Modalities Ch. 14 Flashcards Preview

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Flashcards in Modalities Ch. 14 Deck (67)
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1

what is sound

form of vibrational or acoustic energy
sounds travel in waves

2

what sounds can we hear?

16,000 - 20,000 Hz

3

ultrasound

inaudible, acoustic vibrations
high frequency
may produce thermal and/or nonthermal physiologic effects

4

types of ultrasound

diagnostic
-internal structure imaging
-5MHz, 3.4 mW/cm2
surgical
-tissue destruction owing to thermal and mechanical effects
-0.10 MHz, 20-100 W/Cm
therapeutic
-thermal and subthermal effects
-0.75 to 3 MHz,

5

therapeutic ultrasound

advantage over other nonacoustic heating modalities
tissues high in collagen (tendons, muscles, ligaments, joint capsules, meniscus, and cortical bone) can be heated to a therapeutic range

6

anatomy of an ultrasound machine

generator
-where electrical current is generated
applicator
transducer
-converts electrical energy to acoustic energy
-houses the crystal
crystal

7

how does ultrasound work

generator produces a high-frequency alternating current
current travels through the coaxial cable
crystal in the transducer converts electrical energy to sound energy
-reverse piezoelectric effect

8

reverse piezoelectric effect

mechanical energy being produced by electric energy

9

what happens to the crystal

crystal expands and contracts
-rarefaction - crystal expands
-neutral
-compression - crystal has a high molecular density
-neutral
-rarefaction
-etc.

10

attenuation

decrease in energy as ultrasound passes through various tissue layers
Law of Grotthus-Draper
-the more energy that is absorbed by superficial leaves less energy to be absorbed by deeper tissues

11

ultrasound effects on tissue

penetrates through tissues high in water content
-fat
absorbed in tissues high in protein
-muscles
-nerves
refracted at joints
reflects or bounces off bone
-certain degree is absorbed in superficial bone

12

how is tissue heated

ultrasound is absorbed by tissue
causes molecules to rotate and bounce off one another
results in heat or nonthermal effects

13

Effective Radiating Area (ERA)

portion of the sound head that is producing the therapeutic effect

14

ERA determinants

size of sound head
size of crystal
quality of crystal

15

beam nonuniformity ration (BNR)

amount of variable intensity within the ultrasound beam
Ratio = variability:average output intensity
should be as close as possible to 1:1
most manufacturers accept <6:1
8.5 w/cm2 can damage tissue

16

PAMBNR

peak area of the maximum BNR

17

ultrasound parameters

duty factor
frequency
intensity
treatment length
treatment size
application technique

18

duty factor

pulsed or continuous

19

frequency

1 and 3 MHz

20

intensity

power

21

treatment length

depends on treatment goals

22

treatment size

depends on area you are treating and sound head size

23

continuous ultrasound

sound waves are delivered continually at the determined frequency

24

pulsed ultrasound

sound waves are delivered in pulses

25

pulse period

length of entire pulse including the off time

26

pulse duration

length of the on time of the pulse

27

duty cycle ratio

% "on time" (pulse duration) in relation to "pulse period"

28

when do you use pulsed?

when you do not want the therapeutic effects

29

frequency

how many times does the crystal change shape
determines depth of treatment
-3 MHz: surface to 2.5 cm
-1 MHz: 2.5-5 cm

30

power

the total amount of ultrasound energy produced by the generator
measure of pulse width and frequency
measures in watts