Ultrasound Flashcards
value defining US
soundwaaves with frequency greater than .02MHz
(≥ 20k Hz)
what is the piezoelectric effect
crystal in the sound head that vibrates when electricity is run through it causing US waves to leave out into the next medium
what does frequency determine
depth of US wave penetration
compare 1 MHz to 3 MHz frequencies
1 - deeper penetration (>2 to 5cm)
3 - superficial penetration (1-2cm)
explain the depth associated with higher and lower frequency US waves
higher - faster vibration, less absorption of US waves
lower - slower vibration, more absorption of US waves
explain the relationship between compression and refraction
compression = US waves bringing cells together
refraction = bounce off of each other
explain longitudinal vs transverse wave propagation and tissues associated
longitudinal = compression and refraction reaction occurring in soft tissue vertically
transverse = compression and refraction occurring perpendicular to soft tissue
what is the idea of attenuation
absorption of US waves will be greatest in the tissue that has a higher collagen content
explain the relationship between US wave intensity and its depth into soft tissue
deeper into material = less intense US wave
definition of thermal effect
US causing increased tissue temperature
definition of non-thermal effect
US wave altering cellular activity
tissues with high attenuation coefficient
tendon
ligament
cartilage
scar tissue
joint capsule
tissues with low attenuation coefficient
muscle
- anything with high water content
cavitation definition
formation of gas-filled bubbles that expand and compress due to US induced pressure changes in tissue fluids
microstreaming definition
unidirectional movement of fluids along cell membrane causing cell to rotate
acoustic streaming definition
steady, circular flow of cell material caused by US waves
compression definition
increased density of material as US waves pass throughr
refraction definition
decrease in density of material as US waves pass through
explain flow of material due to microstreaming? why does this happen?
very small flow of material due to gas bubbles
–> rotation of cell will change what it comes into contact with
continuous US definition and associated benefit
current is delivered continuously to transducer
thermal
pulsed US definition and associated benefit
current delivered for limited portion of time to transducer
non thermal
duty cycle definition
amount of time current is being delivered
ie = period of time on compared to total pulse period
how does pulsed US percentage differ from ratio
% = on time / total time
ratio = on time : off time
ie 1:4 ratio is a 20% pulse
1 on : 5 total
frequency definition
number of compression refraction cycles per second
measured in HZ
power definition and unit
amount of energy per unit of time
in Watts
intensity definition and unit
power/unit of area
W / cm²
spatial peak intensity
peak intensity of US output over transducer area
spatial average intensity
average intensity of US output over the transducer area
beam non uniformity ratio
ratio of spatial peak intensity to spatial average intensity
what is the value associated with beam non uniformity ratio that is acceptable
5:1 or 6:1
what is the effective radiating area
area of the transducer from which the US energy radiates half the size of the transducer energy
in a general sense, what is preferred when considering the beam nonuniformity ratio
lower the better
ERA associated with US head
5-10 cm² ERA
≈ 1.5 in
relationship between ERA and treatment area and effect
if treatment area is 2-3x ERA
thermal
non-thermal effects of US
increased:
skin / cell permeability
macrophage responsiveness
chemotactic factor and histamine
protein synthesis by fibroblasts
NO synthesis in endothelial cells
proteoglycan synthesis
when are non-thermal effects indicated
inflammation phase of healing
wound healing
blood flow promotion to local area
skin permeability for topical meds
benefits of thermal US
increased:
collagen extensibility
joint freedom/ROM
blood flow
tissue repair
decreased:
muscle spasms
pain
how does absorption coefficient relate to temperature changes
higher coefficient = greater temp change
lower = less change
relation of intensity and frequency for temperature change
less intensity is needed with higher frequencies
what is the time associated with optimal US treatment
5-10 min
stage of healing associated with intended benefit
acute/inflammatory - non thermal
proliferative = non and thermal
what is effective for trigger point treatment
US in combination with e-stim
what is sonic accelerated US? what is the idea behind it/special considerations
introducing microdamage to chronic disorderly tissue in hopes to stimulate body’s natural inflammatory response
need MD referral
what are coupling agents
medium in which US waves are transmitted through
conducting gel vs immersion vs gel pad or water bladder
conducting gel = direct contact
immersion = US through water
gel pad = US through pad/bladder
relationship between coupling agent and absorption
direct contact = most absorption
when would immersion or gel/water bladder coupling agent be indicated
highly contoured or uneven surface area of body
effectiveness of direct coupling agents
gel > water bladder > immersion
temperature increase associated with tissue extensibility
> 4° C
clinical applications of US
pain reduction
heating tendons/ligaments
scar tissue/joint contractures
soft tissue healing
detection of stress fx
removal of plantar warts
when should pts feel warmth when intending on gaining thermal benefit of US
2-3 minutes
what variables would cause duration need to be increased
low intensity
low frequency
larger ERA
thermal effect desired
in relation to treated area, what factor of ERA size contraindicates US
> 4 x size of ERA
dosage related to US
effect should be observed within 1-2 treatments
thermal effect dosage suggestion
subacute/chronic stage
usually 3x a week
non-thermal effect dosage suggestion
acute stage
daily
explain the timing of US in your overall treatment plan
during / prior to stretching if goal is to increase tissue extensibility via thermal effects
not after any treatment that alters sensation
how long do the effects of US last
10-15 minutes
what is the rate at which the sound head should be moved
4cm / second
ie fast enough to preserve motion / slow enough to maintain contact
contraindications of US
acute fracture
pregnancy (no low back/abdominal)
malignancy
thrombophlebitis
over metal/plastic devices
bleeding
non-closed growth plates
pacemakers
thought behind thrombophlebitis contraindication
what about implants
could dislodge a clot
could heat up molding that holds implant and dislodge it
how to document for US
indicate if pulsed or continuous
treatment method (if not direct with gel)
if medication was included
frequency (MHz)
intensity (W/cm²)
duration
pt response
