist
  • allows multiple focal points
A

Electronic focusing

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6
Q

With focusing ______ the diameter of the beam at the focal zone

A

decreases

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7
Q

With focusing ______ the beam diameter in the far field

A

increases

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8
Q

With focusing ______ the beam diameter in the near field

A

decreases

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9
Q

ability to accurately display moving structures over time

  • higher the frame rate, higher the temporal resolution
  • determined y frame rate, lines per frame & image depth
  • reducing size of FOV = increased PRF = increase FR & resolution
  • limited by FR, monitor, storage device & human eye
  • slowest component determines resolution
  • speed of sound in ST. cannot be alter to improve
  • single focus, narrow sector, & low line density = best resolution
  • M MODE is best
  • Color doppler - worst
  • activation harmonic imaging, spatial compounding, increase depth, FOV , adding focal zone = degrade of resolution
A

temporal resolution

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10
Q
  • aka slice thickness
  • set by manufacturer
  • a measure of beam with perpendicular to image plane
  • disc shaped elements allow thinest slices = best
  • linear transducers = poorest res
  • mechanical focusing w/ lens reduces slice thickness & improves RES
  • transducer array allow for add focusing along axis of beam = improved res
A

slice thickness

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11
Q
  • ability of image to display to distngiuishh tissues to to subtle variations in reflection intensity
  • depends on # of bits per pixel in image memory
  • more bits per pixel, more shades of gray = contrast res improves
    -varies w/ impedance mismatch of tissues
  • can be changed y sono changing dynamic range , rejection & c contrast settings on moniotr
    -poor res = more black and white
    -very black & white image - increase image contrast but = reduced contrast res
  • B - color or colorize functions improve res
  • fewer shades = few choices, black & white , narrow dynamic range high contrast
    more shades = many c choices, gray scale, wide dynamic range, low contrast
A

contrast resolution

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12
Q
  • Occur due to bending (refraction, redirection (reflection) or reverberaton of sound wave
  • Refraction artifact
  • Degrades lateral resolution
  • Must use at least two imaging planes to eveulate a suspected artifact
A

Propagation artifact

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13
Q
  • Incrroect placement of object location on image
  • Second structre appears more lateral than the actual structure
  • Caused by refraction of tbeam between two dissimilar media
  • u/s interperats refracted or bent beam as if it went in a straight path to & from reflctor
  • commonly caused at the interfacte of the rectus abdominis msucles
A

Misregistration/refraction

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14
Q
  • also called refractive shadowing
  • caused by a reduction of refected echoes by bending of the sound waves that touch the margin of a rough boundary
  • caused by refraction of sound
  • commonly seen in transverse vies of blood vesells cysts and testicular exams
A

Edge shadowing/ Defocusing

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15
Q
  • primary beam strikes a rounded or rougly surfaced structure & the secondary reflection moves at an angle away from transducer
  • secondsary refulecton occurs off an addiotnal object that redirects the reflection to the probe
  • Secondary reflected beam has longer go return tie than actual reflection (a second copy of reflector is displayed deeper on the display
  • Leads to subtle degradation of image
A

Multipath

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16
Q
  • Caused byt repeated reflection of sound waves back & forth between teo closely space reflectors
  • Appears as multiple reflections separated by equal spacing
  • Each new reflection is weaker and siaplyed deeper on image than previous one
  • Looks like a step ladder
  • Can occur between transducer & another structure between two separate structures
  • Comet tal and ring down are reverberation artifacts
A

Reverberation

17
Q
  • Type of reverberation cause by tissue gas interface
  • Creates a long verticle strip composed of call echogenic horiztonal lines
  • Can be helpeful in diagnosis of emphysematous cholecytsits and pneumbolia
A

Ring down

18
Q
  • Type of reverbation
  • Numerous repated reflections between two sturtcujreds in close proximity
  • Multiple reflction froma highly reflective object
  • Forms a single short hyperechoic line paraell to the u/s beam (shorter than ring down)
  • Theg reater the acoustic layer mismatch the greater the likelihood of comet tail formation
A

Comet tail

19
Q
  • Creates as sound reflects off of a strong reflector
  • Appears as a second copy of the structure deeper on the image
  • Diaphragm commonly exhbits this phenomeon
A

Mirror image

20
Q
  • Single element probe
  • Weak off axis lobes decrease lateral resolution
  • Can cause reflectors to appear in incorrect locations & multiple
  • Can cause an anechoic structure to fill in with echoes
  • Increasing rejection or decreasing compresson can help eliminate the low level artifactual echoes
A

Side lobe

21
Q
  • Seen in transducer arrays
  • Commonly affect linear arrays
  • Weak off axis lobes that decrease lateral res
  • Causes clutter through main axis
  • Artifact and true relfectors are side by side at same depth
  • Us system process reflection from the off axis beams part of the reflection from the main beam and the artifact is dempnstrated on imnage
  • Can cause reflectors to appear in incorrect locarions& multiple locations
  • Can cause an anechoic structure to fill in with echoes
A

Grating lobe

22
Q
  • Varying the voltage applie to different eleiments in an array that are forming the same pulse
  • Maximixing voltage to central elements and reducing voltage to the outer elements will reduce artifact
A

Apodization

23
Q
  • Each element is divided into sublement which are wire togetegrh to operate a single element
A

SUbdicing

24
Q
  • Using only a few elements to listen for the returning echoes narrows the beam info returned
A

Dynamic aperture

25
Q
  • Vertical misregistration
  • Sonographic equipment is calibrated for a propagation velocity of 1540
  • Reglectors will inappropriately positioned if reflteor is more shallow then it really is
  • Greater than 1540 will place the reflector more shallow than it is
  • If progation is less than 1540 it will be placed deeper
A

Propagation speed error

26
Q
  • Produces by interference of reflected waves from tiny reflectors
  • More speckle seen with lower freq transdcuers
  • Scaterring causes wave interference, resulting in speckled or granular appearance
  • Typically associated with liver, spleen kidney
  • Degrades contrasr & spatial res
  • Reduces signal to noise ration b/c noice is increase
A

Noise/Speckle

27
Q

– less detail seem with low line desnity

A

Spatial res artifact

28
Q

– two objets side by side appear as one object, related ot beam width, occurs when beam is wider than the reflrctor in the body

A

lateral res artifact

29
Q

two objects at different depths appear as one object, related to pulse length occurs when pulse is longer than the reflctor in body

A

axial res artifact

30
Q

– image flicker with low frame rate resultis in inaccurate positioning of moving structures

A

temporal res artifact

spi review questions (7 decks)

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