Ultrasound Flashcards
what is a ultrasound?
Located in the Acoustical, therapeutic tissue healing, or tissue destruction
Thermal & Non-thermal effects
“Continuous” vs “Pulsed”
We use it for therapeutic effects
Can deliver medicine to subcutaneous tissues (phonophoresis)
what does the transducer do?
A device that converts energy
what is the piezoelectric crystal?
Piezoelectric crystal: a crystal that produces (+) and (-) electrical charges when it contracts or expands
Crystal of quartz, barium titanate, lead zirconate, or titanate housed within transducer
what is the reverse (indirect) piezoelectric effect?
Reverse (indirect) piezoelectric effect: occurs when an alternating current is passed through a crystal resulting in contraction & expansion of the crystal
US is produced through the reverse piezoelectric effect
Vibration results in high-frequency sound waves
what type of Piezoelectronic effect does ultrasound use?
Reverse (indirect) piezoelectric effect
what is the frequency?
Frequency: number of times an event occurs in 1 second; expressed in Hertz or pulses per second
Hertz: cycles per second
Megahertz: 1,000,000 cycles per second
In the U.S., we mainly use ultrasound frequencies of 1, 2 and 3 MHz
what are the ultrasounds we use for ultrasound?
In the U.S., we mainly use ultrasound frequencies of 1, 2 and 3 MHz
1 = low frequency; 3 = high frequency
when frequency decreases what happens to depth of penetration?
increases
when frequency decreases what happens to the sound wave?
frequency = sound waves are absorbed in more superficial tissues (3 MHz)
what is the equation for frequency?
F=1/ℷ
what are the three influences on transmission of energy?
reflection, refraction, absorption
what is reflection?
occurs when the wave can not pass through the next density
what is refraction?
is the bending of the sound wave due to a change in the speed as the wave enters a medium with a different density
what is absorption?
occurs when the tissue wave is collecting the waves energy.
what is attention?
Decrease in a wave’s intensity resulting from absorption, reflection, & refraction
when frequency increases what happens to the attention?
increases due to the molecular friction the waves must overcome to pass through the tissues.
What does US penetrate through and what does it absorb through?
US penetrates tissues that are high in water content
US absorbs in tissues that are dense in protein
When absorption is high what is the frequency?
frequency increases like at 3 MHz
penetration increases what occurs to the absorption?
the absorption decreases (1 MHz)
When penetration is high what is the relationship between frequency and absorption?
decreases in frequency and decreases in absorption (1 MHz)
tissues that are higher in water content have what type of absorption rate?
low absorption rate
tissue type: fat
tissues that have a high protein content have what type of absorption rate?
high
tissue type: peripheral nerve and bone
describe the absorption rate as it passes through tissues with increased tissue protein
blood
fat
nerve
muscle
skin
tendon
cartilage
bone
(increasing in density of protein content)
https://www.physio-pedia.com/Therapeutic_Ultrasound#/media/File:Protein_content.jpg,
what is the acoustic impedance for ultrasounds?
Determines amount of US energy reflected at tissue interfaces
If acoustic impedance of the 2 materials forming the interface is the same, all sound will be transmitted
The larger the difference, the more energy is reflected & the less energy that can enter the 2nd medium
what is the ERA?
effective radiating area: area of the sound wave that produces the waves. expressed in cm2
measured 5 mm from the face of the sound head: but represents all the areas where the sound wave is producing more than 5% of max power output.
always a smaller area than the size of the sound head.
what do the beams look like with differing diameter heads?
Large diameter heads – column beam
Small diameter heads – more divergent beam
what is power in relation to us?
it measured in watts and is the amount of energy being produced by the transducer
what is intensity in relation to US?
strength of the sound waves at a given location within the tissues being treated.
What is spacial average intensity (SAI) as it pertains to US?
amount of US energy passing through the US head’s ERA;
expressed in watts per square centimeter (W/cm2) (power/ERA)
what is the spacial peak intensity (SPI) in relation to ultrasound?
max. output (power) produced within an ultrasound beam
What is the BNR?
Beam Nonuniformity Ratio (BNR)
ratio between the SPI spatial peak intensity (SPI) to the average output as reported on the units meter.
The lower the BNR the _________.
the lower the BNR the more uniform the beam is.
what is the cut off BNR for safety?
BNR greater than 8.
Why is it important to know the BNR when it comes to application?
because of “hot spots” in the beam it is pessary to keep the US head moving.
what is the Duty cycle?
percentage of time tat the US is actually being emitted from the head.
when using a pulse mode what does the duty cycle consist of and what is the equation?
when using a pulse mode the duty cycle is between the pulse length and the pulse interval.
equation: pulse length/ (pulse length+pulse interval)x100
what would a 100% duty cycle mean?
there is constant sound waves being produced. CONSTANT OUTPUT
How would one place the duty cycle for non thermal effects?
lower duty cycle. under 20%
What are the methods for a coupling medium?
