Pulsed ultrasound

Question 1

What is a pulsed ultrasound?

Answer 1

When the crystal cannot transmit and receive simultaneously. Therefore, in pulsed systems the transducer must pause or “listen” after transmitting

Question 2

In pulsed ultrasound, what does a master synchronizer do?

Answer 2

The master synchronizer sends an electronic signal to pulser

Question 3

In pulsed ultrasound, the pulse is generated two ways, what are they?

Answer 3

1. The electrical output from a generator is gated to apply a rapidly alternating voltage to the crystal
2. A charged capacitor is discharged through the crystal which is stimulated to vibrated at a resonance frequency

Question 4

How does a pulsed ultrasound differ from a continuous ultrasound

Answer 4

In a continuous wave ultrasound the crystal never stops vibrating

Question 5

What are the pulsed ultrasound parameters?

Answer 5

1. Pulse duration
2. Spatial pulse length
3. Pulse repetition frequency
4. Pulse repetition period
5. Duty factor

Question 6

What does PD (pulse duration) mean?

Answer 6

The time it takes for a pulse to occur

Question 7

What is the PD formula?

Answer 7

PD = (T)(Cycles in a pulse)

Question 8

Does PD include dead time?

Answer 8

No

Question 9

What is the unit of measure for PD?

Answer 9

Microseconds or uS

Question 10

What is spatial pulse length?

Answer 10

Simply the length of a pulse

Question 11

What is the formula for SPL (spatial pulse length)?

Answer 11

SPL= (lambda)(cycles in a pulse)

Or

SPL = (wavelength)(cycles in a pulse)

Question 12

What is the typical units of SPL?

Answer 12

mm

Question 13

If we increase frequency what will happen to wavelength and SPL

Answer 13

Wavelength would decrease which would decrease SPL

Question 14

If we decrease the number of cycles in a pulse what happens to SPL?

Answer 14

It decreases the SPL

Question 15

What does decreasing the SPL do?

Answer 15

Increases our image resolution

Question 16

What is Pulse repetition frequency PRF?

Answer 16

Number of pulses emitted in one second

Question 17

What are common units for ultrasound in PRF?

Answer 17

Hz or kHz

Question 18

When doing PRF calculations what is recommended we do for units?

Answer 18

Get units into meters and meters per second

Question 19

What is Pulse repetition period (PRP)?

Answer 19

The time from the beginning of one pulse to the beginning of the next

Question 20

What is the measurement of PRP?

Answer 20

Units are in seconds or microseconds

Question 21

What is the formula for PRP?

Answer 21

PRP = D/C

Question 22

What is the relationship between PRF and PRP?

Answer 22

Regardless of their names they are still frequency and period, therefore they are reciprocals of one another

PRF = 1/ PRP

Question 23

What is Duty factor (DF)?

Answer 23

The fraction of time that a pulsed ultrasound is on and is expressed in percentage

Question 24

What is the duty factor of a continuous wave?

Answer 24

100%

Question 25

A higher PRF or PD increases what? And why?

Answer 25

Increase the DF because there is less “listening” time between the pulses

Question 26

What is the DF formula?

Answer 26

DF = (PD/PRP)(100)

Question 27

What is density?

Answer 27

The mass of an medium per unit volume or the concentration of matter

Question 28

If all other factors remain constant, an increase in density will do what?

Answer 28

Impede the rate sound travels

Question 29

What does compressibility indicate?

Answer 29

The fractional decrease in volume when pressure is applied to material. (How squishy is it)

Question 30

What happens when we compress the material?

Answer 30

We slow the velocity

Question 31

Dense materials typically have low compressibility, what does this do to sound?

Answer 31

Increased sound velocity

Question 32

What is bulk modulus?

Answer 32

The reciprocal of compressibility or the negative ratio of stress and strain. “Stiffness”

Question 33

As bulk modulus increases what happens?

Answer 33

Compressibility decreases and velocity increases

Question 34

What is elasticity?

Answer 34

The ability of an object to return to its original shape and volume after force is no longer caring on it

Question 35

How does ultrasound waves cause elastic deformation?

Answer 35

By separation and compression of molecules

Question 36

If only density of a medium increases what happens?

Answer 36

The velocity of sound in that medium decreases

Question 37

If the compressibility of a medium increases what happens to it’s stiffness?

Answer 37

The stiffness is decreasing

Question 38

If the stiffness is decreasing then what happens?

Answer 38

The velocity of sound in that medium will decrease as well

Question 39

What does temperature do to sound?

Answer 39

The hotter it is the faster sound will travel