A r t i f a c t s
Download
1 / 96

A r t i f a c t s - PowerPoint PPT Presentation


  • 98 Views
  • Uploaded on

A r t i f a c t s. Artifacts. - are echoes that appear on the image but do not have a true correspondence to an anatomical structure. It is important to recognize them so that they may be ignored, eliminated or made useful. Artifacts. Not real Missing information Improperly represented

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' A r t i f a c t s' - quintessa-knox


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

Artifacts
Artifacts

- are echoes that appear on the image but do not have a true correspondence to an anatomical structure.

It is important to recognize them so that they may be ignored, eliminated or made useful.


Artifacts1
Artifacts

  • Not real

  • Missing information

  • Improperly represented

    • Location

    • Size

    • Brightness

    • Shape


Causes of artifacts
Causes of Artifacts:

  • Ultrasound equipment assumptions

  • Equipment malfunction or design

  • Operator assumptions and/or errors


Ultrasound equipment assumptions
Ultrasound Equipment Assumptions

  • Sound travels in a straight line

  • Reflections are produced only by structures along the main axis of the sound beam

  • Intensity of an echo corresponds to a reflector’s scattering strength

  • Sound travels directly to & from a reflector

  • Imaging plane is thin

  • Sound travels at exactly 1540 m/sec


Effects of artifacts
Effects of Artifacts

  • Measurement errors can occur because the equipment is calibrated to 1540 m/s (range ambiguity)

  • Interpretation errors can occur due to artifacts (localizing, cyst vs. solid, turbulence)

  • Aids in determining cyst vs. solid, (enhancement & shadowing)


Artifacts associated with resolution
Artifacts Associated with Resolution

  • Axial resolution

  • Lateral resolution

  • Acoustic speckle

  • Section thickness


Axial resolution
Axial Resolution

- the ability to distinguish 2 structures that are in close proximity to each other from anterior to posterior

  • Multiple structures along the main axis of the beam appear only as 1 reflector on the image

  • Contributes to incorrect representation of size & shape of interfaces & to missing interfaces


Lateral resolution
Lateral Resolution

  • resolution is the minimum distance of 2 side-by-side structures that can be separated & still produce 2 distinct echoes

  • can contribute to incorrect representation of size & shape of interfaces & to missing interfaces


Acoustic speckle
Acoustic Speckle

- is produced by wavelet interference resulting in image degradation

  • Appears as grainy images & spectral displays

  • Dominates near the face of the transducer

  • Interferes with the ability of the system to detect low-contrast objects


Section thickness
Section Thickness

  • AKA slice thickness, out-of-plane focusing, elevational resolution, or width focusing

  • is the thickness of the scanned tissue volume perpendicular to the scan plane

  • Extra echoes appear in the image making a structure more echogenic than it really is


Artifacts associated with propagation
Artifacts Associated with Propagation

  • Reverberation

  • Mirror image artifact

  • Multipath artifact

  • Refraction artifacts

  • Side lobes

  • Range ambiguity

  • Propagation Speed Error Artifacts


Reverberation artifacts
Reverberation Artifacts

  • appear as ‘echoes’ of echoes

  • A portion of the sound beam reverberates between 2 highly reflected surfaces sending back multiple echoes from the same 2 interfaces

  • Appear as multiple, equally-spaced reflections on the image, decreasing in intensity; however somewhat compensated by the gain control

  • Only the first two reflections closest to the transducer are real



  • Comet tail
    Comet-tail

    - is a form of reverberation artifact caused by 2 closely spaced strong reflectors in a soft tissue medium with a high propagation speed (surgical clips) & appear as multiple small bands



    Ring down artifact
    Ring-down Artifact

    - is another type of reverberation that is produced by small gas bubbles, such as air & appear as a single, long, strong echo behind the reflector




