Therapeutic Ultrasound Jennifer Doherty-Restrepo, MS, LAT, ATC Entry-Level ATEP Therapeutic Modalities
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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 Transmission of Acoustical Energy in Biological Tissue 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 not travel in a _______________ Travels in waves in all directions Longitudinal and transverse waves Longitudinal Waves Primary waveform for travel in soft tissue Molecular displacement occurs along the ___________________ ___________ Transverse Waves Primary waveform for travel in ______ Molecular displacement is _______________ to direction of wave propagation Frequency Of Wave Transmission Audible sound = _______________ Ultrasound > _______________ Therapeutic Ultrasound = _______________ (1,000,000 cycles/sec) Penetration and absorption are ____________ related Lower frequencies = ______ depth of penetration Higher frequencies = superficial ______________ Velocity Of 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 _______________ Attenuation _______ in energy intensity as the ultrasound wave is transmitted through various tissues ________ is due to absorption, dispersion, or scattering, which result from __________ and __________ Penetration vs. Absorption _______________ relationship Absorption increases as frequency __________ Tissues high in water content _________ absorption Blood Tissues high in protein content ________ absorption Bone, nerves, muscles, and fat Ultrasound at Tissue Interfaces 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 _______________ Acoustic Impedance 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” 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 Ultrasound Generator Electrical Output Mechanical Vibration Acoustic Soundwave Absorbed In The Tissues Therapeutic Ultrasound Generator Control Panel Timer Power meter Intensity control _______________ Duty cycle switch _______________ Selector switch for continuous or pulsed Automatic shutoff if transducer overheats Transducer AKA: _______________, or _______________ Not interchangeable Piezoelectric crystal Quartz Synthetic ceramic crystal Converts ____________ energy to _____ energy through mechanical deformation Piezoelectric Effect When an alternating current generated at the same frequency as the crystal resonance is passed through the peizoelectric crystal, it will ________ and _______________ 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 Effective Radiating Area (ERA) 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 Frequency of Therapeutic Ultrasound 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 _______________ The Ultrasound Beam Concentrates energy in a limited area Larger transducer = more ____________ _________ beam Smaller transducer = more _________ beam 1 MHz frequency more divergent than 3 MHz frequency 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 Beam Nonuniformity Ratio (BNR) 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 _______________ point of intensity = 6 W/cm2 Average output of intensity across transducer = 1 W/cm2 Maximal 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 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 _________ Pulsed Ultrasound and Duty Cycle 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 Amplitude 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 (______________) Power vs. Intensity 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 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: watts = 1.5 W/cm2 cm2 6 4 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 dependent are temperature dependent, not time Physiologic Effects of Ultrasound Thermal vs. Non-Thermal Effects 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 4045°C for a minimum of ___ minutes Baseline Mild heating: temperature of _____ metabolism healing and healing Moderate heating: temperature of ______ muscle temperature is _________ pain and muscle spasm Vigorous heating: temperature of ____ extensibility of collagen and joint stiffness Thermal Effects of Ultrasound Increased collagen extensibility ________ blood flow ________ pain Reduction of muscle spasm ________ joint stiffness Reduction of _______________ Ultrasound Rate of Heating Per Minute Intensity W/cm2 1MHz 0.5 1.0 1.5 2.0 .04°C .2°C .3°C .4°C 3MHz .3°C .6°C .9°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 0.5 1.0 1.5 2.0 .04°C .2°C .3°C .4°C 3MHz .3°C .6°C .9°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 Non-Thermal Effects of Ultrasound ________ fibroblastic activity ________ protein synthesis Tissue _______________ Reduction of __________ Bone healing Pain modulation All of these Non-Thermal Physiologic Effects of Ultrasound Occur Through Acoustic Microstreaming and/or Cavitation Acoustic Microstreaming 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 Cavitation 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 Therapeutic benefits are derived only from stable cavitation Non-Thermal Effects of Ultrasound 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 Techniques of Application Frequency of Treatment 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 Duration 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 Size of