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Therapeutic Ultrasound

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  1. Therapeutic Ultrasound Chapter 8

  2. Description • Acoustical energy (sound waves) above the range of human hearing • Therapeutic range: 0.75 to 3.3 MHz • Effects: • Thermal • Nonthermal (mechanical)

  3. Uses • Calcific bursitis • Inflammatory conditions • Joint contractures • Pain • Muscle spasm • Acute orthopedic injuries (low pulses, low intensity)

  4. Production of Ultrasound • An alternating current is passed through a crystal • The current causes the crystal to vibrate • Electropiezo effect • Vibrating crystal produce high-frequency sound waves

  5. Effective Radiating Area (ERA) • Area of the crystal that actually produces sound waves • Produces more than 5% of the energy at 5 mm from the transducer face • ERA is always smaller than the transducer face • Energy is concentrated near the center ERA

  6. Spatial Peak Intensity Beam Profile • Multiple waves emerge from the head • Energy diverges as it moves away from the source • Energy is uniform close to the head • Near zone (Fresnel zone) • Becomes less consistent farther away from the head • Spatial peak intensity

  7. Beam Nonuniformity Ratio (BNR) • Describes the amount of variation in the beam • Ratio between: • Spatial peak intensity (SPI) • Average intensity (SAI - metered output) • BNR = SPI/SAI • Perfect beam would have a BNR of 1:1 • Minimally acceptable BNR is 8:1 • The actual peak output is equal to the SAI * the BNR • 10 W total output * 6:1 BNR • 60 watt SPI Spatial Peak Intensity Spatial Average Intensity(Displayed on the unit)

  8. Modes of Application Continuous • Ultrasonic energy is constantly produced • Can produce thermal effects based on: • Output intensity • Treatment duration Pulsed • Ultrasonic output is regularly interrupted • Produces nonthermal effects

  9. Pulsed Output • Ultrasonic output is cycled “On” and “Off” • On = Pulse length • Off = Pulse interval • Expressed as a Duty Cycle • ON/(ON+OFF) * 100 • 20mSec/(20mSec+10mSec) * 100 • 20/30 * 100 • 67% Continuous Output (100% Duty Cycle) Pulsed Output (67% Duty Cycle)

  10. Output Frequency • Measured in megahertz (MHz) • 1 MHz = 1,000,000 waves per second • Determines the depth of effects • 1 MHz Output • Penetrates 5 to 7 cm • Thermal effects last longer • More divergent beam • 3 MHz Output • Penetrates 2 to 3 cm • Heats 3 times faster than 1 MHz output • More collimated beam

  11. Power and Intensity Spatial Average Intensity Spatial Average Temporal Peak Intensity Spatial Average Temporal Average Intensity

  12. Spatial Average Intensity (SAI) • Describes the energy per unit of area • Total output (watts)/area • Watts/effective radiating area (cm2) • W/cm2 • 15 watts being applied with a 10 cm2 ERA • 15 Watts / 10 cm2 • 1.5 W/cm2

  13. Power Measures – Pulsed Output Spatial Average Temporal Peak Intensity (SATP) • The average energy delivered during the “On” time of the duty cycle. Spatial Average Temporal Average Intensity (SATA) • Energy delivered over time • Spatial Average Intensity * Duty Cycle • Meaningful only during pulsed output

  14. Biophysical Effects Thermal

  15. Thermal Effects • Increased sensory nerve conduction velocity • Increased motor nerve conduction velocity • Increased extensibility of collagen-rich • Increased vascular permeability structures • Increased collagen deposition • Increased blood flow • Reduction of muscle spasm • Increased macrophage activity • Enhanced adhesion of leukocytes to damaged endothelial cells

  16. Heating Classifications Increase Used For Mild 1°C Mild inflammation Accelerate metabolism Moderate 2° – 3°C Decreasing muscle spasm Decreasing pain Increasing blood flow Chronic inflammation Vigorous 3° – 4°C Tissue elongation Scar tissue reduction

  17. Heating Rate • Heating rate and magnitude is based on: • Duty cycle • Output frequency • Intensity • Target tissues • Size of the treatment area

  18. Thermal Effects • Same as other heat modalities • Smaller volume of tissue • Shorter duration of effects • Preheat the skin with a moist heat pack • Decreases the time to reach vigorous heating • Poorly vascularized, collagen-rich tissues are preferentially heated • Fascia, tendon, scar tissue • Tissues containing an increased proportion of fluid do not heat as well • Adipose tissue, articular fluid

  19. Biophysical Effects Nonthermal

  20. Increased cell membrane permeability Altered rates of diffusion across the cell membrane Increased vascular permeability Secretion of cytokines Increased blood flow Increased fibroblastic activity Stimulation of phagocytosis Granulation tissue production Synthesis of protein Synthesis of collagen Reduction of edema Diffusion of ions Tissue regeneration Formation of stronger deformable connective tissue Nonthermal Effects

  21. Nonthermal Application • Pulsed output • 20 to 25% duty cycle • Nonthermal output intensity • Continuous output • 100% duty cycle • Output intensity of less than 0.3 W/cm2

  22. Acoustical Streaming • Ultrasound causes interstitial fluids to flow • Fluids strike cell membranes • Produce eddy currents • Eddy currents displace ions and molecules • Alter: • Cell membrane permeability • Cellular function

  23. Effect on Injury Response

  24. Cellular Response • Acoustical streaming: • Increases cell membrane permeability • Alters cell membrane diffusion rate • Increased histamine release • Mast cell degranulation • Increased rate of protein synthesis • Thermal effects: • Increased cell metabolism • Increased rate of inflammation

