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
