Ultrasound

DPT 5025 Practical

Ultrasound

Type of sound and consists of waves that transmit energy by alternately compressing and rarefying material. used for thermal and non-thermal effects. high-frequency wave that can be described by its intensity, frequency, duty cycle, effective radiating area, and beam nonuniformity ratio.

Frequency

between 1-3 megahertz (1-3MHz)

Method of Action

• US passes through tissue

• Produces molecular motion/vibration as it is absorbed in the tissue

• Causes friction between the particles/tissues which produces heat

• Non-thermal happens are at the cellular level and changes membrane permeability

Conversion

converts electrical energy to mechanical (vibration/sound) energy through the use of a crystal in the transducer (soundhead) of the ultrasound unit.

Property of Conversion

these sound waves can penetrate tissues, promoting healing and reducing pain through thermal and non-thermal effects. the mechanical energy from the ultrasound waves interacts with the tissues, enhancing circulation and tissue repair.

Attenuation

the intensity (energy; heating ability) of ultrasound waves DECREASING as the waves travel through tissue.

What happens to the energy?

1. Absorption (accounts for 50% of attenuation)

2. Reflection (bouncing back of sound waves)

3. Refraction (bending sound waves)

Attenuation– Absorption

to achieve heating, tissue must ABSORB the ultrasound energy. absorption coefficients (attenuation coefficients) are HIGHER in tissues with more collagen content and lower in tissue with more water content.

Which heats faster: Bone or Blood?

Bone

Which heats faster: Cartilage or Fat?

Cartilage

Which heats faster: Tendon or Muscle?

Tendon

Indications for Ultrasound

as a deep heating modality (thermal- compromised tissue extensibility/joint contraction, muscular pain)

to facilitate healing (non-thermal- open wounds, chronic inflammation of soft tissue)

Thermal (Heating) Effects of Ultrasound

• increased metabolic rate

• increased circulation

• increased soft tissue extensibility

• decrease pain

• decrease muscle spasm

• decrease nerve conduction velocity

Non-Thermal (non-heating) Effects of Ultrasound

• increase intracellular calcium

• increase skin permeability (phonoph)

• increase cell membrane permeability

• increase protein synthesis (for soft tissue healing)

• and more all of which impact activity and tissue repair

Ultrasound: Phonophoresis

the use of non-thermal ultrasound to enhance the delivery of topically applied medications; utilizes ultrasounds ability to enhance skin/tissue (cellular) permeability to facilitate drug phoresis (hydrocortisone cream)

• therapeutic medication is mixed within the US gel

• or the medication placed between two layers of US gel and will mix during application

Contraindications for Biophysical Agents

• malignancy

• pregnancy

• pacemaker

• impaired sensation

• impaired mentation

Contraindications Specific to Ultrasound

• malignancy

• pregnancy

• CNS tissue

• joint cement

• plastic components

• pacemaker

• thrombophlebitis

• eyes

• reproductive organs

Precautions for Ultrasound

• acute inflammation

• epiphyseal plates

• fractures

• breast implants

Ultrasound Adverse Effects

Ultrasound rapidly heats plastic and cement, which can cause damage to the material in the patient. Metal, however, is known to be fine. 

What are 3 potential adverse effects of ultrasound?

1. Burn (superficial bone)

2. Cross Contamination (spreading of infection from transducer head)

3. Blood cell stasis due to standing waves (endothelial damage)

Ultrasound: Application Parameter: Soundhead

• available in variety of sizes

• US is produced by a crystal’s (quartz or synthetic ceramic) vibration when subjected to a high frequency alternating electrical current

• sounded (transducer) produces a high frequency alternating current form from 0.75mHz to 3.3mHz. 

Effective Radiating Area (ERA)

Can be found on the US unit or on the tag on the cord. The area of the face that is transmitting the ultrasound waves and influences the treatment. It determines the size of the area that can be treated. 

