Pulsed Ultrasound

Question 1

Describe pulsed ultrasound

Answer 1

• a master synchronizer sends and electronic signal to a pulse
• the transducer must pause (listen) after transmitting
• the crystal can not transmit and receive at the same time

Question 2

In pulsed ultrasound the pulse can be generated in two ways describe these ways.

Answer 2

1- electrical output from generator is gated to apply rapidly alternating voltage to crystal

2- charged capacitor is discharged through crystal which is stimulates to vibrate at resonance frequency (not common)

Question 3

What are the 5 wave parameters of pulsed sound

Answer 3

Pulse duration
Spatial pulse length
Pulse repetition frequency
Pulse repetition period
Duty factor

Question 4

The time it takes for one pulse to occur is called?

Answer 4

Pulse duration (PD)

Question 5

What is the formula for PD?

Answer 5

PD = T times cycles in a pulse

Question 6

What does the pulse duration NOT include and what are the units it is measured in?

Answer 6

PD does not include the dead time

Usually measured in microsecond (us)

Question 7

If frequency was increased what would happen to the pulse?

Answer 7

The pulse would decrease, go down (it would get shorter)

Question 8

The length of the pulse is called ?

Answer 8

SPL

Question 9

What is the formula for SPL? And what is it usually measured in?

Answer 9

SPL = wavelength times cycles in a pulse

Typically measured in millimeters (mm)

Question 10

Cycles in a pulse is also known as ?

Answer 10

Ring down

Question 11

If frequency is increased what happens to the spatial pulse length?

Answer 11

Increasing frequency will decrease the wavelength which will result in the SPL being decreased as well

Question 12

If frequency (wavelength) decreases the SPL, what else will decrease the SPL?

Answer 12

Decreasing the ring down (number of cycles in a pulse ) will also decrease the SPL

Question 13

Decreasing the SPL does what to our image on the screen?

Answer 13

Improves the image resolution

Question 14

The number of pulses emitted in one second is called what?

Answer 14

Pulse repetition frequency (PRF)

Question 15

Ultrasound probes typically emit how many pulses per second?

Answer 15

Few thousand pulses per second

Question 16

What affects pulse repetition frequency?

Answer 16

Depth!!

Question 17

If depth is decreased, what will happen to the PRF?

Answer 17

The PRF will be increased.

Half the distance, now the sound is being reflected back quicker so it can send out another wave sooner

Question 18

What is the time from the beginning of one pulse to the beginning of the next called?

Answer 18

Pulse repetition period (PRP)

Question 19

PRP is another way of expressing the —— calculated in the range equation.

Answer 19

Time (there and back)
D D
PRP = —— T = ——
C C

Question 20

What is the relationship between PRF and PRP

Answer 20

Reciprocals
1 1 C D
PRF = —— PRP = —— PRF = —— PRP = ——
PRP PRF D C

Question 21

What is the fraction of time that a pulsed ultrasound if on, expressed as a percentage?

Answer 21

Duty factor (DF)

Question 22

Continous wave is on what percent of the time?

Answer 22

100%

Question 23

A higher PD and PRF does what to the DF?

Answer 23

This increases the DF because there is less “listening” time,
pulse length goes up

Question 24

What is the equation for DF as a percentage?

Answer 24

PD
DF = ——— times 100
PRP

Question 25

Sound velocity is dependent on the medium it travels through. What two characteristics of the medium determine the velocity?

Answer 25

Density

Compressability

Question 26

The mass of a medium per unit volume….concentration of matter is called ?

Answer 26

Density

Question 27

If ONLY density increases (all other factors are constant) what will happen to the velocity?

Answer 27

The velocity will decrease.

More mass requires more energy for particle motion

Question 28

What has a greater transfer of energy, something more stiff or something less stiff?

Answer 28

More stiff!!

Think of people putting hands against one another and having floppy arms versus locked arms

Question 29

Indicating the fractional decrease in volume when pressure is applied to the material is known as?

Answer 29

Compressibility

Question 30

The more dense the material (less compressible) results in a decreased or increased sound velocity?

Answer 30

Increased

Question 31

The easier it is to compress a material the higher or slower the velocity ?

Answer 31

Slower

Question 32

The reciprocal of compressibility is known as ?

Answer 32

Bulk modulus (stiffness)

Question 33

If bulk modulus (stiffness) is increased, what happens to compressibility and velocity?

Answer 33

Bulk modulus increases
Compressibility decreases
Velocity increases

Question 34

The ability of an object to return to its original shape and volume after a force is no longer acting on it is referred to as?

Answer 34

Elasticity

Question 35

Does ultrasound cause elastic deformations by separation and compression or molecules?

Answer 35

Yes it sure does

Question 36

What is the dominant factor, stiffness or density?

Answer 36

Stiffness baby

Question 37

If only the density increases then the velocity in that medium

Answer 37

Decreases

Question 38

If compressibility increases then stiffness is

Answer 38

Decreasing

Question 39

If stiffness increases then the velocity

Answer 39

Increases

Question 40

Does Temperature effect the speed of sound?

Answer 40

Yes

Question 41

If temperature increases the velocity of sound will

Answer 41

Increases as well

Question 42

How is a pulsed system different then a continous wave system ?

Answer 42

Pulsed - one crystal to send THAN listen

Continous - two crystals, send and listen at same time

Question 43

How does pulse repetition frequency relate to the operating frequency of the probe?

Answer 43

NOT RELATED jokes on ya

Question 44

Is pulsed ultrasound or continous wave ultrasound capable of obtaining an image.

Answer 44

Pulsed