Deep Heating Agents: Therapeutic Ultrasound and Diathermy Flashcards
human ear can hear sound waves
16- 20,000 Hz
ultrasound
any sound wave ABOVE 20,000Hz
THERAPEUTIC US : range 750,000 - 3,000,000 Hz
most frequently used: 1 MHz and 3 MHz
imaging us: 3.5 MHZ - 10 MHZ
acoustic energy
- different than electromagnetic energy
- must travel through a medium
- like electromagnetic energy: can be reflected, refracted, and absorbed
therapeutic ultrasound
- deep heating agent
- thermal and non-thermal effects
- converts electrical energy into acoustical energy
transducer
converts one form of energy into another
Piezoelectric crystal
crystal capable of contracting and expanding –> creates “piezoelectric effect”
- -> electric current
- —-> mechanical vibration of crystal
- ——–> wave of acoustic energy results
- if damaged, can cause “hot spots” irregular sound waves, burn athletes
Reverse piezoelectric effect
as the AC reversed polarity, the crystal expands and contracts, producing US energy
- –> high frequency sound waves (acoustical energy) delivered to the body
- —> travels through tissues and is absorbed
Effective Radiating Area (ERA)
the area of the sound head that produces ultrasonic waves (expressed in cm squared)
- energy output is greater at the center of ERA
- temp is greater at the center of the ERA
- always less than actual sound head
Beam profile
beam of energy emitted from crystal is NOT uniform
- multiple waves emerge from head (areas of high and low intensity)
- energy is more uniform closer to head
- energy diverges as it moves away from source
- becomes less consistent farther from head
- –> spatial peak intensity: most energy in far field
2 TYPES:
- divergent: goes out at angles
- collimating: lines up, parallel, straight down
Beam Nonuniformity Ratio (BNR)
- the consistency (uniformity) of the US output
- ratio between the highest intensity in and ultrasound beam and the output reported on the meter
- lower ratio = more uniform beam = 1:1 perfect
- 8:1 ratio = unsafe
lower ratio =
- more comfortable
- less hot spots
- less risk of periosteal pain
- cost more
- safer, more effective
because of hot spots, keep head moving
Sound Energy Absorption
- higher protein density = more absorption
ex: tendon, ligaments, muscles - high water and low protein content = less absorption
ex: blood, fat
*although cartilage and bone have lots of protein, the majority of US energy striking the surface of either of these tissues is likely to REFLECT
Parameters: Frequency
determined DEPTH of treatment
depth inversely related to frequency
higher frequency = less depth of penetration
of waves per second
Hertz: cycles per second
Megahertz: 1 million cycles per second
1 MHz = low frequency = greater depth of penetration = deep tissue ~4cm (5 or more cm) = .2 deg C per minute per w/cm2 SLOW = heating effects last 2x longer = relatively divergent beam profile
3 MHZ = high frequency = less depth of penetration = superficial tissue 2 cm (0.8 - 3cm) = heats tissue 3 x faster than 1 MHz - .6 deg C per minute per w/cm2 FAST = absorption occurs faster --> danger of burn = relatively collimating beam profile
Parameters: Dosage
Watts/ surface area (cm2)
higher dose = more sound energy delivered to tissues in less time
—> longer tx time for lower intensities
common dose: 1.5 w/cm2
doses greater than 2.5-3 may cause tissue damage
- depends on type of tissue, condition, duration
Rate of Ultrasound Heating
Temperature Increase per Minute
INTENSITY 1 MHz 3 MHz
(TISSUE DEPTH) (5cm) (1.2 cm)
0.5 0.04 deg C 0.3 deg C
1.0 0.2 deg C 0.6 deg C
1.5 0.3 deg C 0.9 deg C
2.0 0.4 deg C 1.4 deg C
treatment area
no greater than 2-3 times the ERA
- keep sound head moving, slowly
- maintain good contact with skin
- larger area = less energy reaching tissue = less temp increase
coupling methods
US requires medium for energy to be transmitted from sound head to body tissue
1) direct coupling - transducer and gel in direct contact with skin
2) pad/bladder method - conforms to irregular shaped areas and limits treatment area size to allow more energy to be transmitted
3) immersion (water) - for treating irregularly shaped areas, sound head ~1” away in ceramic/plastic/rubber tub
If patient complains of pain or excessive heat
DECREASE intensity
INCREASE time
Parameters: Duration
5-10 min (not <3min)
time based on treatment area
larger = longer
daily, decrease with improvement
Parameters: Duty Cycle
continuous vs pulsed
continuous (100%) = thermal effects
pulsed (50%, etc.) = non thermal effects at cellular level, maybe some thermal effects but not as much as continuous
Thermal Effects
MILD heating of 1 deg C
- -> increased metabolic activity, initiation of inflammatory process
- subacute phase (instead of pulsed)
MODERATE heating of 2-3 deg C
- -> increased blood flow
- -> decreased pain
- -> decreased muscle spasm
- -> decreased chronic inflammation
- used most often (ex: tendonitis)
VIGOROUS heating of 3-4 deg C
- -> improved viscoelastic properties of collagen
- used post surgical, when trying to break up scar tissue
Non Thermal Effects
- primarily occur with pulsed US
- little heat is produced due to dissipation that occurs during off time
CAVITATION - stable = Good
- unstable = bad
ACOUSTIC MICROSTREAMING
Cavitation
formation of gas filled bubbles that expand and compress –> pressure changes in tissue fluids
(1) stable cavitation: rhythmic contaction and expansion of gas bubbles
- facilitate fluid movement and membrane transport
- -> GOOD
(2) unstable cavitation: formation of bubbles at the low pressure part of the US cycle
- results in bubble collapse and tissue damage
- -> BAD
Acoustical Microstreaming
unidirectional movement of fluids along the boundaries of cell membranes
- us causes interstitial fluids to flow
- fluids strike cell membranes
- -> altering cell membrane permeability to Na and Ca ions important in the healing process
- –> altering cell function
CELLULAR RESPONSE:
- increases cell membrane permeability
- alters cell membrane diffusion rate
- increased histamine release
- mast cell degranulation
- increased rate of protein synthesis
Indications
- maybe prior to stretching and manual therapy when pt has restricted ROM
- calcific tendonitis of the shoulder
- scar tissue and joint contracture
- -> inc tissue temp = inc elasticity
- nontherapeutic use: identifying stress fx
- continuous at 1 MHz, move slow, gradually increase intensity to 2.0 w/cm2