    Mirror image artifact
    Mirror Image Artifact

    - occur when a structure is located in front of a highly reflective surface (i.e.. pleura, diaphragm,& bowel) causing the anatomy to be reproduced or duplicated on the other side of the interface

    • Reflector & object (true & false image) are equidistant from strong reflector

    • Mirror image duplicate always appears deeper than the true anatomic structure




    Multipath artifact
    Multipath Artifact

    - occurs when the beam strikes an interface at an angle & is reflected from a 2nd (or 3rd) interface before being reflected to the transducer resulting in incorrect axial location of an interface due to  time in reaching the receiver


    Refraction artifacts
    Refraction Artifacts

    - are caused be refracted reflections to appear in improper locations

    • AKA - ghost image artifact

    • Appears as a replication of the anatomical region to be placed side-by side to the real anatomy



    Edge refraction
    Edge Refraction

    - produces shadowing at the edges of structures that are large compared to the width of the ultrasound beam because the refracted beam diverged to much & do not appear as echoes on the image from the area they would have demonstrated reflections from.

    Region beyond the refraction appear anechoic



    Side lobes
    Side Lobes

    • off the main axis of single crystal transducers

    • can introduce positioning artifacts of highly reflecting structures appearing as a duplicate of the true reflector lateral to & at the same depth as the anatomy

    • Array transducers produce off-axis grating lobes (these beams are stronger than side lobes) that can also cause reflectors to be displayed in improper locations.

      • Sub-dicing has for most part eliminated this artifact


    Range ambiguity artifact
    Range Ambiguity Artifact

    - is the misplacement of an interface when the assumption “each echo is derived from the most recent pulse” is violated

    The structure is placed closer to the surface than it should be


    Propagation speed error artifacts
    Propagation Speed Error Artifacts

    • If the speed of sound > 1540 m/s, reflector is placed too close to the transducer

    • If the speed of sound < 1540 m/s, reflector is placed too far from the transducer.

      Example:

      lesion in the posterior liver may cause the diaphragm posterior to the lesion to be displaced too far from the transducer


    Artifacts associated with attenuation
    Artifacts Associated with Attenuation

    • Acoustic shadowing

    • Enhancement


    Acoustic shadowing
    Acoustic Shadowing

    - the absence or reduction of echo intensity distal to a reflector

    • caused by the sound beam passing through a highly attenuating structure (i.e. calcium, calcified plaque)

    • useful in diagnosing, e.g., cholelithiasis

    • harmful by not demonstrating disease due to lack of echo reflection





    Enhancement
    Enhancement

    - when the sound beam passing through an area of very low attenuation (i.e. fluid) causes an increase in echo brightness distal to the structure, especially when compared to the same type of tissue on either side

    True tissue enhancement is useful in distinguishing cystic from solid masses





    Horizontal enhancement
    Horizontal Enhancement

    • horizontal banding produced from focusing

    • due to the increased intensity of the beam in the focal zone

      Adjust the TGC to correct this artifact


    Banding artifact
    Banding Artifact

    - can be produced by improper TGC settings

    Adjust the TGC to correct this artifact


    Artifacts associated with doppler color flow instrumentation
    Artifacts Associated with Doppler & Color Flow Instrumentation

    • Aliasing

    • Flash artifact

    • Color bleed

    • Color noise


    Aliasing
    Aliasing Instrumentation

    - occurs when the Doppler shift frequency exceeds ½ PRF

    Correct by  the PRF or  the Doppler shift frequency


    Aliasing color
    Aliasing - Color Instrumentation


    Flash artifact
    Flash Artifact Instrumentation

    - the sudden burst of color that encompasses the frame caused by anatomical motion changing the interface position

    Can be suppressed by  the color filter,  the persistence & reducing the width of the color field of view


    Color bleed
    Color Bleed Instrumentation

    - the extension of color beyond the region of flow to the adjacent tissue

    Eliminate by  the transmit power&  color gain


    Color noise
    Color Noise Instrumentation

    - is random variation in signal detection causing areas with no flow to be color encoded

    Eliminate by  the transmit power&  color gain


    Color noise1
    Color Noise Instrumentation


    Equipment artifacts
    Equipment Artifacts Instrumentation

    Electronic noise (from the equipment itself or other electrical equipment) may cause low-level echoes to appear as vibrating vertical bands on the image filling in cystic structures and affect contrast resolution.



