CBET Rehabilitation and Physical Therapy Equipment

Question 1

A therapeutic ultrasound unit used in physical therapy has a duty cycle setting. What does a 20% duty cycle at 1 MHz mean?

Accepted Answer

The unit pulses on for 20% of each cycle period and is off for 80%, delivering pulsed (non-thermal) ultrasound

Answer

The unit operates at 20% of its maximum output intensity

Answer

The unit runs for 20 minutes and automatically shuts off

Answer

Only 20% of the transducer crystal surface is active

Question 2

During PM testing of a TENS (Transcutaneous Electrical Nerve Stimulation) unit, a BMET measures the output current to verify it matches the set parameter. What is the primary reason TENS units use alternating or pulsed current rather than continuous DC?

Accepted Answer

Continuous DC causes electrode polarization and tissue damage due to ion migration under the electrode

Answer

AC is cheaper to generate in battery-powered devices

Answer

AC penetrates deeper into tissue than DC at the same voltage

Answer

Pulsed current bypasses sensory nerve fibers and only stimulates motor fibers

Question 3

A shortwave diathermy (SWD) unit must be kept at minimum distances from other electronic equipment and implanted devices. At what RF frequency does most therapeutic SWD operate, and why is this frequency regulated?

Accepted Answer

27.12 MHz — an ISM (Industrial, Scientific, Medical) band allocated by the FCC to minimize interference with communications

Answer

1 MHz — regulated because it interferes with AM radio broadcasts

Answer

2.45 GHz — the same frequency as microwave ovens, regulated for the same heating safety reasons

Answer

50 Hz — the power line frequency, regulated by NFPA 99

Question 4

A BMET is testing a phototherapy unit used to treat neonatal hyperbilirubinemia (jaundice). Which characteristic of the light output is MOST critical to measure during PM?

Accepted Answer

Irradiance (spectral power) in the 430–490 nm (blue) wavelength range at the treatment surface

Answer

Color temperature in Kelvins

Answer

Total luminous flux (lumens) across the visible spectrum

Answer

Ultraviolet output above 380 nm to ensure bactericidal effect

Question 5

A motorized cervical traction unit is set to apply 15 lbs of traction. During PM, the BMET's tension scale reads 11 lbs at the 15 lb setting. What is the percentage error, and does this require repair before returning to service?

Accepted Answer

26.7% error — yes, this exceeds the typical ±10% tolerance and requires repair

Answer

26.7% error — no, traction devices have a ±30% tolerance by design

Answer

4 lbs error — only absolute lb errors matter; percentages are not used for traction PM

Answer

13.3% error — acceptable, as traction forces are inherently variable due to patient movement

Question 6

A NMES (Neuromuscular Electrical Stimulation) unit used for muscle rehabilitation produces biphasic waveforms. What is the clinical advantage of a balanced (charge-balanced) biphasic waveform over an unbalanced monophasic waveform for long-term stimulation?

Accepted Answer

The equal positive and negative charge phases cancel net DC charge accumulation, preventing electrode-skin interface damage during extended use

Answer

Balanced biphasic waveforms stimulate type II fast-twitch fibers more selectively

Answer

Biphasic waveforms deliver twice the energy per pulse, reducing treatment time by 50%

Answer

Balanced waveforms prevent patient perception of the electrical stimulus, improving compliance