ultrasound ,waves of ultrasound,beats and resonance

Medical physics

1. Ultrasound [email protected] [email protected]

2. History Methods to generate and detect ultrasound first became available in the United States in the 19th century. The first large-scale application of ultrasound was for SONAR (Sound Navigation and Ranging ) during World War II. Ultrasound was found to heat tissue with a high collagen content, such as tendons, ligaments , or fascia and, for the past 50 years or more, has been widely used in the clinical setting for this purpose More recently , ultrasound has also been found to have non thermal effects and, over the past 20 years, therapeutic applications of these effects have been developed .

3. Definition Ultrasound is defined as sound with a frequency of greater than 20,000 cycles per second (Hertz . Hz ). Ultrasound refers to mechanical vibrations, which are essentially the same as sound waves but of a higher frequency. Such waves are beyond the range of human hearing and can therefore also be called ultrasonic . Audible sound – 20 to 20000 Hz U ltrasound – Greater then 20000 Hz Infrasound – Less than 20 Hz T herapeutic ultrasound – 0.5 to 5 MHz – 1 to 3 MHz

4. Nature of sonic (sound) waves Sonic waves are series of mechanical compressions and rarefactions in the direction of travel of the wave, hence they are called longitudinal waves. The passage of these waves of compression through matter is invisible because it is the molecules that vibrate about their average position as a result of the sonic wave.

5. Sound waves will pass more rapidly through material in which the molecules are close together, thus their velocity is higher in solids and liquids than in gases . Air – 344 m/s Water – 1410 m/s Salt water – 1500 m/s Muscle – 1540 m/s

6. Generation of Ultrasound Piezoelectric property : The property of piezoelectricity, the ability to generate electricity in response to a mechanical force or to change shape in response to an electrical current. OR The production of a small e.m.f . across certain substances on being subjected to external pressure. A variety of materials are piezoelectric including bone, natural quartz and synthetic plumbium zirconium titanate (PZT), and barium titanate. At this time , ultrasound transducers are usually made of PZT because this is the least costly and most efficient piezoelectric material readily available.

7. Ultrasound is generated by applying a high-frequency alternating electrical current to the crystal in the transducer of an ultrasound unit. The crystal is made of a material with piezoelectric properties causing it to respond to the alternating current by expanding and contracting at the same frequency at which the current changes polarity. when the crystal expands it compresses the material in front of it, and when it contracts it rarefies the material in front of it. This alternating compression-rarefaction is the ultrasound wave.

8. Terminology in U.S Transducer (sound head): A crystal that converts electrical energy into sound. This term is also used to describe the part of an ultrasound unit that contains the crystal . Power: The amount of acoustic energy per unit time. This is usually expressed in Watts. Intensity: The power per unit area of the sound head . This is usually expressed in Watts/centimeter squared.

9. Spatial Average Intensity: The average intensity of the ultrasound output over the area of the transducer. Spatial Peak Intensity: The peak intensity of the ultrasound output over the area of the transducer. The intensity is usually greatest in the center of the beam and lowest at the edges of the beam. Beam Non uniformity Ratio (BNR): The ratio of the spatial peak intensity to the spatial average intensity. For most units t his is usually between 5:1 and 6:1, although it can be as low as 2:7

10. Continuous Ultrasound : Continuous delivery of ultrasound throughout the treatment period. Pulsed U ltrasound : Delivery of ultrasound during only a portion of the treatment period . Delivery of ultrasound is pulsed on and off throughout the treatment period. Pulsing the ultrasound minimizes its thermal effects. Duty Cycle : The proportion of the total treatment time that the ultrasound is on. This can be expressed either as a percentage or a ratio .

11. Effective Radiating Area (ERA): The area of the transducer from which the ultrasound energy radiates. Because the crystal does not vibrate uniformly, the ERA is always smaller than the area of the treatment head .

