Questions
2–4 questions in professional BPT/BMRIT papers
Difficulty
Medium
Importance
High yield for clinical viva and theory exams
Overview
Ultrasound therapy is a therapeutic modality utilizing high-frequency sound waves to induce physiological changes in biological tissues. It is a fundamental topic in electrotherapy for health sciences, frequently examined due to its dual-action capacity for thermal tissue heating and non-thermal cellular healing. Aspirants must master the parameters of frequency, intensity, and coupling to explain its clinical effectiveness.
Thermal and Non-Thermal Effects
The mechanical vibration of the sound head causes alternating compression and rarefaction, which converts kinetic energy into heat. Non-thermal effects, primarily driven by acoustic streaming and stable cavitation, promote tissue repair and permeability without significant temperature elevation.
- Thermal effects: Increased collagen extensibility and blood flow
- Non-thermal effects: Improved macrophage activity and protein synthesis
- Stable cavitation: Rhythmic oscillation of gas bubbles
- Unstable cavitation: Violent collapse, potentially hazardous to tissues
- Acoustic streaming: Unidirectional movement of fluids along cell membranes
Phonophoresis
Phonophoresis is the application of ultrasound to enhance the transdermal delivery of medicinal drugs through the skin. It works by increasing the porosity of the stratum corneum, allowing larger molecules to permeate the tissue barrier.
- Uses ultrasonic energy to push medication molecules
- Common agents: Hydrocortisone and salicylates
- Requires coupling medium to remain drug-permeable
- Increases kinetic energy of drug particles
- Non-invasive alternative to iontophoresis
Dosage and Application
Clinical dosage is determined by frequency (1 MHz for deep, 3 MHz for superficial) and the duty cycle. Proper application mandates continuous movement of the transducer head to prevent periosteal overheating.
- 1 MHz penetrates up to 5cm deep
- 3 MHz penetrates 1-2cm deep
- Duty cycle: Continuous (100%) vs Pulsed (20%, 50%)
- Intensity measured in W/cm2
- ERA: Effective Radiating Area of the transducer
- BNR: Beam Non-uniformity Ratio; lower is safer
Formula Sheet
ERA = Total area of crystal surface emitting sound
Duty Cycle = (On time / (On time + Off time)) * 100
Intensity (W/cm2) = Power (W) / ERA (cm2)
Exam Tip
Always differentiate between 'thermal' and 'non-thermal' by referencing the duty cycle; remember that pulsed ultrasound at 20% is purely non-thermal.
Common Mistakes
- Confusing the depth of penetration for 1 MHz vs 3 MHz frequencies.
- Neglecting the necessity of continuous transducer movement, leading to patient burns.
- Failing to distinguish between stable cavitation (therapeutic) and unstable cavitation (damaging).
More Revision Notes
Ready to test yourself?
Play topic-wise Ultrasound Therapy questions in Aspirant Arcade — gamified MCQ practice.
Download Free