Chapter 14 Flashcards
what are the 2 major functions of the US system?
1) preparation and transmission of electrical signals to the transducer (creates the sound beam)
2) reception of electrical signals from the transducer, with subsequent processing into clinically meaningful images and sounds
what are the 6 major components of the US system?
transducer, pulser and beam former, receiver, display, storage, and major synchronizer
during transmission the ______ transforms electrical energy into acoustic energy, during reception it converts the returning acoustic energy into electrical energy
transducer
the ______ determines the amplitude, pulse repetition period, and pulse repetition frequency, while the ______ determines the firing delay patterns for phased array systems. together they create and control the electrical signals sent to the transducer that generate sound pulses
pulser, beam former
______ transforms the electrical signals from the transducer into a form suitable for display
receiver
______ presents precessed data, may be a flat screen monitor, a transparency, a spectral plot, or a variety of other formats
display
______ archives the US studies, typical devices include computer hard drives, CD, DVD, videotape, magneto-optical discs, paper printouts, photographs, and USB drives
storage
______ maintains and organizes the proper timing and interaction of the systems components
master synchronizer
the ______ creates electrical signals that excite the transducers PZT crystals and create sound beams, functions during transmission
pulser
what is the range of the magnitude of the pulsers electrical voltage spikes?
near 0 to approximately 100 volts (can be adjusted by the sonographer)
what happens when you change the pulser voltage? what happens when it is low compared to high?
modifies brightness of the entire image displayed on the systems screen
low voltage vibrates gently, and a week sound beam is transmitted into the body and image is dark
high voltage vibrates forcefully, and transmits stronger sound beams into the body and image is brighter
what are the terms used to describe pulser voltage?
output gain, acoustic power, pulser power, energy output, transmitter output, power, or gain (this term is vague and should be avoided)
______ pulser voltages are desirable because they decease transmitted acoustic energy and minimize patient exposure to ultrasonic energy and likelihood of bioeffects
lower
______ is loosely defined as a random and persistent disturbance that obscures or reducers a signal’s clarity, contaminates images with low-level, undesirable information
noise
______ is a comparison of the meaningful information (signal) in an image, compared to the amount of contamination (noise)
signal-to-noise
what happens when the signal-to-noise ratio is high or low?
high-the signal is much stronger than noise and the image is of high quality
low-the strength of the signal is closer to the strength of the noise, the image contains a larger amount of visible contamination, an has less diagnostic value
when transducer output is ______, noise is more likely to degrade the image, as the sonographer ______ output power, the signal-to-noise ratio does the same.
low, increases
______ output power is the most common way to improve the signal-to-noise ratio
increasing
the pulser determines the time between one voltage spike and the next, the ______
pulse repetition period (reciprocals to PRF) also determines the maximum imaging depth
when the PRP is short, the PRF is ______, and the system spends less time listening (superficial imaging)
high
when the PRP is long, the PRF is ______ and the system listens for a longer time (deeper imaging)
low
______ is a sophisticated electronic device that receives the pulser’s single electrical spike and distributes it to the numerous active elements of an array transducer
beam former
______ is when the beam former adjusts electrical spike voltage to reduce lobe artifacts
apodization
during ______, the beam former establishes the correct time delays used for dynamic receive focusing
reception
the beam former controls ______ by varying the number of PZT crystals used during both reception and transmission
dynamic aperture
what is the technology that the beam former uses to produce signals in digital format called?
digital beam former
what are the advantages of the digital beam former?
the system updates require only software programming and are more flexible, extremely stable, versatile (can use transducers with a wide range of frequencies)
during pulse creation the voltage from the US system to the transducer are very ______, during reception the voltages from the transducer back to the US system are extremely ______
high, low
the ______ protects the delicate receiver components from the powerful signals that are created for pulse transmission, it also directs the electrical signals from the transducer to the appropriate electronic and processing components within the US system
switch
a ______ is made up of a single PZT element in the transducer, the electronics in the beam former/pulser, and the wire that connects them
channel
what determines the number of elements in an array transducer that can be excited simultaneously?
the number of channels in the US system: most have between 32 to 256 channels
the ______ prepares the information contained in the minuscule signals that return to the transducer for eventual display on the system’s monitor
receiver
what 5 operations must be preformed for the system to function properly?
amplification, compensation, compression, demodulation, and reject
in the ______ process, each electronic signal returning from the transducer is made larger (each signal undergoes an equal amount of this)
amplification (also known as receiver gain)
why is amplification required?
because the electrical signals are to low to be displayed on the monitor
what happens when the sonographer adjusts the receiver gain?
the entire image is made brighter or darker (receiver gain is affected identically by amplification)
can amplification alone make an image uniform brightness from top to bottom?
no, it does not improve signal to noise ratio either
what are the measurements and typical value of amplification?
decibels; from 60-100 decibels
______ is the process of improving the quality of a signal before it is amplified
preamplification (occurs close to the PZT, often within the transducer)
what is preamplification designed for?
prevent electronic noise from contaminating the tiny electrical signals created by the transducers active elements during reception
______ is the process where the receiver corrects for attenuation, creates an image with uniform brightness from top to bottom
compensation (without it the images will get darker with deeper depth)
what are the units for compensation?
decibels
what are the synonyms for compensation?
TGC, depth gain compensation (DGC), and swept gain
what is the order that the TGC goes in as it gets deeper?
near gain, delay, slope, knee, far gain
______ keeps the electrical signal levels within the accuracy range of the systems electronics
(first) compression
______ keeps an image’s gray scale content within the range of detection by the human eye
(second) compression
humans can distinguish around ______ shades of gray, and compression allows us to visualize different tissues within these gray shades
20
what are the synonyms for compression?
long compression or dynamic range
what are the units for compression?
decibels
______ compression is an adjustable compression where small differences in weak signals are displayed and seen as different gray shade levels (a wide range of strong signals are all displayed as bright white)
log
why is log compression important?
most meaningful backscattered signals from biologic tissues are very weak and the sonographer must be able to see differences in these weak reflections
______ is a two-part process that changes the electrical signals within the receiver into a form more suitable for display on a monitor (changes the form)
demodulation (only process not adjustable)
______ converts all negative voltage into positive voltage, it corrects for, or eliminates, negative voltage
rectification
______ (or enveloping) places a smooth line around the “bumps” and evens them out
smoothing
______ allows the sonographer to control whether low-level gray scale information within the data will appear on the displayed image
reject (its desirable to display low-level reflections but noise should not appear)
what are the synonyms for reject?
threshold or suppression
as a result of damping, sound pulses used for imaging contain a wide range of frequencies and are described as ______ or ______
wide bandwidth or broadband
systems with dynamic frequency tuning use only the high frequency part of the reflected pulses bandwidth to create the ______ of the image because higher frequency sound has superior axial resolution
superficial portion
______ affects image brightness by altering the strength of the sound pulse that the transducer sends to the body
output power
______ alters the strength of the voltage in the receiver that the transducer created during reception
receiver gain (also called amplification)
patient exposure to sound energy is affected by alterations in ______ but not by changes in ______
output power, amplification
the ______ principle states that when modification to either output power or receiver gain can improve the images diagnostic quality, the first and best choice is the one that will minimize the patients US exposer
ALARA
