Final Study Material Part 1 Flashcards
When would you use 3.3MHz? what is the minimal intensity for a thermal effect?
- 3 MHz is superficial target tissue (<1 inch below the surface)
- minimal dosing is .5 W/cm2
When would you use 1MHz? what is the minimal intensity for a thermal effect?
for a deeper target tissue
- 1-2” below surface = minimal dosing is 1 W/cm2
= >2” below surface = minimal dosing is 1.5 - 2 W/cm2
The intensity of radiation absorbed is maximum when there is no angle between the surface & the source, but as the angle between the radiation (beam) and surface is increased, less energy is absorbed
Cosine law
- The amount of energy absorbed varies as a Cosine function of the angle between the surface and the source.
The intensity of energy received on a surface is inversely proportional to the square of the distance from the source; the greater the distance = the lower the intesity
inverse square law
The crystal located in the US head vibrates by _______ in response to an alternating current creating US at the ______ of the applied current
expanding and contracting; frequency
the changing of electrical energy to mechanical energy; The applied voltage causes compression of the crystal in US head; alternating current compresses and expands the crystal creating the linear compression waves
Reverse Piezoelectric Effect
- electrical energy converted to mechanical
Movement of molecules are perpendicular to the direction of sound wave propagation
Transverse wave
- only occurs in solids
- occurs in bones
Movement of molecules are parallel to the direction of sound wave propagation
Longitudinal wave
- occur in liquids and solids
- occur in soft-tissue and bone!
Increased concentration of molecules and increased pressure in regions called
condensations
- areas of high pressure (molecule compression)
Decreased concentration of molecules and decreased pressure in alternating regions called
rarefactions
- areas of low pressure (molecule expansion)
- This is where heat is produced!!
- this is when molecules move
average intensity of all regions of the sound beam, and is most affected by the Spatial Peak Intensity.
Spatial average intensity
Spatial peak intensity / spatial average intensity
beam nonuniformity ration (BNR)
- usually 6:1
- depends on US head
- if SPI gets larger than BNR, it could be a danger to your patient
What does the intensity setting on the US machine represent?
- with continuous = Spatial average intesnity
- with pulsed = temporal peak intensity
What does BNR mean clinically?
- the BNR represents where the treatment field is highest
- for example, BNR is 5:1 - the average intensity to treatment area will be 1 W/cm2, but at the concentrated area (in the center of the beam), the intensity of the wave is actually 5 W/cm2
- this is why the ultrasound head must be moved around with adequate speed (4cm/sec) to avoid hot spots
setting on US machine during continuous wave US. Represents the average intensity of the sound beam and is sensitive to all high and low strength regions, but is most sensitive to the Spatial Peak Intensity
Spatial average intensity
The greatest intensity anywhere in the within the US beam
spatial peak intensity
The US machine setting (W/cm2) during pulsed ultrasound. It does not equal the actual intensity of ultrasound energy received by the patient during pulsed ultrasound
Temporal peak intensity
the average ultrasound intensity received by the patient over the time of the pulse; the actual ultrasound energy received by the patient during pulse ultrasound
Temporal average intensity
- To determine the Temporal Average Intensity you must understand the Duty Cycle of Pulsed Ultrasound
What kind of US would you use for acute and subacute inflammation?
pulsed US
what does the cosine and inverse square laws apply to?
- Microwave Radiation
- Infrared Radiation
- Ultraviolet Radiation
How does US decrease muscle spasms caused by musculoskeletal injury?
- US decreases the frequency of discharge of Type II muscle spindle afferents
- US increases the frequency of discharge of Type Ib GTO afferents (inhibits α-motoneurons)
What is needed to transmit mechanical sound waves from the US crystal (head) into the body tissues?
Denser mediums
- water, US gel, mineral oil, lotions
- lotions and creams contain more air bubbles causing acoustic impedance
Continuous uninterrupted movement of charged particles (+ ions or – ions) in one direction for at least 1 second.
