Study guide test 2 Flashcards
Which component organizes and functions?
master synchronizer
Which component excites the crystal?
pulser
Choose the area on the TGC curve where the attenuation is occurring:
far gain
What creates the pattern for phased array?
beam former
What are the functions of the receiver?
Amplification-receiver gain
Compensation-TGC
Compression-20 shades of gray, keeps large signal large, small signal small
Demodulation-rectification, smoothing
Reject-rejects low level echoes
Who decides the acoustic power of the sound beam?
the sonographer
In regards to a pulser, which form has the elctrical signal in a sine wave?
continuous wave
What can improve the signal-to-noise ratio?
Increasing output power increases signal-to-noise ratio, which improves the image quality.
If an image is too dark or too bright, what are your options?
What tools may you use to improve the image?
Amplification(receiver gain) changes the overall brightness of an image
high amplification=brighter image
Compensation(TGC) corrects for attenuation by creating an image of uniform brightness
Which receiver function handles reflector depth?
Compensation(TGC):sound attenuates as it travels
The image gets darker as the depth increases
controlled by compensation
What are PRP and PRF?
PRP(pulse repetition period) determines the maximum imaging depth(depth of view)
PRF(pulse repetition frequency) reciprocal of PRP
PRP is short- PRF is high (system spends less time listening)
1
What are the components of an ultrasound system?
master synchronizer:
communicates with all components
organizes timing and functions
2
What are the components of an ultrasound system?
transducer:
converts electrical energy into acoustic energy
converts returning acoustic energy during reception
3
What are the components of an ultrasound system?
pulser:
functions during transmission
controls electrical signals sent to the transducer
determines amplitude, PRP, PRF
4
What are the components of an ultrasound system?
receiver:
transform electrical signals to a form suitable for display
5
What are the components of an ultrasound system?
display:
monitor
6
What are the components of an ultrasound system?
storage:
film, sony paper, CD/DVD, video, magnetic disc, USB drives, PACS
What can you do when the image is too bright?
What is the better choice?
output power vs receiver gain
output power:changes brightness of entire image, alters signal-to-noise ratio, alters patient exposure, bioeffects concerns, decrease this first if image is too bright
receiver gain:changes brightness of entire image, does not affect signal-to-noise ratio, does not change patient exposure, no bioeffect concerns, increase this first if image is too dark
Which function affects the strength of every signal?
amplification
What are the disadvantages of an analog scan converter?
Image fade
Image flicker
Instability
Deterioration
What are the advantages of a digital scan converter?
Uniformity
Stability
Durability
Speed
Accuracy
What is responsible for gray scale imaging?
scan converters
Know about shades of gray and bits (how to convert them):
each pixel’s shade of gray is determined by the cluster of bits assigned to it
8 bits=1 byte, 2 bytes(16 bits)=1 word
We are able to see 20 shades of gray
Read Magnification
uses old data
postprocessing
larger pixel size
same # of pixels as in the original ROI
unchanged spatial resolution
Write magnification
acquires new data
preprocessing
identical pixel size
more pixels than in the original ROI
improved spatial resolution
may improve temporal resolution
Preprocessing
time gain compensation
log compression
write magnification
persistence
spatial compounding
edge enhancement
fill-in interpolation
Postprocessing
any change after freeze frame
black/white inversion
read magnification
contrast variation
3-D rendering
Analog-Digital-Analog Process
Electrical signals created by the transducer are converted from analog to digital by the analog-to-digital (A-to-D) converter
Digital info is stored in the scan converter’s computer memory. Any processing of the reflected signals before storage is called preprocessing
Image info (still in digital form) continues to be processed by the ultrasound system’s computer. Any processing after storage in the digital scan converter is postprocessing
Digital signals must be translated back into analog form by a digital-to-analog (D-to-A) converter, because digital signals cannot be directly displayed on analog display devices
Signal is now in analog form and can be presented on the analog video display for interpretation
Pixels and shades of gray
fewer bits/pixel: fewer shades of gray, degraded contrast resolution
more bits/pixel: more shades of gray, improved contrast resolution
bistable and grayscale imaging
bistable: black and white, high contrast
grayscale: many shades, low contrast
What is spatial resolution?
the details in an image
high line density= excellent spatial resolution
Analog vs Digital Numbers
analog: real world, unlimited # of choices, continuous values
digital: computer world, limited choices, discrete values
what is coded excitation?
method of improving image quality
coded excitation provides: higher signal-to-noise ratio, improved axial resolution, improved spatial resolution, improved contrast resolution, deeper penetration
What is spatial compounding?
It is a process of compounding several different frames
it reduces shadowing artifact
What is frequency compounding?
it is a technique that reduces speckle artifact and noise
What is edge enhancement?
it is an image processing method that makes pictures look sharper
What is temporal compounding
(persistence)?
it is a technique that super imposes the current frame on previous frames to create smoother image
What is fill-in interpolation?
it is a technique that fills in the missing data between the scan lines
What is elastography?
it takes the levels of stiffness in a structure and gives us info into the densitty (mass) of an object