  25. Inflammation • May lead to an earlier onset of proliferation • Increased fibroblast proliferation • Release of growth factors and platelets • Increased macrophage activity • Leukocytes bind to damaged endothelial cells • Cell division is increased

  26. Inflammation Frequency Specificity • 1 MHz Output • Release of preformed fibroblasts • 3 MHz Output • Increased synthesis and secretion of fibroblast precursors • Increased in areas of high collagen concentration

  27. Blood and Fluid Dynamics • May increase blood flow for 45 minutes • Thermal effects • Decreased vascular tone • Histamine release • Causes vasodilation • Moist heat application prior to treatment decreases net increase in blood flow

  28. Pain Control Direct Pain Reduction • Increased nerve cell sodium permeability • Alters nerve function • Increases pain threshold Indirect Pain Reduction • Increased blood flow • Increased capillary permeability • Increased oxygen delivery • Decreased muscle spasm

  29. Muscle Spasm • Reduced secondary to: • Decreased pain • Altered nerve conduction velocity • Increased temperature (counterirritant effect) • Muscle relaxation

  30. Tissue Elasticity • Ultrasound preferentially heats collagen-rich tissues (tendon, fascia, scar tissue) • Temperature must be increased 7.2°F • Stretching window lasts approximately 3 minutes following the treatment • Place tissues on stretch during application • Perform stretching/mobilization immediately following the treatment • Multiple treatments are required to gain length

  31. Wound Healing Tendon Healing • Continuous US application may: • Increase tensile strength • Increase collagen deposition Skin Ulcers • 3 MHz, low-intensity pulsed output may assist the healing process • Cover the wound with an occlusive dressing

  32. Electromagnetic Field • In vitro bone deformation produces piezoelectric currents and streaming potentials • Electromagnetic (EM) devices are based on Wolff’s Law that bone responds to mechanical stress: Exogenous EM fields may simulate mechanical loading and stimulate bone growth and repair • Clinical efficacy very controversial

  33. Types of EM Devices • Microamperes • Direct electrical current • Capacitively coupled electric fields • Pulsed electromagnetic fields (PEMF)

  34. PEMF • Approved by the FDA for the treatment of non-unions • Efficacy of bone stimulation appears to be frequency dependent • Extremely low frequency (ELF) sinusoidal electric fields in the physiologic range are most effective (15 to 30 Hz range) • Specifically, PEMF signals in the 20 to 30 Hz range appear more effective than those below 10 Hz

  35. Ultrasound • Low-intensity ultrasound is approved by the FDA for stimulating healing of fresh fractures • Modulates signal transduction, increases gene expression, increases blood flow, enhances bone remodeling and increases callus torsional strength in animal models

  36. Ultrasound • Human clinical trials show a decreased time of healing in fresh fractures • Has also been shown to decrease the healing time in smokers potentially reversing the ill effects of smoking

  37. Low-intensity pulsed output Accelerates rate of fracture healing for: Acute fractures Nonunion fractures Stress fractures Requires specialized unit Biophysical Effects: Mechanical (sound) energy strikes bone Microvibration of bone triggers growth (osteogenesis) PARAMETERS Frequency 1.5 MHz ERA 3.88 cm2 Intensity 30 mW/cm2 Treatment Duration 20 minutes Daily Fracture Healing

  38. Acute conditions (thermal mode) Ischemic areas Areas of impaired circulation Over areas of deep vein thrombosis Anesthetic areas Over cancerous tumors Sites of active infection or sepsis Over the spinal cord or large nerve plexus in high doses Exposed penetrating metal (eg, external fixation devices) Around the eyes, heart, skull, or genitals Over the thorax in the presence of an implanted pacemaker Pregnancy when used over the pelvic or lumbar areas Over a fracture site before healing is complete Stress fracture sites or sites of osteoporosis Over the pelvic or lumbar area in menstruating female patients Contraindications

  39. Where are we going?

  40. Ultrsound • Ultrasound uses: • Diagnostic (low intensity) • Fracture • Surgical (high intensity) • Therapeutic • Therapeutic US widely used for deep heat

  41. Ultrasound • Primary clinical use: • Soft tissue repair • Pain relief (analgesia)

  42. Effective Radiating Area (ERA) • Total area on surface of transducer producing soundwave • Ideally ERA should match size of transducer • Treatment area should not exceed 2-3 times ERA

  43. Frequency of Ultrasound • Determined by number of times crystal deformed/sec. • 2 most common utilized in U.S. • 1.0 MHz • 3.0 MHz • Determines depth of penetration, unlike ES

  44. Frequency of Ultrasound • Inverse relationship between frequency and depth of penetration • Penetrating depths: • 1.0 MHz: 2-5 cm • 3.0 MHz: 1-2 cm • Absorption rate increases with higher frequency

  45. Pulsed vs Continuous • Most new generators produce both • Both produce thermal & nonthermal effects

  46. Pulsed vs Continuous • Continuous: • Sound intensity remains the same • Commonly used for thermal effects

  47. Pulsed vs Continuous • Pulsed: • Intensity periodically interrupted • Average intensity reduced over time

  48. Physiological Effects of Ultrasound • Thermal effects • Non-thermal effects • Cavitation • Acoustic microstreaming

  49. Thermal Effects • Clinical effects: • Increased extensibility of collagen fibers • tendons • joint capsule • Decreased joint stiffness

  50. Thermal Effects • Clinical effects: • Reduction in muscle spasm • Pain modulation • Increased blood flow • Increased nerve conduction