Ultrasound

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

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

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

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

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

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 Stable cavitations Unstable 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..

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.

 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 SwitchesMeter

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

 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). 

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