Therapeutic Ultrasound for Physical Therapists: What to Know Before You Buy

If you’re setting up a clinic, adding to an existing modality lineup, or shopping for a portable unit for home visits, therapeutic ultrasound is one of the more straightforward purchases. But the spec sheets can be confusing, and cheap units can produce uneven or unreliable output. This page covers what actually matters.

For a clinical overview of how therapeutic ultrasound works and when to use it, see our Therapeutic Ultrasound page.

Continuous vs. Pulsed Mode

Every therapeutic ultrasound unit should offer both modes.

Continuous mode delivers sound waves without interruption. It produces both thermal and non-thermal effects. Use it when the goal is tissue heating: increasing extensibility before stretching, addressing trigger points, or treating chronic conditions where heating is appropriate.

Pulsed mode delivers sound waves in on/off cycles (commonly 20% duty cycle). It produces primarily non-thermal effects. Use it for acute presentations, wound healing, or any situation where heating is contraindicated.

A unit that only offers one mode is not worth buying.

Frequency: 1 MHz vs. 3 MHz

Frequency determines how deep the sound energy penetrates.

Frequency	Penetration Depth	Best For
1 MHz	2 to 5 cm	Deep tissues: hip, shoulder, larger muscle groups
3 MHz	1 to 2 cm	Superficial tissues: tendons, ligaments, small joints

Dual-frequency units give you the most clinical flexibility. If you primarily treat extremities and superficial structures, 3 MHz alone may be sufficient. For a general outpatient ortho setting, get dual frequency.

Intensity and Duty Cycle

Intensity is measured in W/cm² and determines how much energy is delivered to the tissue.

• Low (0.1 to 0.3 W/cm²): non-thermal applications, wound healing, acute stages
• Medium (0.3 to 1.0 W/cm²): general tissue effects
• High (1.0 to 2.0 W/cm²): thermal applications, chronic conditions

Most clinical applications fall between 0.5 and 2.0 W/cm². You want a unit with a wide adjustable range and reliable output at each setting.

Duty cycle (in pulsed mode) is the percentage of time the unit is actively emitting. A 20% duty cycle is the most common for non-thermal treatment. Look for units that let you adjust this rather than locking you into fixed presets.

ERA and BNR: The Two Specs Most Buyers Ignore

These two numbers tell you a lot about output quality.

ERA (Effective Radiating Area): The actual portion of the sound head that emits ultrasound. Smaller ERA means more focused output, better for small treatment areas. Larger ERA covers more surface area efficiently. The labeled size of the head is not the ERA. Look for the ERA on the spec sheet.

BNR (Beam Non-uniformity Ratio): Measures how evenly the sound energy is distributed across the ERA. A BNR of 6:1 means the peak intensity is 6 times the average. High BNR means uneven output and potential hot spots in tissue. Lower is better.

• BNR of 6:1 or less: acceptable
• BNR of 3:1 or less: good
• BNR above 8:1: avoid

Reputable manufacturers publish both numbers. If a unit’s spec sheet doesn’t list BNR, that’s a reason to look elsewhere.

Portable vs. Cart-Mounted

Portable units are compact, battery-powered or plug-in, and designed for easy transport. They’re ideal for home visits, small clinic spaces, and multi-location practices. Trade-off: some sacrifice output consistency or adjustability for size and price.

Cart-mounted units are larger clinic devices with more precise controls, better displays, and generally more reliable calibration. Better for high-volume outpatient settings where the unit is used multiple times a day.

For most solo or small clinic settings, a quality portable unit is entirely sufficient.

A Note on Evidence

The evidence base for therapeutic ultrasound is mixed and worth knowing before you invest. Strong support exists for specific applications including calcific tendinitis of the shoulder and plantar fasciitis. Support is weaker for non-specific low back pain and osteoarthritis as standalone treatment.

This does not mean the modality is without value. It means it works best as part of a broader treatment plan, applied to the right diagnosis at the right parameters. Understanding the evidence helps you use it appropriately and set realistic expectations with patients.

US Pro 2000 2nd Edition: A Closer Look

The US Pro 2000 2nd Edition (by Current Solutions) is one of the more popular portable units in small clinic and home visit settings. It offers both 1 MHz and 3 MHz frequencies, continuous and pulsed modes, and a notable feature not found on all portables: a head-warming element that pre-heats the sound head applicator to approximately 95°F before treatment.

It is compact, reasonably priced, and straightforward to operate. Build quality is solid for the price point. It is not a high-end clinic unit and should not be evaluated against one, but for a portable device used in appropriate clinical contexts it performs well.

Worth noting: Some users have reported issues with the power cord over time. If longevity is a priority, verify the current warranty terms and whether replacement parts are available before purchasing.

What to Check Before You Buy

• Dual frequency (1 MHz and 3 MHz)
• Continuous and pulsed modes
• Adjustable duty cycle
• BNR listed on spec sheet (aim for 6:1 or less)
• ERA listed on spec sheet
• Output calibration certificate or calibration standard noted
• Warranty length and service availability
• Replacement transducer availability

References

• Robertson VJ, Baker KG. A review of therapeutic ultrasound: effectiveness studies. Phys Ther. 2001;81(7):1339-1350.
• Gam AN, Johannsen F. Ultrasound therapy in musculoskeletal disorders: a meta-analysis. Pain. 1995;63(1):85-91.
• Ebenbichler GR, Erdogmus CB, Resch KL, et al. Ultrasound therapy for calcific tendinitis of the shoulder. N Engl J Med. 1999;340(20):1533-1538.
• Magee DJ, Zachazewski JE, Quillen WS. Scientific Foundations and Principles of Practice in Musculoskeletal Rehabilitation. St. Louis: Saunders/Elsevier; 2007.