Ultrasound Flashcards
what is ultrasound?
Application of acoustic (sound wave) energy, inaudible to the human ear. Causes mechanical vibration which:
-At Pulsed duty cycle: Non-thermal Effects of Ultrasound
At Continuous duty cycle: Thermal Effects of Ultrasound
Pulsed duty cycle
Non-thermal Effects of Ultrasound
- Causes acoustical streaming, micro-streaming, and cavitation which Increases cellular metabolism: results in increased enzyme activity, stimulates immune system, increased oxygen uptake, increased cellular permeability.
- Facilitates tissue repair (increased phagocytic activity, fibroblast & granulation tissue formation)
- Increases pain threshold (decreases muscle spasm, increases conduction of peripheral nerves, serotonin release)
Continuous duty cycle
Thermal Effects of Ultrasound
• In addition to non-thermal effects, thermal ultrasound also produces the following benefits
• can produce deep heat (up to 5cm) through conversion of the kinetic energy in the tissue (remember superficial heat agents heat up to 1-2 cm deep)
• allows for soft tissue (collagen) extensibility
• increases blood flow
• increases cellular metabolism
types of ultrasound
Sound is audible up to 20 kHz. Anything above that is considered ultrasound. Medical ultrasound is generally between .8 Mhz to 3.0 MHz
• Low intensity: Diagnostic : sonogram
• Medium intensity: therapeutic
• High intensity: tissue destruction (ie. tissue ablasion for fibroids or tumors)
background of ultrasound
1800 ‘s Pierre & Marie Currie found that mechanical compression of certain crystals create vibration. This is called the piezoelectric effect (production of +/- charges when crystal expands and contracts).
1930-40’s: Piezoelectric transducer used to detect submarines during WWII. Research begins on medical application of effect on US on human tissue for medical diagnosis and treatment.
1950’s: AMA recommends use of US as a modality for use of soft tissue healing and pain. Often used in MD offices by non-trained individuals
1960’s regulations tightened by states and ultrasound mainly prescribed for use by PT. OT began used of US in a widespread manner by 1980’s.
1990’s: National push to demand OT’s competence. Driven mainly by APTA. Individual states established regulations. NY state OT regulations indicate OT’s must receive training in modalities that includes a background in physics.
transducer
Also called the sound head. This is the device that is held aimed at the patient’s skin (with gel or water as medium). It houses the crystal which is immediately behind the face plate of the transducer. Choose size of sound head based on area treating.
• Movement of the sound head on the surface should occur at 4 cm (1.5 inches) per second in
o overlapping circles or
o back and forth, side to side with overlap
crystal
Housed in the transducer it is more recently made of ceramic or a synthetic material. It is only about 1/16” thick.
• subject to breakage if sound head is dropped.
• Damage can occur if not in contact with transmission medium/skin prior to turning on.
• Check 1-2 x per year to assure intact: Biomedical Engineering Department
• Informal integrity test: submerging in H2O and observe for bubble formation on surface indicating crystal is functioning
Reverse Piezoelectric Effect
When alternating current is applied (an electrical charge) to the crystal it responds by expanding and contracting. When the crystal expands and contracts it results in a mechanical response in the tissue in front of it (this mechanical response is the Reverse Piezoelectric Effect) The alternating compression – rarefaction is the ultrasound wave
• Compression of crystal: moves the tissue together
• expanding of crystal: causes rarefaction or pulling the tissue apart
penetration
Degree to which the sound wave passes through the tissue without regard to absorption by the given tissue
transmission medium
also called coupling agent (% transmission or penetration of sound waves)
• Ultrasound Gel: (97%). This is a water based gel that is hypoallergenic
o recent research: warmed gel 10% less effective
• Ultrasound Lotion (90%)
• Hydrocortisone Cream (0-10%): commonly used in the 80’s & early 90’s
• Other medications infused in gels (88%): ie. Betamethasone .05%, lydocaine (fluoninocide) .05%
• Water: submersion technique can be used for surfaces that are bony. Transducer is then placed ½ inch away from the skin surface.
Phonophoresis
application of ultrasound with a topical drug
attenuation
is the process of energy loss.
• Absorption is a main way energy is lost either into tissue or into the transmission medium
• Reflection: redirection away in the equal and opposite direction; generally occurs at skin surface if not enough transmission medium.
• Sound waves decrease in intensity as they travel through the tissue
• Refraction: redirection of a sound wave generally due to a blockage by foreign tissue
absorption
the degree to which the sound wave is transferred into the tissue thereby limiting penetration. Denser tissues with more protein and collagen have greater absorption of the sound wave.
