Ultrasound Flashcards
What is Ultrasound?
Ultrasound is a type of mechanical vibration.
Longitudinal waves made up of a series of mechanical compressions and rarefactions that are separated by a fixed distance (i.e. a wavelength)
What is Ultrasound?
Metal plate of treatment head oscillates to generate a stream of compression waves creating an ultrasound beam.
* Frequency of waves is between 1 MHz and 3 MHz
Ultrasound Absorption
As ultrasound passes through a material the energy is dissipated or attenuated
Estimated half-value depth for therapeutic ultrasound in different tissues
Ultrasound Reflection
As ultrasound crosses a tissue boundary some of the energy is reflected back and the remainder is refracted.
Proposed Physiological Effects
Thermal
- Deep healing
Non-thermal
- Cavitation
- Standing waves
- Acoustic streaming
- Micromassage
Pulsed Ultrasound
Reduces the average intensity of waves delivered to the tissues and therefore reduces the heating effect but still produces the mechanical effects.
Proposed Therapeutic Benefits
- Might increase healing of chronic pressure ulcers
- Might increase healing of soft tissue injuries
- Could improve extensibility of scar tissue
- Could improve fracture healing – requires low intensity pulsed ultrasound
Safety Considerations
Burns – poor technique (gel, movement, contact of head)
Tissue damage – high intensities
Periosteal pain – treatment near bony prominences
* If there is superficial bone nearby use a low intensity (< 0.5 W/cm2) and move the sound head more quickly
Contraindications
- Near cardiac pacemaker or any other inbuilt stimulator
- Circulatory insufficiency
- Exacerbation of existing conditions (e.g. acute infections, recent radiotherapy, etc)
- Risk of dissemination (e.g. acute infections, tumours, etc)
- Application to eyes or testes or over a pregnant uterus
- Inability to communicate
- Sensory loss – hot/cold and sharp/blunt discrimination skin test
Skin Safety Tests
Thermal sensitivity test
AND
Sharp/blunt discrimination test using a toothpick, paperclip or sharp pen.
Ultrasound Parameters: Method
Method: Direct contact or water bath
* Water bath useful for hands/feet
Ultrasound Parameters: Mode
Mode: Continuous or pulsed
Acute: Pulse 1 :4/3
Sub Acute: Pulse 1 : 2/1
Chronic: Pulse 1: 1/continous
Ultrasound Parameters: Frequency
Frequency: 1 or 3 MHz
* 1 MHz for deeper tissues (approx 6 cm)
* 3 MHz for more superficial structures (approx 3 cm)
Ultrasound Parameters: Duration
often calculated from 1min No. applicator heads that could fit over treatment area (often equates to approx. 5-10 min)
* Need to adjust for pulse ratio (if used)
Ultrasound Parameters: Intensity: in Watts/cm2
- Acute & subacute: 0.1 – 0.5 W/cm2
- Chronic: 0.3 – 1 W/cm2 (some studies have used up to 3 W/cm2)
Ultrasound Application
- Machine check to ensure there is an output
- Clean the treatment site and apply the couplant/gel to the skin surface
- Position the treatment head on the treatment site and only turn on the output while the treatment head is in contact and moving
Avoids damage to the transducer and reduces burning risk - Maintain good contact with the skin
- Move at a speed of approximately 4 cm/s
- Turn machine off while the treatment head is still in contact and moving
Might facilitate bone healing
- Delivered at a much lower intensity than traditional ultrasound energy ▪
o Delivery = 1.5 MHz at 0.03W/cm2, 20% duty cycle - Applied for 20 mins daily for a period of 4-6 weeks
- Has a low heating effect due to very low intensity
