Ultrasound Slides

t/f you are able to do ultrasound in a vacuum

FALSE

you cannot do it in a vacuum because there are no collisions in a vacuum

general principles of ultrasound

acoustic form of radiant energy

high frequency acoustic vibrations

how do ultrasound waves move

high density compression waves then low density rarefaction waves

almost how a slinky moves

absorption rate

bone> nerve> tendon (fascia & ligament) >muscle> fat

absorption

tissues that absorb more energy will heat faster

• high water content low absorption rate

  • high protein content high absorption rate

acoustical impedance

the amount of resistance that a sound wave encounters as it enters a tissue or material

acoustical impedance effect on transmission

the greater the difference in the acoustical impedance the greater the amount of sound wave energy that will be reflected and less that will be transmitted

acoustical impedance and standing waves

very large differences in acoustical impedance will cause most of the sound energy to be reflected

thermal effects of ultrasound

increased blood flow, increased extensibility of soft tissue, decreased viscosity of fluid, increased metabolic rate, decreased muscle spasm and promotes muscle relaxation, decreased pain

non thermal effects of ultra sound

sound waves move around the cell (microstreaming), air bubbles can act like a micro massage (cavitation)

cavitation

formation of gas filled bubbles that expand and compress causing pressure changes in tissue fluids

effect: increased blood flow in the fluid around the vibrating bubbles

microstreaming

unidirectional movement of fluid along the boundary of cell membranes

effects:

• alters cell membrane permeability to sodium and potassium (important in healing)

  • fibroblast activity is stimulated (will increase protein synthesis, tissue regeneration and blood flow)

nonthermal vs thermal effects

nonthermal effects always occur during ultrasound

thermal effects occur only when the treatment parameters allow

transducer

the crystal in the sound head

piezoelectric effect

as altering current is passed through the crystal, the crystal will contract and expand producing the sound waves

characteristics of an ultrasound generator

power, sound head size, effective radiating area (ERA), intensity, spatial average intensity

power

total amount of energy in the ultrasound beam (watts)

effective radiating area (ERA)

portion of the transducer or sound head that actually produces sound waves (the size of the crystal in the sound head)

intensity

the rate at which energy (power= watts) is being delivered per unit area

spatial average intensity

the power of the output divided by the ERA

watts/cm²

beam nonuniformity ratio (BNR)

the amount of variability the ultrasound beam intensity has

the lower it is the more uniform the output and the more uniform the healing

what determines how high you are able to go with intensity

BNR

5:1 or 6:1 usually

you want the highest peak to be between 8-10 (under 10)

frequency

1 MHz- deeper effect

3 MHz— superficial

pulsed output

on/off time

duty cycle

duty cycle calculation

“on time”- pulse duration

“off time”

pulse period- “on time” + “off time”

equation: on/ pulse period (on + off)

pulsed output

temporal average intensity

average power output during both the on and off period pulse period

maximizing nonthermal effects

temporal average intensity

spatial average intensity x duty cycle

when are nonthermal effects maximized

at temporal average intensities of .1-.2 watts/cm²

contraindications for ultrasounds

lack of temperature sensitivity, compromised circulation, epiphyseal areas in children, malignancies, should not be placed over reproductive organs, eyes, heart, spinal cord, and joint prothesis

treatment parameters for ultrasound

size of treatment area, frequency, continuous or pulsed output, intensity, desired tissue temperature increase, estimated rate of tissue temperature increase, treatment time

size of treatment area

ERA

soundhead can be used for a rough estimate; must recognize that ERA will be smaller than the sound head

frequency

depth of target tissue

usually 1 or 3 MHz

when to use non-thermal or thermal

non-thermal: inflammatory/ fibroblastic repair stage

thermal: maturation/ remodeling

non-thermal effects

intensities of .1-.2 watts/cm²

need to consider spatial and temporal average intensities

intensity

BNR

rate of healing

vigorous heating

3-4* C increase in tissue temperature— tissue elongation

t/f tendon heats faster than muscle

TRUE

treatment time

based on frequency selected, intensity, desired tissue temperature increase, estimated rate of tissue temperature increase

phonophoresis

sound waves open pathways that allow the medication to diffuse through the skin

put medication on the skin and then the sound wave over the medicine to help the medicine diffuse into the skin— you need to make sure that the acoustical impedance is correct

treatment time equation

desired temperature= rate of increase x time

do the examples in the slides

do the examples in the slides