US Flashcards
1
Q
US
A
- Sound with frequency greater than 20,000 cycles per second that when applied to the body produces thermal and non-thermal effects
- Measure in Hz & MHz
- 1 Hz = 1 cycle / second
- 1 MHz = 1 million cycles / second
- Audible sound 16 – 20,000 Hz
- Ultrasound is above 20,000 Hz
- Therapeutic ultrasound – 0.7-3.3 MHz
- Maximizes energy absorption at a depth of 2-5 cm
- Travels faster through denser material
- More quickly dissipated
- Heats tissues with high collagen content such as tendons, ligaments, or fascia
- Sinusoidal pattern
- Diverge from source
- If higher frequency, then less divergence
- Wave length = distance between 2 successive peaks
- Frequency is inversely related to wave length
- Velocity = frequency x wavelength
- In all tissues except compact bone, waves travel longitudinally
- Compact bone waves travel longitudinally & transversely
- Increases danger of burning at level of bone
- Delivers acoustic vibrations via a transducer that utilizes a quartz crystal to convert electrical energy to ultrasonic waves (acoustic energy)
- The US waves transmit energy by alternately compressing and rarefying material.
- Collagen in the tissue absorbs this energy
- Muscle, tendon, ligaments
- Produces thermal and non-thermal effects
2
Q
Conversion
Energy Transfer
A
- Conversion: The process of changing energy from one form to another
- US: Electrical energy converted to acoustic energy
- Energy absorbed by tissues with high collagen content such as tendons, ligaments, or fascia
- Produces thermal and mechanical (non-thermal) energy
- Travel by deforming & vibrating molecules
- They bump next molecule & transfer energy
- Chain reaction until energy is dissipated
- Coupling Agent
- Must go through a medium
- Decreases impedance of air
3
Q
Frequencies
A
- 1 MHz-low- MORE likely to use this. penetrates DEEPER
- Increase intensity watts
- Penetrates to about 5 cm
- 3 MHz –high- PIP/ snuff box not as deep
- Decrease intensity watts
- Penetrates 1-2 cm
4
Q
Intensity
A
- Determined by strength of energy produced
- Measured in W/cm2 (watts per centimeter squared)
- Higher intensity leads to higher temps
- Crystal of US head vibrates unevenly
- Intensity varies
- Highest intensity occurs where crystal vibrates most: spatial peak average intensity
- Average power delivered: spatial average intensity
- Effective Radiating area (ERA)
- treatment area should not be more than 2-3 times the ERA
- Beam nonuniformity ratio- want lower ratio ideally 3:1
- Ratio of spatial peak intensity & spatial average intensity
- < 6:1 are acceptable
5
Q
Duration
A
- Duration: The amount of time the US treatment is applied
- 5-10 minutes most typical
- Increase duration for the following:
- When lower frequencies/intensities are used
- When treating larger areas
- When the goal is to further increase the tissue temp.
- Increase duration for the following:
- 5-10 minutes most typical
6
Q
Attenuation
A
Attenuation: as sound waves travel through tissue it gradually decreases in intensity
Waves are attenuated by reflection/refraction and absorption
Reflection: redirection of a beam away from a surface at an angle equal and opposite to the angle of incidence
Refraction: redirection of a wave at an interface at a different angle in which it entered the tissue
7
Q
Absorption
A
- Absorption is greatest in tissues with a high collagen content
- Absorption of energy per cm
- Blood 3%
- Fat 13%
- Muscle 24%
- Blood vessel 32%
- Skin 39%
- Tendon 59%
- Cartilage 68%
- Bone 96%
- Impedance: resistance to transmission (absorption)
8
Q
Terms
A
- Intensity__: The power per unit area of the sound head, expressed in watts per cm squared (W/CM²)
- World Health Organization limits therapeutic US to 3 W/cm²)
- Frequency__: The number of compression-rarefaction cycles per unit of time. Expressed in cycles per second or Hertz.
