Ultrasound Flashcards
Definition of deep heating agent
Capable of causing tissue temperature change at depths of 2 cm or >
Capable of causing tissue temperature changes in deep tissues without causing excessive overheating of superficial tissues
models for deep heating agents
Ultrasound
Shortwave diathermy
Microwave
definition of ultrasound
A molecule set to vibrate will cause its neighbor to vibrate also; the neighbors will then cause their neighbors to vibrate and so on until the vibration has passed through the entire material (propagation of vibratory motion is sound)
what really iiiissssss ultrasound
soundwaves occurring at a frequency greater than can be heard by the human ear
compression phase
molecules compress
rarefaction
molecules spread out again
sound wave motion/ dispersion - longitudinal wave
Molecules are compressed in the direction the wave travels from its source
sound wave motion/dispersion - shear wave
Molecule movement is at a right angle or perpendicular to the source of the wave
Dominant in liquid
1 cycle of ultrasound =
1 compression phase + 1 rarefaction phase
definition of attenuation
the reduction of energy as it travels through the medium
scattering
Deflection of soundwave from its path by reflection/refraction at interfaces
Overall effect is that US beam is decreased in intensity the deeper it passes
what happens as a sound wave hits a boundary
- it loses energy
- some of this energy loss is due to reflection of the sound wave
reflection
redirection of an incident beam away from a
reflecting surface at an angle equal and opposite to the angle of incidence
refraction
The redirection of a wave at an interface continuing through the tissue at a different angle than the angle of incidence
standing wave
Incoming and reflected waves hit each other
- why it hurts when you stop moving
absorption
US is absorbed by tissue, and converted to heat at that point
The lower the frequency of the soundwave the lower the absorption
Velocity increases as material density increases
3 MHz
most sound waves are absorbed within the 1st cm of penetration
1 MHz
most sound waves are absorbed within the first 5 cm of penetration
Absorption of 1 MHz from least to most
blood
fat
muscle
blood vessel
skin
tendons
cartilage
bone
acoustical impedance
resistance of a medium to passage of sound waves
clinical implications of attenuation
• Low frequency for deeper tissues
• High frequency for superficial tissues
• Bone is very absorbent — want little exposure
• Travels well through fat
Frequency
# of wave cycles per second
Wave duration/length decreases as frequency increases
Therapeutically 1-3 MHz are used
Near field
before the beam becomes divergent –> before it hits its first interface
far field
after the beam becomes divergent
what causes changes in distribution of energy?
Uneven pressure
Size of soundhead (central 1/3 is primary area of energy)
Interface in near field
Average intensity
spatial peak intensity
Maximum intensity appearing at any point in the beam
Spatial average intensity
The intensity measured within 5mm of the transducer and averaged over the effective radiating area of the transducer
BNR
- beam non uniformity ratio
- relationship of SPi and SAi (SPi:SAi)
clinical significance of BNR
- want a small BNR
- spatial average is what we put into the units
- characteristics of different machines may make it feel more or less warm
PAMBNR
- peak area of maximal BNR
- the area of SPi is not equal among US manufacturers
- Difference in the area of SPi may alter how warm the sonation is perceived
Temporal Peak Intensity (TPi)
- Peak intensity during a cyclic period
- In continuous mode it is = to the average intensity
Temporal Average Intensity (TAi)
- pulse (going to be half of what we put in)
- the average amount of energy delivered to the tissue during the application of ultrasound per unity of time
Duty Cycle (Mark:Space ratio)
percentage of time the ultrasound intensity is on during a cycle
duty cycle vs mark:space ratio
- duty cycle: 50%= 1/2
- mark:space ratio: 50% = 1:1
when duty cycle is high….
the temporal peak intensity can also be high
thermal effects of ultrasound are dependent on:
Absorption characteristics of the tissue
The number of times the transducer passes over the part
The efficiency of the circulation through the insonated area
The amount of heat developed is directly proportional to the intensity and duration of insonation in continuous use
The thermal effect is less in the pulsed mode
Reflection of soundwaves at tissue interfaces
clinical significance of thermal effects
- too big of an area won’t have thermal effects
- time
- how much energy is really getting through
- no one responds to the same intensity of US in an identical fashion
thermal effects - increased collagen tissue extensibility
High ultrasound uptake (absorption) occurs in tissues with high collagen content
Tissue temperature needs to be maintained for at least 5 minutes for increased extensibility
clinical significance of increased collagen tissue extensibility
- US penetrates superficial tissue with only minimal attenuation so can get to collagen and protein rich tissue easily
- need to maintain tissue temp for 5 minutes to gain increased extensibility
thermal effects - reduction in muscle spasm
- ask Daniela
- decreased spindle activity
- increased blood flow and metabolism - if you are doing it long enough
thermal effects - altered blood flow
at 2.0 w/cm2, 1 MHz, 10-20 mins see increase blood flow, but other studies show decrease or no change in BF
Ultrasound change in nerve conduction velocity - sensory nerve
decrease in distal latency and increased velocity
ultrasound change in nerve conduction velocity - motor nerve
- pulsed mode decrease/no change in velocity
- continuous mode increased velocity
increased pain threshold
- as seen with any thermal agents
- full understanding of mechanics causing increased pain threshold are unclear
US effect on bone growth
Short term therapeutic joint temperature elevation, used as part of the treatment of contractures, are not harmful to bone growth provided that no thermal damage is done and
no pain is observed.
