Flashcards in Therapeutic Ultrasound Deck (24):
Ultrasound is a(n)
a) Mechanical modality
b) Electrotherapeutic modality
Which is not a characteristic of a US wave pattern?
d) all or none of the above
d, all of the above are characteristics.
Frequency is usually 1 or 3 MHz, wavelength in tissue for 1MHz is 1.5mm, for 3MHz is 0.5mm, and velocity is about 1500 m/s (similar to saline solution)
How are the characteristics of ultrasound related to each other?
Answer: V = F*Wavelength
Why does a higher frequency stay more superficial?
Answer: because the energy is absorbed and dissipated at a faster rate
What is the half value depth? How does the density of tissues affect this?
Answer: this is the depth that only half the energy delivered is still available. While the density of the tissue will affect this measure by absorbing more energy, the average half value depths are still used: 4-6 cm for 1MHz, 2 cm for 3MHZ
Note: since higher density tissues (like bone) and superficial tissues absorb more energy from ultrasound, there is a possibility that these tissues are more likely to respond to US treatment.
How is treatment intensity defined and what is it represented by (include unit)?
Answer: It is the amount of energy delivered to a certain area (W/cm2) represented by the Spatial Average Intensity (SAI) which is:
W (power) / ERA (effective radiating area)
If the mode is pulsed, the intensity might be an average of the intensity so the SAI becomes SATA, which is just the SAI x duty cycle (%)
What is BNR? Is it better to be smaller or larger in value?
Beam Non-Uniformity Ratio, better to be smaller value since this means the energy delivered is more consistent
Why is it important to use gel with ultrasound?
Gel helps prevent the reflection of energy that would happen at the metal/air boundary of the sound head (reflection and refraction can happen at points of transition of mediums)
When would you use intensities under 1.0 W/cm2? What kind of pulse ratios would be used?
Answer: For non-thermal effects. For thermal effects, 1.5 W/cm2 may be fine. Intensity is usually determined for non thermal based on the phase of tissue healing:
Inflammatory: 0.1 - 0.3 Proliferative: 0.2 – 0.5 Remodeling: 0.3 – 1.0
Pulse ratio: 1:3 – 1:4 1:2 – 1.1 1:1 or continuous
Watson also has a table to adjust these values for different tissue depths, which may be more effective.
What mode (continuous or pulsed) is usually used for thermal effects?
Answer: continuous – more energy delivered over the treatment time.
How are pulse duration, pulse ratio, pulse frequency, duty cycle, and coefficient of operation related?
Pulse frequency is the inverse of the pulse period. (if 100Hz – 1/10ms, pulse period is 10 ms and with a ratio of 1:4 makes it 2ms on and 8 ms off)
Adjusting pulse frequency without changing the ratio will modify pulse duration and period (for example, 50Hz is 1/20ms with a ratio of 1:4 is 4ms on and 16ms off – therefore decreasing the frequency would increase the pulse duration and period with the same ratio)
Duty cycle is the percentage of cycle that energy is delivered (for example, ratio of 1:4 is 20%)
Coefficient of operation is the inverse of the duty cycle, which is by how many times you have to increase the treatment time to deliver the same amount of total energy. You can find this by adding the numbers in the pulse ratio: 1:4 = 5
Why is it necessary to keep the head moving? If the area to treat was 2X larger than the head, how much longer would the treatment time be? What are the max and min treatment areas?
The head must move due to the BNR, max is 4X area, min is twice the size since it can't be the same size (needs to be moving right)
what is cryotherapy usually used for?
reduce pain and limit formation of edema
why is cold the modality of choice for acute injury?
limits bleeding, vasoconstriction, limits histamine etc, limits secondary hypoxic tissue injury by slowing the metabolism of cells
what are some things to watch out for when using cryotherapy?
slower nerve conduction velocity will also affect sensation and proprioception -careful about balance tasks
decreased force production in muscles
cold packs utilize conduction, convection, or evaporation?
what is the minimum amount of time to use crushed ice after an acute injury?
what are the two main uses of heat?
relieve pain and relieve stiffness (increase tissue viscoelasticity)
what should be avoided if tissue is raised above 40 degrees? what happens at this temperature?
tissue viscoelastic properties change, so there is less load required for increasing length, but also can rupture under increased heat so avoid overly aggressive stretching right after heat
how deep do most heat modalities hit?
how frequent should US be for acute/subacute/chronic scar?
daily for 10 days for chronic scar
factors to keep in mind when applying cold
size of area
coldness of cold thing
how long it will stay cold
what kind of tissue it's going on (metal?!)
length of time on area
how hot are hot packs? what about parrafin?
hydroculator - 70-75
parrafin - 45-50