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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
The matching layer is _ wavelength thick
1/4
26
Matching layer: Differences in impedance result in
reflections at | boundaries
27
Larger reflections occur with
greatest | impedance differences
28
The impedance of PZT is about _ times greater than the | impedance of skin
20
29
The matching layer is designed with an impedance in | between
that of the active element and the skin
30
The impedance of gel is between that of
the matching | layer and biologic media.
31
Multiple matching layers of different impedances further _ the percent of sound transmission.
increases
32
Usually around _ matching layers [with different impedances] are used, in some cases _ layers.
2 | 3
33
The matching layer and gel increase the efficiency of
sound transfer between the PZT and the skin
34
Decreasing order of impedence
PZT > matching layer > gel > Skin
35
The thickness of the matching layer is _ of the wavelength of sound in the matching layer
1/4
36
The thickness of the active element is _ of the | wavelength of sound in the active element
1/2
37
Component: Active element Thickness:
1/2 wavelength
38
Component: Matching layer Thickness:
1/4 wavelength
39
Bonded to the back of the PZT
Backing material
40
Reduces “ringing” of the PZT
Backing material
41
When an electrical spike excites the PZT, the backing material_. The emitted sound pulse is _ which makes it short in duration and length.
restricts the extent of PZT deformation. Dampened
42
Plays an essential role in optimizing the pulses | created by imaging transducers.
Backing material
43
Without the damping material, the crystal will
vibrate longer and create pulses that are long in | length and time.
44
Backing material substantially _ the vibration of the PZT. This creates pulses that are
decreases short in length and duration which improves axial resolution.
45
Characteristics of Backing Material
High degree of sound absorption Acoustic impedance similar to PZT Made of metal powder and epoxy resin
46
There are three consequences of using backing material in transducers:
1. Decreased sensitivity 2. Wide bandwidth 3. Low quality factor
47
The backing material not only decreases vibration of the active element on transmission but also _. This makes the transducer
during reception less responsive to the reflected sound waves returning from the body.
48
During reception, transducers with damping | material are less able to
convert low-level sound reflections into meaningful electrical signals.
49
the range of frequencies in the pulse; the difference between the highest and lowest frequencies
Bandwidth
50
A single frequency produced is called a
resonant | frequency.
51
Backing material prevents PZT from vibrating | freely which causes _. Although the click is short, it contains _
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
the main frequency of a | transducer divided by the bandwidth
Quality factor
53
Relationship between qualityy factor and bandwidth
Inversely
54
Quality factor is commonly called
Q factor
55
Wide bandwidth probes have _ Q factor
Low
56
Narrow bandwidth probes have _ Q factor
High
57
Because imaging probes use backing material and have a wide bandwidth, they are often referred to as
Low-Q
58
Shorter pulse= _ Q factor
lower
59
Longer pulse= _ Q factor
Higher
60
A 3 MHz transducer with a bandwidth of 4 MHz | has a Q-Factor of
3/4 or 0.75
61
The piezoelectric properties of lead zirconate | titanate (PZT) are created by
exposing the material to a strong electrical field while being heated to a substantial temperature. This process is called polarization
62
The temperature at which PZT is polarized is | called the
Curie temperature or the Curie point
63
Piezoelectric properties can be destroyed by
exposure to a high temperature (depolarization).
64
The frequency of sound emitted by a continuous | wave probe is equal to
the frequency of the | electrical signal
65
A pulsed wave system creates _ that travels through the wire and strikes the PZT crystal in the transducer
a short | duration electrical spike
66
The frequency of sound created by the active element of a pulsed wave transducer depends upon
the characteristics of the active element of the transducer.
67
Two characteristics of the PZT combine | to determine the frequency of sound
Speed of sound in the PZT | Thickness of the PZT
68
The speed of sound in PZT and the frequency of | sound are _ related.
Directly
69
Higher speed of sound in PZT= _ frequency
Higher
70
Lower speed of sound in PZT = _ frequency
Lower
71
The speed of sound in most piezoelectric | materials
from 4 to 6 mm/μs
72
_ Is a characteristic of each piece of PZT and | cannot be changed
Speed
73
PZT thickness and frequency are _ | related
inversely
74
Thinner active elements create pulses with | _ frequency, _ wavelength cycles.
Higher | Shorter
75
Thicker active elements create pulses with _ frequency, _ wavelength cycles
Lower | Longer
76
Thickness of PZT crystals in diagnostic | imaging transducers range from
0.2 to 1 | mm.
77
The thickness of the PZT crystal in a | pulsed wave transducer is equal to
one- half of the wavelength of sound in the PZT.
78
Frequency (MHz) =
sounds speed in PZT (mm/us)/ 2 x thickness (mm)
79
Characteristics of high frequency pulsed wave imaging transducers
Thinner PZT | PZT with higher speeds
80
Characteristics of low frequency pulsed wave imaging transducers
Thicker PZT | PZT with lower speeds
81
Advantages of backing material
Reduces # of cycles in a pulse Reduces pulse duration and SPL Improves resolution
82
Disadvantages of backing material
reduces amplitude decreased sensitivity wide bandwidth low Q-facto

Physics (25 decks)

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