Ultrasound Background/Terminology Flashcards
Ultrasound (definition)
Application of acoustic (sound wave) energy, inaudible of the human ear which causes a mechanical vibration.
Produces non thermal effects of ultrasound
Pulsed duty cycle
Pulsed ultrasound causes:
Acoustical streaming, micro-streaming, and cavitation which increases cellular metabolism.
Increased cellular metabolism produced by ultrasound results in: (4)
1) Increased enzyme activity
2) Stimulates immune system
3) Increased O2 uptake
4) Increased cellular permeability
Pulsed ultrasound facilitates and increases (2) specific things:
1) Facilitates tissue repair (increased phagocytic activity, fibroblast, & granulation tissue formation)
2) Increases pain threshold (decrease muscle spasm, increase conduction of peripheral nerves, serotonin release)
Produces thermal effects of ultrasound
Continuous duty cycle
In addition to non-termal effects, thermal ultrasound also produces the following (4) benefits:
1) Can produce deep heat (up to 5cm)
2) allows for soft tissue (collagen) extensibility
3) Increases blood flow
4) Increases cellular metabolism
Three types/intensities of ultrasound
1) Low intensity: Diagnostic- Sonogram
2) Medium Intensity: Theraputic
3) High Intensity: Tissue destruction (tumors)
Medical ultrasound is generally between what Mhz’s
.8Mhz to 3.0Mhz
Ultrasound in the 1950’s
AMA recommends use of US as a modality for use of soft tissue healing and pain. Often used in MD offices by non-trained individuals.
Ultrasound in the 1960’s
Regulations were tightened by states and US mainly perscribed for use by PT. OT began use of US in a widespread manner by 1980’s.
Ultrasounds in the 1990’s
National push to demand OT’s competence. Driven mainly by APTA. Individual states established regulations. NY state regulations indicate OT’s must receive training in modalities that include a background in physics.
This is the device that is held/aimed at the pts. skin (with gel or water as a medium)
Transducer: Also called the sound head
Movement of the sound head on the surface should occur at how many cm per second:
Which two motions can be used:
4cm (1.5 inches) per second:
1) overlapping circles
2) back and forth, side to side with overlap
This is housed in the transducer it is more recently made of ceramic or a synthetic material and is only about 1/6” thick
Crystal
Characteristics (4) Of the crystal
1) Subject to breakage if sound head is dropped.
2) Damage can occur if not in contact with transmission medium/skin prior to turning on.
3) Check 1-2x per year to assure it is intact.
4) Informal integrity test: submerging in H20 and observe for bubble formation on surface indicating crystal is functioning.
Reverse Piezoelectric effect
When alternating current is applied (to an electrical charge) to the crystal it responds by expanding and contracting. When the crystal expands and contracts it results in a mechanical response in the tissue in front of it.
The alternating compression - rarefaction is the ultrasound wave.
Compression of crystal
Moves the tissue together
Expanding of crystal
Causes rarefaction or pulling the tissue apart
Degree to which the sound wave passes through the tissue w/o regard to absorption by the given tissue
Penetration
5 types of transmission mediums (coupling agents)
1) Ultrasound gel (97% %= transmit ion or penetration of sound waves) Water based gel that is hypoallergenic (warmed gel is 10% less effective)
2) Ultrasound lotion (90%)
3) Hydrocortisone cream (0-10%) Used in the 80’s-Early 90’s.
4) Other medication infused gels (88%)
5) Water: submersion technique can be used for surfaces that are bony. Transducer is then placed 1/2” away from the skins surface.
Application of ultrasound with a topical drug
Phonophoresis
The process of energy loss
Attenuation
4 ways attenuation occurs
1) Absorption is a main way energy is lost either into tissue or into the transmission medium .
2) Reflection- redirection away in the equal and opposite direction; generally occurs at skin surface if not enough transmission medium.
3) Sound waves decrease in intensity as they travel through the tissue.
4) Refraction- redirection of a sound wave generally due to a blockage by foreign tissue.
The degree to which the sound wave is transferred into the tissue there by limiting penetration.
Absorption
What tissues have a greater absorption of the sound wave
Denser tissues with more protein and collagen.
Formation, growth, and pulsation of gas and vapor filled bubbles caused by the non-thermal mechanical effects of ultrasound.
Stable Cavitation
The steady flow of cellular fluid induced by the mechanical effects of ultrasound
Acoustical Streaming
This number reflects the intensity of the ultrasound output as it varies from the center of the sound head to the outer edges.
Beam Non-Uniformity (BNR)
BNR is greatest at the center.
Those with a ratio that is lower have a more desirable BNR and are generally 2:1.
The highest ratios are 5:1 or 6:1
Why is the BNR important
Hot Spots.
The higher the ratio the ore important it is to you to have constant movement and slightly faster movement of the ultrasound head to prevent hot spots.
The area on the transducer face where the ultrasound energy radiates.
Effective Radiating Area (ERA)
This area is smaller than the actual size of the face of the traducer as the crystal is smaller than the actual face size.
