Ultrasound

Question 1

What is Ultrasound?

Answer 1

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)

Question 2

What is Ultrasound?

Answer 2

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

Question 3

Ultrasound Absorption

Answer 3

As ultrasound passes through a material the energy is dissipated or attenuated
Estimated half-value depth for therapeutic ultrasound in different tissues

Question 4

Ultrasound Reflection

Answer 4

As ultrasound crosses a tissue boundary some of the energy is reflected back and the remainder is refracted.

Question 5

Proposed Physiological Effects

Answer 5

Thermal
- Deep healing

Non-thermal
- Cavitation
- Standing waves
- Acoustic streaming
- Micromassage

Question 6

Pulsed Ultrasound

Answer 6

Reduces the average intensity of waves delivered to the tissues and therefore reduces the heating effect but still produces the mechanical effects.

Question 7

Proposed Therapeutic Benefits

Answer 7

• 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

Question 8

Safety Considerations

Answer 8

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

Question 9

Contraindications

Answer 9

• 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

Question 10

Skin Safety Tests

Answer 10

Thermal sensitivity test
AND
Sharp/blunt discrimination test using a toothpick, paperclip or sharp pen.

Question 11

Ultrasound Parameters: Method

Answer 11

Method: Direct contact or water bath
* Water bath useful for hands/feet

Question 12

Ultrasound Parameters: Mode

Answer 12

Mode: Continuous or pulsed
Acute: Pulse 1 :4/3
Sub Acute: Pulse 1 : 2/1
Chronic: Pulse 1: 1/continous

Question 13

Ultrasound Parameters: Frequency

Answer 13

Frequency: 1 or 3 MHz
* 1 MHz for deeper tissues (approx 6 cm)
* 3 MHz for more superficial structures (approx 3 cm)

Question 14

Ultrasound Parameters: Duration

Answer 14

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)

Question 15

Ultrasound Parameters: Intensity: in Watts/cm2

Answer 15

• Acute & subacute: 0.1 – 0.5 W/cm2
• Chronic: 0.3 – 1 W/cm2 (some studies have used up to 3 W/cm2)

Question 16

Ultrasound Application

Answer 16

• 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

Question 17

Might facilitate bone healing

Answer 17

• 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