Unit 4: Ultrasound Flashcards
Ultrasound
-Inaudible, acoustic, mechanical vibrations of high frequency that produce thermal and non-thermal physiological effects.
-Therapeutic US is typically 1.0-3.3 MHz.
-Ultrasound waves are produced by “running” an alternating current across a piezoelectric crystal in the sound head.
-A mechanical pressure (sound wave)
Sound waves with a frequency between 20 to 20,000 Hz are audible
-Ultrasound is defined as sound above 20 KHz.
Transducer
-Part of the ultrasound unit that contains a crystal.
-The crystal converts electrical energy to sound waves.
Piezoelectric Effect
Ability of a material to generate electricity when mechanically deformed
Reverse Piezoelectric Effect
-Electrical input causes a mechanical deformation (contraction and expansion of crystal, quartz or ceramic)
-Crystal in US head vibrates in response to electricity
Attenuation
Loss of energy in the US beam due to scattering (reflection and refraction) and absorption
Absorption
-Causes the thermal effects of US as Us is converted to heat in the tissues
-Different types of tissues absorb energy and “heat up” at different rates (tendon vs. muscle)
Less Absorption > More Absorption
Fat > Water > Blood > Muscle > Nerve > Skin > Tendon> Bone
Frequency Ranges for Ultrasound
-1 MHz = 1 million cycles per second; 5 cm depth
-3 MHz = 3 million cycles per
second; 2 cm depth
-3 Mhz heats up 3-4x faster than 1 Mhz*
-High frequencies are absorbed more quickly
Frequency Indicator (Hz):
-The number of compression/ rarefaction cycles per unit of time. Expressed in cycles per second – hertz (Hz).
-Increased frequency causes a decrease in the depth of penetration and concentration of US on superficial tissues
-3Mhz US heats tissues 3-4x’s Faster!!
Power (Acoustic Power: Intensity)
Amount of acoustic energy per unit of time
-Expressed in Watts (W)
Intensity (Acoustic Power: Intensity)
-Spatial Average (SA) intensity: W/cm2
-Watts (power) per unit area (ERA in cm) of the sound head
-Influences the rate of heating, strength of US
Intensity does NOT influence… (ultrasound)
Depth of penetration
Intensity usually creates in the… (ultrasound)
Center of the beam
Intensity lowest at… (ultrasound)
The edges
Intensity and BNR (ultrasound)
-High intensity areas within the ultrasound beam are a primary cause for “hot spots”.
-“Hot Spots” are prevented in part by keeping the sound head moving throughout the treatment
-Caution should be taken with using higher intensities with units that have poor BNR
Beam Nonuniformity Ratio (BNR)
-Refers to the uniformity of the US output ratio
-The ratio of the highest intensity (spatial peak intensity) found in the US beam to the spatial average intensity
-The smaller/lower the BNR the more homogeneous the beam produced by the transducer and the safer and more effective the treatment
A poor BNR
> 6:1 = Potential to create hot spots
-If you are doing an US set at 1.0 W/cm2, there will be an area of the beam as intense as 6 W/cm2
(8:1 max permitted)
Cliniacal Relevance of BNR
-BNR of 2:1 to 5:1 move ultrasound head 1cm/sec
-BNR of 6:1 to 9:1 move ultrasound head 4cm/sec
(indicated on unit by manufacturer)
Ultrasound Coupling
US attenuates quickly in air, and is reflected at the
air-tissue interface
-KEEP SOUND HEAD MOVING AND IN CONTACT WITH PATIENT’S SKIN!
-You will need a coupling agent (Ultrasound gel) to get the ultrasound energy into the desired tissue
-If you use other agents such as Vaseline, eucerin cream, hydrocortisone cream=no US energy is transmitted
-Ultrasound head should be kept in a consistent flat plane in relation to the skin
Effective Radiating Area (ERA) sq.cm
-Area of the ultrasound from which the energy radiates
-The crystal does not vibrate uniformly which causes the ERA to be smaller than area of the ultrasound head
-Treatment area should be 2*-3 times the size of the ERA (This is not 2x’s the diameter of the sound head)
-Physical size of sound head should match body part being treated
Duty Cycle
The amount of Time sound waves are penetrating tissue …Expressed in on/off cycle of time
-Continuous Ultrasound: US on all of the time 100% duty cycle
-Pulsed Ultrasound: 20% 50% on/off
-Duty Cycle: 2 ms on, 8 ms off: 2ms on/10ms total=20%
-Delivery of the ultrasound during a segment of time: 20% duty cycle (Minimizes thermal effect and serves primarily as mechanical effect)
Continuous Ultrasound
US on all of the time 100% duty cycle
-Increase in peripheral blood flow
-Increase in metabolic rate
-Increase in oxygen uptake
-Increased temperature in tissues with local hyperemia
-Elevated pain threshold
-Changes sensory and motor nerve conduction (research inconclusive)
-Increased skin temperature, if applied over sympathetic nerves
-Increased collagen tissue extensibility (why??)
