Flashcards in Chapters 14 Deck (62):
What are the six major components of the ultrasound system?
What does the pulser of the US system do?
determines the amplitude, PRP. and PRF
creates electrical signals that excite the PZT crystals and create sound beams
What does the beam former of the US system do?
determines the firing delay patterns for phased array systems
What does the receiver do?
transforms the electrical signals from the transducer (produced by the reflected sound) into a form suitable for display
What does the display do?
presents processed data. the display may be a flat screen monitor, a transparency, a spectral plot. or a variety of other formats
What does the storage do?
archives the ultrasound studies. typical storage devices (or media) include computer hard drives, CD, DVD, videotape, magneto-optical discs, paper printouts, photographs, and USB drives
What does the master synchronizer do?
maintains and organizes the proper timing and interaction of the systems components
When does the pulser function?
What happens when changes are made to the pulser voltage?
it modifies the brightness of the entire image displayed on the systems screen
What happens when the pulser voltage is set too low?
PZT vibrates gently, and a weak sound beam is transmitted into the body. The reflected echoes are weak, and the entire image tends to be dark
What happens when the pulser voltage is set too high?
PZT vibrates more forcefully, and transmits a stronger sound beam into the body. the reflected echoes are stronger, and the entire image is brighter
What happens to the entire image when the gain is increased?
What happens to the entire image when the gain is decreased?
What are synonyms for pulser voltage?
output gain, acoustic power, pulser power, energy output, transmitter output , power, or gain
Is the pulser adjustable?
Why are lower output power desirable?
decrease transmitted acoustic energy and minimize patient exposure to ultrasonic energy . lower pulser voltages minimize the likelihood of bioeffects
What is noise?
a random and persistent disturbance that obscures or reduces a signals clarity. Noise contaminates images with low level, undesirable info
What is siginal to noise ratio?
a comparison of the meaningful info (signal) in an image compared to the amount of contamination (noise)
What does high signal to noise ratio mean?
the signal is much stronger than the noise and the image is of high quality
What does low signal to noise ratio mean?
the strength of the signal is closer to the strength of the noise. the image contains a larger amount of visible contamination and has less diagnostic value
How is signal to noise ratio related to output power?
What does the PRP determines?
the max imaging depth also called depth of view
What happens when the PRP is short?
higher PRF and the system spends less time listening. This results in superficial imaging
What happens when the PRP is long?
low PRF, more listening time. the imaging is deeper
When you change depth of view, what are you changing?.
What is it called when the beam former adjusts electrical spike voltages to reduce lobe artifacts?
What things does the beam former control?
dynamic receive focusing and dynamic aperture
What are advantages of digital beam formers?
What part of the US systems contains the transmit receive switch?
What does the switch do?
protects the delicate receiver components from the powerful signal that are created for pulse transmission
Also directs the electrical signals from the transducer to the appropriate electronic and processing components within the US system
What is a channel?
is made up of a single PZT element, the electronics in the beam former/pulser, and the wire that connects them.
What are the receiver operations?
What is other word for amplification?
How are all electrical signals in the receiver affected?
identically by amplification
When amplification is adjusted what is affected?
the entire image is made brighter or darker
is amplification adjustable?
yes- the gain control
What are the units for amplification?
What are typical values for amplification?
What is preamplification?
the process of improving the quality of a signal before it is amplified. are designed to prevent electronic noise.
What does preamplification occur?
as close to the active elements as is practical, often within the transducer itself
The receiver function that corrects for attenuation?
compensation or TGC
What does compensation do?
creates an image that is uniformly bright from top to bottom
is compensation adjustable?
What are the units for compensation?
is a form of variable amplification so the units are the same dB
What are synonyms for compensation?
TGC, DGC or swept gain
Can compression be adjustable?
alters the gray scale mapping
rank of signals large to small or vice versa
What are synonyms for compression?
log compression, or dynamic range
Why is log compression important in clinical US?
b/c most meaningful backscattered signals form biologic tissues are very weak and the sonographer must be able to see differences in these weak reflections
What does demodulation do?
a two part process that changes the electrical signals within the receiver into a form more suitable for display on a monitor
coverts all negative voltages into positive voltages. Corrects negative voltages
is demodulation adjustable?
What is the purpose of demodulation?
change the form of the electrical signal
What are synonyms for reject?
threshold or suppression
What does reject do?
gets rid of low level signals and allows the sonographer to control whether low level gray scale info within the data will appear on the displayed image
Is reject adjustable?
What kind of effect on the image does reject have?
affects all low level signals on the image, regardless of their location. rejection does not affect bright echoes.
Signals treated differently based on reflector depth is what receiver function?
Signals treated differently depending on strength is what receiver function?
what receiver function prepares electrical signals to be suitable for display?
what receiver function affects only weak signals and does not affect strong signals?