Therapeutic Interventions Week 10 - Ultrasound

Physical Principles of Ultrasound

• Ultrasound is a high-frequency mechanical wave that delivers acoustic or sound energy.
• Sound waves cause molecules to vibrate and transmit energy to adjacent molecules.
• Transmission is more efficient in denser tissues due to higher molecular density.
• Coupling agents like aqueous gels are used to enhance transmission, filling air gaps between the applicator and skin.
• Sound waves travel through compressions (increased density) and rarefactions (decreased density).
• The magnitude of compressions and rarefactions depends on the energy wave's intensity.
• The duration of compressions and rarefactions depends on the frequency of the wave.
• Waves can be reflected, refracted, or absorbed at tissue density changes.
• Absorption converts kinetic energy into thermal energy.
• Refraction bends waves passing through denser tissue.
• Reflection depends on the angle of incidence at tissue interfaces. Reflected waves can interact to enhance or diminish intensity.
• Body tissues behave as liquids of varying densities, except bone, which acts as a solid.
• Longitudinal waves predominate in most tissues, but bone transmits both longitudinal and transverse waves.
• Dense tissues like ligaments and tendons attenuate ultrasound waves faster than muscle or adipose tissues.
• Applying ultrasound over bone can increase temperature of the periosteum and cause discomfort due to potential standing waves.

Production of Ultrasound Waves

• Ultrasound devices have two main components: an applicator and a generator.
• The applicator includes a piezoelectric crystal and a sound head.
• The piezoelectric crystal (lead zirconate or titanic ceramic) expands and compresses with alternating current (reverse piezoelectric effect).
• Compression and expansion of the crystal produce acoustic waves.
• The crystal alternates between compression and expansion 1 to 3 million times per second.
• The effective radiating area (ERA) is the area of the crystal that moves.
• The sound head (aluminum, stainless steel, or ceramic) covers the crystal and conducts acoustic energy to the skin via a gel.
• The ERA is smaller than the actual sound head size.
• The generator contains an electrical oscillator that matches the intensity and frequency parameters of the crystal.

Phonophoresis

• Phonophoresis uses ultrasound to enhance absorption of topical agents through the skin.
• Ultrasound is thought to physically push the agent through the skin and increase dermal permeability.
• Application is usually with pulsed or continuous ultrasound.
• Current evidence does not strongly support phonophoresis.

Treatment Parameters – Frequency

• Frequency is the number of waves per second, ranging from 0.75 to 3.3 MHz.
• Most units deliver 1 MHz and 3 or 3.3 MHz.
• Lower frequencies penetrate deeper such as 1 MHz can penetrate to a depth of up to 6 cm, whereas 3 MHz is effective up to 2.5 cm.
• Increasing intensity does not increase depth of penetration.
• 3 MHz ultrasound is absorbed three times faster than 1 MHz, leading to faster tissue heating.
• 3 MHz is used for superficial structures and 1 MHz for deeper structures.
• Depth of penetration depends on frequency, not intensity.

Treatment Parameters; Intensity and Dosage

• Power of ultrasound energy is a product of wave phase duration and amplitude/intensity.
• Power is often expressed as spatial average intensity (SAI) in watts per centimeter squared.
• SAI is calculated by dividing power (watts) by the ERA.
• Practitioners should use the lowest effective intensity to achieve the desired therapeutic effect.
• Dosage is affected by ERA and should be considered with intensity and duration.

Treatment Parameters – Mode

• Ultrasound machines can deliver continuous or pulsed ultrasound.
• Continuous ultrasound delivers constant energy.
• Pulsed ultrasound has periods of no energy delivery, reducing total energy.
• Temporal average intensity describes the lower energy level of pulsed ultrasound.
• Continuous ultrasound is primarily for heating, while pulsed ultrasound is for non-thermal effects.

Other Principles of Therapeutic US

• BNR (Beam Non-uniformity Ratio) is the ratio of spatial peak intensity within the ERA.
• High BNR units are more likely to cause discomfort due to hot spots.
• The ultrasound head should be moved continuously to distribute hot spots.
• The treatment area should ideally be two times the ERA and no more than four times the ERA when using 1 MHz.

Variation in Treatments and Ultrasound Units

• Vigorous heating of tissue is defined as an increase of about 7 degrees Fahrenheit and increases tissue distensibility.
• Treatment duration depends on the area size, ultrasound settings, intensity, frequency, mode, and specific condition.
• Treatment protocols vary, two to three times a week for 10-15 treatments
• Clinicians must adjust protocols based on the unit, applicator, patient, and condition.

Variability in Application Medium

• Radiating waves of the US should be kept perpendicular to the skin surface.
• The applicator should remain in contact with the skin surface when possible.
• Coupling medium is required between the applicator and the skin.
• The applicator face plate must be continuously moved during treatment.
• Keep radiating waves perpendicular to the skin (90 degrees) to avoid excessive reflection.
• If the incident angle is greater than 15 degrees off perpendicular, almost complete reflection can occur.
• Aqueous gel, water immersion, and gel pads can be used as a coupling medium, but ultrasound gel has 100% transmission of US waves.

