Ultrasound Flashcards
Indication (Thermal Effects)
- Pain relief in chronic bursitis, myositis, tendonitis and arthritis.
- Pain relief from neuromas (pinched nerve).
- Adhesive Scars
- Affects nerve conduction velocity (by changing nerve conduction velocity you can reduce pain).
- Improve extensibility of connective tissue by loosening chemical bonds(loosen tissue before stretching).
Indications (Non-Thermal Effects)
- Cavitation may break down calcium deposits (aka calcifications)
- Affects nerve conduction velocity, possibly altering pain perception
- Phonophoresis to drive chemicals through the skin (Increase the rate of healing)
CONTRAINDICATIONS
- Where heat is not indicated (When using thermal effects such as:
Severe Cardiac Disorder
Malignancy
Sepsis - Hemophiliac patients
- Over deep vein thrombosis (sudden death, clot breaks free and ca get stuck in unwanted areas like the brain, heart, lungs)
- Over Neoplasm (a new growth, never provide heat to a new growth, it will only speed up the process)
- Over the pregnant uterus
- Over the eyes (like an egg cause changes in proteins)
- Over the heart
- Near a pacemaker (lump under the left side of the skin).
- Over growth plates (mainly in adolescents, if you heat over a growth plate you can cause the plate to close prematurely).
Precautions
- Over a healing fracture
- Over the spinal cord (don’t go back and forth, lift up head after your done with one side, then move to the other).
- Over metal implants ( diathermy and metal is no bueno. Metal is a great conductor of sound so it heats up quickly, also use caution when US over a cemented joint).
Ultrasound Controls
- Frequency
- Beam Nonconformity Ratio (BNR)
- Duty Cycle
- Intensity
- Treatment Time
- Head Movement
- Alcohol Wipe Between Uses
Frequency
1 MHz penetrates to 5 cm (2 inches)
3 MHz penetrates to 1 cm (0.5 inches)
Beam Nonconformity Ratio (BNR)
BNR rates the quality of the head, a 1:1 head is perfect and sound intensity is equal over ALL of the head. A BNR of 6:1 is the minimal acceptable.
BNR affects the ultrasound treatment in that the poorer the BNR the faster the sound head must be kept moving in order to avoid “hot spots”. With a low BNR, the sound head can be moved as slowly as 1cm/sec. With a high BNR you may need to move the sound head at 4 cm/sec.
Duty Cycle
Pulsed vs. Continuous
Continuous US gives both a thermal and a non-thermal effect. Pulsed US, especially below 10% gives only non-thermal effects. Typically if heat is not contraindicated, continuous US is used. If heat is contraindicated, as in a recent injury, pulsed US may be used for tissue healing effects without heating the area.
Acute injury use 10 - 20% (non-thermal)
Subacute injury use 30 - 50%
Chronic Injury use 60 - 100%
Intensity
Watts/cm^2
Maximum intensity is determined by the patient tolerance. Typical maximum intensity is 1.5 w/cm^2 but a machine with a poor BNR might be uncomfortable at that intensity. Alternatively, if a deep structure that is not near a bone is to be heated the patient may safely tolerate intensities above 1.5 w/cm^2
1 MHz
- Acute injury desire .1 - .2 w/cm^2
- Subacute injury desire .3 - .8 w/cm^2
- Chronic Injury use .9 - 1.5 w/cm^2
3 MHz
- Acute injury desire .1 - .2 w/cm^2
- Subacute injury desire .1 - .3 w/cm^2
- Chronic Injury use .3 - 1 w/cm^2
Intensity (Always Consider Depth)
If the injury is deeper than the surface, you will need to adjust your intensity for depth and loss of energy.
For 1 MHz, Intensity should be increase by .25/cm depth
For 3 MHz, Intensity should be increased by .4/cm depth.
Example: For 1 MHz at 4 cm, and desired acute intensity of .2 w/cm^2. The intensity should be set at
Desired + (Depth)(Ratio)(Desired)
.2 + (4 cm) (.25/cm) (.2)
.2 + ( 1 cm) (.2)
.2 + .2 = .4 w/cm^2
Effective Radiating Area
(ERA) is the area of the sound head which is producing an ultrasonic wave.
Treatment Time
As a rule of thumb, an 8-10 minute treatment of US can cover an area twice the are of the sound head size. If a larger are is covered, treat is segments, each twice the sound head size, with similar additional time.
Example: You want to treat an area of 24cm^2 and you have an 8.5 Head ERA, what is you treatment time. Well we know that a head with an 8.5 ERA can cover an area of 17 cm^2 for 8-10 min. But that wont cover the whole area so 24/17 = 1.41176 or 14 minute treatment time for 24cm^2
US Movement Speed
Head movement speed is between 1-4 cm/sec.
1 cm/sec for a BNR of 3 or less.
4 cm/sec for a BNR greater than 3.
Attenuation
(loss of energy) A decrease in energy within a sound beam as it travels through a tissue.
This results from three processes:
- Reflection
- Refraction - energy can bend
- Absorption - the transfer of energy from the sound beam to the surrounding tissues. Absorption increase as frequency increases. As absorption increases, there is less sound energy available to propagate further through the tissue. At frequencies greater than 20 MHz superficial absorption becomes so great, that less than 1% of the sound penetrates beyond the first centimeter.
Ultrasound Units
Basic Components
- Power supply
- Oscillator circuit
- Transformer
- Coaxial cable
- Applicator
Frequency is generated by an oscillator circuit carefully tuned by the manufacturer.
Intensity is determined by the electrical voltage applied to the transducer.
Voltage is controlled by the setting of the intensity control.
Some machines may produce pulsed mode.
