9 - Ultrasound Flashcards
US background
- High frequency sound waves
- Deep heating modality
- mechanical effects
UC mechanism
- electrical current passes through a crystal –> vibration
- soundwaves are generated by vibrating crystal
UC duty cycle
- continuous = 100%
- pulsed = 50%
Piezoelectric effect
mechanical deformation of a crystal causes an electrical current to form
Reverse Piezoelectric effect
- alternating current is passed through a crystal
- results in very fast contractions and expansion of the crystal
- this vibration proudces high frequency sound waves
Near field
treatment area
Far field
indirect effect
What determines the quality of US?
- Effective Radiating Area (ERA)
- Beam Nonuniformity Ratio (BMR)
Effective Radiating Area (ERA)
Area of the sound head that produces energy
- Will always be smaller than the size of the US head
Beam Nonuniformity Ratio (BNR)
amount of variability of the US beam
- BNR = (spatial peak)/(spatial average)
- Ideal ratio = 1:1
- Lower BNR = more uniform intensity,
- US beams are not uniform across the US head
- Ratio btwn Peak Intensity of the US beam, divided by Average Intensity of US beam
- Used to compare quality of different machines
Peak Area of Maximum Beam Nonuniformity Ratio (PAMBNR)
describes the area of the sound head covered by the peak insitensity
- Large PAMBNR = peak intensity covers a small area, thus LESS UNIFORM heating
Conducting media
used to help prevent reflection of sound waves by air
- keep sound head flat against can, 90°
Gel Pad for indirect ultrasound
pad will decrease intensity of US current
Underwater ultrasound
- indirect US
- use plastic basin/bucket
- wipe bubbles from skin and sound head occasionally
Amplitude for US
- dosage = amount of energy per square centimeter (W/cm2)
- more watts = more heat (NOT greater penetration)
frequency for US
affects depth of tissue, and time
- high-frequency (3 MHz) = superficial tissue
- low-frequency (1 MHz) = deep tissue
Duty cycle for US
- interrupted (pulsed)
- Continuous = more energy delivered and absorbed. Greater tissue healing
Absorption of US
- Skin and fat absorb the least
- [higher] of tissue = more absorption
US Scatter
occurs when US wave entoucters a boundary btwn tissues
- Reflection = occurs at soft tissue(muscle)/bone interface
- Refraction = occurs at fascia/muscle interface (ie where tendons join bone)
US tissue heating
- causes increase metabolic activity
- Good for REPAIR PHASE
- Increase temp => decrease muscle spasm
US Tx time
- Deep tissue = 10 minutes
- Superficial tissue = 5 minutes
US Therapeutic effects
- Increase: collagen fiber of tendons, blood flow, metabolism,
- Decrease: joint stiffness, spasms
- Healing = tendon, ligament, muscle
Pulsed US
- Little/no tissue heating
- Affects tissue healing at cellular level
- Works via acoustical streaming and stable cavitation
Acoustical streaming
movement of fluids along cell membranes due to mechanical pressures exerted by soundwaves
Cavitation
formation of gas filled bubbles from pressure changes in tissue fluids
stable cavitation
arithmetic expansion and contraction of bubbles during repeated pressure changes over many acoustic cycles
Unstable cavitation
collapse of gas bubble which may cause tissue damage
- associated with low-frequency, high intensity US
US risks
- bony prominences
- epiphyseal plate
US intensity
0.5 – 2.5 W/cm2
- higher intensity is NOT necessarily more effective
- do not exceed peak intensity of 8.0 W/cm2
- general rule: intensity = 1.0 w/cm2‑
US Tx time
5 – 8 minutes
- depends on size of treatment area
- never Tx for 15 minutes
Phonophoresis (Sonophoresis)
using soundwaves to drive medication into tissue
- lacks supporting efficacy
Combo: US + Stim
US head becomes the treating lecture when used with the dispersal pad
- trigger points
- epicondylitis
- superficial pain in areas
- decrease adhesions
low intensity pulsed ultrasound (LIPUS)
- stimulation of fracture healing
- good evidence backing it
