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Ultrasound. HEAT 4100 Chapter 7-8 p. 156. Ultrasound - p. 158. Transmission of inaudible sound waves Thermal & non-thermal effects Frequency of US dictates effects (imaging, thermal,etc). Production of Ultrasound - p.159.

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Ultrasound l.jpg

Ultrasound

HEAT 4100

Chapter 7-8

p. 156


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Ultrasound -p. 158

  • Transmission of inaudible sound waves

  • Thermal & non-thermal effects

  • Frequency of US dictates effects (imaging, thermal,etc)


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Production of Ultrasound-p.159

  • AC current passing through a crystal -) vibration of the crystal (piezoelectric effect)

  • High frequencies produced & requires a medium for transmission

  • Figure 6-2, p.272

  • Transmitted acoustic energy


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Ultrasound Transmission-p. 160

  • Reflection-Energy is not absorbed due to tissue density; partial vs. complete; i.e.-echo

  • Refraction-Energy is partially absorbed; speed changes dictated by density changes; i.e.-prism

  • Absorption-Acoustic energy converted to kinetic energy (heat); partial vs. complete


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Physics of Ultrasound-

  • Law of Grotthus-Draper-p. 101

    • An inverse relationship exists between energy absorbed & energy penetrating the next level

  • Arndt-Schultz Principle--p. 396

    • For energy to affect the tissues, it must be absorbed at a level which stimulates a physiological change; The amount of change is dictated by the level of phys. response


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Ultrasound Parameters—p. 157; Table 7-1

  • BNR--Beam nonuniformity ratio—

    • consistency of the US output;

    • Greater than 8:1 is unsafe

    • FDA mandates that BNR be given on the US unit

    • 3:1 @ 2 W = US occasionally reaches 6W (keep sound head moving!)—Fig. 7-6, p. 171

      Duty Cycle--on/off cycles

    • 100%= continuous output (thermal)

    • lower duty cycle= lower thermal effects


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Ultrasound Parameters--p. 159

  • ERA--effective radiating area

    • amount of sound head which actually emits sound waves

    • Measured in square cm.

  • Frequency–number of waves occurring in 1 sec.

    • output which dictates tissue penetration

    • 1 MHz = 5 cm depth of penetration

    • 3MHz= 2cm penetration

    • Higher frequencies are absorbed more rapidly


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Power & Intensity –p. 162

  • Measured in Watts or Watts/Cm2

  • Describes the amount of energy produced at the transducer

  • Half-layer value—depth at which 50% of the US energy has been absorbed

  • Total energy produced and passed into the tissues increases with ERA

  • W/cm2 used to indicated power as a product of ERA


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Treatment Duration—p. 280

  • Duration dictated by:

    • Desired effect (thermal vs. nonthermal)

    • Intensity (greater intensity = lower duration)

    • Size of area treated (greater area = longer duration)

  • Treatment area should only be 2x-3x the size of the US transducer head

    • Use multiple tx’s if area is too large

    • 10-12 min. tx’s are common with 1 MHz

  • Table 7-5, p. 167; Table 8-3, p. 179


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Effects of US on Blood Flow—p. 169

  • Continuous US may increase blood flow for 45 min.

  • US promotes vasodilation

  • Combine with thermal modalities?


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Effects of US on Tissue Healing–p. 169

  • Accelerates the inflammatory stage

  • Promotes cell division in proliferation stage

  • Enhances fibroblast formation in high-collagen tissues (muscles/tendons)

  • Enhances collagen deposition in superficial wounds (1 MHz)


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Effects of US on Tissue Elasticity—p. 169

  • Combine US with ROM exercises

  • Collagen becomes more elastic with US

  • Target temp = 5°C elevation

  • “Stretching Window” longer with 1 MHz

    • Place tissues on stretch during the tx

    • Stretch immediately after tx

    • Shorter window and shorter duration of effects with 3 MHz


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Effects of US on Pain Control—p. 169

  • Nerve transmission altered through increased permeability of Na+ (elevates pain threshold)

  • Thermal US Counterirritant effect

  • Decreased spasm & Increased relaxation  decreased pain


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Phonophoresis—p. 170

  • Introduction of medication into tissues

  • Transmission Factors: Table 6-8,p. 293

  • Thermal effects dilate points of entry

  • Nonthermal effects enhance diffusion rates

  • Preheating the area increases absorption

  • Greatest limitation: transmission medium

  • Cover remaining med with occlusive dressing to complete absorption

  • Common Meds:Table 7-7, p. 171


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US and E-stim (Combo)—p. 180

  • Concurrent US and ES treatment

  • US head becomes the active stim electrode

  • Benefits of both modalities with shorter tx duration

  • Commonly used to decrease spasm and trigger point sensitivity


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Modes of US Application—p. 166

  • Continuous—

    • Thermal effects

    • Penetration up to 5 cm

  • Pulsed—

    • Primarily Nonthermal effects

    • Decreased penetration of US

  • Table 7-4, p. 166


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Coupling Agents—p. 175

  • Direct Coupling—p. 175

  • Water Immersion—p. 176

  • Bladder Method—p. 177


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Direct Coupling—p. 175

  • Traditional method

  • Applied directly to skin

  • Blocks air and maintains contact of transducer with skin

  • Works best with broad flat surfaces

  • Maintain .44- 1.32 pounds of pressure

  • Faster speed decreases thermal effects

  • Table 8-1, p. 176


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Water Immersion—p. 176

  • Most effective in treating irregularly shaped areas

  • Body part and transducer are immersed in water

  • Transducer does not touch skin (approx. 1” away)

  • Decreases thermal effects because of dispersion of sound waves

  • “Echo Chamber” effect

  • Fig. 8-4, p. 177


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Bladder Method—p. 177

  • Water-filled balloon or plastic bag coated with US gel

  • Better transmission to irregularly shaped areas

  • Avoid air pockets in the bladder

  • Fig. 8-5, p. 178


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Biophysical Effects of Nonthermal US—p. 166

  • Table 7-46, p. 166

  • Reduces edema

    • Increases cell membrane permeability

    • Increases diffusion rates across the cell membrane

    • Stimulation of phagocytosis

  • Stimulates collagen synthesis

  • Stimulates protein synthesis

  • Forms stronger connective tissues


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Biophysical Effects of Thermal US—p. 166

  • Thermal effects dictated by tx duration, intensity, and duty cycle

  • Thermal of effects of 1MHz treatment are more superficial, but longer lasting

  • Maintain elevated tissue temp for 3-5 minutes

  • Thermal effects greatest in hydrated tissues

  • Nonvascular tissues warm faster

  • Reflection/refraction may lead to greater temperature increases


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Summary

  • Thermal & Nonthermal modality

  • Penetration dictated by frequency (1MHZ vs. 3 MHz)

  • Phonophoresis

  • Combo treatment