Ultrasound

Ultrasound general considerations

• Commonly used

• Indicated for tissue repair and pain relief

• Acoustic rather than electromagnetic

• For heating = Deep heat like Daithermy I.e. raises tissue temperature

Ultrasound defined

• Inaudible, acoustic vibrations of high frequency that may produce either thermal or non-thermal physiologic effects.

• As a clinician you need to know what your trying to accomplish

Transmission of Acoustic Energy

• Use molecular collision. A coupling medium is used to enhance absorption, cause vibration.

• Through the medium a minimum amount of displacement occurs to the surrounding issues, allowing the molecules to vibrate.

• Eventually this wave of vibration has propagated through the entire medium.

• Biologic vibration

Wave transmission• Two types of waves travel through a solid

medium:• 1. Longitudinal: Molecules are displaced in the

direction the wave travels. In this wave, areas of high molecular density are called compressions, molecules get squeezed together. Travel in solids and liquids. Rarefaction: lower molecular density molecules spread out.

• 2. Transverse waves: molecules become displaced perpendicular to the direction in which the wave is moving. Solids such as bone interfaces.

Frequency of wave transmission

• Audible sound is transmitted bet 16kHz and20 kHz.

• Therapeutic US is between .75- 3MHz.

• The > the frequency the more focused the beam of sound produced

• In humans the lower the frequency the greater the depth of penetration.

Velocity

• Velocity of US propagation is directly related to the density. The more dense and rigid materials have a higher velocity of transmission.

Attenuation

• Transmitting through various tissues reduces the intensity of the US energy.

• Decreased energy may be due to absorption,• Dispersion,or scattering of the sound wave after

reflection or refraction.• Therefore penetration and absorption are

inversely related. • As the frequency increases, the absorption

increases, thus less energy is transmitted to deeper tissues

Acoustic Impedance

• DEF: reflection or refraction of a sound wave when it encounters a boundary or an interface between 2 tissues.

• If the acoustic impedance is the same for both structures, all the the sound will be transmitted and none will be reflected.

• Standing waves or hot spots develop when the energy reflected at the tissue interfaces meets new energy being transmitted. This new energy can cause tissue damage.

Components of an Ultrasound Generator

• US generator is made up of a High Frequency electrical generator and transformer.

• A frequency of 1MHz means the crystal deforms 1 million times / second

Transducer

• Aka; APPLICATOR OR SOUNDHEAD

• Composed of piezoelectric crystal such as quartz, or synthetic ceramic.

• The crystal in the transducer converts the electrical energy to acoustic energy through mechanical deformation of the piezoelectric crystal

Piezoelectric Effect

• Created by generating an AC current at the same frequency as the crystal. The piezoelectric effect is the expansion and contraction of the crystal in response to the passage of current.– 1. Direct piezoelectric effect– 2. Indirect (Reverse) piezoelectric effect

Effective Radiating Area

• Def: surface of the transducer producing the sound wave.

• Dependent on the surface area of the crystal.

• Experiments have shown when treating 10’ using: 2 ERA will increase temperature 3.6C( vigorous)6 ERA 1.1C increase (mild heating)

Frequency of Therapeutic US

• Frequency is the # of wave cycles/second. • Clinically use 1 and 3MHz.

– 1 MHz : less energy is absorbed in the superficial tissues and thus there is greater penetration.

– 3 MHz: Newer units. More superficial heating then 1 MHz.

– Clearly, the intensity of US does not determine penetration depths, the frequency does.

The Ultrasound Beam

• The larger the sound head the more focused or collimated the US beam.

• Beams generated at 1 MHz are more divergent than US at 3 MHz.

BNR: Beam Nonuniformity Ratio

• Variability of the ultrasound beam intensity.

• FDA acceptable between 2 and 6. Labeled.

• The lower the BNR, the more uniform the output of the machine.

Pulsed vs. Continuous Wave US

• 1. Continuous: sound intensity is constant throughout treatment. US energy is produced 100% of the time.++++++++++

• 2. Pulsed: interrupted intensity. No US energy is produced during the off period. In this case the average intensity over time is reduced. Duty cycle refers to on time.

