Bioeffect Of  Ultra Sound
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  • NOT completely safe
  • Cavitation: contrast agents to enhance echogenicity and,therefore, visualisation of blood vessels andcapillaries in a diagnostic image.
  • Blood flow, redistribute any heat generated
  • grow by a process known as rectified diffusion i.e. small amounts of vapour (or gas) from the medium enters the bubble during its expansion phase and is not fully expelled during compression. The bubbles grow over the period of a few cycles to an equilibrium size for the particular frequency applied. It is the fate of these bubbles when they collapse in succeeding compression cycles which generates the energy for chemical and mechanical effects
  • In vitro: within a glass. Sometimes: when shearing forces are high.
  • Doppler: vastly beneficial in high-risk pregnancies management
  • Living organisim
  • Stone fragmentation by the mechanical interaction of the acoustic waves with the kidney stone
  • Difficulty in learning, reading, spelling in kids
  • De. Dwelltimes & total exposure times. If adjustable, de. Intensities. (dwell t: amount of time that the transducer remains in one place.)

Transcript

  • 1. Biological effects of UltraSound
    King Saud University, college of Applied medical sciences, Radiological Sciences Department.
    Radiological Protection Course
    Presented by:
    Shatha Jamal Al Mushayt
    At 2009-2010
  • 2. Main Objectives
    • What are the biological effects of ultrasound and how do they occur?
    • 3. How can they be predicted and prevented?
    • 4. How did they help in developing other techniques?
    • 5. Examples of some reported effects and if their relationship with ultrasound is proved or not yet.
  • Introduction
    • Ultrasound is a high frequency mechanical waves
    that are above the human hearing range(>20,000 Hz).
    • They are produced by converting the electrical energy
    into mechanical energy.
    • When transmission is through biological tissues
    & under certain conditions, they may cause
    biological effects.
  • 6. Biological Effects of US
  • 7. Thermal effects
    Def:  temperature within a medium (locally).
    How? As the sonic energy is absorbed &
    converted into heat.
    Thermal effect depends on:
    Beam intensity, tissue absorption coefficient, blood
    flow, exposure parameters(e.g. Duration
    of exposure, frequency, …)
    1.
  • 8. Transducer Self-heating
    • Electrical energy is converted to thermal
    energy instead of sonic energy.
    • More likely to occur with endocavity probes where the probe is enclosed within the body & can be almost
    stationary for several minutes.
    • Clearly express thermal injury
    e.g. trans-esophageal exams.
    Endocavity probe
  • 9. Mechanical(direct) effects
    e.g.Particledisplacement & fluid streaming:
    Target particles are pushed away from
    the transducer acoustic streaming in fluids,
    cell distortion* and lysis.
    Non-thermal effects
    2.
  • 10. Non-thermal effects
    2.
    B. Cavitation
    Regions of compression & rarefaction are created in the medium.
    increases & decreases in pressure alternatively.
    Gas bubbles form(how?) & grow until critical size then collapse.
     generates the energy for mechanical effects.
  • 11. Cavitation Types
    Cavitation may be transient or stable.
    • Transient cavitation : very rapid expansion &
    violent collapse.
    • Causing high temp. & pressure, release of free radicals
    • 12. May cause genetic damage in vitro.
    • 13. Stable cavitation : bubbles oscillating with sound
    beam.
    • Cause mechanical damage, membrane rupture
    & sometimes cell lysis.
  • 14. Safety Indices Thermal Index (TI) & mechanical Index (MI)
    Not perfect; but they are the most common &
    practical measurements available at present.
    Indicate the probability of thermal & non thermal
    effects.
    Assist the sonographer in  patient exposure. How?
    > By keeping these indices as low as possible while
    obtaining the best possible diagnostic images.
  • 15. Thermal Index(TI)
    An indicator of the temp. elevation possible
    at a particular equipment setting.
    TI has 3 subdivisions :
    Soft tissues (TIS);
    bone (TIB);
    and adult cranial exposure (TIC).
  • 16. An indicator of the probability of cavitation
    events.
    Generally, MI should be < 1.9
    Mechanical Index(MI)
  • 17.
    • MI & TIS are displayed on screen.