12. Near and Far Field The ultrasound beam delivered from a transducer initially converges and then diverges. The near field, also known as Fresnel zone , i s t he convergent region, and the far field, also known as the Fraunhofer zone , is the divergent region. In the near field there is interference of the ultrasound beam causing variations in ultrasound intensity. In the far field there is little interference, resulting in a more uniform distribution of ultrasound intensity . The length of the near field is dependent on the ultrasound frequency and the ERA of the transducer.

13. Ultrasound Reflection & Refraction: Reflection: The redirection of an incident beam away from a reflecting surface at an angle equal and opposite to the angle of incidence. Ultrasound is reflected at tissue interface. Refraction : The redirection of a wave at an interface. When refraction occurs, the ultrasound wave enters the tissue at one angle and continues through the tissue at a different angle.

14. Absorption Conversion of the mechanical energy of ultrasound into heat. The amount of absorption that occurs in a tissue type at a specific frequency is expressed by its absorption coefficient. The absorption coefficient is determined by measuring the rate of temperature rise in a homogeneous tissue model exposed to an ultrasound field of known intensity. Absorption coefficients are tissue and frequency specific. They are highest for tissues with t he highest collagen content and increase in proportion to the ultrasound frequency.

15. Attenuation Attenuation: A measure of the decrease in ultrasound intensity as t he ultrasound wave travels through tissue. Attenuation is the result of absorption, reflection , and refraction, with absorption accounting for about one-half of attenuation. Attenuation coefficients are t issue and Frequency specific . They are higher for tissues with a higher collagen content and increase in proportion to the frequency of the ultrasound.

16. Standing Waves Intensity maxima and minima at fixed positions one-half wavelength apart. Standing waves occur when the ultrasound transducer and a reflecting surface are an exact multiple of wavelengths apart, allowing the reflected wave to superimpose on the incident wave entering the tissue. Standing waves can be avoided by moving the sound head throughout the treatment.

17. Cavitation The formation, growth, and pulsation of gas- or vapor-filled bubbles caused by ultrasound. During the compression phase of an ultrasound wave , bubbles present in the tissue are made smaller , and during the rarefaction phase they expand . Cavitation may be stable or unstable. With stable cavitation, the bubbles oscillate in size throughout many cycles but do not burst . With unstable cavitation, the bubbles grow over a number of cycles and then implode. This implosion produces large brief , local pressure and temperature increases and causes free radical formation. Stable cavitation has been proposed as a mechanism for the nonthermal therapeutic effects of ultrasound, while unstable cavitation is thought not to occur at the intensities of ultrasound used therapeutically.

18. Micro streaming : Micro scale eddying that takes place near any small, vibrating object. Micro streaming occurs around the gas bubbles set into oscillation by cavitation . Acoustic Streaming : The steady, circular flow of cellular fluids induced by ultrasound. This flow is larger in scale than with micro streaming and is thought to alter cellular activity by transporting material from one part of the ultrasound field to another.

19. Phonophoresis The application of ultrasound with a topical drug in order to facilitate transdermal drug delivery. In summary ultrasound is a high-frequency sound waves that can be described by its intensity , frequency, duty cycle, ERA and BNR. It enters the body and is attenuated in the tissue by absorption, reflection and refraction .

20. Effects of Ultrasound Thermal Effects : The thermal effects of ultrasound, including acceleration of metabolic rate, reduction or control of pain and muscle spasm, alteration of nerve conduction velocity , increased circulation, and increased soft tissue extensibility, are the same as those obtained with other heating modalities , except that the structures heated are different. Ultrasound reaches more deeply and heats smaller areas than most superficial heating agents. Ultrasound also heats tissues with high ultrasound absorption coefficients more than those with low absorption coefficients. Tissues with high absorption coefficients are generally those with a high collagen content, while tissues with low absorption coefficients generally have a high water content. Thus, ultrasound is particularly well-suited to heating tendons, ligaments, joint capsules and fascia while not overheating the overlying fat . Ultrasound is generally not the ideal physical agent for heating muscle tissue because muscle has a relatively low absorption coefficient; also most muscles are much larger than the available ultrasound transducers.