General Rule of ERA

Treat the area equal to twice the ERA of the soundhead.

Beam Nonuniformity Ratio (BNR)

the ratio of the highest intensity to the average intensity emitted

• beam emitted from soundhead is not uniform; varying intensities (w/cm²)

• found on soundhead or transducer handle

• best are between 3:1 and 6:1

• the greater the BNR value, the less homogenous the sound beam and the greater risk for “hot spots” in treatment area

• this is another reason to keep the soundhead continuously moving during treatment

Ultrasound: Mode of Delivery

1. Establish the desired effect of your treatment to determine the wave type. 

2. Determine Frequency (MHz) based on depth of penetration desired. 

3. Select Intensity (w/cm²) based on desired effects (thermal vs. non-thermal)

4. Select duration of treatment (minutes)

Continuous Wave at Higher Intensity

Thermal Effect (104-113℉)

Continuous Wave at Lower Intensity

Non-Thermal Effect (less than 104℉)

Pulsed Wave

Non-Thermal Effect (less than 104℉)

Duty Cycle

By setting the ultrasound parameters of “duty cycle” to either Pulsed or Continuous waves, either thermal or non-thermal effects can be produced. Remember that the “duty cycle” impacts the amount of heating– even with non-thermal ultrasound, some thermal effects still occur, though the effects are minimized, and vice-versa.

Continuous Ultrasound

Used when heating/thermal effects are desired.

Pulsed Ultrasound

Used when minimal heat/non-thermal effects are desired. 

For thermal effects, what is the “duty cycle” set at?

100% (continuous)

For non-thermal effects, what is the “duty cycle” set at?

20% (pulsed)

Greater Frequency

• less depth of penetration 

• more (even) tissue heating 

• greater rate of US absorption

Depth of Penetration

1.0MHz= approximately 5.0cm

2.0MH= approximately 2.6cm

3.0MHz= approximately 1.5 cm

General Principles of Intensity

• greater intensity= greater heating

• tissues with higher collagen content require lower intensities than tissues with lower collagen content (muscles, fat)

• bone reflects sound waves; decrease the intensity of tissue if directly next to bone (periosteal pain)

• increase intensity by 0.5w/cm² if water is used as a coupling agent. 

Duration General Rule

more time= more heating

less time= less heating

3 Methods of Ultrasound Application

1. Direct Contact

2. Cushion Contact

3. Water Immersion

Coupling Medium

• air is a poor transmitter

• medium must be placed between pts skin and the US soundhead

• this ensures effective US transmission to pt

• types of coupling media are: commercial gel (direct contact method), commercial gel pad (cushion contact method), and tap water (water immersion method)

Cooler Coupling agents are most effective for what type of tissues?

Deeper tissues (64℉)

Cooling the soundhead may assist with what?

Deeper Penetration

What type of water is best for superficial lesions?

Room Temperature

What happens if skin temperature exceeds 85 degrees?

It is difficult to achieve vigorous deep tissue healing. Cooler skin results in deeper penetration.

Motion of the Soundhead

Should be moved throughout the treatment in a circular pattern or a back and forth pattern. 

Speed of Soundhead

Approximately 4cm/second. Sufficient to maintain constant contact and motion; avoid increasing the size of the treatment.

Frequency/Duration

If no progress in 3 sessions, then re-evaluate. 

Generally no more than 8-12 sessions.

Acute injury: non thermal US have 3 days between treatments. 

Subacute and chronic conditions: daily to every other day. 

Decision Making Tree

Ultrasound: Billing

timed code, 8 minute minimum treatment

If 5 minutes of US is clinically indicated, can it be billed?

Yes, you are not just billing for time of Ultrasound delivery, but entire time involved including set up, patient, education, screening, etc.

The intensity (energy; heating ability) of ultrasound waves decrease as the wave travel through tissue. Why? What happens to the energy?

It is absorbed, refracted, and reflected.