Stable Cavitation
formation , growth, and pulsation of gas and vapor filled bubbles caused by the non-thermal mechanical effects of ultrasound.
Acoustical Streaming
The steady flow of cellular fluid induced by the mechanical effects of ultrasound
Beam Non-Uniformity (BNR)
this number reflects the intensity of the ultrasound output as it varies from the center of the sound head to the outer edges. Intensity is greatest at the center. The units manual will tell you this ratio. Those with a ratio that is lower (less difference between the center and the outer edge) have a more desirable BNR and are generally 2:1. The highest ratios are expressed as 5:1 or 6:1.
• The higher the ratio the more important it is for you to have constant movement and slightly faster movement of the ultrasound head to prevent hot spots.
Effective Radiating Area (ERA)
the area on the transducer face where the ultrasound energy radiates. This is smaller than the actual size of the face of the tranducer as the crystal is smaller than the actual face size.
• Therefore need to move sound head in a slightly larger area than you want to treat.
application of frequency
Frequency: Number of compressions – rarefactions cycles per second (MHz)
• Increased frequency = decrease depth of penetration
• 1 MHz or 3 Mhz (one MHz = 1 million cycles per seconds)
o 3 MHz penetrates 1-2 cm deep
o 1 MHz penetrates deeper up to 5 cm dependent on intensity and absorption
• Remember sound is audible at 20 kHz (one KHz = 1000 cycles per second)
• Frequency can be selected either by the sound head chosen or by a knob on the device
application of duty cycle
Duty Cycle: percentage of time the sound head is delivering sound waves. This determines whether you are delivering continuous (thermal) or pulsed (non-thermal) ultrasound
• May be set as a percentage or some US units have only set setting that may be reflected by a visual icon or a percentage number
• Duty cycle for continuous ultrasound is 100%
o Use when you desire the thermal effects in addition to mechanical effects
o Thermal effect remains for 8-10 minutes post treatment
• Duty cycle for pulsed ultrasound is generally 20%: this reflects the sound head is on 20%
o Use pulsed ultrasound in acute stages, when client does not improve from continuous or in cases where client experiences periosteal pain (a dull ache)
application of dosage/intensity
Dosage or Intensity: Strength of the acoustic energy at the site of the application
• Measured in power per unit area of the sound head – watts/centimeter squared w/cm2.
• 0.1 – 2.0 w/cm2: typical use for therapeutic purposes
o Must be greater than 1.0 w/cm2 to produce thermal effect
• General rules for Intensity
o Acute conditions: 0.1 – 0.5 w/cm2
o Subacute conditions: 0.5 – 1.0 w/cm2
o Chronic conditions: 1.0 – 2.0 w/cm2
application of time
Time: duration of application of sound wave measured in minutes
• Typically 5 - 12 minutes. Determined by area treated: Count how many sound heads it takes to cover the area you wish to treat. That number equals the number of minutes of treatment.
• Number of treatments: 12 -14 max. Then need to skip two weeks if you really need to continue.
o Ultrasound can deplete red and white blood cells. Need time for re-generation.
Contraindications for Ultrasound:
- Never over the eye, heart, pregnant uterus, or reproductive organs.
- Never over central nervous system tissue or pacemaker
- Malignancy or area of infection
- Area of decreased circulation or thrombophlebitis
- Area of impaired sensation
- Never high intensity (greater than 1.0) over growth plates: officially can do low intensity under 18 years but use judiciously. Many practitioners avoid US completely with under 18 years.
- Never allow sound head to be stationary
- Stop if patient has any pain
Precautions
- Metal or plastic implants: keep moving
- Unhealed fracture sites: some literature indicates low frequency promotes bone growth
- Acute inflammation or edema
application
Position body part in a position of relaxation, apply medium, set parameters. Spread medium evenly over area testing tolerance for sound head pressure if needed. While moving sound head turn on, move constantly in overlapping pattern. Assure sound head is in full contact with skin entire time by rotating around body part to assure full contact.
Documentation
include frequency (MHz), intensity (w/cm2), duty cycle(pulsed or continuous), length of treatment (minutes), tolerance/response to treatment
Advantages to choosing ultrasound
significant tissue healing, very localized, short application
Disadvantages to choosing ultrasound
patients feel little sensation, pressure of sound head not always tolerated, large areas are difficult to treat.