    Quality control of ultrasound instruments1
    Quality Control of Ultrasound Instruments Instrumentation

    • Quality Control (QC) is the routine, periodic evaluation of the ultrasound unit and transducers and is not to be confused with QA

    • Quality Assurance – QA are all the programs designed to render a a diagnostic exam to the patient in the best way possible. This includes: scheduling, patient preparation, report generation & QC


    Quality control
    Quality Control Instrumentation

    • Detects image quality problems and assures proper operation of the equipment before it effects imaging or causes equipment failure.

    • Ensures that the diagnostic quality of the ultrasound image is constant and maintained


    Quality control1
    Quality Control Instrumentation

    • A file of the following documents should be maintained for each unit:

    • QA tests results

    • problem documentation & f/u service report

    • (PM) reports

    • original equipment PO

    • equipment specs

    • warranty


    Quality control2
    Quality Control Instrumentation

    • Reports are necessary for hospital and/or department accreditation as well as to document the need to replace equipment


    Parameters to be evaluated
    Parameters to be Evaluated Instrumentation

    • Axial resolution

    • Lateral resolution

    • Vertical (depth) calibrations

    • System sensitivity

    • Horizontal calibrations

    • Dead zone

    • Registration


    Equipment for evaluation of parameters
    Equipment for Evaluation Instrumentation of Parameters

    Various test objects & test phantoms are:

    • AlUM 100 mm test object

    • Tissue phantoms

    • Dopplerphantoms


    Alum 100 mm test object
    AlUM 100 mm Test Object Instrumentation

    - composed of a series of .75 mm diameter stainless steel rods arranged in groups. These are contained in a transparent plastic tank filled with a mixture of alcohol and water equal to a propagation speed of 1540 m/s at room temperature.


    Axial resolution1
    Axial Resolution Instrumentation

    -determined by scanning the middle rod group (E) from the top

    • Rods are placed in an oblique plane and are separated by 1, 2, 3, 4, & 5 mm.

    • Smallest separation of the 2 closest rods seen represents the axial resolution of the transducer


    Alum 100 mm test object1
    AlUM 100 mm Test Object Instrumentation


    Lateral resolution1
    Lateral Resolution Instrumentation

    - determined by scanning the unevenly spaced vertical rod group (C) from the side or by measuring the width of the echo from each of the six vertical equidistant rods.

    The smallest separation seen represents the lateral resolution of the transducer.

    The unevenly spaced rods are spaced 3, 5, 10, 15, 20, & 25 mm apart.


    Depth calibration
    Depth Calibration Instrumentation

    - performed by scanning the vertical (A) & horizontal (B) equidistant rods from the top. Each rod is separated by 20 mm.

    The measured distance between the rods tests the accuracy of the electronic calipers& the distance calibration


    AlUM 100 mm Test Object Instrumentation


    Dead zone
    Dead Zone Instrumentation

    - (ring down) is created by reverberation within the transducer & is determined by scanning the uppermost rod group (D).

    • These rods are spaced at 2, 4, 6, & 8 mm from the top surface of the test object.


    System sensitivity
    System Sensitivity Instrumentation

    • is a measure of the weakest echo signal that can be visualized. Determined by the gain setting, with no TGC, at which a particular rod produces an echo. The bottom rod group (B) of 6 vertical equidistant rods is used.

      System sensitivity can  with a damaged transducer or malfunction of the unit. If more than a dB of gain is required to see the same rod, the sensitivity is  & a service call should be made.


