Most therapeutic ultrasound machines have a choice of 1 or 3 megahertz frequencies, and the clinician is left to determine which of these frequencies is necessary. This is the definition of megahertz and the frequency of which is indicated during ultrasound therapy.
Megahertz is defined as the abbreviated MHz, unit of alternating current (AC) or electromagnetic (EM) wave frequency equal to one million Hertz (1,000,000 Hz). This frequency is not audible to humans, since for humans the audible frequency is lost at 20,000 Hz.
The frequency of therapeutic ultrasound is important depending on the area being treated for pain relief, or to accelerate healing due to injury. There is an inverse relationship between higher frequency and penetration depth. As the frequency increases from 1 to 3 MHz, the penetration depth decreases, i.e. the higher the frequency, the less penetration.
The depth of penetration is important if the ultrasound treatment is on the ankle, joint, elbow, TMJ (mandibular joint), knee, or other area that is close to the surface to be treated. To create heat for the ankle, the doctor will set the frequency to 3 MHz, because the treated area is close to the surface, and the higher frequency has less penetration, so healing tissues are better oriented.
If the patient suffers from back pain, sciatica, shoulder pain, hip pain or other areas where the tissue is located deeper near the joints with the muscle tissue or where the muscle tissue is the target tissue, then 1 MHz is used because the affected district.
Many therapeutic ultrasound devices come with a choice of frequencies; however, for home use it is necessary to have several frequency options, but it is more important to have the frequency necessary for the patient's condition. In acute situations, it is most beneficial for the patient to take an ultrasound device for home use, and not to go back and forth at a higher price to the clinics for short ultrasound procedures.
