Ultrasound

1. Ultrasound HEAT 4100 Chapter 7-8 p. 156

2. Ultrasound -p. 158 • Transmission of inaudible sound waves • Thermal & non-thermal effects • Frequency of US dictates effects (imaging, thermal,etc)

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. Effects of US on Blood Flow—p. 169 • Continuous US may increase blood flow for 45 min. • US promotes vasodilation • Combine with thermal modalities?

11. 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)

12. 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

13. 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

14. 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

15. 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

16. 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

17. Coupling Agents—p. 175 • Direct Coupling—p. 175 • Water Immersion—p. 176 • Bladder Method—p. 177

18. 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

19. 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

20. 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

21. 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

22. 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

23. Summary • Thermal & Nonthermal modality • Penetration dictated by frequency (1MHZ vs. 3 MHz) • Phonophoresis • Combo treatment