21. Thermal Effects Increase in the extensibility of collagen Decrease in joint stiffness Reduction of muscle spasm Modulation of pain Increased blood flow Mild inflammatory response May help in the resolution of chronic inflammation

22. Non thermal Effects Ultrasound has a variety of effects on biological processes that are thought to be unrelated to any increase in tissue temperature. These effects are the result of the mechanical events Produced by ultrasound, including cavitation, micro streaming , and acoustic streaming. When ultrasound is delivered in a pulsed mode, with a 20% or lower duty cycle, the heat generated during the on time of the cycle is dispersed during the off time, resulting in no measurable net increase in temperature.

23. Nonthermal Effects Increased cell membrane permeability Altered rate of diffusion across cell membrane Increased vascular permeability Secretion of cytokines Increased blood flow Stimulation of phagocytosis Production of healthy granulation tissue Synthesis of protein Synthesis of collagen Reduction of edema Diffusion of ions Tissue regeneration Formation of stronger, more deformable scar

24. Ultrasound with a low average intensity has been shown to increase 1. intracellular calcium 2. increase skin and cell membrane permeability 3. increase mast cell degranulation 4. increase chemotactic factor and histamine release 5. increase macrophage responsiveness 6. increase the rate of protein synthesis by fibroblasts

25. Techniques of Application Frequency of treatment Acute vs. chronic How many treatments should be given? Duration of treatment Dependent on treatment goal Keep the transducer moving!!!

26. Coupling Methods Direct contact Immersion Watch for bubbles COUPLING MEDIA To avoid the impedance(Z) by air Best is Aqua sonic gel(water based gel)

27. TECHNIQUES OF APPLICATION Note : check equipment before application DIRECT CONTACT Should move concentric circles Turn off and on in contact with patients T hree times the size of treatment head WATER BATH Immerse treatment part in water (without bubbles) Keep the head 1cm from treatment part 35

28. WATER BAG Rubber bag filled with water Apply coupling media on bag and treatment area Move the US head same like direct method AB 36

29. DOSAGE ACUTE Intensity – 0.25 Wcm -2 – 0.5 Wcm -2 Duration 2-3 Minutes Use pulsed mode (Very acute – 1:7 , Acute – 1:1) CHRONIC Intensity 0.8 Wcm -2 – 2 Wcm -2 Duration upto 4 – 8 Minutes Use continuous mode AB 37

30. Clinical Application of Ultrasound Soft tissue shortening Pain control Dermal ulcers Surgical skin incisions Tendon injuries Resorption of calcium deposits Bone fractures Carpal tunnel syndrome Phonophoresis Plantar warts Herpes zoster infection

31. Soft tissue shortening Soft tissue shortening can be the result of immobilization, inactivity or scarring , and can cause joint ROM restrictions , pain, and functional limitations . Shortening of the j oint capsule, surround ing tendons , or ligaments is frequently responsible. The deep heating produced by 1 MHz continuous ultrasound at 1.0 to 2.5W/cm2 has been shown to be more effective at increasing hip joint ROM instead the superficial heating produced by infrared radiations when applied in conjunction with exercise.

32. Soft Tissue Stimulates release of histamine from mast cells May be due to cavitation & streaming  transport of calcium ions across membrane that stimulates histamine release Histamine attracts leukocytes, that clean up debris, & monocytes that release chemotactic agens & growth factors that stimulate fibroblasts & endothelial cells to form a collagen-rich, well-vascularized tissue

33. Clinical Applications – Soft Tissue & Plantar Warts Pitting edema -  temp. makes thick edema liquefy thus promoting lymphatic drainage  fibroblasts = stimulation of collagen production = gives CT more strength Plantar Warts - 0.6 W/cm 2 for 7-15 min.

