Test 2 Flashcards
what is an artifact?
incorrect representation of anatomy or function
what can happen to a structure with an artifact?
- not real
- missing
- misplaced
- incorrect brightness, shape, or size
why may artifacts may be not helpful?
- provide us misinformation (show us structures that are not there)
- limit our study (hide structures we are trying to see)
why may artifacts be helpful?
- provide us with useful information
- some are characteristic of particular structures/pathologies
what is artifact assumption #1?
sound travels in a straight line
-pulse is sent straight out and comes straight back (not always true)
what is artifact assumption #2?
echoes originate only from structures along the beam axis
what is artifact assumption #3?
amplitude of the returning echo depends only on the interface it strikes
-brightness is only dependant on the reflector boundary (not always true)
what is artifact assumption #4?
sound travels at 1.54 mm/us
-constant speed through all tissue=13 us/cm (not always true)
what are groups of artifacts?
- propagation related
- attenuation related
- doppler artifacts
what is propagation related artifact relate to?
travel of the sound
what is attenuation related artifact related to?
relating to change in intensity of the beam
what are some propagation related artifacts?
- slice thickness
- speckle
- reverberation
- mirror image
- refraction
- grating lobes
- speed error
- range ambiguity
- resolution artifact
what is slice thickness artifact also known as?
- section thickness artifact
- partial volume artifact
- fill-in artifact
what is an assumption for slice thickness artifact?
ultrasound beam is razor thin (not true)
with slice thickness artifact, because its a 2D image, thickness collapses into __________
zero thickness
echoes picked up from all structures covered by __________
thickness
wat may slice thickness artifact happen with?
small cystic structures (cysts, carotid, GB)
what better resolution does slice thickness artifact need?
better elevational resolution
what is the treatment for section thickness artifacts?
THI-narrower and thinner beam
focusing in 3rd dimension
what is speckle?
granular appearance of images that is caused by constructive/destructive interference patterns of scattering
what is scattering?
echo sound waves take different paths on the way back to the transducer
how may waves come back with scattering?
constructively or destructively
constructive interference (in phase)
intensity will be much stronger than individual sound waves
destructive interference (out of phase)
waves will cancer out
what does speckle result in?
-varying intensities (dark and light)
grainy appearance
what is the treatment for speckle?
- newer machines have complicated ‘speckle reuction’
- persistence
- increasing fo
when does specular reflection occur?
when the object is large and the wavelength is small
when does scattering occur?
the object is small and the wavelength is large
what does increasing fo do to wavelength/
reduces wavelength
reverberations are multiple reflections between what?
- a structure and the transducer
- between structures
- within a structure
what causes reverberations?
sound bouncing between 2 strong reflectors
what are reverberation subtypes?
- anterior reverberation
- comet-tail artifact
- ring-down artifact
- twinkling
where does anterior reverberation occur?
the transducer face
-sound bouncing between transducer and a strong reflector
what does anterior reverberation trick the machine into thinking?
that there are multiple echoes coming back with different travel times
why is each deeper echo weaker in anterior reverberation?
the time of flight is longer on each echo, with more attenuation associated with the more time spent in the tissue
what is another name for anterior reverberation?
main bang-shows within a cystic structure
when does comet tail artifact occur?
between closely spaced structures
what is comet tail artifact caused by?
small structures
- surgical clips
- adenomyomatosis
- GB pathology of cholesterol deposition in the wall
how is ring-down artifact different from comet tail artifact?
ring down has no attenuation
when may ringdown artifact occur?
liquid trapped between gas bubbles produce vibrations
ring down resonance
resonance of the bubbles produce vibrations which can be perceived as individual echoes
twinkle artifact appearance
focal ‘aliasing’ on calcifications/stones
- can have prominent comet-tail
- sometimes called ‘color comet-tail artifact’
how will you know if its twinkling and not aliasing?
will not decrease or disappear with increased PRF
what can a strong reflector do to sound?
sometimes a strong reflector will create a new path for the sound beam
what does a mirror image involve?
a strong reflector (gas/diaphragm)
what does refraction require?
oblique incidence through different media
sound beam path may bend going through and on the way back
what may refraction result in?
lateral position errors (linea alba)
displaces structures laterally from their correct location
define refraction
lateral position error
what is the treatment for refraction?
window
spatial compounding
side lobes/grading lobes
weak beams that are produced along the edges of elements
what can side lobes/grading lobes mimic?
