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Physics > Chapter 8 > Flashcards

Chapter 8 Flashcards

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1
Q

A _ is any device that converts one

form of energy into another

A

Transducer

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2
Q

Ultrasound transducers perform two
functions: During transmission _,
During reception _

A 
During transmission, electrical energy 
from the system is converted into 
sound.
During reception, the reflected sound 
pulse is converted into electricity.
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3
Q

the property of
certain materials to create a voltage
when they are mechanically deformed
or when pressure is applied to them.

A

The piezoelectric effect

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4
Q

a process
in which piezoelectric materials change
shape when a voltage is applied to
them.

A

Reverse Piezoelectric Effect

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5
Q

Materials which convert sound into electricity

and vise versa

A

Piezoelectric Materials

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6
Q

Piezoelectric Materials AKA

A

ferroelectric

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7
Q

_ is a synthetic

material used in clinical transducers

A

Lead zirconate titanate or PZT

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8
Q

PZT AKA

A

The ceramic
Active element
Crystal

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9
Q

The _ of the transducer protects the internal

components of the transducer from damage

A

case

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10
Q

The _ of the transducer insulates the patient from electrical shock

A

case

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11
Q

The case is made of _

A

Plastic or metal

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12
Q

A thin metallic barrier lining inside the case

A

Electric shield

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13
Q

The _ prevents electrical signals that are unrelated to

diagnostic information from entering the transducer

A

Electrical shield

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14
Q

The _ prevents electrical noise from contaminating the clinically
important electrical signals

A

Electrical shield

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15
Q

A thin barrier of cork or rubber that isolates the
internal components of the transducer from the
case.

A

Acoustic insulator

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16
Q

The acoustic insulator prevents _

A

vibrations in the case from inducing an

electrical voltage in the PZT of the transducer.

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17
Q

In a simple probe, the PZT is shaped like a _

A

coin

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18
Q

The characteristics of the sound beam emitted by the transducer
are related to

A

the dimensions of the active element

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19
Q

The PZT is _ wavelength thick

A

1/2

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20
Q

Provides an electrical connection between the PZT and the

ultrasound system

A

Wire

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21
Q

During _, the voltage from the US system causes

the crystal to vibrate and produce an ultrasonic wave.

A

Transmission

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22
Q

During _, the crystal’s vibration produces a voltage

that must return to the system for processing into an image.

A

Reception

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23
Q

Increases the efficiency of sound energy transfer

between the active element and the body

A

Matching layer

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24
Q

Matching layer protects _

A

The active element

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25
Q

The matching layer is _ wavelength thick

A

1/4

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26
Q

Matching layer: Differences in impedance result in

A

reflections at

boundaries

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27
Q

Larger reflections occur with

A

greatest

impedance differences

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28
Q

The impedance of PZT is about _ times greater than the

impedance of skin

A

20

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29
Q

The matching layer is designed with an impedance in

between

A

that of the active element and the skin

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30
Q

The impedance of gel is between that of

A

the matching

layer and biologic media.

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31
Q

Multiple matching layers of
different impedances further
_ the percent of sound
transmission.

A

increases

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32
Q

Usually around _ matching layers
[with different impedances] are
used, in some cases _ layers.

A

2

3

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33
Q

The matching layer and gel increase the efficiency of

A

sound transfer between the PZT and the skin

34
Q

Decreasing order of impedence

A

PZT > matching layer > gel > Skin

35
Q

The thickness of the matching layer is _ of the wavelength of sound in the matching layer

A

1/4

36
Q

The thickness of the active element is _ of the

wavelength of sound in the active element

A

1/2

37
Q

Component: Active element
Thickness:

A

1/2 wavelength

38
Q

Component: Matching layer
Thickness:

A

1/4 wavelength

39
Q

Bonded to the back of the PZT

A

Backing material

40
Q

Reduces “ringing” of the PZT

A

Backing material

41
Q

When an electrical spike excites the PZT, the backing material_. The emitted sound pulse
is _ which makes it short in duration and length.

A

restricts the extent of PZT deformation.

Dampened

42
Q

Plays an essential role in optimizing the pulses

created by imaging transducers.

A

Backing material

43
Q

Without the damping material, the crystal will

A

vibrate longer and create pulses that are long in

length and time.

44
Q

Backing material substantially _ the vibration of the PZT. This creates pulses that are

A

decreases

short in length and
duration which improves axial resolution.

