Question 1

What is the difference between continuous and pulsed therapeutic ultrasound?

Accepted Answer

Continuous output generally produces greater heating, intended to increase local blood flow and collagen extensibility before stretching. Pulsed output reduces average heating because the beam is interrupted, and any remaining effect is attributed to proposed mechanical mechanisms such as acoustic streaming and stable cavitation. Both effects can coexist, depending on intensity and duty cycle.

Question 2

How does frequency affect treatment?

Accepted Answer

Frequency influences depth of treatment: around 3 MHz is absorbed more superficially, while around 1 MHz penetrates more deeply, although depth is not exact or uniform across tissues. Absorption is greatest in collagen-rich tissue such as tendon, ligament and joint capsule, which is why those tissues are the usual targets.

Question 3

Does therapeutic ultrasound work for soft tissue problems?

Accepted Answer

The evidence does not support routine use. Trials are numerous but small, vary in dose and are often poorly blinded, and any benefit over sham is small, inconsistent or absent. NICE advises against offering it for chronic primary pain, osteoarthritis, and low back pain with or without sciatica.

Question 4

Is low-intensity pulsed ultrasound the same thing?

Accepted Answer

No. LIPUS is a dedicated device used at home for 20 minutes daily at fixed low-intensity settings, to stimulate bone healing. NICE device guidance supports one system for stable, well-aligned long bone non-union after 9 months, while procedure guidance finds the efficacy evidence inadequate and requires special arrangements. Neither transfers to conventional physiotherapy ultrasound.

Therapeutic Ultrasound

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