Lecture 4 Flashcards
What is Therapeutic Ultrasound?
it is a deep-penetrating agent that produces changes in tissue through thermal & non-thermal (mechanical) mechanisms
What type of heat transfer is U/S?
conversion transfer
- converting one form of energy into another
- sound wave will oscillate tissue and produce heat
What is the Piezoelectric Effect?
- Electric charge travelling through a piezoelectric crystal
- high frequency alternating current is introduced to the crystal causing it to expand & contract producing a sound wave
What does acoustic energy rely on for transmission
-acoustical energy relies on molecular collision for transmission
How does a P-wave (primary) work?
compressional wave - molecules collide & bend forward & elastically rebound - travels through the material in the direction of the release
How does a S-wave (secondary) work?
sliding & rebounding against rigid material - in liquid a shear wave doesn’t transmit but in bone it does
How do Longitudinal Waves work?
- displacement of particles occurs parallel to the direction of the sound
- combination of rarefaction & compression
- capable of passing through liquids & solids (doesn’t pass through gas well)
How do Transverse (shear) Waves work?
- Perpendicular to the direction of the sound waves
- common in solids
- occur when ultrasound hits a bone
What are Standing Waves?
- occurs when U/S travelling through tissues of various impedance
- when reflected wave meets incoming incident wave
- increases intensity of the energy creating areas of high & low pressure
- can be avoided by keeping the sound head moving
How does the Frequency of U/S work?
- measured in cycles per second (Hz)
- size & shape of crystal determines the frequency
- divergence vs. collimating
- the lower the frequency (1mHz) the greater the divergence (3mHz)
- frequency determines depth of penetration
- frequency also determines the rate of absorption
- w/a higher frequency you will get a greater rate of absorption
- superficial
What are the types of U/S?
Continuous & Pulsed
What is Continuous U/S?
- continuous waves which come out a constant speed & within an equal distance
- generates thermal effects as well as mechanical effects
What Pulsed U/S?
Bursts of waves (interrupted at various rates)
-Generates non-thermal effects only
What does the Duty Cycle of U/S consist of?
it is the duration of how long the pulse is on
i. e.
- pulsed ratio
- on for 1 off for 5
10% = 1/10 (on for 1, off for 9)
What is Propagation?
- velocity at which the vibration is propagated through the conduction medium is directly related to the density
- denser materials will have a higher velocity of transmission
EXAM Q: Define Half-Value, Half Layer Rate
depth at which 50% of the ultrasonic energy has been absorbed by the tissue
EXAM Q: What is Half Value Distance?
- 3MHz sound head = effects occur at 1.5cm (.8 to 3cm according to starkey)
- 1MHz sound head = effects occur 5cm
What is Effective Radiating Area (ERA)?
- the area of the U/S head that produces mechanical waves, normally measured in cm2
- measured 5mm from the faces of the sound head, the ERA represents all areas producing more than 5% of the max. power output of the transducer
- always lesser area that the actual size of the transducers face
What materials can you use as Coupling Agents?
- Gel
- Petroleum based creams
- water based lotions
- immersion in water -1/4 inch to 1/2 inch from treatment area
- temperature of coupling agent
- phonophoresis
How could you use cold for adhesive capsulitis (frozen shoulder)?
Want to reduce pain so you can take them through full ROM
What is acoustic spectrum
Acoustic energy requires a medium for transmission of energy
Transmitted by mechanical waves that deform the medium
Any hard substance when compressed that lets off a current is _____ in nature
piezoelectric
What is acoustic energy?
Mechanical wave in which energy is transmitted by the vibrations of the molecules of the biological medium through which the wave is traveling
ultrasound cannot pass through the skin dry - to get passed the skins barrier ultrasound requires a ____
medium
