Ultrasound Physics

Front 1

Sounds waves are comprised of:

Back 1

rarefactions and compressions

Front 2

7 parameters that describe sound wave:

Back 2

period
frequency
amplitude
power
intensity
propagation speed
wavelength

Front 3

Frequency affects:

Back 3

penetration and axial resolution (image quality)

Front 4

Formula for intensity:

Back 4

power (watts)
---------------------
beam area (cm2)

Front 5

Speed of sound in soft tissue:

Back 5

1.54 km/s
1540 m/s
1.54 mm/us

Front 6

Density and speed = ______ directions

Back 6

opposite

Front 7

Stiffness and speed = ______ directions

Back 7

same

Front 8

Propagation speed formula:

Back 8

frequency (hz) x wavelength (meters)

Front 9

The operator can change the:

Back 9

amplitude, power and intensity. The values of these parameters decrease as sound propagates through the body.

Front 10

Period, frequency and wavelength are changed when:

Back 10

a new transducer with a diff freq is used.

Front 11

What is determined by the sound source?

Back 11

period, frequency, amplitude, power, intensity

Front 12

What is determined by the medium:

Back 12

propagation speed

Front 13

What is determined by the sound source and the medium?

Back 13

the wavelength

Front 14

Pulse duration:

Back 14

the time from the start of a pulse to the end of that pulse, only the ACTUAL TIME that pulse is on.

Front 15

Pulse duration will be longer when using a new transducer with:

Back 15

lower frequency (longer period)
more ringing (more cycles in a pulse)

Front 16

_____ Intensity is the most relevant to tissue heating.

Back 16

Spatial peak Temporal Average (SPTA)

Front 17

______ intensity has the highest value.

Back 17

Spatial peak temporal peak (SPTP)

Front 18

______ intensity has the lowest value.

Back 18

Spatial average Temporal average (SATA)

Front 19

___ intensity is maximum in time.

Back 19

Temporal peak (TP)

Front 20

__ intensity is averaged only during the pulse duration (on time only)

Back 20

peak average (PA)

Front 21

__ intensity is averaged during the pulse repetition period (both on and off times)

Back 21

temporal average (TA)

Front 22

The rank of intensities from the largest to the smallest is:

Back 22

SPTP, IM, SPPA, SPTA, SATA

Front 23

3 DB means _____

Back 23

2 times, the final intensity is 2 times bigger than the original intensity.

Front 24

6 dB means ______

Back 24

two times, two times.
The final is 4 times bigger than the original

Front 25

20 dB means_____

Back 25

ten times, ten times. The final is 100 times bigger than the original intensity.

Front 26

The decrease in intensity, power and amplitude as the sound wave travels is termed:

Back 26

attenuation

Front 27

Units for attenuation is:

Back 27

dB (must be negative, since the attenuation causes intensity to decrease)

Front 28

In soft tissue, the _______ frequency, the _______ the attenuation.

Back 28

greater, greater. This is why we do not image deep with high freq sound.

Front 29

3 components of attenuation:

Back 29

absorption, scattering and reflection.

Front 30

Absorption:

Back 30

sound energy converted into heat energy

Front 31

If the boundary between 2 media has irregularities (with a size similiar to or a bit smaller than pulse's wavelength) then the wave maybe redirected into a number of different directions.

Back 31

scattering

Front 32

If the reflector is much smaller than the wavelength of sound, the ultrasounic energy is uniformly diverted in all directions. Higher frequency sound undergoes more of this. A rbc is this.

Back 32

Rayleigh scattering

Front 33

Reflection occurs when:

Back 33

some of the propagating sound energy strikes a boundary between 2 media and is returned toward the transducer.

Front 34

The amount of attenuation per centimeter is termed:

units: dB/cm

Back 34

attenuation coefficient.

Front 35

In soft tissue, attenuation coefficient (dB/cm) is estimated at approximately:

Back 35

half of the freq (Mhz), or 0.5 dB/cm/Mhz

Front 36

Impedance increases when:

Back 36

density increases or
propagation speed increases

Front 37

Impedance formula:

Back 37

impedance (rayls) = density (kg/m3) x propagation speed (m/s)

Front 38

____________ ___________

does not change when path length changes.

Back 38

attenuation coefficient.

Front 39

________ is higher in both bone and in lung compared to soft tissue.

Back 39

attenuation

Front 40

IN SOFT TISSUE, the attenuation coefficient in dB per cm ranges from ____ to ____ times the ultrasonic frequency in MHz.

Back 40

0.5 to 1.1

Front 41

With oblique incidence:

Back 41

1) reflection angle = incident angle and

2) % transmission + % reflection = 100%

Front 42

Refraction occurs when:

Back 42

there are different propagation speeds and oblique incidence.

Front 43

Snell's law:

Back 43

sine transmission angle prop speed2
___________________= __________

sine incident angle prop speed 1

Front 44

If propagation speed 2 is ____ than propagation speed 1, then the transmission angle is less than the incident angle.

Back 44

less

Front 45

If propagation speed 2 is greater than propagation speed 1, then the transmission angle is ________ than the incident angle.

Back 45

greater

Front 46

Reflection angle =

Back 46

incident angle

Front 47

In reflection with normal incidence you look for?

Back 47

diff impedance's

Front 48

Reflection with oblique incidence?

Back 48

we don't know!!

Front 49

This is derived from reflection information:

Back 49

transmission

% transmission + % of reflection = 100%

Front 50

For refraction we need to look for?

Back 50

oblique incidence and different speeds

Front 51

13 usecs, the reflector is __ cm deep in the body

Back 51

1

Front 52

If the reflector is 4 cm deep in the body, how many us is that?

Back 52

52 usecs