• +++ +++ +++

Amplitude, Power and Intensity

• Amplitude: magnitude of the vibration from a point of equilibrium. Cm or cm2

• Power: Watts. Total US energy in the beam .• Intensity: Rate of energy delivery per unit area.

– Spatial averaged intensity– Spatial Peak intensity– Temporal peak intensity– Temporal averaged intensity– Spatial averaged temporal peak

Physiologic Effects of US

• Thermal and non thermal

• Thermal: Attenuation is caused by the conversion of US energy to heat through absorption and to a lesser degree by scattering and beam deflection

Clinical Effects of Thermal US

1.Increased extensibility of collagen in jt. Capsules and tendons.

2. Decreased joint stiffness.

3. Decreased m spasm

• 4. Modulation of pain• 5. Increased bl fl• 6. Mild inflamm

response that may reduce chronic inflamm

Advantages of Thermal US

• Tissues with high concentrations of collagen such as ligs, m ,tendons, jt. Capsules, jt. Menisci, intermuscular interfaces, NR, periosteum, cortical bone, and other deep tissues which may be selectively heated to the therapeutic range without causing a significant tissue temp increase in the skin or fat.

Effects of Non Thermal US• Cavitation; formation of gas filled bubbles that

expand and compress because of ultrasonically induced pressure changes in tissue fluids– 1. Stable cav. Occurs 2ary to regularly repeated

pressure changes over many acoustic cycles.– 2. Unstable cav. Violent large swings before implosion

and collapse occurs. High intensities at low frequencies.

– 3. Acoustic microstreaming- unidirectional movement of fluids along the boundaries of cell membranes resulting from mechanical pressure waves in an US field

Non thermal Therapeutic Effects

• 1. Stimulation of fibroblast activity

• 2. Bone healing and repair of non union fracture

Techniques of Application

• 1. Frequency: Acute low intensity or pulsed OD to BIW 6-8 days until acute sx subside.

• Chronic seen alternating days, continue until improvement. Without improvement following 3-4 tx, D/c or change parameters

• 2. Duration: – Size of area to be tx– Intensity in w/cm2– Frequency– Desired temperature increase

Summary of Effects of US

Effect Temperature inc Application

Non thermal None 37.5 baseline

Acute inj, edema, healing

Mild thermal 1C Subacute inj, hematoma

Mod thermal 2C Chronic

itis,pain, TP

Vigorous 4C Stretch collagen

Coupling Medium/Methods

• Decreases impedance at the air skin juncture. Eliminates air from body part bet US head and tx surface.

• For optimal tx effects, the sound head should be ll and perpendicular to tx surface.

Exposure Techniques

• Direct contact; surface must be larger than the transducer

• Immersion: can be used when the treatment area is smaller than the transducer. Treatment area is irregular.

• Plastic, ceramic, rubber basin should be used• Tap water• Move transducer ll to surface you are txing. @ .5

– 1 cm away. Wipe away air bubbles. Intensity should be increased up to 50%

Indications UltrasoundAcute/subacute cond

Soft tiss heal/repair

Scar tissue Jt.contracture

Chr itis Inc collagen extensibility

Dec m spasm

Pain

Inc bl fl Soft tiss repair

Inc Pr- syn Tiss regen

Bone healing

Repair non-union fx

Inflamm assoc Myos. Ossificans

Plantar warts

Myofascial trigger points

ContraindicationsAcute/post acute cond.(Thermal)

Areas of decreased temp sensation

Areas dec circ

Vasc. Insuff Thrombophleb Eyes

Reproductive organs

Pelvis immed after menses

Pregnancy

PPM Malignancy Growing epiphysis

TJR Precaution not directly over

Infection tumors

Phonophoresis

• US used to drove in whole molecules of topical meds. Safe painless, noninvasive. Active transport as a result of increased membrane permeability during sonation.

US in Combination with other Modalities

• There is no proof that US in combination with other modalities is more beneficial. In fact a HP may increase superficial attenuation therefore decreasing the depth of penetration.

• Pulsed US and cold should however be a choice to promote soft tissue healing.

Documentation

• Record specific parameters in order to reproduce or change treatments.

• Include: Frequency, Intensity, Pulsed/continuous, Duration, pt. position,

Direct/immersion. Pt response to modality.