ULTRASONIC DIATHERMY APPARATUS

Typical Number in Hospital: 5

Cost Bands: 3,4

References: 4,10

Internal heating of tissues can be achieved by the application of a strong ultrasound beam to the skin surface. Ultrasound beams in the low MHz frequencies are commonly used in the physiotherapy department for the treatment of inflammation of joints. The ultrasonic transducer produces a beam of about 1 W/cm2 which may be applied directly to the skin through a coupling oil or jelly, or the patient (or affected part) may be immersed in water.

It is likely that the beneficial effect of this treatment is due solely to the heat liberated in the tissue as the ultrasonic beam is absorbed, but other mechanisms have been suggested. Most heat is believed to be delivered to the periosteum and hence it is used extensively for treatment of inflamed joint capsules. Most devices deliver a continuous wave, but some have pulsed or pulsating waveforms which may be intended to create a kind of 'ultrasonic massage'.

The apparatus consists of an oscillator, and an amplifier delivering between 1 and 5 W to a resonant piezoelectric transducer. A different transducer is required for each frequency, typically 1, 2 and 3 MHz. At 1 MHz approximately half the energy is released in the first 5 cm. Controls may include intensity and waveform selection.