Test 2 ppts Flashcards by Miss Nancy

hydrophone also called a ____________-

microprobe

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Device used to measure the acoustic
output of an ultrasound imaging
instrument

hydrophone/ microprobe

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What does hydrophone do

Measures radiation pressure from
transducer.

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Voltages displayed on an ______________

oscilloscope

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Acoustic pressure can be measured at
specific locations within the sound
beam, the sound intensity distribution
can be plotted.

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how many type of hydrophones are there

◦ Used in ultrasound: A small transducer element
is mounted on the end of a hollow needle that is
calibrated so intensities and other output
measurements can be derived
◦ Another type of a hydrophone consists of a
large piezoelectric membrane with small
metallic electrodes on both sides but in this
model only a small area in the center of the
membrane is pressure sensitive (membrane is
made of polyvinylidene fluoride), not preferred

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From the oscilloscope display……. what can be determined?

period,
pulse repetition period,
pulse duration

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From the oscilloscope computations…… what can be calculated

frequency,
PRF,
duty factor,
pressure
amplitude,
wavelength,
SPL,
intensities (=power(w)/area(cm2))

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Measurement of acoustic output

intensity

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____________- the quantity of energy
absorbed per unit mass of tissue

Dose

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Used to describe the “dose” of
ultrasound

intensity

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 No known bio-effects below (Max.
allowed)
______________ SPTA unfocused
 1 W/cm2 SPTA focused

100 mW/cm2

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 No known bio-effects below (Max.
allowed)
____________ SPTA focused

1 W/cm2

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Range of intensities in diagnostic U/S=

0.002 W/cm2 - 0.5 W/cm2

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Range of intensities in therapeutic U/S=

0.5 W/cm2 - 2.0 W/cm2

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biological effects depend on what 3 things

 The intensity of sound
 Rate of energy flow per unit area &
 The length of time during which
the ultrasound is delivered.

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temporal dependence

 As transducer emits pulses, it causes
large fluctuations of intensity in the
region through which the pulses
propagate
 Each pulse consists of multiple cycles
that produce intensity variations
 Variations in relation to TIME

 Temporal Peak (TP) - the maximum
intensity
 Pulse average (PA) - the intensity
averaged over the duration of a single
pulse
 Temporal average (TA) - the intensity
averaged over the entire pulse

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 ______________ - the maximum
intensity

Temporal Peak (TP)

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 ____________ - the intensity
averaged over the duration of a single
pulse

Pulse average (PA)

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 ______________ - the intensity
averaged over the entire pulse

Temporal average (TA)

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Variations in relation to SPACE

spatial dependence

 Spatial Peak (SP) - maximum intensity
of all measured values within the
sound field
 Spatial Average (SA) - average
intensity over the cross-sectional area
of the beam

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 ____________ - maximum intensity
of all measured values within the
sound field

Spatial Peak (SP)

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 __________ - average
intensity over the cross-sectional area
of the beam

Spatial Average (SA)

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SPTP
SPTA
SPPA
SATP
SATA
SAPA

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____________________________- also called the SP/SA factor- is a unitless ratio that describes the distribution of an ultrasound beam in space. It is the spatial peak intensity divided by the spatial average intensity.

Beam Uniformity Coefficient (BUC)

SP/SA Factor =

spatial peak intensity (W/cm sq)/spatial average intensity (W/cm sq)

 SP/SA is analogous to the duty factor, except it relates to space rather then time.  SP/SA has min value of ________, and a max value greater than ___________. UNITLESS!

1.0 1.0  *Note: The closer the SP/SA factor is to 1, the more even or homogeneous the beam is. The larger the SP/SA factor, the brighter is the center of the beam compared with its edges.

Most frequently used intensity is the _______________-

SPTA  Approximated by the ratio of ultrasonic power to the cross- sectional area of the beam  Intensity is determined by the pulse length and the degree of focusing

Ratio of acoustical power produced by the transducer to the power required to raise the temperature in tissue 1 C

Thermal index

TI = 1.0 then possible elevation in temperature is _________

1 degree celsius

Ultrasonic biological effects produced by are _________________________-.

heat and cavitation

Most common result of high intensity U/S = _____________________.

heat

Value computed from the peak rarefactional pressure and the frequency

mechanical index Related to the likelihood of producing cavitation

Routine, periodic evaluations of the ultrasound system and peripherals to guarantee optimal imaging quality

quality assurance

2 types of tissue phantoms

Tissue-equivalent phantoms Tissue-mimicking test objects

which tissue phantom Can demonstrate scattering and attenuation properties

Tissue-equivalent phantoms -Mimics soft tissue -Usually made of graphite-filled gel or urethane -Conduction velocity is 1540 m/s and attenuation coefficient is similar to soft tissue -Phantom is imbedded with strategically located pins as well as structures that mimic cystic and solid masses

what are the three Tissue-mimicking test objects Provide some specific measure of instrument performance

AIUM 100mm Test Object Beam profile/slice thickness test object Particle image resolution test object

An test object with an array of strategically located pins or nylon fibers placed in it By scanning the object, the accuracy and performance of the ultrasound machine may be evaluated Has a propagation speed similar to that of soft tissue, however, it does not have similar attenuation properties Lack of similarity to soft tissues limits the evaluation of attenuation or gray scale.