- amniotic bands on OB
- aortic flap/dissection on abdominal U/S
what is the treatment of side lobes/grading lobes?
- apodization (GL only)
- subdicing
- THI
speed error
we assume sound travels at 1.54 and all tissue 13 and this is not always true. This is an average velocity
speed of sound in fat
1.45 mm/us
speed of sound in muscle
1.58 mm/us
is propagation speed (c) is larger than 1.54 the object will be places too ___
close
if the propagation speed (c) is smaller than 1.54 the object will be places too __
far
what happens with speed error?
slower c-posterior structures are placed further
range ambiguity artifact
places structures closer to the surface
when does range ambiguity artifact occur?
2nd pulse is sent out before all echoes returned from the 1st pulse
detail resolution
being unable to separate two distinct objects-cause neighbouring objects to blend/connect
what are attenuation artifacts?
- shadowing
- enhancement
- edge shadow
acoustic shadowing
increased attenuation
increased % reflection (IRC)
is acoustic shadowing helpful or not?
helpful-characterize structures
clean shadowing
stones
dirty shadowing
gas
what is acoustic enhancement also known as?
through transmission
acoustic enhancement
decreased attenuation
decreased %reflection (IRC)
what is enhancement?
strengthening of echoes distal to a weakly attenuating structure
is acoustic enhancement helpful or not?
helpful
focal enhancement or focal banding
brightening of echoes can be caused also by the increased intensity in focal region
what does edge shadows involve?
curved structures with high c
-multiple refractions at the borders
what does edge shadows cause to the intensity?
decrease intensity of beam beyond
what is the treatment for edge shadows?
- new window
- spatial compounding
what are some doppler related artifacts?
- aliasing
- multiple angle artifact
- acoustic shadowing
- mirror image
- clutter
what does aliasing look like on spectral?
doppler spectral info on wrong side of baseline
what does aliasing look like on colour?
incorrect colour from the opposite side of baseline on the colour map
PRF needs to be set relativiely ______ in colour doppler?
high
NL=
1/2 PRF
what is the treatment for aliasing?
- increase PRF
- Shift baseline
- increase doppler
- lower fo
- use CW
what may increasing doppler and lowering frequency do?
- possibly of error
- loss of resolution
what does CW do to our image?
poor range resolution
what is multiple angle artifact?
flow is in a single direction but appears as 2 colours
- 90 to vessel
- tortuous vessels
acoustic shadowing in doppler
a calcified anterior wall can mimic occlusion of an artery
what is acoustic shadowing in doppler treatment?
- window
- power doppler to assess for true stenosis
- use upstream/downstream clues
what causes mirror image in doppler?
same as grey scale-strong reflector
what is the treatment for mirror image in doppler?
change window
what is mirror image in spectral also known as?
cross-talk
what are reasons for mirror image in spectral doppler?
- gain is too high-causes cross talk
2. near 90 degrees will show flow on both sides of baseline
how do we fix spectral doppler mirror image?
proper gain and angle
why may 90 degree interrogation experience 2 direction flow?
because beams are focused and not cylindrical portions of the beam
clutter/flash artifact
anything that is moving may cause doppler shift (valves/tissue motion)
what is the treatment for clutter/flash artifact?
- increase wall filter
- turn down gains
what happens in the pulser?
voltage pulse in created, delayed, and sent out
what happens at the transducer?
voltage is converted to a sound pulse
what happens after striking multiple reflectors through multiple layers of tissue?
the corresponding echoes return to the transducer
what happens to echoes upon returning to the transducer?
echoes converted back into an analog voltage signal
what happens in the beam former?
- the signal is amplified to compensate for attenuation
- echoes from various depths are built into scan lines
- this info is digitized for processing
what happens in the signal processor?
unnecessary frequencies and amplitudes are removed
what happens in the image processor?
scan lines are built into frames
- each pixel within a frame will be assigned a # based on
- intensity
- depth
- direction
where are frames stored?
image memory
what happens to frames after being retrieved from the image memory?
retrieved from image memory and processed again before being converted to analog voltage signals
THESE ARE SENT TO THE DISPLAY
CRT
cathode ray tubes
what does CRT contain?
