Ultrasound

Question 1

what is ultrasound?

Answer 1

acoustic energy
not audible
>20,000 Hz, usually frequency in therapeutic range of .7-3.3 MHz

Question 2

therapeutic function of ultrasound

Answer 2

deep heater of small areas in the body

Question 3

How does ultrasound heat?

Answer 3

waves transmit energy by cycles of compressing and rarefacting material, these pulses propagate through tissue and produce heating

Question 4

rarefaction

Answer 4

decreasing an item’s density, the opposite of compression

Question 5

piezoelectricity

Answer 5

ability of some materials like crystals or ceramics/bone to generate an electric potential in response to applied mechanical stress

Question 6

how does a piezoelectric crystal generate an electrical charge?

Answer 6

separation of electric charge across a crystal lattice
this charge creates a voltage across the material
crystal expands and contracts to create an ultrasound frequency

Question 7

direct peizoelectric effect

Answer 7

production of electricity in a material when electricity is applied
reversible

Question 8

converse peizoelectric effect

Answer 8

production of stress or strain when an electric field is applied

Question 9

near field

Answer 9

convergent area of beam
where rays are aligned, more intense

Question 10

far field

Answer 10

where beams diverge
less intensity

Question 11

which frequency penetrates deeper, high or low frequency?

Answer 11

low frequency gets deeper tissue
higher frequency heats more shallow depths

Question 12

when ultrasound meets tissue, it causes 5 effects:

Answer 12

pulse
scatter
absorption
reflection and transmission

Question 13

refraction

Answer 13

waves bend slightly and change direction as they enter tissue instead of going straight down

Question 14

reflection

Answer 14

return of energy, waves bounce back
waves move back in the opposite angle
increases at skin with poor ultrasound head contact
dangerous if bone reflects waves into soft tissue as it can create burns

Question 15

absorption

Answer 15

conversion of the mechanical energy of an ultrasonic wave into heat
higher frequency increases absorption
wave goes into tissue

Question 16

attenuation

Answer 16

absorption 50% + reflection and refraction 50%
increases with higher frequency

Question 17

scatter

Answer 17

combination of refraction, diffraction, and reflection
wave moving in many/any direction other than the target

Question 18

absorption coefficient

Answer 18

tissue and frequency dependent
highest for tissues with highest collagen content
higher coefficient means more heat is absorbed

Question 19

attenuation coefficient

Answer 19

tissue and frequency specific
higher in tissues with a higher collagen content

Question 20

which tissues respond best to ultrasound?

Answer 20

high absorption coefficient
high collagen content
poor response in those with high water content

Question 21

heat behavior in tissues: which tissues have the greatest rise in temperature?

Answer 21

tendons rise up to 14-15 degrees
muscle rises around 5 degrees

Question 22

how does scattering of ultrasound waves apply to multiple layers of tissue?

Answer 22

scatter effect occurs at each layer, and only waves that are absorbed transmit to the next layer where they are scattered again
this results in a loss of heat at greater depths

Question 23

tissues best suited to ultrasound include:

Answer 23

tendons
ligaments
joint capsules
fascia

Question 24

fat and ultrasound

Answer 24

fat can be overheated, need to be careful when applying ultrasound to area with overlying fat

Question 25

is ultrasound effective at heating muscle?

Answer 25

Not well low absorption coefficient muscles are often too big and deep

Question 26

half value depth

Answer 26

tissue depth at which 50% of the ultrasound delivered has been absorbed

Question 27

half value depth of 3 mHz

Answer 27

2.5 cm

Question 28

half value depth of 1 mHz

Answer 28

4 cm

Question 29

power

Answer 29

amount of acoustic energy per unti time watts

Question 30

intensity

Answer 30

amount of power per area W/cm2

Question 31

frequency

Answer 31

number of cycles per unit time Hz cycles/s

Question 32

spatial average intensity

Answer 32

average intensity of US input over the area of the transducer

Question 33

spatial peak intensity

Answer 33

peak intensity of US output over area of transducer greater in the center and lower in the periphery

Question 34

effective radiating area

Answer 34

area of crystal from which US waves radiate

Question 35

beam nonuniformity ratio

Answer 35

BNR is ratio of set intensity to max peak intensity 2:1, 3:1 is safe, 6:1 or higher is dangerous and can form hot spots

Question 36

pulsed US

Answer 36

some on/off time percentage of on time or ratio of on/off

Question 37

duty cycle

Answer 37

on:off time in total cycle time 1:5 is 20% on, 2 s on 8 s off

Question 38

non thermal effects of US

Answer 38

cavitation: sonically generated gas activity acoustic streaming: circular flow of cellular fluids microstreaming: eddying near vibrating object, gas bubbles oscillating, causing cellular effects

Question 39

why do you need to move US head?

Answer 39

if it is held in the same place the same wave will be repeated over the same path, leading to extreme heating

Question 40

does 3 or 1 MHz heat faster?

Answer 40

3 MHz, by factor of 3 1 Mhz heats at .2 C/min

Question 41

changing which parameters leads to faster heating

Answer 41

increasing intensity, frequency applying to higher protein tissue getting more reflection

Question 42

effects of heating on the body

Answer 42

increase metabolic rate/enzyme activity rate vasodilation increased collagen extensibility decreased neural sensitvity increased pain threshold decreased m spasm altered n conduction

Question 43

non thermal effects: physiologic

Answer 43

increased: membrane permeability intracellular Ca mast cell degranulation Histamine release proteinn synthesis rate fibroblast stim macrophage

Question 44

indications for US

Answer 44

soft tissue shortening pain control dermal ulcers surgical incision tendon injury resorption of Ca deposits bone fracture carpal tunnel syndrome phonophoresis plantar warts herpes infection

Question 45

How does US help ulcers?

Answer 45

nonthermal effects cause wound contraction, protein synthesis accelerate healing of infected wounds

Question 46

How does US help tendon healing?

Answer 46

faster recovery of tendon strength

Question 47

phonophoresis

Answer 47

facilitate transdermal drug delivery with ultrasound for local and systemic drug delivery

Question 48

appropriate size treatment area is:

Answer 48

2-4 times the size of the ERA effective radiating area of head

Question 49

application patterns of US

Answer 49

overlapping circles, completing 1 circle in 2 s longitudinal strips overlapping and alternating directions creating a rectangle

Question 50

pulsed vs continuous: thermal effect

Answer 50

100% max thermal effect 50% mod thermal effect 20% no thermal effect

Question 51

contraindications to US

Answer 51

pregnancy - abd/low back active epiphysis cancer TB bleeding dx impaired circulation myositis ossificans DVT acute injury radiated tissue impaired sensation implanted devices repro organs eyes anterior neck implants regenerating nerves