Chapter 3: Imaging Principles and Instrumentation Flashcards by Billie Harney

A mode

amplitude mode

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x- axis =

depth

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y-axis =

strength of reflector

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B mode

Brightness mode

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displays brightness of echoes at dots of varying brightness

B mode

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very strong reflectors

hyperechoic

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very weak reflectors

hypoechoic

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no return echo

anechoic

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amplitude of B mode is represented on the ____

z-axis

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states that the distance to the reflector is equal to the propagation speed multiplied by the round trip time

range equation

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d=0.77t

range equation

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it takes __s for sound to travel to a depth of 1 cm and return

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motion of reflectors on a single scan line

m mode

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m mode

motion mode

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one scan line represented over time with depth along the y-axis and time along the x-axis

M-mode tracing

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controls timing of signals sent to individual elements for steering and focusing of the beam

beam former

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determine sequence of voltage pulses sent to the individual elements in an array transducer

beam former

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used to decrease risk of grating lobes; works by decreasing strength of voltage pulse sent to outermost elements

apodization

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transmitter or pulse generator

pulser

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controls strength, or amplitude, of electricity striking the elements, as well as the PRF and PRP

pulser

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controls amount of power entering patient

output power

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ALARA

as low as reasonably achievable

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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

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soft tissue imaged at various frequencies and averaged

frequency compounding

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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