AIUM 100mm Test Object

The slice thickness is a measure of the beam geometry in the plane that is perpendicular to the imaging plane.  This important measurement is not obtained with other more traditional test objects.  Increased slice thickness diminishes spatial resolution and reduces the ability of a system to distinguish small, low contrast lesions.

Beam profile/slice thickness test object

 PIRTO  Filled with small polystyrene spheres that are randomly distributed in a low attenuation, low-scatter gel.  Evaluates detail resolution throughout the image.

Particle image resolution test object

2 doppler system test

1) String test objects 2) Flow phantoms

Echoes from a vibrating string imitate reflections from red blood cells. Useful in checking the accuracy of calculated flow speeds on spectral displays Does not give a flow profile because the Doppler shifted echoes are stronger than those encountered in blood

1) String test objects

Shows a physiologic model of flow in a tissue-equivalent environment Phantom can be used to assess the accuracy of pulsed, continuous wave, and color systems Has problem with bubbles and non-uniform flow

2) Flow phantoms

Measures certain parameters of ultrasound imaging to ensure sonographic depiction is accurate ➢Image uniformity ➢Detail resolution ➢Contrast resolution ➢Depth of Penetration ➢Dynamic range ➢Compensation operation ➢Range accuracy

performance measurements

dead zone

DEPTH CALIBRATION

resolution

measurements

contrast resolution

MECHANISMS OF ACTION BETWEEN ULTRASOUND AND BIOLOGICAL CELLS AND TISSUES

bioeffects

MECHANISMS BY WHICH ULTRASOUND ENERGY CAN PRODUCE DAMAGE OR INJURY

* THERMAL (HEAT) * CAVITATION

* _________________ IS OCCURRING THE ENTIRE TIME YOU ARE SCANNING

attenuation * ATTENUATION OCCURS DUE TO ABSORPTION * ABSORPTION - CONVERSION OF ULTRASOUND ENERGY INTO HEAT

* MAXIMUM HEATING IS RELATED TO THE _____________ INTENSITY

SPTA * THE CURRENT FDA REGULATORY LIMIT IS 720MW/CM2 SPTA

* AMOUNT OF HEAT PRODUCED DEPENDS ON THE ________________________________

APPLIED INTENSITY , THE FREQUENCY OF SOUND, BEAM FOCUSING

* HEATING DECREASES/INCREASES AS INTENSITY OR FREQUENCY INCREASES

increases

* ______ INTENSITY (increase POWER, decrease BEAM WIDTH)

increase

* __________ FREQUENCY (increase ATTENUATION COEFFICIENT) * ABSORPTION COEFFICIENT IS HIGHEST IN BONE AND LOWEST IN FLUID

increase

TEMPERATURE RISES ___________ ARE CONSIDERED SIGNIFICANT,

greater than 2 degree Celsius A 2-4 DEGREE RISE IN TESTICULAR TEMPERATURE CAN CAUSE INFERTILITY

* TIS vs TIB

* TIS – THERMAL INDEX IN SOFT TISSUE * TIB – THERMAL INDEX IN BONE

*________________—A SMALL BUT MEASURABLE FORCE EXERTED BY A SOUND BEAM ON TISSUES

RADIATION FORCE

2 types of cavitation

* STABLE * TRANSIENT

THE INTERACTION OF SOUND WAVES WITH MICROSCOPIC, STABILIZED GAS BUBBLES IN TISSUES.