- phosphor-coated florescent screen (matrix of pixels)
- electron beam generator
- magnetic deflection coils
Electrons which strike the inside of the screen will cause the pixels at that spot to temporarily ________
light up
The brightness of the dot on the screen = ___________________
the strength of the electron beam
where does the strength in the screen come from?
strength of returning echo
what do magnetic deflection coils do?
can deflect the electron beam one way or another
raster scanning
the CRT will generate electron beams that will ‘sweep’ the inner surface of the screen and cause lines to appear on the screen
how many lines does raster scanning involve?
525 horizontal lines
what are horizontal lines in raster scanning grouped into?
odd and even fields (262.5 lines/field)
twin interlacing
in a given moment, one field is constructed, in the next moment, the other is contructed
how many fields are shown per second in raster scanning?
60 fields per second
BUT each field is only half an image
therefore 30 images/second (30 Hz)
refresh rate
raster scanning on a CRT displays 30 images per second
RR (refresh rate)=
how many images are shown on the screen per second
what does RR involve?
this involves retrieval from our image memory, digital to analog conversion, and then voltages to the display
frame rate (Hz)
how quickly frames are built # of images entered into the image memory per second
what does refresh rate limit?
frame rate (we see RR)
frame rate-
frame rate-image memory-refresh rate
there are more frames built that we can see live canning, where are they?
we can see them in cineloop
how many cathode ray tubes involve colour displays?
3
-1 per colour (RGB)
what will provide a desired mix of colour?
CRT will fire electrons into appropriate groupings to provide desired mix of color
what is flat panel display also known as?
liquid crystal display (LCD)
what is Flat Panel Display (LCD)?
matrix of ‘photo-electric elements’
what is a common matric of ‘photo-electric elements’?
1024x768
what will decide luminance (brightness of element)?
amplitude of voltage
is there raster scanning in flat panel display?
no raster scanning
what does RR= on a typical LCD
60 Hz
what are LCD advantages over CRT?
- The display is much lighter and much, much thinner
- Excellent image quality: brighter image and higher contrast
- Significantly reduced eyestrain
- Perform very well in a wide range of ambient light environments
- Lower power consumptions and energy emissions
flat panel display (plasma)
- electrical charge ionizes gas producing UV light
- UV light hits a phosphor coated screen which will glow
- 85Hz
flat panel display (organic LED)
- latest greatest, even thinner
- involves Light Emitting Diode
what are some display modes?
B-mode
M-mode
A-mode
B-mode
brightness mode (grayscale, 2D)
what does B-mode do?
suggests the brightness of each reflector at each anatomical position
M-mode
motion mode (cardiac structures)
what does M-mode display?
information from a single scan line
-beam is stationary
M-mode and amplitude
amplitude at each depth represents of reflector like B-mode
M-mode y axis
depth
M-mode x axis
time
A-mode
amplitude mode
what does A-mode display?
information from a single scan line
-bean is stationary
A-mode y axis
amplitude (brightness)
A-mode x axis
depth
in A mode what are brighter areas represented by?
higher peaks
when is A mode used?
ophthalmic imaging
What are types of image storage?
- RAM
- ROM
- PROM
what does RAM stand for?
random access memory
RAM
information storage
temporary, very quick to access
very volatile, memory is dumped often
what may happen with RAM?
information is lost when the machine is turned off
what uses RAM inside the machine?
image memory
-information is lost once un-frozen
what does ROM stand for?
read-only memory
ROM
permanent info in storage
can still be accessed
not to be changes
how is ROM different from RAM?
information will remain even if the machine is turned off
what does PROM stand for?
programmable ROM
PROM
permanent info in storage
can still be accessed, adjusted, erased
will the info remain when machine is turned off in PROM?
yes
where might the images we take and store fall under?
PROM
what are extensions of image storage?
recording and archiving
mass storage
large amounts of information stored
floppy disks
magnetic medium
what are the advantages of floppy disks?
archiving capability
were very colorful
what are disadvantages of floppy disks?
poor access
small memory 1.44 Mb
what are advantages of video tapes?
record motion
what are disadvantages of video tapes?
poor resolution
poor access
what are advantages of thermal paper?
- printer itself is small
- relatively inexpensive
- no wet chemical is required
what are the disadvantages of thermal paper?
- fair image quality
- archival properties were poor
digital image recording
hard disk drive
optical disks (CD/DVD)
magnetic optical disks
flash memory (USB/memory cards)
hard disk drive
standard component on computers
uses rotating platters with magnetic surfaces
what are the advantages to hard disk drive?
