Key Terms (Ch.3)

Question 1

aperture

Answer 1

size of a transducer element (for a single-element transducer) or group of elements (for an array)

Question 2

apodization

Answer 2

nonuniform (i.e., involving different voltage amplitudes) driving of elements in an array to reduce grating lobes

Question 3

array

Answer 3

a transducer assembly containing several piezoelectric elements

Question 4

axial

Answer 4

in the direction of the transducer axis (sound travel direction)

Question 5

axial resolution

Answer 5

the minimum reflector separation along the sound path that is required to produce separate echoes (i.e., to distinguish between two reflectors)

Question 6

beam composite

Answer 6

region containing continuous wave sound; region through which a sound pulse propagates with a combination of a piezoelectric ceramic and a nonpiezoelectric polymer

Question 7

convex array

Answer 7

curved linear array

Question 8

crystal

Answer 8

element

Question 9

curie point

Answer 9

temperature at which an element material loses its piezoelectric properties

Question 10

damping

Answer 10

material attached to the rear face of a transducer element to reduce pulse duration; the process of pulse duration reduction

Question 11

detail resolution

Answer 11

the ability to image fine detail and to distinguish closely spaced reflectors (see axial and lateral resolution)

Question 12

disk

Answer 12

a thin, flat, circular object

Question 13

dynamic aperture

Answer 13

aperture that increases with increasing focal length (to maintain constant focal width)

Question 14

dynamic focusing

Answer 14

continuously variable reception focusing that follows the increasing depth of the transmitted pulse as it travels

Question 15

element

Answer 15

the piezoelectric component of a transducer assembly

Question 16

elevational resolution

Answer 16

the detail resolution in the direction perpendicular to the scan plane. it is equal to the section thickness and is the source of section thickness artifact

Question 17

far zone

Answer 17

the region of a sound beam in which the beam diameter increases as the distance from the transducer increases; also called far field

Question 18

focal length

Answer 18

distance from a focused transducer to the center of a focal region or to the location of the spatial peak intensity

Question 19

focal region

Answer 19

region of minimum beam diameter and area

Question 20

focal zone

Answer 20

length of the focal region

Question 21

focus

Answer 21

the concentration of the sound beam into a smaller beam area than would exist otherwise

Question 22

grating lobes

Answer 22

additional weaker beams of sound traveling out in directions different from the primary beam as a result of the multielement structure of transducer arrays

Question 23

lateral

Answer 23

perpendicular to the direction of sound travel

Question 24

lateral resolution

Answer 24

minimum reflector separation perpendicular to the sound path that is required to produce separate echoes

Question 25

lead zirconate titanate

Answer 25

a ceramic piezoelectric material, abbreviated PZT

Question 26

lens

Answer 26

a curved material that focuses a sound or light beam

Question 27

linear

Answer 27

adjectival form of line

Question 28

linear array

Answer 28

array made of rectangular elements arranged in a straight line

Question 29

linear phased array

Answer 29

linear array operated by applying voltage pulses to all elements, but with small time differences (phasing) to direct ultrasound pulses out in various directions

Question 30

linear sequenced array

Answer 30

linear array operated by applying voltage pulses to groups of elements sequentially

Question 31

matching layer

Answer 31

material attached to the front face of a transducer element to reduce the reflections at the transducer surface

Question 32

natural focus

Answer 32

the narrowing of a sound beam that occurs with an unfocused flat transducer element

Question 33

near zone

Answer 33

the region of a sound beam in which the beam diameter decreases as the distance from the transducer increases; also called near field

Question 34

operating frequency

Answer 34

preferred (maximum efficiency) frequency of operation of a transducer (see resonance frequency)

Question 35

phased array

Answer 35

an array that steers and focuses the beam electronically (with short time delays)

Question 36

phased linear array

Answer 36

linear sequenced array with phased focusing added; linear sequenced array with phased steering of pulses to produce a parallelogram-shaped display

Question 37

piezoelectricity

Answer 37

conversion of pressure to electric voltage

Question 38

probe

Answer 38

transducer assembly

Question 39

resolution

Answer 39

the ability to distinguish echoes in terms of space, time, or strength (called detail, temporal, and contrast resolutions, respectively)

Question 40

resonance frequency

Answer 40

operating frequency

Question 41

scanhead

Answer 41

transducer assembly

Question 42

sector

Answer 42

a geometric figure bounded by two radii and the arc of the circle included between them

Question 43

sensitivity

Answer 43

ability of an imaging system to detect weak echoes

Question 44

side lobes

Answer 44

weaker beams of sound traveling out from a single element in direction different from those of the primary beam

Question 45

sound beam source

Answer 45

an emitter of ultrasound where a region of a medium that contains virtually all of the sound produced by a transducer

Question 46

transducer

Answer 46

a device that converts energy from one form to another

Question 47

transducer assembly

Answer 47

transducer element(s) with damping and matching materials assembled in a case

Question 48

ultrasound transducer

Answer 48

a device that converts electric energy to ultrasound energy, and vice versa

Question 49

vector array

Answer 49

linear sequenced array that emits pulses from different starting points and (by phasing) in different directions