Artifact

anything that is not properly indicative of the structures or events

Benefits to artifacts

shadowing
enhancement

- tell the difference between solid and fluid
- characterize masses

Negative attributes of artifacts

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

Artifacts can be due to improper equipment settings

receiver gain
compensation settings
pre/post processing
range ambiguity

Artifacts can be due to ultrasound pysics

ring down
enhancement
edge shadowing
shadowing
reverberation
mirroring

Artifacts occur from assumptions

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

Doppler artifacts

incorrect spectral flow
aliasing
range ambiguity
mirror imaging
speckle

Slice thickness artifact

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

Cause of slice thickness artifact

beam is not razor thin

AKA slice thickness artifact

section thickness
elevational resolution
partial volume artifact

What transducers are prone to slice thickness artifacts?

linear array

due to poor elevational resolution

why are machines good at axial resolution?

axial resolution does not change with depth

what artifacts is similar to multipath?

mirror

What causes multipath?

returning echoes do not return in a direct line

Multipath

gives wrong depth

cause of acoustic speckle

small amplitudes of sound waves interfering with each other

Acoustic speckle

liver

specular reflections

incorrect texture

How to improve acoustic speckle?

THI

What are the problems associated with acoustic speckle?

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

liver - pathological degrees of fatty filtration

Reverberation

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 artifact

ring down occurs with gas filled loops of bowel

tends to occur with dirty shadowing

Comet trails

squeezed out reverberation

reflectors close

mirror image

and improper location caused by a change in propagation speed

caused by an adjacent strong reflector

What frequently causes mirror image?

diaphragm

Spectral mirroring

when spectral doppler appears in both sides of the baseline

what is a common cause of spectral doppler?

receiver gain too high

How do you fix spectral mirroring?

change angle
turn down receiver gain
change to higher frequency

What type of transducer produces side lobes?

single element

What type of transducer produces grating lobes?

array transducers

What causes lobes?

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

the reflected echoes become misplaced.

How do you get rid of lobes?

subdicing the element

using dynamic apodization

apodization

weakening of the outside elements

listening is decreased on the side

How do speed errors occur?

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

Where is the object placed if the speed is faster than 13 μs/cm?

closer

Where is the object placed if the speed is slower than 13 μs/cm?

farther

Split off artifact

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

step off artifact

aka split off artifact

cut artifact

aka split off artifact

What causes Range ambiguity?

caused by deep echoes from a previous pulse

what is range ambiguity?

object is placed closer and near the scan plane

How can you correct range ambiguity?

Change frequency

change depth

change PRF

most systems will adjust PRF

What is shadowing

shadows distal to strong attenuator

What causes shadowing?

strong reflector bouncing all sound back imediately

strong absorber - no echoes left to return

What causes edge shadowing?

reflections bouncing away when hitting a curved object - none return

Dirty shadowing

usually occurs with bowels

shadowing when internal echoes are present

What is enhancement

hyperechoic areas distal to a a weak attenuator

cysts

What causes enhancement

an unexpected increase in amplitude

focal enhancement

increased enhancement at the focus

What can you do to correct focal enhancement?

spacial compounding

what is thru transmission?

aka enhancement

Aliasing

peaks cut off and place on bottom

speeding ticket

blood travels faster than the nyquist limit

What can cause aliasing?

insufficient spatial sampling

insufficient temporal sampling

What can correct aliasing?

raise PRF - chance of range ambiguity

increase doppler shift

shift baseline - cosmetic

switch to continuous wave

What is the nyquist limit?

1/2 PRF

PRF

pulses per second

Artifact cause

axial resolution

pulse length

Artifact cause

lateral resolution

pulse width

Artifact cause

section thickness

pulse width

Artifact cause

speckle

interference

Artifact cause

reverberation

multiple reflections

Artifact cause

refraction

refraction

Artifact cause

multipath

multiple reflections

Artifact cause

mirror image

multiple reflections

Artifact cause

side lobes

side lobes

Artifact cause

grating lobes

grating lobes

Artifact cause

comet trail

reverberation

Artifact cause

ring down

resonance

Artifact cause

speed error

speed error

Artifact cause

range ambiguity

high PRF

Artifact cause

shadowing

high attenuation

Artifact cause

enhancement

low attenuation

Artifact cause

edge shadowing

refraction

Artifact cause

focal enhancement

focusing

Artifact cause

aliasing

low PRF

Artifact cause

spectral mirroring

high doppler gain

Which testing is the most challenging?

Doppler

What part of the system is most likely to break down?

transducer

electric shock

Why do we perform performance testing?

to prevent degradation of image

What do acoustic output testers evaluate?

beam former and transducer acting together as a source of ultrasound

what do flow testers evaluate?

Doppler

What do detail testers evaluate?

lateral and axial resolution

What so output testers evaluate?

sound output

What is the goal of system testers?

detect gradual changes in system performance

Who does the responsibility of quality assurance rest?

sonographer

How often should equipment be tested?

one a month

Perfecting these methods is _____ but must be done & must be ______.

difficult

repeatable

What do AIUM test objects test for?

slice thickness

beam width

detail resolution\depth accuaracy

measurement accuracy

dead zone

What is the main problem with AIUM test objects?

no attenuation properties

What is the AIUM test object usually filled with?

water

but sometimes no water

What is the main advantage of the AIUM test object

price

What does the tissue/cyst phantum test for?

detail resolution

dynamic range

time gain compensation

contrast resolution

What does the cyst phantom contain

columns of simulated cysts

How do you fix lateral smearing?

decrease depth (increases frame rate - improves temporal resolution)

Describe the constructions of the tissue phantum

rubber face & sides

plexiglass base

cosists of cystic, nylon other materials

What is the test phantom filled with?

gel - 1.54

rubber - 1.45

How would you test the dead zone?

