Chapter 8, 9, 10

Question 1

What is axial resolution?

Answer 1

In order to show two seperate items in line with the the beam, the space between them needs to be documented. If a pulse’s length is too long they will be blurred.

Question 2

What is axial resolution determined by? Is it adjustable.

Answer 2

It is not adjustable and is determined by SPL and PD

Question 3

What are the equations for axial resolution?

Answer 3

SPL/2

Question 4

What is the equation for SPL? Is it directly or inversely related to axial resolution

Answer 4

wavelength x cycles. it is inversely related to axial resolution

Question 5

What are the two ways to create a shorter pulse with axial resolution?

Answer 5

1. Increase frequency to create a shorter wavelength
   2.Use backing material to dampen the pulse/ decrease the number of cycles in the pulse.

Question 6

What are the other terms for axial resolution? (what does LARRD stand for)

Answer 6

Longitudinal, Axial, Range, Raidal, Depth

Question 7

What is lateral resolution?

Answer 7

distinguishing between two objects that in line perpendicularly to the beam

Question 8

What are the other terms for lateral resolution? (what does LATA stand for?)

Answer 8

Lateral, Angular, Transverse, Azimuthal

Question 9

What is lateral resolution determined by?

Answer 9

The width of the sound beam.

Question 10

Why is lateral resolution related to depth?

Answer 10

The beam’s width changes with the depth

Question 11

Do higher frequency beams have increased lateral or axial resolution? Why?

Answer 11

Both. Axial resolution increases in the entire image because the wavelength is shorter. Lateral resolution increases in the far field only, as the beam will diverge less.

Question 12

What is the equation for lateral resolution?

Answer 12

lateral resolution (mm) = beam width (mm)

Question 13

What is focusing?

Answer 13

Concentration of the beam to narrow it and improve lateral resolution

Question 14

What is the difference between internal and external focusing?

Answer 14

Internal is achieved with a curved PZT crystal. External involves focusing with an acoustic lens

Question 15

What is fixed/ conventional/ mechanical focusing

Answer 15

When the focal zone cannot be changed. It is created when the probe is manufactured.

Question 16

What does phased array mean?

Answer 16

focusing by using electronic means to change the crystals and therefore the beam.

Question 17

Are phased array transducers adjustable? Why or why not?

Answer 17

Yes. Electronic focusing is adjustable- you can use a focus button to change the focusing depth.

Question 18

When you focus, the focal zone is smaller. What happens to the near field, far field, and depth?

Answer 18

The depth is shallower, the near field decreases while the far field increases

Question 19

What is a transducer

Answer 19

A device that transfers one form of energy to another.

Question 20

How is SPL related to axial resolution? What about the axial resolution value?

Answer 20

Inversely related to AR, directly related to the value.

Question 21

What does Piezoelectric material do? What does it allow for?

Answer 21

Piezoelectric material allows for sound energy to be both transmitted and received. It allowes for pulsed wave ultrasound to be achieved with one transducer.

Question 22

what does Piezoelectric mean? when do we use it?

Answer 22

pressure makes electricity. this happens when we convert sound to electrical energy.

Question 23

What is reverse Piezoelectric? when do we use it?

Answer 23

energy makes pressure. we do this when sending out a signal to create sound energy.

Question 24

what is PZT?

Answer 24

Man-made Piezoelectric material. also called the crystal, ceramic, or active element.

Question 25

How does PZT work?

Answer 25

The crystals have molecular structures arranged in a latice formation with dipoles. When the crystal heats, the molecules move freely and when it cools it freezes them.

Question 26

What is a dipole

Answer 26

seperate regions of + and - charges in a molecule

Question 27

What is the purpose of the matching layer?

Answer 27

The impedance mismatch between the skin and the ultrasound beam is huge, and gel is not enough. the matching layer helps the beam enter the body.

Question 28

How thick is the matching layer in the transducer? How thick is the active element?

Answer 28

The matching layer is 1/4 the wavelength. The active element is 1/2 the wavelength

Question 29

How does the backing material decrease sensitivity

Answer 29

Reduces active element vibration during both transmission and reception

Question 30

What is a bandwidth? What kind of bandwidth does pulsed ultrasound have?