Direct Current (DC)
The continuous bi-directional flow of charged particles; The change in direction of flow occurs at least once every second
Alternating Current (AC)
What is AC used for (modality-wise)?
NMES of innervated muscle; pain control
What waveforms produce polarity?
- polarity occurs when there is a net DC
What is DC used for (modality wise)?
Iontophoresis, hyperhidrosis, NMES of denervated muscles
he brief (< 1 sec;usually microseconds) unidirectional (monophasic) or bi-directional flow of charged particles separated by a brief period of no flow
Pulsed Current (PC)
What is PC used for (modality wise)?
Edema control, Pain control, treatment of resistant wounds, and NMES of innervated muscle
When is paraffin wax indicated?
- Arthritis of hands & feet
2. Shoulder hand syndrome a.k.a. Complex Regional Pain Syndrome or Sudecks Sympathetic Dystrophy
How is phonophoresis properly applied?
- Clean surface of oils
- apply medication with a gloved hand
- apply ultrasound
- apply appropriate US application
What is the effective on off time for muscle stimulation for muscle strengthening?
On time = 6-10s
Off time = 50-120s
- long off time for minimal muscle fatigue
- on off ration of 1:5, decreasing gradually to 1:4 or even 1:3
What effects does frequency have on muscle contraction and fatigue?
- low frequency = m. twitch; m. requires 35- 50pps in order to produce a tetanizing contraction
- high frequency 50-80 results in m fatigue
- 50 pps is best for results
- takeaway - high frequency results in more fatigue
What waveforms do not produce polarity?
biphasic symmetrical balanced waveforms
What is the chemical reaction that takes place underneath the cathode in DC application?
Cathode = negative electrode
- produces NaOH
2Na + H2o -> 2NaOH + H2
What is the chemical reaction that takes place underneath the anode in DC application?
Anode = positive electrode
- produces HCl
2Cl2 + 2H2O -> 4HCL + O2
Does the cathode or anode produce a more caustic effect to the skin in DC current?
Cathode; NaOH is more caustic to the skin
How does the burst frequency effect the burst period?
The burst frequency breaks up the period into “x” amount of bursts per second; SO, if the burst frequency is 50 bursts per second, it breaks up the charge output to 20 ms burst periods; amount of those burst periods “on” is controlled by % duty cycle
What is a constant voltage stimulator?
The stimulator keeps the voltage constant; if resistance goes up (for instance, by dry electrodes), the current will decrease, resulting in a decreased muscle contraction
V = IxR
What is a constant current stimulator
Seen in iontophoresis; if resistance goes up, the voltage also increases to keep the current constant
- these can cause serious burns!
- most of these stimulators are voltage limited and shut off at a certain voltage
I = V/R
A group of 2+ AC cycles or 2+ pulses; modulated in a time of milliseconds
burst modulated current
What produces a greater muscle force, 2500 Hz or 5000 Hz carrier frequency?
2500 Hz
- carrier frequency determines the cycle duration (meaning the amount of time the charge is delivered)
How do you determine the pulse duration when stimulating a denervated muscle?
pulse duration needs to be greater than the chronaxie
- if chronaxie = 10 ms, pulse duration must be greater than 10 ms
What is the difference in muscle fatigue caused by estim and physiological muscle contractions?
Estim m contractions fatigue faster
- with estim, muscle fast twitch fibers are activated first
- another difference: physiologic m contractions have smooth onset where estim contractions are rapid and jerky
What is the order of recruitment of nerve fibers in estim?
- Fast twitch type II (largest diameter)
- Slow twitch type I (smaller diameter fibers)
- opposite in physiological contraction
Why is a negative charge more excitable to a nerve?
- Under positive electrode, you have positive built up on the outside of the membrane and negative attracted on the inside (hyperpolarized axon)
- Under negative electrode, you have negative built up on the outside of the membrane and positive attracted on the inside (depolarized membrane and excitable); Having polarity with a negeative charge creates and excitable nerve
What is the importance of current density in exciting tissue? what effect does the size of the electrode have on the current density?
Greater current density results in greater excitability
- a smaller electrode has more charge density
