Lecture 1 - Ultrasound

General Principles of US (2)

- acoustic form of radiant energy

- high frequency acoustic vibrations

Longitudinal Wave Propagation (2)

- compression happens in high density soft tissue

- rarefaction happens in low density soft tissue

Absorption (3)

- tissue that absorb more energy will heat faster

- higher water content absorbs less

- higher protein content absorbs more

Absorption Rate

- (heats up the fastest) bone - nerve - tendons and ligaments - muscle - fat (heats up the slowest)

Acoustical Impedance

- the amount of resistance the sound wave encounters as it enters a tissue or material

Effect on Transmission

- the greater the difference in the acoustical impedance the greater the amount of sound wave energy that will be reflected and less that will be transmitted

Standing Wave (2)

- very large differences in acoustical impedance will cause most of the sound energy to be reflected

- the reflected energy will meet new incoming energy

Physiological Effects of Thermal US (6)

- increased blood flow

- increased extensibility of soft tissue

- decreased viscosity of fluid

- increased metabolic rate

- decreased muscle spasm and increase muscle relaxation

- decreased pain

Non-thermal Effects of US

- cavitation

- micro-streaming

Non-thermal: Cavitation (3)

- formation of gas filled bubbles that expand and compress

- causes pressure changes in tissue fluids

- unstable vs. stable

Non-thermal: Cavitation Effect

- increase blood flow in the fluid around the vibrating bubbles

Non-thermal: Micro-streaming

- unidirectional movement of fluid along the boundary of cell membranes

Non-thermal: Micro-streaming Effects (2)

- alters cell membrane permeability to Na and K

- stimulates fibroblast activity which increases protein synthesis, tissue regeneration, and blood flow

What are Na and K important for?

- the healing process

When do non-thermal effects occur? When do thermal effects occur?

- non-thermal effects always occur

- thermal effects occur when the treatment parameters allow it

Transducer (2)

- the sound head

- contains a piezoelectrical crystal

Piezoelectric Effect

- as alternating current is passed through the crystal, the crystal will contract and expand producing the sound waves

Characteristics of an US Generator

- power

- sound head size

- effective radiating area

- intensity

- spatial average intensity

Power

- total amount of energy in the US beam (watts)

Effective Radiating Area (ERA) (3)

- portion of the head that actually produces sound waves

- size of crystal determines the treatment area

- use ERA, not the size of the sound head

Spatial Average Intensity (SAI) (3)

- the power of the output divided by the ERA

- power / ERA = intensity of US

- W/cm2

Beam Nonuniformity Ratio (BNR) (4)

- the amount of variability the US beam intensity has

- the intensity of spikes of US output

- the lower the BNR, the more uniform the output and heating

- how high you can go with no pain

BNR Factors (4)

- peak:average (want 1:1)

- should stay below 8-10 w/cm2 for pt comfort

- if BNR is 5:1, intensity can only be 2 w/cm2 = 10

- if BNR is 6:1, intensity can only be 1.5 w/cm2 = 9

Frequency (2)

- 1 MHz = deeper effect, 3-5cm

- 3 MHz = superficial effect, 1-2cm

Types of Output (2)

- continuous

- pulsed = on/off time, duty cycle

Duty Cycle (2)

- on time (pulse duration) / pulse period (on time + off time)

- on time 1 second, off time 4 seconds = 20% duty cycle

Factors of Pulsed Output (2)

- temporal average intensity = average power output during both the on and off period pulse period

- off time makes effects last longer = max non-thermal effect

Temporal Average Intensity (TAI) (3)

- non-thermal effects are max if TAI is 0.1-0.2 watts/cm2

- SAI x DC = TAI

- 1 SAI x .2 duty cycle = .2 watts/cm2

Contraindications of US (5)

- lack of temperature sensitivity (can't fell burning)

- compromised circulation

- epiphyseal areas in children

- malignancies

- over reproductive organs, eyes, heart, spinal cord, and joints

Treatment Parameters (7)

- size of treatment area

- frequency

- continuous or pulsed output

- intensity

- desired tissue temperature increase

- estimated rate of tissue temperature increase

- treatment time

Size of Treatment Area (3)

- ERA = treatment area should be 2-3 sizes of the ERA

- sound head size is just a rough estimate

- must recognize that the ERA will be smaller than the head

Frequency

- depth of target tissue

- 1 MHz for deep, 3 MHz for superficial

How to decide if you want to do heat. (4)

- are ready for heat?

- moderate to minimum protection

- want tissue elongation

- deep target tissue (US goes deeper than hot pack)

How to decide if you just want to do non-thermal. (3)

- if you want to promote healing

- inflammatory or fibroblastic repair phase

- high irritability

What do you need to look at if you just want non-thermal effects. (4)

- SAI and TAI

- want .1-.2 watts/cm2

- SAI .1-.2 and DC 1

- SAI 1-2 and DC .1

Intensity (2)

- BNR

- rate of heating

Desired Tissue Temperature Increase (3)

- normally we want tissue heating

- vigorous heating is 3-4 degrees C

- this allows for tissue elongation

Estimated Rate of Tissue Temperature Increase

- want tissue to be 4° so multiply the intensity by time until you get 4°

Tissue Temp Increase: Order of heating by slowest to longest.

- 1 MHz muscle ➝ 1 MHz tendon ➝ 3 MHz muscle ➝ 3 MHz tendon

Level of Intensity to Time for 1 MHz Muscle (4)

- .5 watts/cm2 = .1°/min (40mins)

- 1 watts/cm2 = .2°/min (20mins)

- 1.5 watts/cm2 = .3°/min (14mins)

- 2 watts/cm2 = .4°/min (10mins)

Level of Intensity to Time for 1 MHz Tendon (4)

- .5 watts/cm2 = .3°/min (14mins)

- 1 watts/cm2 = .6°/min (7mins)

- 1.5 watts/cm2 = .9°/min (4mins)

- 2 watts/cm2 = 1.2°/min (3mins)

Level of Intensity to Time for 3 MHz Muscle (4)

- .5 watts/cm2 = .3°/min (14mins)

- 1 watts/cm2 = .6°/min (7mins)

- 1.5 watts/cm2 = .9°/min (4mins)

- 2 watts/cm2 = 1.2°/min (3mins)

Level of Intensity to Time for 3 MHz Tendon (4)

- .5 watts/cm2 = .9°/min (4mins)

- 1 watts/cm2 = 1.8°/min (2mins)

- 1.5 watts/cm2 = 2.7°/min (1 and a half mins)

- 2 watts/cm2 = 3.6°/min (1min)

What should you apply in treatment time? (4)

- frequency selected

- intensity

- desired tissue temperature increase

- estimated rate of tissue temperature increase

What do you do if the BNR is 5:1 or 6:1 and the pt is not feeling the heat? (2)

- you have to increase the treatment time, not the intensity

- you can increase intensity if the BNR is lower

What are other considerations when applying US? (4)

- speed of sound head movement

- coupling technique (gel or water)

- frequency of treatment and number of visits

- integrate with other treatments (stretching, joint manipulation)

Phonophoresis (3)

- sound waves open pathways that allow the medication to diffuse through the skin

- medicine on skin and US over that

- only works if there is good acoustic impedance