  • Thermal effects
    Temperature rise of less than 1.5 degrees C
    no hazard to human (including fetus).
    Temp. rise of 4 degrees C, lasting for 5 min or
    more  hazardous specially to a fetus.
  • 18. Imaging modes and thermal effects
    In routine practice :
    B-mode, M-mode and 3D imaging are less likely
    to give rise to thermal injury. >> figures
    Doppler US can cause significant temp. rises.
    Doppler image
    M-mode image
    B-mode image
  • 19. Mechanical Effect
    • No mechanical bioeffects have been reported
    in humans from currently used exposure in diagnostic US.
  • 20. Cavitation
    Currently,
    • No significant cavitation damage in vivo caused by diagnostic or physiotherapy beams.
  • How did these mechanisms help in developing other techniques
    The development of new imaging techniques
    e.g. IV Injection of gas-filled micro bubbles as contrast agents to enhance the echogenicity.
    New therapeutic applications.
    e.g. (next slides)
    Maintaining the safe use of diagnostic US.
  • 21. Therapeutic U/S
    Usually continues US wave or
    pulses of much higher intensities than in diagnostic.
    Examples of applications:
    Lithotripsy, (mechanical)
    Tumor therapy by high intensity focused ultrasound
    (HIFU): heat tissue (thermal) & produce necrosis.
  • 22. Diagnosis vs. Therapy
    Diagnostic exposures are designed to  the interaction of US with tissue to avoid potential bioeffects.
    Therapeutic application depends on the direct interaction of US with tissue to produce the
    desired beneficial bioeffect.
    Exposure parameters are often different.
    Therapeutic intensities, pulse durations far
    exceed the diagnostic devices output.
  • 23. US Exposure During Pregnancy
    • Almost 100% of fetuses in the developed world
    receives one or more US scans.
    Risks & benefits are different depending on:
    Types of US, stages of pregnancy, machines, centers,
    & sonographers Each situation must be judged in
    its own merit.
    Major centers are preferable for better trained sonographers & powerful machines No long or
    repeated scans.
  • 24. Long Term Edverse Effect During Pregnancy
    Some reported fetal effects of US exposure:
    Delayed speech, dyslexia*, growth restriction,
    & non-right-handedness.
    • BUT up to date(7/2009), there is insufficient justification
    to conclude that there is a causal relationship between diagnostic US & long-term adverse fetal effects.
  • 25. Recommendation for clinical practice of diagnostic US
    No routine US with no clear indications for use.
    Should only be used when benefits outweigh risks.
    Users should know the exposure parameters of US
    equipment they employ.
    Users must know how to alter machine settings so as to
    reduce exposure.
    Instruments must be checked routinely to maintain the capability of obtaining reliable diagnostic information at
    ALARA exposures.
  • 26. Recommendation for clinical practice of diagnostic US
    For US scans for operator training, memorial
    pictures & videos of the fetus, or research, a lower
    threshold is recommended ) TI 0.5 , MI 0.3 (
    It is not recommended to use colorDoppler mode
    of the 1sttrimester embryo routinely; as this mode has a potential to produce significant temp. rises.
    Acoustic output from B-mode, M-mode, 3D imaging is
    safe during all pregnancy stages(if used as needed).
  • 27. THANK YOU
  • 28. References
    • MECHANICAL BIOEFFECTS OF ULTRASOUND - Annual Review of Biomedical Engineering and the Rochester Center for Biomedical Ultrasound- D Dalecki - access with KSU password
    • 29. Article: Ultrasound safety and collapsing bubbles: http://www.highbeam.com/doc/1G1-4600240.html- access with KSU password
    • 30. [PDF] Ultrasonic imaging of the human bodyP N T Wells.
    • 31. Practical radiation protection in healthcare, by Martin & Sutton
    • 32. [PDF] Guidelines for the Safe Use of Diagnostic Ultrasound
    • 33. Ultrasound Physics and instrumentation by Hedrick, hykes, starchman >>image
    • 34. [PDF] ULTRASOUND: AN OVERVIEW OF THE LITERATUREhttp://www.sonochemistry.info/Research.htm
    • 35. http://pain.about.com/od/testingdiagnosis/f/ultrasound_types.htm