- can read and write to these surfaces quickly
- large storage capacity
what are the disadvantages to hard disk drive?
requires power
can crash-require backups
optical disks
CD/DVD
written and read by lasers
what are advantages to optical disks
- can read and write to/from these surfaces quickly
- medium storage capacity
- no power required
what are the disadvantages to optical disks?
can break
lose it
what are different types of optical disks?
- read only
- write once, read many
- rewritable
magneto-optical disks
combination magnetic/optical
rewritable
what are advantages to flash drives?
- can read and write to/from these surfaces quickly
- larger storage capacity than CD’s now
- no power required
what are the disadvantages to flash drives?
can lose them
what does HIS stand for?
hospital information system
HIS
integrated info system designed to manage the administrative financial and clinical aspects of a hospital
what does RIS stand for?
radiology information system
RIS
electronic system built to manage the workflow in the radiology department
what does PACS stand for?
picture archiving and communication system
PACS
storage, retrieval and distribution of images
what are some examples of PACS?
- When you store images for the radiologist, it goes into PACS
- When you review images on your workstation, you access PACS
What are the benefits to quality assurance?
- promote properly working equipment
- detect declining performance
- prevent equipment malfunction and downtime
- optimize operator and patient safety
who does good quality typically involve?
- physicians/radiologists
- the sonographer/manager
- service personnel
physicians /radiologists and QA
to assess image quality and direct protocol
sonographers/managers in QA
- assess image quality
- preform some routine testing and record keeping
- perform routine basic maintenance
service personnel
- assess image quality
- preform diagnostic testing
- preform maintenance
- repair malfunctioning equipment
- maintain service records
preventative measures?
DAY to DAY tasks
- clearing hard drive
- cleaning the machine
- cleaning the dust out of the filters
- checking the wires for damage
how often is QA testing done?
semi annual (6 months) to annual
what does QA testing involve?
- record keeping
- can involve service personnel
what are the 2 main types of testing?
- operational QA
2. acoustic output
operational QA
- anatomical imaging/measurements
- doppler evaluation
acoustic output
- beam former
- related to bioeffects
TEP
tissue equivalent phantoms
what is TEP also known as?
tissue mimicking phantom (TIM)
what is TEP?
- mimics soft tissue characteristics
- we scan along the top
what is TEP filled with?
- graphite-filled aqueous gels
(1. 54 mm/us) - urethane rubber
(1. 45 mm/us)
what is the propagation speed in TEP?
about 1.54 mm/us
what is the attenuation coefficient in TEP?
about 0.5 dB/cm/MHz
what is used to demarcate echogenic points?
nylon strings
what does TEP come with?
blueprints
what resolution do we check with blueprint and TEP?
- axial resolution
- lateral resolution
what can TEP mimic?
cysts
solids
when looking at solids what did we check for?
contrast resolution
what is contrast resolution associated with in TEP with contrast resolution?
lesion detection
what are operational QA parameters?
- detail/contrast resolution
- sensitivity (lesion detection)
- uniformity
- TGC
- accuracy of depth and distance (caliper accuracy)
- maximum penetration
TO=
test objects
what is TO?
thin scattering wires provide outlines/interfaces
check measurements, resolution, accuracy e.t.c
doppler TEP
contains tubular areas with pumps
-flow mimicking fluid (check flow direction)
doppler TO description
- cheaper
- less accurate
- moving solid object
- can do pulsatile and reverse motions
what can doppler TO be programmed to mimic?
normal waveforms
what is acoustic output related to?
bioeffects
what is a hydrophone?
small transducer element on a long hollow needle ( less than 1mm diameter)
point transducer at hydrophone, hydrophone picks up pressure wave and converts to ____________
voltage
Polyvinylidene Fluoride Membrane (PVDF)
converts pressure wave to voltage
what can be connected to a oscilloscope?
both a microprobe/PVDF membrane
what can we figure out from a oscilloscope chart?
- T
- PD
- PRP
- DF
- f
- wavelength
- SPL
spectrum analyzer
connected to oscilloscope: able to break down incoming bandwidth to individual frequencies
most importantly, the oscilloscope readings can calculate what?
amplitude-based on the peaks of the signal
what does amplitude relate to?
intensity
