Ultrasound and Diathermy Flashcards
what is ultrasound
deep-penetrating agent that produces changes in tissue via thermal and nonthermal (mechanical) mechanisms
-uses sound waves
uses of ultrasound
-diagnostic imaging (.5-50 mW/cm2)
-therapeutic deep tissue healing (1-3 W/cm2)
-tissue destruction (.2-200 W/cm2)
what are the two frequencies of therapeutic ultrasound
1 Hz
3 Hz
which ultrasound frequency penetrates deeper
1 Hz
ultrasound production
-produced by alternating current through crystal which is housed within the transducer
-AC current enters the crystal causing it to contract and expand, this produces the ultrasound waves
-requires a coupling medium (gel, water, ultrasound pads) in order for energy to pass from transducer into the tissues
reverse piezoelectric effect
converts electrical energy to mechanical energy (creates the sound waves)
what shape wave are ultrasound waves
sinusoidal (goes up and down in a wavy formation)
longitudinal waves
-molecule displacement occurs parallel to direction of sound, travels in the same direction
-can travel thru solid (bone) and liquids
how does ultrasound waves pass through soft tissue
via longitudinal waves
transverse (shear) waves
-molecule displacement in transverse waves are displaces perpendicular to the direction of energy
-cannot pass thru fluids
-only found when ultrasound waves hit a bone
Fresnel zone
portion of the ultrasound beam used for therapeutic purposes
treatment area for ultrasound
-area is only slightly larger than the diameter of the sound head
-never cover an entire muscle or limb, it needs to be broken up into smaller groups and focused separately
effective radiating area (ERA)
-proportion of the transducers surface area that produces ultrasonic energy (cm2)
large ERAs
produce collimated, focused beam
-when treating a trigger point, its like a light saber and only focuses on 1 pinpoint spot
smaller ERAs
yields a more divergent beam
-treats a larger area like a muscle strain
frequency
MHz
-how deep the wave penetrates
-1 or 3 Hz is commonly used for ultrasound
–1 Hz beam diverges more than 3 Hz
what does high-frequency (3MHz) treat and how
treats superficial tissue because energy is rapidly absorbed and heats 3x faster than 1MHz
how to calculate treatment time
desired temp/heating rate
which frequency has a longer treatment time
1 MHz
power
energy, measured in watts (W)
intensity
describes the strength of the sound waves at a given location within the tissues being treated
spatial average intensity (SAI)
amount of energy passing through the sound heads effective radiating area (W/cm2)
total watts (W)/ERA (cm2) = W/cm2
duty cycle
pulse length (on time)/ (pulse length (on) + pulse interval (on+off)) * 100
continuous output
100% DC, always on
-causes thermal effects (increase blood flow, viscoelasticity, inflammation, muscle temp)
-used for tissues 5cm or more deep
pulsed output
-causes nonthermal (mechanical) effects
-decreases temporal avg intensity, reducing thermal effects and increasing proportion of nonthermal effects
spatial average temporal peak intensity (SATP)
-avg intensity during the on time of the pulse
-total amount of energy delivered to the body during the treatment
spatial average temporal average intensity (SATA)
-measures the power of utlrasonic energy delivered to the tissues over a given time (total watts/time)
-energy delivered to the tissues per unit of time
SATA = output * duty cycle (decimal)
beam nonuniformity ration (BNR)
describes the variation between the peaks, the spatial peak intensity, and valleys
-ratio of the highest intensity to the avg intensity
BNR = spatial peak intensity/spatial avg intensity
-there is going to be an unknown value, use “x”