the Treatment Area 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 Intensity Recommendations for specific intensities make little sense Ultrasound intensity should be adjusted to _______ ____________ Increase intensity to the point where the patient feels _______, then decrease the intensity slightly to elicit general heating in the treatment area If you decrease intensity during treatment you should increase _______________ Ultrasound treatments should be temperature dependent, not time dependent Frequency Determines _______________ Determines _______________ Energy produced at 3 MHz is absorbed 3 times faster than that produced from 1 MHz ultrasound Results in faster heating Reduce 3 MHz treatment durations by _________ Coupling Methods Greatest amount of energy reflection occurs at the _______________ Reduce amount of energy reflection by holding transducer ____________ (90° angle) to treatment area Coupling mediums further _________ reflection _______________ = substance used to decrease acoustical impedance at the air-tissue interface Maximize contact with the tissue to facilitate passage of ultrasound energy Include gel, water, mineral oil, distilled water, glycerin, analgesic creams Direct Contact Transducer should be small enough to treat the injured area Gel should be applied liberally Heating gel does not increase the effectiveness of the treatment Immersion Technique Good for treating irregular surfaces A plastic, ceramic, or rubber basin should be used Tap water is useful as a coupling medium Transducer should move ______ to the surface at a distance of _________cm from the treatment area Air bubbles should be wiped away Bladder technique Good for treating irregular surfaces Uses a balloon filled with water Both sides of the balloon should be liberally coated with a _______________ Moving The Transducer Applicator should be moved at a rate of _______________ An ultrasound generator with a low BNR allows for ________ transducer movement An ultrasound generator with a high BNR may cause unstable ___________ and “hot spots” if the transducer is moved ______ _________ Clinical Applications For Ultrasound Ultrasound is recognized clinically as an effective and widely used modality in the treatment of soft tissue and boney lesions There is relatively little documented, databased evidence concerning its efficacy Most of the available data-based research is unequivocal Soft Tissue Healing and Repair During the __________________________ of healing, stable cavitation and _______________ increase the transport of calcium across cell membranes, thus releasing histamine Histamine stimulates… ___________ to “clean up” the injured area ___________ to produce collagen (Dyson, 1985, 1987) Scar Tissue and Joint Contracture Increased tissue temperature causes an increase in elasticity and a ___________ in viscocity of collagen fibers (Ziskin, 1984) Increased tissue temperature ___________ mobility in mature scar tissue (Gann, 1991) Chronic Inflammation Few clinical or experimental studies have observed the effects of ultrasound treatment on chronic inflammation Ultrasound does seem to be effective for increasing blood flow to the treatment area, which may facilitate the healing process and reduce pain (Downing, 1986) Bone Healing Ultrasound ___________ fracture repair Ultrasound given to an __________ fracture during cartilage formation may cause cartilage proliferation and delay union (Dyson, 1989) No effect on _______________, but may help reduce surrounding inflammation (Dyson, 1982, Pilla et al., 1990) (Ziskin, 1990) Not effective in detecting _______________ Pain Reduction Ultrasound treatments are not used specifically for pain modulation Ultrasound may increase the ___________ ____________ of free nerve endings Superficial heating may effect gating of pain impulses - _______________ (McDiarmid, 1987) (Williams et al. 1987) Increased nerve conduction velocity creates a _______________ effect (Kitchen, 1990) Placebo Effects A number of studies have demonstrated a placebo effect in patients using ultrasound (Lundeberg, 1988, Dyson, 1987, Hashish et al., 1986) Phonophoresis Ultrasound energy used to drive topical application of selected medications into the tissues _______________ Cortisol Salicylates Dexamethasone _______________ Lidocaine Phonophoresis ___________ effects of ultrasound increase tissue permeability and acoustic pressure drives molecules into the tissue Effectiveness of phonophoresis is debatable Early studies demonstrated effective penetration (Griffin, 1982, Kleinkort, 1975) More recent studies show ineffectiveness (Oziomek et al, 1991, Benson et al., 1989) Ultrasound and Other Modalities US and Hot Packs = _______________ US and Cold Packs = _______________ Cooling the tissues does not facilitate an increase in temperature (Remmington 1994, Draper, 1995) Analgesic effects of ice can interfere with perception of heating Pulsed US may be beneficial during InflammatoryResponse Phase of healing US and E-Stim = _______________ Effective in treating myofascial trigger points when used in combination with stretching (Girardi, et al. 1984) Ultrasound Treatment Indications and Contraindications Table 5-8, p. 127 --- Memorize!!! Guidelines for the safe use of ultrasound equipment, p. 126-127