Ultrasound Flashcards
○ Beyond 20,000 Hz
○ Cannot be heard (since ang hearing
range is from 15000-20000 Hz)
○ Limit between 1 Hz and 3 mega Hz for
therapeutic purposes
Frequency
○ Distance between the 2 equivalent points
of the waveform in the particular
medium
○ 1 mega Hz on average tissue = 1.5 mm of
wavelength
○ 3 mega Hz = 0.5 mm
Wavelength
○ refers to the speed of the wave as it
passes through the medium (differ based
on medium)
○ Passes through a saline solution – 1,500
m/sec
○ Waves travel on a more dense medium
Velocity
○ longitudinal in wave form that contains
compression and rarefaction –
approximation and separation of waves
as it passes through a vacuum
Sound Waves
● As electric current passes through the TUS, it
passes through a crystal
○ causing deformation and vibration
○ Electricity across the crystal causes
deformation and vibration
piezoelectric effect
a crystal that produces
(+) or (-) electrical charges when it contracts or
expands
Piezoelectric crystal
● A device that converts one form of energy to
another
Transducer
○ area of the ultrasound beam on the
transducer used for therapeutic purposes
○ Beam emitted nearest to the transducer
head
○ Prone for hot spots due to focalization of the
beam (yang center ng blue beam)
Fresnal/Freznel (near field)
○ located away from transducer head; beam is
more uniform (even heating) and gently
divergent; can also be used for therapeutic
purposes
○ Hotspots are not significant
Fraunhoffer’s zone (far field)
● The average intensity of the US output over
the area of the transducer
● Intensity is the dosage on how much heat is
emitted within the transducer head
Spatial Average Intensity
● The peak intensity of the US output over the
area of the transducer (middle)
Spatial Peak Intensity
● The ratio of the spatial peak intensity to the
spatial average intensity
● Indication of near field interference in relation
to the amount of intensity produced
Beam Non-uniformity Ratio (BNR)
continuos delivery of US all
throughout the
treatment period
● Generate
thermal effects
Continuous Ultrasound
● Delivery of US during only a portion of the
treatment period
● Pulsing the US produces non-thermal effects
● Duty cycle – period of on and off time
● Generate non-thermal effect
Pulsed Ultrasound
● The proportion of the total treatment time
that the US is on
● This can be expressed either as a
percentage or a ratio
Duty Cycle
● The number of compression-rarefaction
cycles per unit time (1 sec)
● Frequency is inversely proportional to its
depth of penetration
Frequency
● The area of the transducer from which the
US energy radiates
ERA
The reduction of acoustical energy (US
intensity) as it passes through the soft
tissue
● Result of absorption, reflection, and
refraction
Attenuation
– chance that there will be
reflection/refraction of the US; cause
periosteal burning (periosteum), causing pain
Cartilage and bone
PHYSIOLOGICAL EFFECTS OF ULTRASOUND
Thermal
which is the uneven
distribution of the acoustical energy
through the sound head
hotspot
formation of gas filled bubbles within
the surrounding tissue and body fluids. Would
enhance the acoustic streaming
Cavitation
the gas filled void/bubbles
would occur at therapeutic doses of ultrasound,
the bubbles would accumulate in the tissue/body
fluids
Stable Cavitation
- There is vibration or
production of movement of particles/fluids near
a vibrating structure, such as the cell membranes
and body structures. This would cause an
activation and may produce an effect to the cell
membrane permeability and then affect the
diffusion rates
Acoustic Streaming