However, low-level temperature elevation applied over a prolonged period of time may accelerate bone growth
clinical significance of US on bone growth
- short term temperature elevation is not dangerous to growing bone
- no US over epiphyseal plate
what are mechanical effects
effects not explained by tissue rise
cavitation
- stimulation of gas bubbles in the fluidous tissues
- stable cavitation may attentuate micro streaming
cavitation
- stimulation of gas bubbles in the fluidous tissues
- stable cavitation may attentuate micro streaming
cavitation
- stimulation of gas bubbles in the fluidous tissues
- stable cavitation may attentuate micro streaming
cavitation
- stimulation of gas bubbles in the fluidous tissues
- stable cavitation may attentuate micro streaming
cavitation
- stimulation of gas bubbles in the fluidous tissues
- stable cavitation may attentuate micro streaming
cavitation
- stimulation of gas bubbles in the fluidous tissues
- stable cavitation may attentuate micro streaming
cavitation
- stimulation of gas bubbles in the fluidous tissues
- stable cavitation may attentuate micro streaming
unstable cavitation
- Dangerous effect where the bubbles collapse on themselves
- The “implosion” creates waves of tissue, which may also further increase tissue temperature
- can release free radicles (never use on pts with cancer)
What is acoustical streaming?
Movement of fluids along the boundaries of cell
membranes as a result of the mechanical pressure wave
May cause changes in ion fluxes with subsequent
changes in cellular activity
Increased cell membrane permeability and vascular wall permeability found with application in therapeutic ranges
what has US been shown to cause a leakage of?
potassium from RBC, increases in fibroblastic activity (i.e. protein synthesis) and increase in calcium fluxes across smooth muscle membranes of a mouse uterus
what is micro streaming
- Eddy or circular currents that take place around the vibrating object
- Occurs outside of the gas bubbles caused by cavitation
Clinical significance of mechanical effects of US
- allows medicinal ions to pass
- improves healing environment
- movement of fluids in the interstitial space may create a massage like effect
Contraindications for US
- same as for superficial heat
- pregnancy - over low back and uterus
- over heart, eyes, spinal cord, carotid sinuses
- laminectomy (cavitation of CSF)
- malignancy
- metal (prothesis)
- growth plates
Principles of Application of US - Frequency
The # of oscillations a molecule undergoes in 1 second
Most therapeutic ranges are 1-3 MHz
Vibration for frequency is achieved using either a quartz or synthetic crystal (barium titinate) and utilizes a reverse piezoelectric effect across its face
Principles of Application of US - Transducer (applicator)
Treatment head containing the crystal
Come in many sizes. Some of the smaller sizes can only be used at 3 MHz
Area to be treated should NOT be larger than 2-3X the ERA of the transducer and definitely not larger than 4X the ERA
Principles of application of US - coupling media
Ultrasonic waves do not transmit through air, therefore some sort of coupling agent is necessary
most to least transmitting couplant
aquaponic gel
glycerol
distilled water
air
should you pre-heat gel before use?
you can, but it breaks down the viscosity
what if you are applying US to an irregular shape?
go underwater or use gel pad
Diagnostic Intensity
< .1 W/cm2
Frequency of .5-5 MHz
therapeutic intensity
.25 – 2.0 (3.0) W/cm2
Frequency of .8 – 3 MHz
high intensity - liposuction
> 10 W/cm 2
Frequency of .1-5 MHz
Duration according to Michlovitz
2-3X the size of the ERA for every 5
minutes of exposure
Definition of Phonophoresis
- the application of US with a topical drug in order to facilitate transdermal drug delivery
- increased drug transmission occurs due to increased permeability of the stratus corneus
- might be another bullet here
Medications commonly used for phonophoresis
- local analgesics - lidocaine
- local anti-inflammatory medications - steroidal medications or non-steroidal medications
- counterirritants - menthol
review mechanisms for ion transfer
what do studies using corticosteroid drug report?
positive drug enhancement with US, but questions remain about the transmission properties of hydrocortisone
most studies agree that what?
US can enhance drug delivery to the subcutaneous level, but have not found increases in penetration at the level of the muscle or joint
when can maximum local effects of US be recorded?
in 2 hours
systemic effects can be measured at 12-24 hrs
for phonophoresis, what intensity should you use?
- in the thermal range unless contraindicated
- 1.5 w/cm2 or higher
what intensity should you use for open wound?
- pulsed US at 0.5-1.0 W/cm2
what does an open wound increase?
rate of diffusion