    Recording device
    Recording Device Instrumentation

    The gray scale display on the film should be matched against the gray scale bar on the monitor.

    Adjustments should be made to the recording device if the bars do not match. (This assumes the display monitor is properly adjusted.)


    Tissue phantoms
    Tissue Phantoms Instrumentation

    • contain a tissue-mimicking medium that has similar attenuation properties and propagation speeds as soft tissue and contain mock cysts and lesions of various diameters as well as several groups of fibers


    Tissue phantoms1
    Tissue Phantoms Instrumentation

    • Evaluates the ability of a system to resolve cystic & solid lesions (contrast resolution).

    • Fibers are used to evaluate axial and lateral resolution and depth calibration.

    • Test phantoms are temperature sensitive


    Doppler phantoms
    Doppler Phantoms Instrumentation

    -assess the accuracy of the Doppler measurement

    • Contain a tube that is connected to a pump that pushes fluid through the tube at adjustable velocities. Spectral Doppler tracings & color flow images can be obtained

      • simulated vessels are positioned at a variety of angles to the imaging surface


    Doppler phantoms1
    Doppler Phantoms Instrumentation

    • Another type involves a string that moves while immersed in a water bath using echoes from the vibrating string to imitate reflections from blood cells.

      • Allows for accurate assessment of the flow velocity under non-clinical conditions

      • Can be used for evaluating flow angle indicators, Doppler sample volumes, wall filters, and sensitivity


    Suggested maintenance schedule

    Daily Instrumentation

    Clean transducers and equipment

    Weekly or bi-weekly

    Check cables & connectors; clean fan filters

    Monthly

    QA on ultrasonic test phantoms and documentation of images

    2 -3 times per year

    Service personnel perform diagnostic tests on the transducers & equipment

    Suggested MaintenanceSchedule


    Bioeffects and safety
    Bioeffects and Safety Instrumentation


    Acoustic exposure
    Acoustic Exposure Instrumentation

    - describes the amount of acoustic energy the patient receives

    Prudent use of diagnostic ultrasound involves ways to  patient exposure.

    Perform an exam when medically indicated, with proper equipment settings, & minimal exposure times.


    The amount of acoustic exposure is determined by the intensity of the sound beam & the amount of scanning time, reducing either reduces the acoustic exposure to the patient

    • The output control will determine the intensity of the ultrasound beam.

    • Use high receiver gain & low output power to minimize patient exposure; low output power reduces the intensity of the beam


    Intensities are important
    Intensities are Important intensity of the sound beam

    • for discussing bioeffects

      Intensity is not uniform over space nor time; this is why several intensities are used


    Determining the intensity of the sound beam
    Determining the Intensity of the Sound Beam intensity of the sound beam

    There are various methods used requiring specialized equipment & is usually done by the manufacturer

    • radiation force balance or scale

    • hydrophone probe


    Typical values for diagnostic equipment
    Typical Values for Diagnostic Equipment intensity of the sound beam

    • SPTA values

    • Power values


    Spta values
    SPTA Values intensity of the sound beam

    • found in the operator’s manual

      Typical values include:

      gray scale: 1-200 mW/cm2

      M-mode: 70-130 mW/cm2

      PW Doppler: 20-290 mW/cm2

      color Doppler: 10-230 mW/cm2


    Power values
    Power Values intensity of the sound beam

    gray scale: 1-20 mW

    M-mode: 1-5 mW

    PW Doppler: 2-20 mW

    color Doppler: 2-20 mW


    Acoustic output labeling standard
    Acoustic Output Labeling Standard intensity of the sound beam

    Acoustic output indices serve as risk indicators.

    Mechanical index & Thermal index are parameters selected because they are relative to potential biologic effects of diagnostic ultrasound. These indices are displayed on screen in real-time.

    • If the index value < 1, the possibility of adverse effects or cavitation is low.

    • If the index value >1, one must weigh the risks against the benefits.