- Therapeutic frequency range: 1-3 MHz
- Increases in frequency decreases the depth of penetration in superficial tissues
- 1 MHz : penetrates up to 5 cm
- 3MHz: penetrates 1-2 cm
- Duty Cycle: The proportion of the total treatment time that the US is on.
- Expressed as a % or ratio ie 20% or 1:5 duty cycle (US is on 20% of the time and off 80%)
- 100% = continuous ultrasound
- Duration: The amount of time the US treatment is applied
- For most non-thermal , thermal treatments 5-10 min
- If goal is to increase tissue temp., duration should be adjusted according to frequency and intensity
- Mode: Know the difference between Continuous and Pulsed US
9
Q
Terms
A
- Spatial average temporal peak intensity (SATP): Highest intensity occurs where crystal vibrates the most
- Spatial average temporal avererage (SATA): Average power delivered
- Effective Radiating area (ERA): the total area of the surface to the transducer that actually produces sound wave
- Beam nonuniformity ratio (BNR): the ratio of the spatial peak intensity to the spatial peak average intensity. Usually between 5:1 and 6:1
- Cavitation: the formation, growth, and pulsation of gas-filled bubbles caused by US.
- Microstreaming: unidirectional movement of fluids along cell membranes via mechanical pressure changes with the US field
- Attenuation: decrease in US intenstiy as it travels through tissue
- Absorbtion: conversion of mechanical energy into heat
- Reflection: redirection of a beam away from a surface at an angle equal and opposite to the angle of incidence
- Refraction: redirection of a wave at an interface at a different angle in which it entered the tissue
10
Q
Mode: Continuous vs. pulsed US
A
- Continuous produces sound wave 100% Thermal effect
- Pulsed US has on / off cycles Nonthermal effect
- Duty cycle = time on / cycle time
- 20% duty cycle most common
- During off time heat can dissipate
11
Q
Thermal and non-thermal effects
A
- Thermal Effects
- Continuous US
- Amount of heat depends on
- Intensity
- Duration
- Size of treatment area
- Properties of tissues
- All effects of heat
- 1 degree C increases metabolism
- 2-3 degree C reduces muscle spasm, pain
- > 4 degree C increases tissue extensibility
- Can reach superficial and deep tissues
Mechanical Effects (Non-Thermal)
- Pulsed US
- Most common: 20% duty cycle
- Ions in fluids move—called microstreaming
- Increase cell membrane permeability and cellular activity
- Gas bubbles expand & contract—called cavitation
- Contribute to changes in cell membrane
- Unstable cavitation = bursting of bubble
- Can lead to tissue destruction
- Unlikely with therapeutic US
12
Q
Muscular effects of US
A
- US has been found to be effective at heating tissues
- Hemodynamic Effects
- Increase blood flow due to heat & changes in cell permeability
- Chose parameters to increase muscle temp. at least 1C
- Max. results occur after 5 minutes
- Longer treatments maintain blood flow
- Return to baseline after 1 minute
13
Q
Connective Tissue Effects
A
- Temperature changes occur faster than in muscle
- Need increase of > 4C temperature to increase extensibility
- Temperature at this level only maintained 4 minutes post treatment
- Stretch during/immediately after US and maintain stretch for at least 4 minutes after US
14
Q
Neurological Effects
A
- Motor NCV mixed depending on parameters
- Sensory NCV increases with thermal US
- Pain threshold raised at 0.8 MHz at 1.5 W/cm2
15
Q
Pain/ Edema reduction
A
Pain
May need to apply w/in 48 hours post injury for best effects
US plus exercise improves pain relief
Continuous US may be effective for reducing pain. Settings @ 1 or 3 MHz, 0.5 to 3.0 W/cm intensity & 3-10 minutes duration.
Edema
Mixed results in studies
In general, studies support US initially supports inflammatory process, but then speeds edema reduction
Generally low intensity pulsed US
