Chapter 10

Question 1

______ is the ability to create accurate images

Answer 1

resolution

Question 2

______ describes one measure of the detail found in an image

Answer 2

axial resolution (measures in mm), it is also called longitudinal, range, radial, or depth resolution

Question 3

axial resolution measures the ability of a system to display two structures that are very close together when the structures are ______ to the sound beams main axis

Answer 3

parallel

Question 4

axial resolution is related to the ______

Answer 4

spatial pulse length (determined by both sound source and the media)

Question 5

______ pulses improve axial resolution, and is also related to pulse duration

Answer 5

short

Question 6

what is the typical values for axial resolution?

Answer 6

0.1 to 1 mm, lower numerical values indicate shorter pluses and improve image accuracy

Question 7

to remember axial resolution synonyms use LARRD, which means

Answer 7

Longitudinal, Axial, Range, Radial, Depth

Question 8

what is the equation for axial resolution?

Answer 8

axial resolution (mm) = spatial pulse length (mm) / 2
In soft tissue it is 0.77 x # cycles in phase / frequency (MHz)

Question 9

what are the two ways that short pulses are created?

Answer 9

less ringing and higher frequency

Question 10

one way to reduce ringing is to ______ the crystals after it has been excited by an electrical signal from the system

Answer 10

dampen

Question 11

if the pulse is short because there are few cycles in the pulse its known as _____

Answer 11

less ringing

Question 12

is the pulse is short because each cycle in the pulse has a short wavelength its known as ______

Answer 12

higher frequency sound

Question 13

what all is the axial resolution associated with?

Answer 13

shorter spatial pulse length, shorter pulse duration, higher frequencies, fewer cycles per pulse, and lower numerical value

Question 14

______ is the ability to distinctly identify two structures that are vary close together when they are side by side or perpendicular to the sound beams main axis

Answer 14

lateral resolution (mm or cm)

Question 15

what is the lateral resolution determined by?

Answer 15

width of the sound beam

Question 16

______ beams have better resolution

Answer 16

narrower; beam diameter varies with depth and lateral resolution changes with depth

Question 17

to remember the synonyms for lateral resolution use LATA which means?

Answer 17

Lateral, Angular, Transverse, Azimuthal

Question 18

Lateral resolution is best at the _____, where the beam is narrowest

Answer 18

focus

Question 19

what is the equation for lateral resolution?

Answer 19

lateral resolution (mm) = beams diameter (mm)

Question 20

axial resolution is better that lateral resolution because ultrasound pulses are ______ than they are wide

Answer 20

shorter; thus the numerical value is less

Question 21

when two side-by-side reflectors are closer to each other than the width of the beam, only ______ reflection is observed on the image

Answer 21

one

Question 22

______ frequencies improve both lateral and axial resolutions

Answer 22

higher

Question 23

______ is improved in the entire image with higher frequency because shorter pulses are associated with high frequency sound.

Answer 23

axial resolution

Question 24

______ is improved by high frequency only in the far field because high frequency pulses diverge less in the far field

Answer 24

lateral resolution

Question 25

changes with depth, smallest diameter crystals are best in near field, largest diameter and highest frequency is best in far field

Answer 25

lateral resolution

Question 26

same at all depths, does not change, shortest pulses are best in far and near fields

Answer 26

axial resolution

Question 27

what are the three methods of focusing?

Answer 27

external focusing (with a lens), internal focusing (with a curved active element), and phased array focusing (with the electronics of the ultrasound system)

Question 28

______, also called conventional or mechanical focusing, includes both external and internal techniques

Answer 28

fixed focusing

Question 29

with external focusing a ______ is placed in front of the piezoelectric material

Answer 29

lens

Question 30

as the arc of the lens becomes more prominent, the degree of focusing ______ and the beam narrows in the focal zone

Answer 30

increases

Question 31

with internal focusing a ______ concentrates that sound energy into a narrower or tighter beam (most common form of fixed focusing)

Answer 31

curved piezoelectric crystal

Question 32

as the curvature of the PZT becomes more pronounced, the degree of focusing ______

Answer 32

increases

Question 33

______ means adjustable or multiple focusing

Answer 33

phased array

Question 34

in phases array transducers, the systems ______ focus the sound beam

Answer 34

electronics

Question 35

what is the effects of focusing the sound beam?

Answer 35

beam diameter in near field and focal zone is reduced, focal depth is shallower, beam diameter in the far zone increases, and focal zone is smaller