Sonography Principles and Instruments: Chapter 6 Artifacts notes Flashcards

anything that is not properly indicative of the structures or events

shadowing
enhancement

- tell the difference between solid and fluid
- characterize masses

improper location
wrong size
wrong shape
wrong acoustical properties
absent
present
absuring

receiver gain
compensation settings
pre/post processing
range ambiguity

ring down
enhancement
edge shadowing
shadowing
reverberation
mirroring

straight line
along the beam axis
amplitude related to the object struck
speed of sound in soft tissue

incorrect spectral flow
aliasing
range ambiguity
mirror imaging
speckle

when 3D is flattened to convert to 2D external echoes show up in the image

beam is not razor thin

section thickness
elevational resolution
partial volume artifact

linear array

due to poor elevational resolution

axial resolution does not change with depth

mirror

returning echoes do not return in a direct line

gives wrong depth

small amplitudes of sound waves interfering with each other

liver

specular reflections

incorrect texture

THI

if too bad you will not be able to see (fat encompassing)

liver - pathological degrees of fatty filtration

bouncy ball

multiple echos (strong reflectors) that appear on the screen

multiple bounces between two or more surfaces

always equal distance

normal declining intensity

ring down occurs with gas filled loops of bowel

tends to occur with dirty shadowing

squeezed out reverberation

reflectors close

and improper location caused by a change in propagation speed

caused by an adjacent strong reflector

diaphragm

when spectral doppler appears in both sides of the baseline

receiver gain too high

change angle
turn down receiver gain
change to higher frequency

single element

array transducers

weak beams that might otherwise be ignored hit a strong reflector.

the reflected echoes become misplaced.

subdicing the element

using dynamic apodization

weakening of the outside elements

listening is decreased on the side

system works on the assumption that sound will make a round trip through soft tissue in 13 μs/cm

closer

farther

object in front of another object causes the sound to travel faster or slower only on a portion of the second object. Part of the object usually the diaphragm is placed incorrectly and the object appears cut

aka split off artifact

aka split off artifact

caused by deep echoes from a previous pulse

object is placed closer and near the scan plane

Change frequency

change depth

change PRF

most systems will adjust PRF

shadows distal to strong attenuator

strong reflector bouncing all sound back imediately

strong absorber - no echoes left to return

reflections bouncing away when hitting a curved object - none return

usually occurs with bowels

shadowing when internal echoes are present

hyperechoic areas distal to a a weak attenuator

cysts

an unexpected increase in amplitude

increased enhancement at the focus

spacial compounding

aka enhancement

peaks cut off and place on bottom

speeding ticket

blood travels faster than the nyquist limit

insufficient spatial sampling

insufficient temporal sampling

raise PRF - chance of range ambiguity

increase doppler shift

shift baseline - cosmetic

switch to continuous wave

1/2 PRF

pulses per second

pulse length

pulse width

pulse width

interference

multiple reflections

refraction

multiple reflections

multiple reflections

side lobes

grating lobes

reverberation

resonance

speed error

high PRF

high attenuation

low attenuation

refraction

focusing

low PRF

high doppler gain

Doppler

transducer

electric shock

to prevent degradation of image

beam former and transducer acting together as a source of ultrasound

Doppler

lateral and axial resolution

sound output

detect gradual changes in system performance

sonographer

one a month

difficult

repeatable

slice thickness

beam width

detail resolution\depth accuaracy

measurement accuracy

dead zone

no attenuation properties

water

but sometimes no water

price

detail resolution

dynamic range

time gain compensation

contrast resolution

columns of simulated cysts

decrease depth (increases frame rate - improves temporal resolution)

rubber face & sides

plexiglass base

cosists of cystic, nylon other materials

gel - 1.54

rubber - 1.45

size and depth variation

axial resolution

smallest distance two pins can be seen as two separate pins

vertical registration / range accuracy

ability to display echoes at the proper depth or top line

Horizontal registration

the ability to position echoes in the their correct position along a line that is perpendicular to the ultrasound beam

lateral resolution

minimum distance two pins can be seen as two separate pins at a specific depth

grayscale / contrast resolution

the ability to discriminate between 2 different objects that have different shades of grey

