Lecture 3: Ultrasound

Question 1

describe the use and misuse of US

Answer 1

Less people are using now than previously

many studies show US no better than placebo

BUT problem may be in the study design and not US itself (want to use in a small area not large, pt variation, etc)

Question 2

what is therapeutic US

Answer 2

high frequency mechanical waves (acoustic)

frequency of 1-3.3 million vibrations per sec

Question 3

advantage of US

Answer 3

depth of tissue penetration

heats 2-5 cm deep

superior heating for structures with high collagen content

thermal and non-thermal effects

Question 4

what does the piezoelectric crystal in the transducer head do

Answer 4

2-3 mm thick

made from synthetic plumbium zirconium titanate

high frequency AS current applied to crystal

converts electric energy to acoustic

crystal = mechanically deformed

Question 5

what is piezoelectric

Answer 5

means it has ability to change shape in response to electric current

expands and contracts at same frequency as applied current

when it expands the molecules in front of it are compressed

when crystal compresses the molecules are rarefied

this then travels as a longitudinal wave

Question 6

what size area is appropriate for US

Answer 6

you dont want to cover an area more than 2 times the sound head surface for 1 treatment (2-3 times the effective radiating area or ERA)

if a larger area is desired, 2 treatments should be completed or else it will lose effectiveness

Question 7

what are the 2 components of beam nonuniformity ratio

Answer 7

spatial peak intensity and spatial average intensity

BNR = peak/average

Question 8

what is spatial peak intensity

Answer 8

peak intensity of the US output over the area of the transducer

usually greatest in the center of the beam and lowest at the edges

Question 9

what is spatial average intensity

Answer 9

average intensity of the US output averaged over the on/off time of the pulse

Question 10

what should be the max BNR of a transducer

Answer 10

5:1 or 6:1

Question 11

what is the relevance of wave transmission frequency

Answer 11

body tissues absorption of US increases with wave frequency

less energy goes deeper

Question 12

how does a wave transmission of 3 MHz work

Answer 12

US waves absorped at 2-3 cm depth

absorption occurs 3-4x faster

Question 13

how does wave transmission of 1 MHz work

Answer 13

effective treatment depth up to 6 cm

absorption occurs slower

Question 14

what is attenuation

Answer 14

as US enters body it gradually decreases i intensity due to attenuation

dependent of frequency and tissue dependent

increases with collagen content of tissue and with higher frequencies

occurs due to absorption, reflection, and refraction of the wave

Question 15

heat produced by US is dependent on what

Answer 15

energy delivered and the absorption coefficient

Question 16

energy delivered depends on what

Answer 16

intensity and duty cycle of US

Question 17

the absorption coefficient depends on what

Answer 17

collagen content and US frequency

Question 18

what is responsible for 1/2 of the attenuation that occurs with US

Answer 18

absorption

Question 19

the remainder of US attenuation (not due to absorption) is due to what

Answer 19

reflection and refraction

Question 20

what is reflection

Answer 20

US beam is redirected from a surface angle equal and opposite of the original beam

Question 21

where does energy absorption, reflection, and refraction usually occur and why is this important

Answer 21

usually at tissue interfaces where there is an impedence to sound changes

air has a high impedance and skin is low; this is why we need US gel

Question 22

where does more heat accumulate with US and why

Answer 22

between bone and soft tissue because that is where most reflection occurs

Question 23

thermal effects of US

Answer 23

increased metabolic rate
decreased pain/muscle spasm
change of nerve conduction velocity
improved circulation
increased soft tissue extensibility

Question 24

US is good for heating what

Answer 24

tendons
ligaments
joint capsule
fascia
scar tissue (more collagen)

Question 25

why is US not ideal for muscles

Answer 25

muscles have a low absorption coefficient and a large surface area so US not ideal

Question 26

what is cavitation

Answer 26

alternating compression and expansion of gas bubbles in tissue fluids caused by mechanical pressure

makes cell membranes more permeable

Question 27

what is microstreaming

Answer 27

eddying that occurs around a vibrating object

Question 28

what is acoustic streaming

Answer 28

movement of fluids along boundaries of cell membranes resulting from mechanical pressure waves

produces alterations in call membrane activity, increased cell wall permeability, and increased intracellular calcium

increased macrophage response and increased protein synthesis

Question 29

non thermal US effects

Answer 29

increased intracellular calcium levels

increased skin and cell membrane permeability

mast cell degeneration

promotes macrophages responsiveness

good for the inflammatory phase of tissue repair

promotes protein synthesis

accelerates tissue healing/reduces time of inflammatory process

Question 30

when is thermal used and what should you be cautious of

Answer 30

continuous frequency

be cautious of hot spots

used before stretching and/or scar tissue mobilization as well as for pain control

Question 31

when is non-thermal used and what is the advantage

Answer 31

pulsed frequency (20% duty cycle)

no concern for hot spots

used for alternating membrane permeability to accelerate tissue healing

Question 32

clinical use of US

Answer 32

soft tissue shortening

tendon/ligament healing

bone fx

joint inflammation

phonophoresis