-Increased heating at interfaces (especially bone-muscle interface; bone absorbs 10 x’s more than soft tissue)
Pulsed Ultrasound
20% 50% on/off
-Effects occur at the cell membrane due to mechanical vibration causing:
-Acoustic Streaming, Micro Massage, Cavitation
Acoustic Streaming:
-Unidirectional movement of fluid within the pressure field that causes structural changes in cell membrane
(Increased cell permeability and ionic exchange)
Acoustic Streaming (pulsed ultasound)
-Unidirectional movement of fluid within the pressure field that causes structural changes in cell membrane
(Increased cell permeability and ionic exchange)
Micro Massage (pulsed ultrasound)
Force which occurs during compression phase of pulsed ultrasound that deforms the cell membrane and massages the cell
Caviation (pulsed ultrasound)
-Formation, growth and pulsation of gas or vapor filled bubbles caused by ultrasound bean
-Stable: Changes in cellular diffusion
-Unstable: Tissue Death
(Pulsed US reduces risk of unstable caviation)
Physiological Effects of Pulsed Ultrasound
Increases cell and vascular wall permeability to calcium and sodium ions
-Resulting in less leakage from the capillaries into the interstitial spaces (decreases edema)
-Increases extensibility of connective tissue (collagen rich tissue)
-Stimulation of tissue regeneration (fibroblast activity)
-Promotes soft tissue and bone repair
-Increase circulation
-Stimulate the release of histamine from mast cells by degranulation. especially within the first few hours of the injury, thus accelerating the healing process
-Decreases inflammatory phase (inhibits the release of inflammatory mediators)
-Stimulates fibroblasts to secrete collagen (increases tensile strength)
-Accelerates wound contraction and healing of the dermis
-Decreases pain
1 MHz (ultrasound)
-5cm
-Increased depth
-Slow heating
-Increased treatment time with increased intensity
-Pulsed: 0.5-1.0 W/cm2
-Continuous: 1.5-2.0 W/cm2
3 MHz (ultrasound)
-1-2cm
-Decreased depth
-Quick heating
-Decreased treatment time with decreased intensity
-Pulsed: 0.5-1.0 W/cm2
-Continuous: 1.0-1.5 W/cm2
Patient Response: Intensity too high
Deep ache from overheating the bone periosteum
Patient Response: Intensity too low
No increased temperature
Clinical Ultrasound Uses
-Sub-acute and chronic soft tissue inflammation (thermal)
-Joint contractures
-Muscle spasm
-Neuroma (thickening of nerve tissue due to compression or irritation of the nerve)
-Loosen scar tissue
-Trigger point areas
-Acute injuries (non-thermal only)
-Bone healing (non-thermal only)
-Tissue repair
Soft Tissue Shortening
-Can penetrate depths of most joint capsules, tendons, ligaments, scar tissue
-Collagen content (high absorption coefficient)
-Increased extensibility of tissue with reducing risk of damaging tissues
-US is more effective when stretch applied to tissue
Thermal Effects (pain control)
-Stimulation of cutaneous thermal recpetors
-Increased soft tissue extensibility
-Change with nerve conduction
Nonthermal Effects (Pain Control)
Modulation of inflammation
Therapeutic Usage
-Surgical Incision
-Healing Fracture
-Tendon Injuries (tendonitis, tendon laceration s/p repair)
-Phonophoresis
Surgical Incision (therapeutic uses)
-Accelerates the development of new blood vessels
-Reestablishes circulation and facilitates wound healing
-Relieves pain from scars
-Accelerates hematoma resolution
Healing Fracture (therapeutic uses)
-Thermal US not used over unhealed fractures
-Low dose pulsed ultrasound can reduce fracture healing time
-Can be painful? Why?
Tendonitis
-Acute Phase: Low intensity pulsed US (non-thermal)
-Chronic Phase: High intensity continuous, if shortening of tissue has occurred (thermal)
Tendon Laceration s/p Repair
-Minimum of 6 weeks post repair (ongoing research)
-Increases extensibility of tissue
-Preparatory method for tendon gliding
Phonophoresis
-Application of ultrasound in conjunction with topical drug
-Enhance delivery of the drug
-Inconsistencies in regard to effectiveness
-MD prescription required for medication
Contraindications
-Over pacemaker or implanted electrical device
-Do not apply after cold pack/ice
-Over the heart, eyes, reproductive areas
-Over CNS tissue (spinal cord post laminectomy)
-Sites of insulin injections
-Over fracture sites before healing, demineralize the bone (thermal setting only)
-Ischemic areas
-Areas with limited sensation
-Do not apply over heart, eye, pregnant uterus, reproductive, organs, children’s growth plates, breast implants
Ultrasound Precautions
-Cognitive/communication impairment
-Impaired pain or temperature sensation
-Reduced circulation
-Acute inflammation
-Joint implants
-Main peripheral nerve branches (controversial)
Ultrasound Contraindications (controversial areas)
-Plastic implants
-Joint cement
-Metal implants
-Peripheral nerve branches
-Epiphyseal growth plates
Ultrasound Documentation
-Area of body treated
-Ultrasound Parameters: Frequency, Intensity, Duty cycle, Treatment duration, Delivery, Patients response to treatment
Guidelines
-Correctly position your patient
-Describe advantages and disadvantages of modality
-Recall precautions and contraindications
-Explain procedure and what the patient should feel
-Select appropriate US settings
-Clean skin with alcohol and/or soap
-Apply gel and position head of US correctly
-Move the US head slowly (pain-free); If pain, decrease intensity
-Ask the patient to describe what they are feeling
-Remove gel and clean transducer
-Inspect
-Document
