Ultrasound Quiz Flashcards
Most common diagnoses for which ultrasound is used
back
shoulder
knee
neck pain
what is ultrasound
high frequency mechanical waves delivering acoustic energy
why is an aqueous conducting gel needed?
ultrasonic energy can be dissipated more quickly in denser substances because they offer more resistance to molecular motion
when the wave is absorbed, what is the kinetic energy transformed into?
thermal energy
what is the angle of reflection dependent upon
the angle of incidence at the interface between tissues of differing densities
ultrasonic energy is more rapidly attenuated and converted to thermal energy in which tissues?
more dense tissues
tendons and ligaments
muscle
Attenuation of ultrasound beam in various tissues
Blood: 3%
Fat: 13%
Muscle: 24%
Blood Vessel: 32%
Skin: 39%
Tendon: 59%
Cartilage: 68%
Bone: 96%
KEY POINT! #1
- More dense connective tissues, such as ligaments and tendons absorb US better than less dense tissues such as fat and muscle
- Thus, US is more effective at heating more dense tissues than less dense tissues
where is the generator located and what is its key component?
- It is located in the “big box”
- Key Component: electrical oscillator that generates the high frequency alternating current that matches the intensity and frequency parameters of the applicator’s piezoelectric crystal
What is the US applicator composed of?
- piezoelectric crystal
- sound head
what is the reverse piezoelectric effect?
- piezoelectric crystal is transversely compressed and expanded by sending an alternating electrical current through it
what is the area of the crystal that moves called?
effective radiating area
what is the range of frequencies?
0.75- 3.3 MHz
Lesser frequencies penetrate deeper
(3.3 means it is absorbing it 3.3 times faster)
what frequency is used to treat superficial structures such as exposed tendons and ligaments?
3 MHz
what frequency is used to treat deeper structures such as most muscles and fascia?
1 MHz
What is the depth of US penetration dependent on?
frequency
depth is inversely proportional to what
frequency
Spacial Average Intensity =
power (watts)/ ERA (crystal’s size in cm)
what is generally recommended regarding US intensity
use the lowest intensity possible to achieve the desired effect
is there a recommended dosage?
no
total energy =
intensity x sound head area x time = Joules (Watt/second)
when keeping time and intensity the same, the bigger the sound head area…..
the bigger the dosage
when utilizing pulsed US, what is reduced?
total energy level delivered
Temporal (time) Average Intensity
- used to describe lesser level of energy in pulsed US
pulse duration
time that energy is flowing
pulse period
combined time of energy flow and lack of flow
What is the degree to which the total energy level is reduced dependent on?
duty cycle
duty cycle equation
pulse duration/pulse period x 100
What is BNR
how the non-uniformity of the crystal is addressed
BNR equation
ratio between the spatial peak intensity and the spatial average intensity
KEY POINT! #2
to minimize the chance of patient discomfort from hot spots, look for devices with low BNR
(but these are typically more expensive)
in order to have a significant heating effect, what should the treatment area be?
2 x the ERA
- the bigger you go, the less heat you get
KEY POINT #3
- Apply US over too large of an area is the biggest mistake made by clinicians when using US
- Area treated with US should not be larger than 4x ERA
- More often than not, the ERA is less than the size of the sound head
vigorous heating is defined as:
an increase of 7 degrees
using 1 MHz, how long does it take to heat skeletal muscle to 6 degrees?
11 minutes
KEY POINT #4
- US units usually differ in the ERA of their applicators and may differ in other ways that affect efficiency of the treatment
- Thus, no two US units can be considered to deliver the same treatment efficiency
- The clinician must readjust the treatment protocols based upon the specific input and applicator being used
- In this manner, each application of US represents a unique or individualized event
when using US with a cotreatment, how long does the clinician have before the treated area cool?
4 to 5 mins
can you determine the reponse a patient will have to US?
no - it varies a ton
3 Important principles that should guide the application of US:
- The radiating waves of US must be kept perpendicular to the skin surface, thus the applicator must remain in contract with the skin surface
- A coupling medium must be used between the US applicator and the skin
- The applicator faceplate must be continually moved during the treatment
3 different coupling mediums
- viscous aqueous gel
- water immersion
- gel pads
two processes that produce nontermal effects
cavitation
acoustic streaming
what is cavitation
- cycles of compression and rarefactions of US exert forces on the cell membranes and tissue fluids, resulting in the formation and accumulation of thousands of gas bubbles under the influence of Bjerknes forces
- formation of bubbles is called cavitation
stable cavitation
cyclical expansion and contraction of gas bubbles in response to the acoustic cycles of compressions and rarefactions
nonstable cavitation
- may occur from an accumulation of large volume of gas bubbles that collapse
- collapse is thought to be a cause for tissue damage
what is acoustic streaming
the forward movement of fluid created by the force of energy of US waves
- no physiologic effects
Key point #5 i think
- a critical evaluation of the literature on US must consider the treatment dosage and size of the area treated, even if described
- far too often, these parameters are poorly described or not described at all
- this makes critical analysis of the literature challenging
3 conditions that have been studied for using US for pain
myofascial pain syndrome
back pain
nonspecific shoulder disfunction
what is phonophoresis
application of US to enhance the absorption of topical agents through the skin
low intensity pulsed ultrasound
- delivery of pulsed, medium frequency US at much lower intensity
- delivers via a stationary applicator
- primary use: bone fractures that show difficulty in healing and in speeding repair and bone tendon junctions
low intensity therapeutic ultrasound
- soft tissue healing
- very low intensity pulsed US administered over 1 to 4 hr period using one or two stationary transducers (called SAM ultrasound applicators)
non contact low frequency US
- aerosolization of saline water with ow frequency US to cleanse and debride tissue
MIST therapy