Moving the Sound Head

• Slow movement over the skin at about 3 to 4 cm per second is recommended.
• There are no significant differences in tissue heating between movement of the US applicator at varying speeds
• Slow stroking and overlapping circles are common application patterns.

Proper Application of US

• Treat the correct size area.
• Select the appropriate duration.
• Adjust intensity for desired effect.
• Use the correct frequency.
• Do not treat all tissues with the same parameters.
• Move the sound head at an appropriate speed.
• If combined with stretching, stretch during the last few minutes and/or immediately after heating.

Documentation Tips for US

• Ultrasound parameters: Intensity, frequency, duty cycle.
• Treatment duration
• Sound head size
• Treatment area
• Coupling agent
• Patient position
• Patient response

Tissue Response

• Tendons heat significantly faster and to a greater extent than skeletal muscle under similar conditions.
• A rapid cooling phase occurs, lasting about 5 minutes, followed by a slower cooling rate until tissues return to normal temperature.
• There are four to five minutes to administer co-treatments while the tissue is heated.

Variability in Responders

• Variables include percentage of body fat, tissue hydration, blood flow, tissue metabolism, and protein content.

Thermal Effects

• Increase in collagen fiber extensibility
• Decrease in joint stiffness
• Reduction of muscle spasm
• Modulation of pain
• Increased blood flow
• Mild inflammatory response
• Tissues must be raised between 40 and 45 degrees Celsius for a minimum of five minutes in order for effects to occur.
• Tissue temperature increases of 1-degree Celsius increases metabolism and healing.
• Tissue temperature increases of 2-3 degrees Celsius decreases pain and muscle spasm.
• Increases of 4 degrees Celsius or greater increase collagen extensibility and decrease joint stiffness.
• Temperatures above 45 degrees Celsius may be potentially damaging to tissues, but patients usually experience pain prior to these extreme temperatures

Non-Thermal Effects

• Cavitation is the formation of gas-filled bubbles that expand and compress due to pressure changes in tissue fluids.
• Stable cavitation provides therapeutic benefits, while unstable cavitation can cause tissue damage.
• Acoustic streaming (microstreaming) is the unidirectional movement of fluids along cell membranes.
• Some literature suggests that non-thermal effects are as important as thermal effects for the treatment of injured tissues
• Therapeutic levels of US may alter the course of immune response

Evidence for Treatment of Pain

• Evidence for treatment of myofascial pain, trigger points, and back pain are substantiated.
• Evidence for treatment of nonspecific shoulder conditions is substantiated.
• For myofascial pain, best evidence suggests 10 min treatments, 4-5 times per week using 1-2 MHz applied continuously, 1-1.5 watts per centimeter squares for two to three weeks.
• For back pain, continuous US, 3 times per week for 10 min, 1 MHz at 2 watts per centimeter squared for 4 weeks is recommended.

Evidence for Treatment of Inflammation

• Evidence for treatment of carpal tunnel syndrome and arthritis is substantiated.
• Evidence for trating calcific tendinitis and bursitis is substantiated.
• For US use for carpal tunnel syndrome, treatment should occur at least 5 times per week for 5-10 min; 1-3 MHz from 0.5-1.5 watts per centimeter squared, continued for 4 weeks is recommended.

Evidence for Treatment of Soft Tissue and Scars

• The evidence for treating soft tissue healing and dermal wounds is conflicting.
• The evidence for trating tissue extensibility is conflicting.
• Protocols include myofascial pain, back pain, nonspecific shoulder conditions, carpal tunnel syndrome, calcific tendinitis, bursitis, and arthritis.

Evidence for Treatment – Clinical Practice Guidelines

• Ultrasound should not be used as part of routine care for non-surgical management of chronic primary low back pain in adults in primary and community care setting.
• Clinicians should not use US to enhance the benefits of stretching treatment in those with plantar fasciitis.
• Clinicians may use phonophoresis with ketoprofen gel to reduce pain in individuals with heel pain/ plantar fasciitis.
• Based on conflicting evidence, a recommendation cannot be made for the use of US as a stand-alone treatment for later elbow pain and muscle function impairments.

Ultrasound; Contraindications, Precautions

• Contraindications for continuous US with moderate to strong evidence include pregnancy (over the abdomen, low back), active bone growth at the epiphysis, cancer, tuberculosis infection, hemorrhagic conditions, and impaired circulation.
• Consensus opinion includes to consider myositis ossificans, deep vein thrombosis, acute injury, recently irradiated tissue, impaired sensation, impaired cognition, implanted cardiac pacemaker, reproductive organs, eyes, and anterior neck as contraindications.
• Precautions for continuous US include plastic or cemented implants, spinal cord and superficial nerves, and metal implants or over the chest, heart, or head.
• Contraindications for pulsed US with moderate to strong evidence include pregnancy (over the abdomen, low back), cancer, and hemorrhagic conditions.
• Consensus opinion is to consider myositis ossificans, deep vein thrombosis, recently irradiated tissue, implanted cardiac pacemaker, reproductive organs, eyes, and anterior neck as contraindications.
• Precautions for pulsed US include active bone growth at the epiphysis, areas of infection, acute injury, impaired sensation, impaired cognition, impaired circulation, skin disease, plastic or cemented implants, spinal cord and superficial nerves, and metal implants or the chest, heart, and head.