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
- 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
Propagation speed error
26
- 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
Noise/Speckle
27
– less detail seem with low line desnity
Spatial res artifact
28
– two objets side by side appear as one object, related ot beam width, occurs when beam is wider than the reflrctor in the body
lateral res artifact
29
two objects at different depths appear as one object, related to pulse length occurs when pulse is longer than the reflctor in body
axial res artifact
30
– image flicker with low frame rate resultis in inaccurate positioning of moving structures
temporal res artifact
