Ultrasound and Diathermy Flashcards
Absorption
Conversion of mechanical energy of ultrasound into heat
Absorption coefficient
The degree to which a material absorbs ultrasound
Absorption coefficients are different for different materials and ultrasound frequencies
Angiogenesis
The development of new blood vessels at an injury site
Attenuation
The decrease in ultrasound intensity as ultrasound travels through tissue
Acoustic streaming
The steady circular flow of cellular fluids induced by ultrasound
The flow is larger in scale that microstreaming
It is thought to alter cellular activity by transporting materials from one part of ultrasound field to another
What is the beam nonuniformity ratio (BNR)?
The ratio of the spatial peak intensity to the spatial average intensity
Usually b/t 5:1 and 6:1
FDA requires max BNR for an ultrasound transducer be specified on the device
Cavitation
The formation growth, and pulsation of gas-filled bubbles caused by ultrasound
Compression
Increase in density of a material as ultrasound waves pass through it
What is the depth of tissue at which the ultrasound intensity is half its initial intensity
Half life
Microstreaming
Microscale eddying that takes place near any small, vibrating object
Occurs around gas bubbles set into oscillation by cavitation
Near field/ far field
The ultrasound beam initially converges and then diverges
Convergent region is known as near field
Divergent field is known as far field
What are other names for the convergent region?
Frensel zone
What is another name for the divergent?
Fraunhofer zone
How do you calculate the length of the near field?
Radius of transducer (squared)/ wavelength of ultrasound
What is the application of ultrasound with a topical drug to facilitate transdermal drug delivery?
Phonophoresis
Piezoelectric
The property of being able to generate electricity in response to a mechanical force Or being able to change shape in response to an electrical current (as in an ultrasound transducer)
What is a decrease in density of material as ultrasound waves pass through it?
Rarefaction
Reflection
The redirection of an incident beam away from a surface at an angle equal and opposite to the angle of incidence.
Ultrasound is reflected at tissue interfaces, with most reflection occurring where the greatest difference is present b/t the acoustic impedance of adjacent tissues
Refraction
the redirection of a waves at an interfaces
When refraction occurs, the ultrasound waves enters tissue at one angle and continues through the tissue at a different angle
Standing wave
Intensity maxima and minima at fixed positions one half wavelength apart
When does a standing wave occur?
When the ultrasound transducer and reflecting surface are exact multiples of wavelengths apart, allowing the reflected wave to superimpose on the incident wave entering the tissue
How can standing waves be avoided?
By moving the ultrasound head throughout the treatment
Ultrasound
Sound with a frequency greater than 20,000 cycles per second that, when applied to the body, has thermal and nonthermal effects
Transducer
a crystal that converts electrical energy into sound .This term is also used to describe the part of an ultrasound unit that contains the crysteal
What can another name for the transducer?
Sound head
What is continuous delivery of ultrasound throughout the treatment period?
Continuous ultrasound
Duty cycle
The proportion of the total treatment time that the ultrasound is on
Can be expressed as a % or a ratio
ie- 20% or 1:5 is on 20% of the time off 80%
Effective radiating area
The area of the transducer from which the ultrasound energy radiates
Since the crystal does not vibrate uniformly, the ERA is always smaller than the area of the treatment head
Frequency
the number of compression-rarefaction cycles per unit of time, expressed in cycles per second or hertz
What is the amount of acoustic energy per unit time? How is it expressed?
Power
It is expressed in watts (w)
Intensity
The power per unit area of the sound head
It is expressed in watts per cm squared (w/cm2)
The World Health Organization limits the average intensity output by therapeutic ultrasound unit to ______.
3w/cm2
What is the usual frequency range for therapeutic ultrasound?
1 to 3 million cycles per second ie- 1 to 3 MHz
What does increasing the frequency of ultrasound cause?
A decrease in the depth of its penetration and concentration of ultrasound energy in superficial tissues
Pulse ultrasound
Intermittent delivery of ultrasound
Minimizes its thermal effects
What are some examples of direct interventions based on the POC?
physical agents, modalities (ther ex, gait & transfer training)
What are some indirect interventions based on the POC?
patient & family education, documentation, coordination & communication w/ others
Spatial average temporal average (SATA) intensity
The spatial average intensity of the ultrasound averaged over the ON time and the OFF time of the pulse
How does the Nagi model help us understand what is happening with the patient?
It allows us to understand what is happening at all levels of the individual, help us appreciate functional limitations and understand individual implications on roles & societal expectations
At what level do physical agents act in the Nagi model?
pathology, impairment, functional limitation, disability, handicap
The application of physical agents primarily has these positive effects?
modification of tissue inflammation & healing, relief of pain, alteration of collagen extensibility, or modification of muscle tone
Name a few nonthermal effects of ultrasound that may alter membrane permeability?
Acoustic streaming, cavitation, and microstreaming
Non-thermal also: Increases rate of protein synthesis by fibroblast
Increases intracellular calcium, skin and cell membrane permeability, mast cell degranulation, chemotactic factor and histamine factor release
Increase macrophage responsiveness
Sound energy is best absorbed in which type of tissues?
Tissues with high collagen content
ie- bone, tendons, ligaments, joint capsules
APTA position statement on the use of clinical modalities
physical agents alone do not constitute effective PT, should be applied in conjunction w/ other direct interventions