Answer 30

the range of frequencies we can hear. Pulsed wave has a wide bandwidth.

Question 31

what is the Q factor equation?

Answer 31

frequency/bandwidth

Question 32

what is a q value? Why do we have one?

Answer 32

the ringing time of the transducer. We get this as a result of dampening the pulse.

Question 33

How are Q factor, SPL, and bandwidth related?

Answer 33

Q value and SPL are Inversely related to bandwidth. A low Q value has short SPL and a wide bandwidth.

Question 34

What characteristics of the PZT is pulsed wave dependent on?

Answer 34

The speed of sound and thickness of the PZT

Question 35

How are the PZT speed and thickness related to frequency?

Answer 35

Frequency is directly related to PZT speed and inversely related to thickness of the crystal.

Question 36

What is the equation for frequency using the speed/thickness of a crystal?

Answer 36

Frequency = speed of PZT / (Thickness x 2)

Question 37

Explain Huygens Principle

Answer 37

The beam is created by a disc shaped crystal. Many particles in the crystal create Huygens wavelets which interfere and create an hourglass beam.

Question 38

What is the width of the focus point of the beam?

Answer 38

1/2 the transducer width

Question 39

What is the Fresnel zone

Answer 39

the near field from the transducer to the focus.

Question 40

What is the Fraunhofer zone

Answer 40

the far field past the focus

Question 41

How is transducer diameter related to the focal depth?

Answer 41

They're directly related. A larger diameter transducer's beam will travel farther into the body.

Question 42

What is divergence? What is it related to?

Answer 42

the spreading out of the beam after the focus in the far field. It is inversely related to crystal diameter and frequency

Question 43

Lateral resolution is dependent on the width of the beam. What frequency or crystal width are best for lateral resolution?

Answer 43

Larger diameter and higher frequency

Question 44

Frequency is determined by crystal thickness. What is this equation?

Answer 44

thickness = wavelength / 2

Question 45

Focal zone is determined by crystal diameter. What is this equation?

Answer 45

focal zone = 1/2 crystal diameter

Question 46

Electrical energy is converted into sound during...?

Answer 46

Transmission

Question 47

A sound pulse is converted into electrical energy during...?

Answer 47

Reception

Question 48

What does the electrical shield do? Where in the transducer is it?

Answer 48

Prevents electrical signals in the air from entering the transducer and contaminating the important diagnostic electrical signals. It is the middle layer between the case and insulator.

Question 49

What is the acoustic insulator? Where is it?

Answer 49

A barrier of cork or rubber that prevents vibrations in the case from the PZT. It is the inner most layer.

Question 50

What does the case do? Where is it?

Answer 50

It protects the inner components of the transducer from damage. It also protects the patient from electric shock. It is the outermost layer.

Question 51

How much greater than the impedance of the skin is the impedance of the PZT?

Answer 51

20 times greater

Question 52

Why do we need backing material for the quality of an image?

Answer 52

Backing material reduces the vibrating time of the transducer and creates a shorter pulse. This shorter pulse creates a better axial resolution.

Question 53

What are characteristics of backing material?

Answer 53

High sound absorption, high acoustic impedance similar to PZT.

Question 54

What are the consequences of using backing material

Answer 54

Decreased sensitivity, wide bandwidth, low Quality factor

Question 55

What happens if PZT is heated above the curie point (350• C)

Answer 55

The piezoelectric properties are destroyed. This is called depolarization of PZT.

Question 56

What is the minimum crystal requirement for continuous wave? Pulsed wave?

Answer 56

1 crystal for pulsed wave

Question 57

Imaging transducers have low sensitivity. Will a lower sensitivity transducer create a short or long pulse? Will this create a wide or narrow bandwidth.

Answer 57

Lower sensitivity transducers create short pulses. wide bandwidth.

Question 58

What determines frequency of sound in a continuous wave transducer

Answer 58

The frequency of the electrical signal = the frequency of sound