the first one has size variation

the second one has depth variation

start by making TGC flat then increase gain from minimum value

the point the echo appears on screen is minimum sensitivity

is the point in which all the pins on an AIUM test object are displayed

is the range that echoes are barely visible to fully sensitivity

the minimum distance that two rods are displayed as two separate images at a specific depth

the depth at which the intensity is the highest and beam is the narrowest

this may be found using beam profiler or hydrophone

change in gain should result in a change in greyscale

the machines ability to display echoes at the proper depth

the accuracy of B mode, m mode and A mode on displaying the depth of reflectors

the machines ability to position echoes in the correct postiion perpendicular to the U/S beam

smallest distance at which two pins are displayed as two separate echoes in their position parallel to the beam

the effective position of the Doppler beam (penetration)

accuracy of measured flow

accuracy volume and flow speed

Blood tissue phantom

Doppler testing object

Doppler testing the mimicks blood

• sephadex in water
• polystyrene microspheres in water/glycerol
• water + machine cutting oil
• starch suspensions

Doppler test object uses controlled movement of strings

• moving solid object
• usually a string ultrasound
  • pulsatile motions
  • reverse motion

1. over estimates peak velocities
2. causes artifactual spectral broadening

an image face

medium

a flow conduit

pump

blood mimick

reservoir

complex

tube connects to a pump

pumps an echogenic fluid through out a known velocity simulates a stenosis.

small transducer on a hollow needle

large piezoelectric membrane with electrodes on both sides

Measure intensity

produce a waveform on an oscilloscope

PVDF

receive sound from all directions measure pressure at a given point within the beam in response to the varying pressure

the hydrophone produces a varying voltage

oscilloscope

bandwidth

frequency

PRF

duty factor

pressure amplitude

wavelength

SPL

intensity

Pulsed Spectral Doppler

Color Doppler

M mode

B mode

hydrophone

U/S is energy and any energy applied to human cells can cause change

risk benefit ratio

any possible benefit must outweigh possible risks

• whenever possible
  • increase benefit
  • decrease risk

Better equipment

• choose best greatest depth higher resolution - output gain will not need to be increased
• harmonic imaging
• appropriate transducer

Better operator

• knowledgable
  • formal
  • informal learning
• experience

decrease output/exposure

• use only when indicated
• minimize length of exam

decrease bioeffects

• lower exposure intensity
• decrease length of exam
• use low output imaging methods

Yes

medical device regulates by the FDA

cavitation

radiation

the amount of force that a beam exerts on an absorber or reflector

heating - attenuation of U/S is primary by heat

cavitation - motion of microbubbles

absorption

absorption involves conversion of U/S to heat

...

rises

rises

Thermal injury

tissue-bone interface

soft tissue adjacent to bone in a fetus

tissue heating

any exam that causes elevation in temperature of less than 2 degrees Celcius

an exam that causes an elevation of temperature of greater than 41 degrees Celcius

RBC to scatter

when the wavelength of the incident sound beam is smaller than the size of the RBC

CW causes higher temperature elevation

unfocused causes higher temperature elevation

* focused has a narrow beam and heat is easily dispersed

the production and behavior of bubbles in a liquid medium

Nucleation sites

tissue with gas bubbles

stable cavitation

transient cavitation

expand and contract

bubbles that oscillate in diameter with the passing pressure of a sound wave

bubbles don't burst

causes shear stress - cutting force

microstreaming

rapid rotational flow that occurs in intact blood vessels

cutting force

bubbles expand and collapse violently

bubbles burst

Collapse / inertial cavitation

destructive effects

shockwaves

light emissions

high temperature

heat production index -

deals with bioeffects caused by heating

acoustic output displayed

Motion production index -

deals with bioeffects caused by cavitation

degrees celcius

Thermal index - more accurate

720 mw/cm²

Thermal index soft tissue

Thermal index bone

Thermal index cranial

expected heating of 2 degrees or less

MI = derated peak rarefractional pressure / sqrt (U/S center frequency

.3 or less

37 degrees C

39 degrees C

37°C x 9/5 + 32 = 98.6°F

(98.6°F - 32) x 1.8 = 37°C

(98.6°F - 32) x 5/9 = 37°C