Therapeutic Ultrasound

Jennifer Doherty-Restrepo, MS, LAT, ATC Entry-Level ATEP Therapeutic Modalities Therapeutic Ultrasound

One of the most widely used modalities in sports medicine _______________ = inaudible, acoustic vibrations of high frequency that produce either thermal or non-thermal physiologic effects Therapeutic Ultrasound

Relies on _______________ for transmission Collisions cause molecular displacement and a wave of _______________ Acoustic energy does ______ travel readily through space Must travel through a _______________ Acoustic energy does nottravel in a _______________ Travels in waves in all directions Longitudinal and transverse waves Transmission of Acoustical Energy in Biological Tissue

Primary waveform for travel in soft tissue • Molecular displacement occurs along the ______________________________ Longitudinal Waves

Primary waveform for travel in ______ • Molecular displacement is _______________ to direction of wave propagation Transverse Waves

Audible sound = _______________ Ultrasound > _______________ Therapeutic Ultrasound = _______________ (1,000,000 cycles/sec) Penetration and absorption are ____________ related Lower frequencies = ______ depth of penetration Higher frequencies = superficial ______________ Frequency Of Wave Transmission

Directly related to tissue ______ (conducting medium) Higher density = ______ velocity of transmission Lower density = ______ velocity of transmission At a frequency of 1 MHz, ultrasound travels through… Soft tissue at _______________ Bone at _______________ Velocity Of Transmission

_______ in energy intensity as the ultrasound wave is transmitted through various tissues ________ is due to absorption, dispersion, or scattering, which result from __________ and __________ Attenuation

_______________ relationship Absorption increases as frequency __________ Tissues high in water content _________ absorption Blood Tissues high in protein content ________ absorption Bone, nerves, muscles, and fat Penetration vs. Absorption

Some acoustic energy scatters due to reflection and refraction ____________________ = determines the amount energy reflected or transmitted at tissue interfaces _______________ X _______________ If the acoustic impedance is equal at the tissue interface, energy will be _______________ The larger the difference in acoustic impedance at the tissue interface, the more energy is _______________ Ultrasound at Tissue Interfaces

Transducer - Air interface: energy is completely _______________ Through fat: energy is transmitted _________________: energy is reflected and refracted Soft tissue - Bone interface: energy is _______________ Creates “standing waves” or “hot spots” Acoustic Impedance

Therapeutic Ultrasound Generators High frequency electrical generator connected through an oscillator circuit and a transformer via a coaxial cable to a transducer housed within an insulated applicator

Electrical Output Mechanical Vibration Acoustic Soundwave Absorbed In The Tissues Ultrasound Generator

Timer Power meter Intensity control _______________ Duty cycle switch _______________ Selector switch for continuous or pulsed Automatic shutoff if transducer overheats Therapeutic Ultrasound Generator Control Panel

AKA: • _______________, or • _______________ • Not interchangeable • Piezoelectric crystal • Quartz • Synthetic ceramic crystal • Converts ____________ energy to _____ energy through mechanical deformation Transducer

Piezoelectric Effect • When an alternating current generated at the same frequency as the crystal resonance is passed through the peizoelectric crystal, it will ________ and _______________ • Direct Effect - An electrical voltage is generated when the crystal expands and compresses

Piezoelectric Effect • ____________ = generation of electrical voltage across the crystal when it is expanded or compressed • __________________________ = the alternating current moving through the crystal reverses its _______ as it expands and compresses resulting in vibration of the crystal at the frequency of the electrical oscillation • This produces the desired therapeutic ultrasound frequency

The portion of the transducer surface that actually produces the _______________ Dependent on the __________ of the crystal Ideally, the surface area of the crystal nearly matches the diameter of the transducer surface Acoustic energy is contained in a ________ ___________ beam that is roughly the same diameter of the transducer Effective Radiating Area (ERA)

Frequency = number of wave cycles completed each _______________ Frequency range of therapeutic ultrasound is _______________ Most generators produce either 1.0 or 3.0 MHz Frequency of Therapeutic Ultrasound

Depth of penetration is __________________ not intensity dependent • 1 MHz = deep heat • _______________ • 3 MHz = superficial heat • _______________ Frequency of Therapeutic Ultrasound

Concentrates energy in a limited area • Larger transducer = more ____________ _________ beam • Smaller transducer = more _________ beam • 1 MHz frequency more divergent than 3 MHz frequency The Ultrasound Beam

Near field • Distribution of energy is _______________ • Area near transducer • Non-uniformity due to differences in acoustic pressure created by the waves emitted from the transducer Ultrasound Beam

Point of Maximum Acoustic Intensity • As acoustic waves move ________ from transducer, they become indistinguishable and arrive at a certain point simultaneously Ultrasound Beam

Far Field • Waves travel beyond the point of maximum acoustic intensity • Energy is more _____ ___________ and the beam becomes more divergent Ultrasound Beam

Indicates the amount of ______________ in intensity within the ultrasound beam Determined by the highest intensity found in the ultrasound beam relative to the average intensity across the transducer Ideal BNR would be _______________ Typical BNR _______________ Maximal point of intensity = 6 W/cm2 Average output of intensity across transducer = 1 W/cm2 Beam Nonuniformity Ratio (BNR)

_____________ = more even the intensity Less risk of developing “hot spots” _______________ = higher nonuniformity Must move transducer faster throughout treatment to avoid “hot spots” Manufacturers must report the BNR Better generators have a ______ BNR, thus providing more even intensity throughout the field Beam Nonuniformity Ratio (BNR)