CAVITATION

cavitation BUBBLES ARE KNOW AS

GASEOUS NUCLEI

A COMBINATION OF _______________ AND ______________ IS MOST LIKELY TO CAUSE CAVITATIONS RESULTING IN TISSUE DAMAGE

low freq high intensity

stable vs transient cavitation

stable..........................transient lower MI levels...........higher MI levels expand & contract..........so large they burst ...................................................cause temp change & destructive effects

MECHANICAL INDEX FORMULATED TO ASSIST USERS IN EVALUATING LIKELIHOOD OF _________________

CAVITATION

* THRESHOLDS FOR CAVITATION IN SOFT-TISSUE AND BODY LIQUIDS HAS BEEN DETERMINED AND ARE RELATED TO TWO SOUND WAVE CHARACTERISTICS

* PEAK RAREFACTIONAL PRESSURE * LOWER FREQUENCY

* THERE IS A GREATER LIKELIHOOD OF CAVITATION BIOEFFECTS AND A HIGHER MI WITH

* ADDITIONAL NEGATIVE PRESSURE * LOWER FREQUENCY

NO INDEPENDENTLY CONFIRMED SIGNIFICANT BIOLOGICAL EFFECTS IN MAMMALIAN TISSUE EXPOSED INVIVO TO -UNFOCUSED ULTRASOUND WITH UNFOCUSED BEAM INTENSITIES BELOW 100 MW/CM2 -FOCUSED BEAM INTENSITIES BELOW 1 W/CM2 -THERMAL INDEX OF LESS THAN 2 -MECHANICAL INDEX OF .3

IN ORDER OF SPTA INTENSITY: * B-MODE → M-MODE → COLOR DOPPLER → PULSE-WAVE DOPPLER (HIGHEST)

* CURRENT FDA REGULATORY INTENSITY LIMIT FOR ISPTA IS 720 MW/CM2 * FETAL DOPPLER IMAGING HAS BEEN APPROVED BY THE FDA

THE GENERAL RANGE OF INTENSITIES IN DOPPLER ULTRASOUND IS

0.2 MW/CM2—400 MW/CM2

Note: refraction is considered a propagation and attenuation artifact However…attenuation does not cause edge shadowing, edge shadowing is caused by refraction

how to improve axial resolution artifact ps- its equal to 1/2 length of pulse

use higher freq transducer

how to improve lateral resolution artifact

Improved by focusing or utilizing a higher frequency transducer

Appearance of false debris in echo-free areas; presentation of cystic objects as echogenic * Caused by echoes being received from structures above or below the beam’s main axis * Beam width is thicker than the structure being imaged

section thickness

* Creates a texture on an image that doesn’t correspond to the actual tissue texture. * Appears close to the transducer typically

acoustic speckle

* Appears as multiple, equally spaced reflections * Caused by two or more strong reflectors lying in the path of a pulse * Sound “ping-pongs” back and forth between the reflectors * Reflections are placed beneath the real reflector at intervals equal to the distance between the transducer and the real reflector

reverberation

* Beam changes direction when passing from one media to another * Caused by difference in Prop Speeds between two media.

refraction * Shadowing from edge-refraction can also hide information (attenuation type)

* Pulse glances off a second structure on the way to or from the primary reflector * Caused when the path lengths to and from a reflector are different * Time delay causes echo to be positioned deeper than true anatomic structure. * Causes weak “acoustic noise” that muddies the image; similar to speckle

multipath

* Displays structures that are on one side of a strong reflector on the other side as well * Sound bounces off a strong reflector in its path * Structure reflects the pulse towards another object * When beam strikes object, some of energy is reflected back to original reflector and then back to transducer

mirror image artifact

* Single element transducer * Small beams propagate in directions different from the primary beam * Weaker than the primary beam * Does not normally produce echoes that are imaged * Reflectors appear in improper locations

side lobes

* Produced by array transducers * Off-axis waves produced as a result of the spacing of the active elements within an array * Improper locations on the image * Uncommon due to process called “sub-dicing” which is performed during transducer manufacturing. * Subdicing is the technique of dividing normal crystal elements into smaller elements

grating lobes

technique of dividing normal crystal elements into smaller elements

subdicing

* A particular form of reverberation * A series of closely spaced reverberations, forms a discrete echo pattern. * Caused by two or more strong reflectors (high impedance) that are close together in a medium with a high propagation speed

comet tail

* Like a comet tail artifact but discrete echoes cannot be identified. * Appears as a bright, long, linear echo extending downward from a structure. * Caused by a resonance phenomenon associated with resonating after bombardment by ultrasound pulse

Ring Down

* VERY common to see these artifacts on US image of the: * gallbladder where air bubbles in a fluid-filled duodenum are able to resonate. * Also common in abscess or in cases of pneumobilia * Common with surgical clips (internal staples) or needle tip during biopsy. * For the boards: You MUST describe what you see (Ringdown vs. Comet tail) and what is causing it in the image.

Reverberation Artifacts

Pulses are sent out before previous echoes are received

RANGE AMBIGUITY

Shadowing occurs behind the edges of objects that are not necessarily strong or weak attenuators

EDGE SHADOWING (REFRACTION) like with baby heads

Test 2 ppts Flashcards

output and performance measurements, bioeffects