45
Q

Characteristics of Backing Material

A

High degree of sound absorption
Acoustic impedance similar to PZT
Made of metal powder and epoxy resin

46
Q

There are three consequences of
using backing material in
transducers:

A
  1. Decreased sensitivity
  2. Wide bandwidth
  3. Low quality factor
47
Q

The backing material not only decreases
vibration of the active element on
transmission but also _. This
makes the transducer

A

during reception

less responsive to the
reflected sound waves returning from the
body.

48
Q

During reception, transducers with damping

material are less able to

A

convert low-level
sound reflections into meaningful electrical
signals.

49
Q

the range of frequencies in the
pulse; the difference between the highest and
lowest frequencies

A

Bandwidth

50
Q

A single frequency produced is called a

A

resonant

frequency.

51
Q

Backing material prevents PZT from vibrating

freely which causes _. Although the click is short, it contains _

A

the pulse from the machine
to be more like a click than a steady long tone.

sound at many
different frequencies (both above and below the
transducer’s main frequency).

52
Q

the main frequency of a

transducer divided by the bandwidth

A

Quality factor

53
Q

Relationship between qualityy factor and bandwidth

A

Inversely

54
Q

Quality factor is commonly called

A

Q factor

55
Q

Wide bandwidth probes have _ Q factor

A

Low

56
Q

Narrow bandwidth probes have _ Q factor

A

High

57
Q

Because imaging probes use backing material
and have a wide bandwidth, they are often
referred to as

A

Low-Q

58
Q

Shorter pulse= _ Q factor

A

lower

59
Q

Longer pulse= _ Q factor

A

Higher

60
Q

A 3 MHz transducer with a bandwidth of 4 MHz

has a Q-Factor of

A

3/4 or 0.75

61
Q

The piezoelectric properties of lead zirconate

titanate (PZT) are created by

A

exposing the
material to a strong electrical field while being
heated to a substantial temperature. This process
is called polarization

62
Q

The temperature at which PZT is polarized is

called the

A

Curie temperature or the Curie point

63
Q

Piezoelectric properties can be destroyed by

A

exposure to a high temperature (depolarization).

64
Q

The frequency of sound emitted by a continuous

wave probe is equal to

A

the frequency of the

electrical signal

65
Q

A pulsed wave system creates _ that travels
through the wire and strikes the PZT
crystal in the transducer

A

a short

duration electrical spike

66
Q

The frequency of sound created by the
active element of a pulsed wave
transducer depends upon

A

the
characteristics of the active element of
the transducer.

67
Q

Two characteristics of the PZT combine

to determine the frequency of sound

A

Speed of sound in the PZT

Thickness of the PZT

68
Q

The speed of sound in PZT and the frequency of

sound are _ related.

A

Directly

69
Q

Higher speed of sound in PZT= _ frequency

A

Higher

70
Q

Lower speed of sound in PZT = _ frequency

A

Lower

71
Q

The speed of sound in most piezoelectric

materials

A

from 4 to 6 mm/μs

72
Q

_ Is a characteristic of each piece of PZT and

cannot be changed

A

Speed

73
Q

PZT thickness and frequency are _

related

A

inversely

74
Q

Thinner active elements create pulses with

_ frequency, _ wavelength cycles.

A

Higher

Shorter

75
Q

Thicker active elements create pulses with _ frequency, _ wavelength cycles

A

Lower

Longer

76
Q

Thickness of PZT crystals in diagnostic

imaging transducers range from

A

0.2 to 1

mm.

77
Q

The thickness of the PZT crystal in a

pulsed wave transducer is equal to

A

one-
half of the wavelength of sound in the
PZT.

78
Q

Frequency (MHz) =

A

sounds speed in PZT (mm/us)/ 2 x thickness (mm)

79
Q

Characteristics of high frequency pulsed wave imaging transducers

A

Thinner PZT

PZT with higher speeds

80
Q

Characteristics of low frequency pulsed wave imaging transducers

A

Thicker PZT

PZT with lower speeds

81
Q

Advantages of backing material

A

Reduces # of cycles in a pulse
Reduces pulse duration and SPL
Improves resolution

82
Q

Disadvantages of backing material

A

reduces amplitude
decreased sensitivity
wide bandwidth
low Q-facto

Physics (25 decks)

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