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
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.
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.
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.
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.
20.
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.
24.
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).
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.)
![Main Objectives ,[object Object]](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)