PAM Thermal Modalities 3 — Questions and Answers
Question 1: Therapeutic ultrasound at 3 MHz is preferred over 1 MHz for treating superficial tissues because:
- 3 MHz penetrates deeper into muscle tissue
- 3 MHz has greater half-value depth absorption in superficial tissues (Correct answer)
- 3 MHz produces less thermal effect
- 3 MHz requires shorter treatment times due to higher intensity
Correct answer: 3 MHz has greater half-value depth absorption in superficial tissues
3 MHz ultrasound is absorbed more rapidly in superficial tissues (1–2 cm depth) due to its shorter wavelength, making it ideal for tendons and superficial structures.
Question 2: In continuous-mode therapeutic ultrasound, the duty cycle is:
- Less than 50%
- Exactly 50%
- Variable between 20–80%
- 100% (Correct answer)
Correct answer: 100%
Continuous mode means the ultrasound beam is on 100% of the time (duty cycle = 100%), producing both thermal and mechanical effects.
Question 3: Which of the following is a CONTRAINDICATION to therapeutic ultrasound?
- Chronic tendinopathy
- Application over a pacemaker (Correct answer)
- Subacute ligament sprain
- Post-surgical scar tissue
Correct answer: Application over a pacemaker
Therapeutic ultrasound is contraindicated over cardiac pacemakers because the energy can interfere with pacemaker function and cause cardiac arrhythmias.
Question 4: What is the ERA (Effective Radiating Area) of an ultrasound transducer and why is it clinically important?
- Total face size; determines coupling gel quantity needed
- Active sound-producing area; determines actual treatment area and SATA intensity calculation (Correct answer)
- Depth of beam penetration; guides frequency selection
- Beam divergence angle; determines applicator angle during treatment
Correct answer: Active sound-producing area; determines actual treatment area and SATA intensity calculation
ERA is the active sound-producing portion of the transducer face, which is always smaller than the total face size and is used to calculate spatial average temporal average (SATA) intensity.
Question 5: Shortwave diathermy produces deep heating primarily through which physical mechanism?
- Radiation of infrared electromagnetic waves
- Conversion of high-frequency electromagnetic energy to heat in tissues (Correct answer)
- Conduction of heat from heated applicator pads
- Acoustic cavitation in tissue fluids
Correct answer: Conversion of high-frequency electromagnetic energy to heat in tissues
Shortwave diathermy converts high-frequency (27.12 MHz) electromagnetic energy into heat through dielectric and resistive heating mechanisms within tissues.
Question 6: During phonophoresis, which ultrasound parameter is MOST important for enhancing transdermal drug delivery?
- High frequency (3 MHz) with low intensity
- Low frequency (1 MHz) with sufficient intensity to promote cavitation (Correct answer)
- Pulsed mode at 20% duty cycle
- Large ERA transducer covering the entire treatment area
Correct answer: Low frequency (1 MHz) with sufficient intensity to promote cavitation
1 MHz ultrasound at sufficient intensity to produce cavitation enhances drug penetration through skin by transiently disrupting the stratum corneum barrier.
Question 7: A therapist applies therapeutic ultrasound over the epiphyseal growth plates of a skeletally immature patient. This is contraindicated because:
- Ultrasound is ineffective on cartilage tissue
- Thermal effects may damage chondrocytes and disrupt longitudinal bone growth (Correct answer)
- Pulsed ultrasound produces excessive cavitation near bone
- Young patients cannot tolerate the intensity required for treatment
Correct answer: Thermal effects may damage chondrocytes and disrupt longitudinal bone growth
Thermal ultrasound over open epiphyseal plates can damage proliferating chondrocytes, potentially disrupting normal longitudinal bone growth in skeletally immature patients.
PAM Thermal Modalities 3
Therapeutic ultrasound at 3 MHz is preferred over 1 MHz for treating superficial tissues because: