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
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
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
4
Q
External - lens, fixed
Internal - curved, element, fixed focal point
A
Mechanical focusing
5
Q
Phased electronic
- adjustable by technologist
- allows multiple focal points
A
Electronic focusing
6
Q
With focusing ______ the diameter of the beam at the focal zone
A
decreases
7
Q
With focusing ______ the beam diameter in the far field
A
increases
8
Q
With focusing ______ the beam diameter in the near field
A
decreases
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
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
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
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
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
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
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
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