Pulsed vs. Continuous Ultrasound • Continuous Ultrasound • Ultrasound intensity remains constant over time • Ultrasound energy produced ________ of the time

Pulsed vs. Continuous Ultrasound • Pulsed • Ultrasound intensity is interrupted with no energy produced during the off time • Average intensity of output over time is _________

Duty Cycle Percentage of time that ultrasound is being generated (pulse duration) over one pulse period Pulse period = mark:space ratio Duty Cycle = duration of pulse (on time) x100 pulse period (on time + off time) Duty Cycle may be set to 20% or 50% Total amount of energy delivered would be only 20% or 50% of the energy delivered if a continuous ultrasound wave was being used Pulsed Ultrasound and Duty Cycle

May be defined 3 ways… Magnitude of vibration in an ultrasound wave Movement of particles in the medium through which the ultrasound wave travels Measured in units of distance (____________) Vibration in pressure found along the ultrasound wave Measured in units of pressure (______________) Amplitude

Both power and intensity are unevenly distributed in the ultrasound beam ______ = total amount of ultrasound energy in the beam Measured in watts _______ = measure of the rate at which energy is being delivered per unit area Power vs. Intensity

Spatial Average Intensity = intensity of ultrasound beam averaged over the ______ _______________ Measured in W/cm2 Power output in watts ERA of transducer in cm2 Example: 6 watts = 1.5 W/cm2 4 cm2 Intensity

Spatial Peak Intensity = _________ value occurring with the beam over time Therapeutic ultrasound maximum intensities range between ___ and ___ W/cm2 Temporal Peak Intensity = __________ intensity during the __ period with pulsed ultrasound Measured in W/cm2 Intensity

Temporal-averaged Intensity Only important with ___________ ultrasound Calculated by averaging the power during both the on and off periods (mean on/off intensity) Intensity settings on ultrasound generators may indicate _________________________ while others indicate ______________________ Intensity

There are no specific guidelines which dictate specific intensities that should be used during treatment Recommendation: use the _______ intensity at the _________ frequency which transmits energy to a specific tissue to achieve a desired therapeutic effect Any adjustment in the intensity must be countered with an adjustment in _______________ Treatments are temperature dependent, not time dependent Intensity

Physiologic Effects of Ultrasound

Thermal effects Tissue heating Non-Thermal effects Tissue repair at the cellular level Thermal effects occur whenever the spatial average intensity is > _______________ Whenever there is a thermal effect there will always be a non-thermal effect Thermal vs. Non-Thermal Effects

To elicit thermal therapeutic effects, tissue temperature must be raised to a level of 40-45°C for a minimum of ___ minutes Baseline muscle temperature is _________ Mild heating: temperature  of _____  metabolism healing and healing Moderate heating: temperature  of ______  pain and muscle spasm Vigorous heating: temperature  of ____  extensibility of collagen and  joint stiffness Thermal vs. Non-Thermal Effects

Increased collagen extensibility ________ blood flow ________ pain Reduction of muscle spasm ________ joint stiffness Reduction of _______________ Thermal Effects of Ultrasound

Ultrasound Rate of Heating Per Minute Intensity W/cm2 1MHz 3MHz 0.5 .04°C .3°C 1.0 .2°C .6°C 1.5 .3°C .9°C 2.0 .4°C 1.4°C • At an intensity of 1.5 W/cm2 with a frequency of 1MHz, an ultrasound treatment would require a minimum of 10 minutes to reach vigorous heating

Ultrasound Rate of Heating Per Minute Intensity W/cm2 1MHz 3MHz 0.5 .04°C .3°C 1.0 .2°C .6°C 1.5 .3°C .9°C 2.0 .4°C 1.4°C • At an intensity of 1.5 W/cm2 with a frequency of 3 MHz, an ultrasound treatment would require only slightly more than 3 minutes to reach vigorous heating

________ fibroblastic activity ________ protein synthesis Tissue _______________ Reduction of __________ Bone healing Pain modulation Non-Thermal Effects of Ultrasound All of these Non-Thermal Physiologic Effects of Ultrasound Occur Through Acoustic Microstreaming and/or Cavitation

Unidirectional flow of fluids along the cell membrane interface resulting from mechanical pressure waves in an ultrasonic field • Alters cell membrane permeability to ______ and ________ ions important in the healing process Acoustic Microstreaming

Formation of gas-filled bubbles that expand and compress due to ultrasonically induced pressure changes in tissue fluids Cavitation

_______________ • Results in an increased fluid flow around these bubbles • _______________ • Results in violent large excursions in bubble volume with collapse creating increased pressure and temperatures that can cause tissue damage Cavitation Therapeutic benefits are derived only from stable cavitation

Can be maximized while minimizing the thermal effects by: Using a ____________________ of 0.1-0.2 W/cm2 with continuous ultrasound Setting duty cycle at ________ at intensity of 1 W/cm2 Setting duty cycle at ________ at intensity of 0.4 W/cm2 Non-Thermal Effects of Ultrasound

Techniques of Application

Acute conditions require more frequent treatments over a _________ period of time 2 treatments/day for _______ days Chronic conditions require fewer treatments over a _______ period of time Alternating days for ________ treatments Controversy Limit treatments to a total of 14 Continue treatments if there is improvement Frequency of Treatment

Considerations for determining Tx time… Size of the area to be treated Intensity of treatment Frequency Treatment goals Thermal vs. non-thermal effects Duration of Treatment

Should be ___ times larger than the ERA of the crystal in the transducer If the treatment area is larger than 2-3 times the ERA, other modalities should be considered _______________, _______________, or _______________ Size of the Treatment Area

Therapeutic Ultrasound