Understanding Ultrasound in Therapeutic Applications

Ultrasound

Sound waves transmitting energy via compression and rarefaction.

Sound Frequency

Greater than 20,000 Hz, inaudible to humans.

Normal Hearing Range

Human audible sound frequency: 16 to 20,000 Hz.

Thermal Effects

Increase in tissue temperature due to ultrasound.

Nonthermal Effects

Include acoustic streaming, microstreaming, and cavitation.

Acoustic Streaming

Steady circular flow of cellular fluids induced by ultrasound.

Microstreaming

Microscale eddying near vibrating objects in ultrasound.

Cavitation

Formation and pulsation of gas bubbles caused by ultrasound.

Therapeutic Ultrasound Frequency

Ranges from 0.7 to 3.3 megahertz (mHz).

Energy Absorption Depth

Maximized at 2-5 cm in soft tissue.

Attenuation

Decrease in ultrasound intensity as it travels through tissue.

Effective Radiating Area (ERA)

Area from which ultrasound energy radiates.

Stable Cavitation

Bubbles oscillate without bursting during ultrasound cycles.

Unstable Cavitation

Bubbles grow and implode, causing pressure and temperature spikes.

Beam Nonuniformity Ratio (BNR)

Ratio of spatial peak intensity to spatial average intensity.

Typical BNR Values

Usually between 5:1 and 6:1 for ultrasound units.

FDA BNR Requirement

Maximum BNR must be specified on ultrasound devices.

Intensity

Power per unit area of ultrasound, measured in W/cm².

Duty Cycle

Ratio of on-time to total time in ultrasound application.

Compression Phase

Phase where sound waves compress material.

Rarefaction Phase

Phase where sound waves expand material.

Cyclic Compression-Rarefaction

Cycles per second measured in hertz (Hz).

Therapeutic US Frequency Range

1 to 3 million cycles per second (1 to 3 mHz).

Depth of Penetration

Increases with lower frequency ultrasound.

Concentration of Energy

Higher frequency ultrasound concentrates energy superficially.

Cell Membrane Permeability

Altered by nonthermal effects of ultrasound.

Transducer

Device converting electrical energy to ultrasound waves.

Beam Nonuniformity Ratio (BNR)

Maximum spatial peak intensity to spatial average intensity.

Spatial Average Intensity

Average power per unit area in W/cm².

Spatial Peak Intensity

Maximum intensity within the ultrasound field.

WHO Intensity Limit

Therapeutic ultrasound output limited to 3 W/cm².

Attenuation

Reduction of ultrasound intensity in tissues.

Absorption

Conversion of ultrasound energy into heat in tissues.

Reflection

Redirection of ultrasound beam at tissue interfaces.

Refraction

Change in ultrasound wave direction at an interface.

Attenuation Coefficients

Tissue-specific and frequency-specific measures of attenuation.

Continuous Ultrasound

Steady release of ultrasound energy during treatment.

Pulsed Ultrasound

Intermittent release of ultrasound energy for nonthermal effects.

Piezoelectric Materials

Materials that convert electrical energy to ultrasound.

Natural Quartz

Common piezoelectric material for thermal ultrasound effects.

Synthetic PZT

Efficient piezoelectric material used in ultrasound transducers.

Barium Titanate

Less costly piezoelectric material for ultrasound applications.

Near Field

Region where ultrasound beam converges.

Far Field

Region where ultrasound beam diverges.

Fresnel Zone

Another term for the near field of ultrasound.

Fraunhofer Zone

Another term for the far field of ultrasound.

Intensity Variations

Changes in ultrasound intensity due to refraction.

Generation of Ultrasound

Produced by high-frequency alternating current to crystal.

Cooling Conduction Medium

Decreases heating rate during ultrasound application.

Thermal Effects of Ultrasound

Includes pain reduction and increased metabolic rate.

HMP Temperature Increase

Heating medium to 25°C enhances heating rate.

Soft Tissue-Bone Reflection

35% reflection at soft tissue-bone interfaces.

Air-Skin Reflection

100% reflection at air-skin interface.

Superficial tissues

Increase in superficial tissue temperature and circulation.

Nerve conduction velocity

Alteration due to ultrasound application.

Soft tissue extensibility

Increased flexibility of soft tissues with ultrasound.

Nonthermal effects of US

Effects of ultrasound without significant temperature increase.

Pulsed US

20% duty cycle; no measurable temperature increase.

High absorption coefficient

Tissues that absorb ultrasound energy effectively.

Low absorption coefficient

Tissues that absorb ultrasound energy poorly.

Intracellular calcium levels

Increased by low-intensity ultrasound application.

Cell membrane permeability

Enhanced permeability of skin and cell membranes.

Mast cell degeneration

Increased release of histamine and chemotactic factors.

Macrophage responsiveness

Promoted by ultrasound, aiding in healing.

Protein synthesis

Increased rate by fibroblast and tendon cells.

Proteoglycan synthesis

Stimulated by ultrasound in chondrocytes.

Scar tissue

Increased collagen content in healing muscle.

Nutrient delivery

Enhanced by ultrasound for healing processes.

Inflammatory phase

Effective treatment during this phase of repair.

Absorption coefficient

Proportional to tissue type for ultrasound application.

Frequency

Higher frequency increases temperature in tissues.

Pain control

1-3 MHz frequency used for pain management.

Average intensity

Higher intensity leads to increased tissue temperature.

Phonophoresis

Ultrasound with medication delivery, specific parameters.

Soft tissue extensibility parameters

0.5-1.0 W/cm2 at 3 MHz for extensibility.

Healing rate

Increased by specific ultrasound application protocols.

Dermal ulcer treatment

0.5-0.8 W/cm2, pulsed for 3-5 minutes.

Ligament treatment

Low-dose pulsed ultrasound at 0.5-1.0 W/cm2.

Bone fracture treatment

Very low dose, 1.5 MHz, 0.15 W/cm2.

Contraindications

Conditions where ultrasound should not be applied.

Adverse effects

Rare but possible with incorrect ultrasound application.

Burn risk

High-intensity continuous ultrasound may cause burns.

Pregnancy risks

Maternal hyperthermia linked to fetal abnormalities.

US head movement

Always move to reduce burn risk during treatment.

Breast implants

High-dose ultrasound contraindicated over breast implants.

Thermal Level Ultrasound

Avoid on impaired circulation and sensation areas.

Superficial Bone

Reduce intensity when treating near superficial bone.

CNS Tissue

US may damage CNS, usually protected by bone.

Blood Cell Stasis

US standing waves can cause blood cell stasis.

Laminectomy Precaution

Avoid US over or near laminectomy sites.

Methylmethacrylate Cement

Used in fixation or prosthetic joints.

Endothelial Damage

US can damage endothelial lining of blood vessels.

Cemented Prosthesis

Avoid US over cemented prosthesis areas.

US Transducer Movement

Move transducer throughout treatment application.

Metal Implants

US can be applied over metal implants safely.

Pacemaker Risks

US may heat and interfere with pacemaker circuitry.

US Frequency Selection

Based on tissue depth for effective treatment.

Reproductive Organs

US may affect gamete development; avoid these areas.

1 MHz Frequency

Used for tissues up to 5 cm deep.

3 MHz Frequency

Used for tissues 1-2 cm deep.