Chapter 3: Imaging Principles and Instrumentation Flashcards
A mode
amplitude mode
x- axis =
depth
y-axis =
strength of reflector
B mode
Brightness mode
displays brightness of echoes at dots of varying brightness
B mode
very strong reflectors
hyperechoic
very weak reflectors
hypoechoic
no return echo
anechoic
amplitude of B mode is represented on the ____
z-axis
states that the distance to the reflector is equal to the propagation speed multiplied by the round trip time
range equation
d=0.77t
range equation
it takes __s for sound to travel to a depth of 1 cm and return
13
motion of reflectors on a single scan line
m mode
m mode
motion mode
one scan line represented over time with depth along the y-axis and time along the x-axis
M-mode tracing
controls timing of signals sent to individual elements for steering and focusing of the beam
beam former
determine sequence of voltage pulses sent to the individual elements in an array transducer
beam former
used to decrease risk of grating lobes; works by decreasing strength of voltage pulse sent to outermost elements
apodization
transmitter or pulse generator
pulser
controls strength, or amplitude, of electricity striking the elements, as well as the PRF and PRP
pulser
controls amount of power entering patient
output power
ALARA
as low as reasonably achievable
sends a series of encoded pulses to form one scan line instead of the one pulse per scan line technique; allows for multiple focal zones, improved penetration, speckle reduction, B-flow imaging, and improved contrast resolution
coded excitation
soft tissue imaged at various frequencies and averaged
frequency compounding
part of the machine responsible for controlling the timing of the echo
master synchronizer
tells pulser to send out a pulse and pays attention to when echoes come back to determine range
master synchronizer
the deeper a wave travels, the more deformed it becomes
nonsinusoidal
multiples of the fundamental frequency
tissue harmonic imaging
If the harmonic signal is very narrow, this results in _____ lateral resolution
excellent
also referred to as signal processor
receiver
increases the relatively weak signal coming from the transducer
preamplification
overall gain; increases or decreases the strength of all the returning echoes equally
amplification
also referred to as TGC; compensates for attenuation
compensation
needed to decrease difference between largest and smallest amplitudes within signal (dynamic range)
compression
Compression is ______ related to dynamic range
inversely
processes signal to make it easier for machine to handle
demodulation
Two components of demodulation
rectification
smoothing
turns negative voltages into positive voltages
rectification
wraps an envelope around signal to make it less “bumpy”
smoothing
discards signal amplitudes below a certain threshold to reduce image noise
rejection
ensures electrical signals travel in the correct direction
transmit/receive switch
ensures the pulser voltages go to the transducer, and the received voltages from the transducer go to the signal processor
transmit/receive switch
part of the machine that makes gray-scale imaging possible
scan converter
responsible for storage of image data
scan converter
utilizes only zeroes and ones instead of numbers 0 through 9
0 represents “off” - black echo
1 represents “on” - white echo
binary system
black and white images
bistable
consists of analog to digital converter, computer memory, digital to analog converter
scan converter
occurs in A-to-D converter, incoming signals assigned shades of gray based on their amplitudes, image still “live”
preprocessing
machine guesses what pixel should be placed between gaps in scan lines
fill-in interpolation
smallest amount of computer memory
Bit
8 bits =
1 byte
The number of bits determines:
the number of shades of gray possible
Number of shades of gray =
2x number of bits
picture element
pixel
smallest part of any picture
pixel
More pixels = better _____ resolution
spatial
volume element
voxel
signal converted back to analog form so it can be sent to PACS
D-to-A converter
preprocessing function, enlarges image by redrawing it
write zoom
postprocessing function, enlarges images by magnifying pixels
read zoom
use of an electron gun to send a stream of electrons toward a phosphor coated screen; beam steered via use of magnetic reflector coils
Cathode Ray tube
works with a light source positioned behind two polarized filters with liquid crystals sandwiched between them; twisting or untwisting of the crystal determines if light shines through to face of display
LCD or flat panel display
uses RAID to store large quantities of data
PACS
imaging computers that use a standardized format to communicate with each other and exchange data
DICOM
echoes on the screen that are not representative of actual anatomic features or occur when there are anatomic structures in the body that are not displayed on the screen
imaging artifacts
occurs when the sound bounces back and forth between two close together strong specular reflectors
reverberation
“step ladder” like appearance
reverberation
can be caused by small structures like surgical clips or adenomyomatosis within gallbladder wall
comet tail
caused by sound interacting with small air bubbles, causing the bubbles to vibrate
ring-down artifact
occurs when the sound is aimed toward a large specular reflector that acts like a mirror and directs some of the sound in a direction other than back to the transducer
mirror image artifact
causes artifacts as the beam is directed away from the path in which it was originally intended to go
refraction
seen when sound strikes a curved reflector
edge shadowing
eliminates beam hits structure at different angles
spatial compounding
Side lobes occur with _____ transducers
all
Grating lobes occur with _____ transducers
linear
tissue propagation speed less than 1540 m/s, objects are
displayed too far away
tissue propagation speed more than 1540 m/s, objects are
displayed too close
occurs when sound travels through an area of higher attenuation compared with surrounding tissue
shadowing
occurs from sound traveling through areas of lower attenuation
acoustic enhancement
occurs because the beam scanned through both the cyst and soft tissue adjacent to the cyst, causing both to appear on the image
slice-thickness artifact
presence of electrical equipment near the ultrasound; causes arc-like bands that move across the screen as long as the machine is in the proximity of unshielded equipment
electrical interference