It is required for US.
it should be water based so that there is low absorption and good penetration.
coupling medium must conform to the body area.
the body area should be clean and relativity hair free.
what is direct coupling
using a gel or cream.
only use approved agents
apply liberally to the area
remove air bubbles by passing the head over the area.
MOVE SLOWLY 4CM/SEC, in circles
moving the head faster will decrease the heat.
if the patient reported discomfit, decrease the output intensity.
How slow should you move the US head?
4cm/sec moving in circles
How might one treat an irregularly shaped area?
Immersion technique
the limb will be immersed in degassed water
he transducer will be placed 1” from the body part.
avoid the formation of air bubbles
If you are using the immersion technique with tap water, how should you change the intensity.
If tap water is used, increase the output intensity by 0.5 w/cm2
What is the pad (bladder method) for ultrasound?
massive conductive gel
conforms to the treatment area
commercial pads help limit the size of the treatment area.
what are the indications of US?
soft tissue healing & repair
joint contractures & scar tissue
muscle spasms
joint contraction
post-acute reduction of myositis ossificans
acute inflammatory conditions (pulsed)
SJM-PA
What are the contraindications for US?
Acute conditions (continuous output)
Ischemic areas or impaired circulation areas
Tendency to hemorrhage
Over/Around eyes, heart, skull, or genitals
Over pelvic or lumbar areas in pregnant or menstruating females
Cancerous tumors
Spinal cord or large nerve plexus (high doses)
Anesthetic areas/Diminished Sensation
Stress fracture sites or over fracture site before healing is complete (continuous); epiphysis???
Acute infection
what are the thermal effects of US?
Increased:
blood flow
sensory & motor NCV
extensibility of structures (collagen)
collagen deposition
macrophage activity
decreased:
joint stiffness
muscle spasm
pain
+ all Nonthermal effects
what are the non thermal effects of US?
increased:
cell membrane permeability
vascular permeability
blood flow
fibroblastic activity
decreased:
edema
Altered rates of diffusion across cell membrane
Stimulation of phagocytosis
Production of granulation tissue
Synthesis of protein
Tissue regeneration
what is the pathophysiology for pulsed ultrasound (non-thermal) ultrasound?
Stimulates phagocytosis (assists w/ decrease of chronic inflammation) & increases # of free radicals (increases ionic conductance on cell membrane)
what is cavitation for pulsed ultrasound/non thermal ?
Cavitation: formation of gas bubbles that expand & compress due to pressure changes in tissue fluids
Stable – occurs when bubbles compress during the -press. peaks followed expansion of bubbles during -press. troughs
Unstable (transient) – compression of bubbles during -press. Peaks, but is followed by total collapse during trough (BAD!)
what is acoustical streaming when it comes to pulsed ultrasounds?
stable cavitation leads to this; unidirectional flow of tissue fluids, & is most marked around cell membranes
what does acoustic streaming help to facilitate?
Facilitates passage of calcium potassium & other ions, etc. in/out of cells
Collagen synthesis, chemotactics secretion, increases update of calcium in fibroblasts, increases fibroblastic activity
what does the length of US treatment time depend on?
size of the area
output intensity
goals of treatment
frequency
How big should the treatment area be?
no larger than 2-3x the surface areas ERA
if the area is to larger split the treatment into smaller treatment zones.
How long should you perform ultrasound to reach vigorous heating?
1mhz: 10-12 min
3 mhz: 3-5 min
what is vigorous heating defined as temperature size?
Vigorous heating is defined as an increase of ~7°F (4°C)
what is the depth of penetration for 1 MHz?
5 or more cm
what’s the depth of penetration for 3 mhz
0.8 to 3cm
what is the beam profile for 1mhz and 3mhz
1 mhz: relativity divergent
3 mhz: relatively collimating
what is the maximum heating rate for 1mhz vs 3 mhz
1mhz: 0.2 degrees c per minute per w/cm2 “slow”
3 mhz: 0.6 degrees c per minute per w/cm2 “fast” 3-4 faster than 1 mhz
what frequency leaves the tissue heater longer?
1mhz is 2x as 3mhz
what is the general rule for depth of the tissue and frequency?
General Rule:
1 MHz = Tissues ≥ 1” Deep (2.5cm)
3 MHz= Tissues ≤ 1” Deep
what is the process used for inducing medications when performing ultrasounds?
phonophoresis
what are the common drugs with phonophoresis
hydrocortisone
dexamethasone
benzydamine
Salicylates
various anesthetics
what is acoustical streaming?
opens pathways to drive molecules into the tissues using ultrasounds heating process.
what is the law that phonophoresis uses?
Based on theory that drug diffuses through skin (Fick’s law)
what does ultrasound do for the medication phonophoresis?
Ultrasound initiates increases in metabolic rate, enzymatic activity, cellular permeability, ion flux, and diffusion
With physiologic enhancement via ultrasound, subsequent increase in efficacy of topical medication