    Mechanical index mi
    Mechanical Index (MI) intensity of the sound beam

    - the parameter that describes the acoustic output in terms of the likelihood of cavitation, Homogeneous soft tissue model is used in determining the mechanical index.

    • Cavitation is the interaction of the sound waves when dissolved gases form microscopic gas bubbles in the tissue. The micro bubbles collapse causing high temperature, membrane tearing & free radical formation.Cavitation is one mechanism that can produce biological effects.


    Us induced cavitation
    US-induced Cavitation intensity of the sound beam

    • No confirmed biological effects have been reported in mammalian tissue that does not contain well-defined gas bodies

    • Related to the temporal peak (SPTP); intensities > 3300 W/cm2 can induce cavitation


    2 forms of cavitation
    2 Forms of Cavitation intensity of the sound beam

    • stable cavitation - bubbles tend to grow and oscillate. Shear stressing and microstreaming may be produced in surrounding fluid

    • transient cavitation - bubbles expand and collapse violently causing the bubble to implode


    Cavitation threshold
    Cavitation Threshold intensity of the sound beam

    - predicted by the ratio of the peak rarefactional pressure to the square root of the frequency. (SPTP : f )

    MI  as you  the output on the unit, ( the peak rarefactional pressure).

    MI  as you  frequency.


    Thermal index ti
    Thermal Index (TI) intensity of the sound beam

    - the ratio of the acoustic power of the transducer to the power required to raise tissue temperature by 1° C

    US system calculates the TI by analyzing: transducer frequency, acoustical power, beam area, absorption, & attenuation properties of the tissue & its thermal properties.


    3 thermal indices
    3 Thermal Indices intensity of the sound beam

    Developed for application to different examinations & corresponding to soft tissue include:

    • TIS - thermal index in soft tissue

    • TIB - thermal index in bone

    • TIC – thermal index in cranial bone


    When sound is absorbed the energy is converted into heat so
    When sound is absorbed, the energy is converted into heat, so…

    • In Dx. US, heating of the tissue is usually very small, due to the amount of off time in the pulse repetition period (PRP)

    • Maximum heating is related to the SPTA intensity

    • These effects can be reduced by not prolonging scanning times


    Alum statement on clinical safety
    AlUM so…Statement on Clinical Safety

    Recommends prudent use of ultrasound in the clinical environment

    The principle of ALARA

    (As Low As Reasonably Achievable) is used to evaluate whether the conditions of use are prudent


    Alara means
    ALARA so…Means

    The conscientious Sonographer minimizes:

    • the exposure time to the patient

    • the intensity

    • type of ultrasound

      Use the lowest quantities while still achieving quality


    Bioeffects
    Bioeffects so…

    • Information comes from several sources

    • Scientists produce effects on tissue and compare intensities required to produce the effect with the output intensity of the ultrasound units


    Research methods
    Research methods so…

    • In vivo

    • In vitro

    • Epidemiological studies


    In vivo studies
    In Vivo Studies so…

    - experiments on animals & plants

    Animal studies have demonstrated various effects in small mammals following US exposure: fetal weight reduction, fetal anomalies, and fetal death. Most effects vary with amount of exposure time.


    In vitro studies
    In Vitro Studies so…

    - are experiments in petri dishes or test tubes upon cells


    Epidemiological studies
    Epidemiological studies so…

    - long-term studies of humans (in our case, human fetuses)that had sonograms

    • Various specific factors evaluated: birth weight, anomalies, IQ, cancer, hearing

    • These children were compared to children that did not have a sonogram pre-natally


    Epidemiological studies1
    Epidemiological studies so…

    • Most studies show no statistical differences between the two groups.

    • These studies have various limitations which include that they are done retrospectively and do not factor in other risks to the fetus which may have produced the effect.

    • The only effect reported was one of low birth weights; other studies did not support this.


    The end
    THE END so…


    ad