How do you evaluate cysts

What does the cyst evaluation show?

size and depth variation

How would you evaluate axial resolution?

What does this test for?

axial resolution

smallest distance two pins can be seen as two separate pins

How would you evaluate vertical registration?

What does this test for?

vertical registration / range accuracy

ability to display echoes at the proper depth or top line

How would you evaluate Horizontal registration?

What does this test for?

Horizontal registration

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

How would you evaluate lateral resolution?

What does this test for?

lateral resolution

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

How would you evaluate grey scale?

What does this test for?

grayscale / contrast resolution

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

What is the difference between these two test for contrast resolution?

the first one has size variation

the second one has depth variation

Minimum sensitivity

start by making TGC flat then increase gain from minimum value

the point the echo appears on screen is minimum sensitivity

Normal sensitivity

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

Sensitivity

is the range that echoes are barely visible to fully sensitivity

lateral resolution

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

Focal zone

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

this may be found using beam profiler or hydrophone

Dynamic range / greyscale

change in gain should result in a change in greyscale

vertical registration / range accuracy

the machines ability to display echoes at the proper depth

depth calibration

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

horisontal calibration

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

longitudinal resolution

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

What do the Doppler performance tools evaluate?

the effective position of the Doppler beam (penetration)

accuracy of measured flow

accuracy volume and flow speed

What do we use for Doppler testing?

Blood tissue phantom

Doppler testing object

What is a Blood tissue phantom

Doppler testing the mimicks blood

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

What is a Doppler testing object?

Doppler test object uses controlled movement of strings

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

What are the disadvantages of the Doppler string phantom?

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

What does a Blood tissue phantom contain?

an image face

medium

a flow conduit

pump

blood mimick

reservoir

How does a Blood tissue phantom work?

complex

tube connects to a pump

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

What is a microprobe?

small transducer on a hollow needle

What is a hydrophone?

large piezoelectric membrane with electrodes on both sides

What are microprobe and hydrophone used for?

Measure intensity

produce a waveform on an oscilloscope

What do microprobe and hydrophone use as a piezoelectric material?

PVDF

How do microprobe and hydrophone work?

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

What is the voltage produced by a hydrophone displayed on?

oscilloscope

What does an oscilloscope display?

bandwidth

What do hydrophones measure?

frequency

PRF

duty factor

pressure amplitude

wavelength

SPL

intensity

Which type of U/S produces the greatest acoustic output?

Pulsed Spectral Doppler

Color Doppler

M mode

B mode

Intensity and output indexes have already been copulated using a ______.

hydrophone

What is the #1 assumption of risk?

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

What is the rule of U/S?

risk benefit ratio

any possible benefit must outweigh possible risks

• whenever possible
  • increase benefit
  • decrease risk

How do we increase benefit?

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

How do we decrease risk?

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

Do you need a Doctors orders for an ultrasound exam?

Yes

medical device regulates by the FDA

What are the two types of mechanical bioeffects?

cavitation

radiation

What is radiation?

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

What are the two types of bioeffects?

heating - attenuation of U/S is primary by heat

cavitation - motion of microbubbles

What is heating primarily due to?

absorption

Why does absorption cause heating?

absorption involves conversion of U/S to heat

U/S produce a temp. rise as it propagates through tissue

What happens to heat when intensity goes up?

rises

What happens to heat when frequency goes up?

rises

What can Rayleighs scattering cause?

Thermal injury

Where are temperature elevations more likely to occur?

tissue-bone interface

What area is of great concern to thermal injury?

soft tissue adjacent to bone in a fetus

What is SPTA associated with?

tissue heating

What exam can be used without fear?

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

What exam may cause harm in a fetus?

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

What does Rayleigh scattering cause?

RBC to scatter

What is Rayleigh scattering?

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

Which causes higher Temperature elevation Pulsed wave or Continuous wave?

CW causes higher temperature elevation

Which causes higher Temperature elevation Focused or unfocused?

unfocused causes higher temperature elevation

* focused has a narrow beam and heat is easily dispersed

What is cavitation?

the production and behavior of bubbles in a liquid medium

Where would a sound wave may cause cavitation?

Nucleation sites

tissue with gas bubbles

What are the two types of cavitation?

stable cavitation

transient cavitation

What is stable 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

What does shear force cause?

microstreaming

What is microstreaming?

rapid rotational flow that occurs in intact blood vessels

What is shear stress?

cutting force

What is transient cavitation?

bubbles expand and collapse violently

bubbles burst

What is another name for transient cavitation?

Collapse / inertial cavitation

What does transient cavitation cause?

destructive effects

shockwaves

light emissions

high temperature

What is Thermal index?

heat production index -

deals with bioeffects caused by heating

If a machine can exceed thermal or mechanical indexes what must be?

acoustic output displayed

What is Mechanical index

Motion production index -

deals with bioeffects caused by cavitation

What is the thermal index measured in?

degrees celcius

Which display is preferred SPTA or Thermal index?

Thermal index - more accurate

What should SPTA be below?

720 mw/cm²

TIS

Thermal index soft tissue

TIB

Thermal index bone

TIC

Thermal index cranial

TI of 2 or less =

expected heating of 2 degrees or less

Mechanical index formula

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

What is threshold for MI?

.3 or less

What is normal body temperature?

37 degrees C

What is the max body temp rise?

39 degrees C

C to F

37°C x 9/5 + 32 = 98.6°F

F to C

(98.6°F - 32) x 1.8 = 37°C

(98.6°F - 32) x 5/9 = 37°C