34. Clinical Applications – Scar Tissue, Joint Contracture, & Pain Reduction  mobility of mature scar  tissue extensibility Softens scar tissue  pain threshold Stimulates large-diameter myelinated n. fibers  n. conduction velocity

35. Clinical Applications Chronic Inflammation - Pulsed US has been shown to be effective with  pain &  ROM 1.0 to 2.0 W/cm 2 at 20% duty cycle Bone Healing – Pulsed US has been shown to accelerate fracture repair 0.5 W/cm 2 at 20% duty cycle for 5 min., 4x/wk Caution over epiphysis – may cause premature closure

36. Treatment Duration & Area Length of time depends on the Size of area Output intensity Goals of treatment Frequency Area should be no larger than 2-3 times the surface area of the sound head ERA If the area is large, it can divided into smaller treatment zones When vigorous heating is desired, duration should be 10-12 min. for 1 MHz & 3-4 min. for 3 MHz Generally a 10-14 day treatment period

37. Thermal Applications

38. Treatment Goal & Duration Adjust the intensity & time according to specific outcome Desired temp.   /min. = treatment min. Ex. For 1.5 W/cm 2 : 2°C  .3 °C = 6.67 min.

39. Pain control ultrasound may control pain by altering its transmis s ion or perception or by modifying the underlying condition causing the pain. These effects may be the result of stimulation of the cutaneous thermal receptors or increased soft tissue extensibility due to increased tissue temperature, the result of changes in nerve conduction due to increased tissue temperature. Continuous ultrasound at 0.5 to 2.0 Wcm2 intensity and 1.5M Hz frequency has also been reported to be more effective than superficial heating with paraffin or infrared or deep heating with short waved diathermy for relieving the pain from soft tissue injuries. Continuous ultrasound applied at 1.5 Wcm2 for 3 to 5 minutes for 10 treatments over a 3-week period followed by exercise has been found to be more effective than exercise alone in relieving pain and increasing ROM in patients with shoulder pain.

40. Dermal ulcers Addition of ultrasound treatment to conventional wound care procedures resulted in significantly greater reduction in the area of lower extremity varicose ulcers. Ultrasound was applied pulsed at 20% duty cycle, at 1.0 Wcm2 intensity, 3 MHz frequency, for 5 to l0 minutes to the intact skin around the border of lower extremity varicose ulcers 3 times a week for 4 weeks .

41. Surgical skin incision The effect of ultrasound on the healing of surgical skin incisions has been studied in both animals and human subjects . Ultrasound applied at 0.5 W/cm2, pulsed 20%, for 5 minutes daily to full thickness skin lesions in adult rats has been shown to accelerate the evolution of angiogenesis, a vital component of early wound healing . Angiogenesis is the development of new blood vessels at an injury site that serves to reestablish circulation and thus limit ischemic necrosis and facilitate repair. It is proposed that ultrasound may accelerate the development of angiogenesis by altering cell membrane permeability , particularly to calcium ions, and by stimulating angiogenic factors synthesis and release by macrophages.

42. Tendon injuries Ultrasound has been reported to assist in the healing of tendons after surgical incision and repair. Enhanced recovery in patients with lateral epicondylitis treated with ultrasound. the ultrasound was applied pulsed with a 20% duty cycle 1.0 or 2.0 W/cm2 intensity, 1 MHz frequency, for 5 to 10 minutes for 12 treatments over a 4- to 6-week period. G reater resolution of calcium deposits, greater decreases in pain, and greater improvements in the quality of life in patients with calcific tendinitis of the shoulder treated wit h ultrasound.

43. Contraindications Malignant tumor Joint cement/Total joint replacements Plastic components Pacemaker Thrombophlebitis Eyes Areas of decreased temperature sensation Areas of decreased circulation Vascular insufficiencies Reproductive organs Acute conditions ( continous output ) Tendency to hemorrhage Over pelvic or lumbar areas in pregnant or menstruating females Spinal cord or large nerve plexus in high doses Anesthetic areas Stress fracture sites or over fracture site before healing is complete (continuous); epiphysis Acute infection\Infections Epiphyseal areas in developing individuals