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Ultrasound

Ultrasound. History:. Available in 19th century. Was for sonar (SONAR  Sound Navigation and Ranging) Sonar  development of clinical U.S. devices. Heating of biological tissues. Used for the past 20 years US  non thermal effects. What is Ultrasound?. Type of sound.

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Ultrasound

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  1. Ultrasound

  2. History: • Available in 19th century. • Was for sonar (SONAR  Sound Navigation and Ranging) • Sonar  development of clinical U.S. devices. • Heating of biological tissues. • Used for the past 20 years US  non thermal effects.

  3. What is Ultrasound? • Type of sound. • Transmits energy by compressing and rarefying materials. • Defined as sound with frequency of > 20,000 Hz (beyond the limits of human hearing). • Therapeutic U.S. frequency is 0.7-3.3 MHz  depth of absorption 2-5 cm. • Like audible sound. • Intensity decrease when travel through material. • Cause circular motion of material.

  4. Terminology: • Transducer (Sound Head): The part that contains the crystals that convert Electrical energy into sound. • Power: Acoustic energy / unit time (in watt) • Intensity: Power / unit area of soundhead (in watt/cm2) (range : 3 watt/cm2) • Spatial average intensity: Average intensity of U.S. / area of transducer • Spatial peak intensity: Peak intensity / area of transducer

  5. Beam Non Uniformity Ratio (BNR): Spatial peak intensity : Spatial average intensity • Continuous U.S.: Continuous delivery of US throughout the treatment. • Pulsed U.S.: Delivery of US in portion of the treatment time (period). • Duty Cycle: The proportion of total treatment time that US is on. • Frequency: The number of compression – rarefaction. Cycles/unit of time (Hz) • Effective Radiating Area (ERA): Area of transducer from which US energy radiates. • Near Field / Far Field: Near field  the fresnel zone is the convergent region. Far field  the fraunhofer zone is the divergent region.

  6. Absorption: Conversion of mechanical energy into heat. Amount of absorption are tissue and frequency specific. • Reflection: 35% at soft tissue-bone interface. 100% at air-skin interface. 0.1% at medium-skin interface. • Refraction: US waves enter the tissue at one angle and continue throughout the tissue at a different angle. • Attenuation: Intensity decreases as U.S. travels through the tissue. Attenuation is tissue and frequency specific. • Half depth: Depth of tissue at which U.S. intensity is half its initial intensity. • Standing wave: Avoid by moving the sound head throughout the treatment.

  7. Effects of non thermal U.S. on tissue: 1. Cavitations: Formation, growth, and pulsation of gas or vapor filled bubbles caused by U.S. • Stable cavitations • Unstable cavitations 2. Micro Streaming: Micro scale eddying takes place near any small vibrating object. 3. Acoustic Streaming: The steady circular flow of cellular fluids induced by U.S..

  8. 4. Phonophoresis: Application of U.S. with a topical drug in order to facilitate transdermal drug delivery. Generation of U.S.: ~Piezoelectrical Transducer~ • Applying high frequency and an alternating electrical current to the crystals in the transducer. • Crystals resonate at a frequency to achieve maximum vibrations. • Single frequency of alternating current  single frequency of U.S. from crystals.

  9. Resonance occur when the U.S. frequency and crystal thickness conform to: F = C / 2t F = Frequency , C = Speed of sound , t = Thickness of crystal Metal electrode fixing to crystals Circuit Power supply Switches Meter

  10. U.S. parameters: * Intensity * Frequency * Size of transducer * Medium (gel, water...) * Mode (pulsed + continuous) * Time of application Effects of U.S.: Physiological and therapeutic. Effects of thermal U.S.: Physiological effects: • Increase temperature of deep tissue • Increase circulation • Increase soft tissue extensibility

  11. Increase tissue healing • Increase Ca+ binding to protein • Decrease pain • Decrease muscle spasm • Decrease joint stiffness • Alternation of N.C.V. It heats deep and small areas. It heats tissue with high absorption coefficient (high collagen).

  12.  Good Luck To You All 

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