Physics - Ch 10 - Axial And Lateral Resolution

Front 1

Resolution?

Back 1

the ability to create accurate images

Front 2

Axial Resolution

Back 2

Describes one measure of detail found in an image.

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

Front 3

Axial Resolution - Units?

Back 3

mm or any other unit of distance

Front 4

Axial Resolution - Determined By?

Back 4

related to spatial pulse length

SPL is determined by sound source and medium

Front 5

____________improve axial resolution

Back 5

Shorter pulses

Front 6

Axial resolution is also related to ____________

Back 6

pulse duration.

Front 7

Axial resolution - Synonyms?

Back 7

Longitudinal range, radial or depth resolution

Front 8

Axial resolution - Adjustable?

Back 8

No

Since SPL for a transducer is fixed, the sonographer cannot change axial resolution

Front 9

Axial resolution - Typical Values?

Back 9

in clinical imaging, ranges from 0.1 - 1mm

Front 10

_______numerical values indicate shorter pulses and improved image accuracy

Back 10

Lower

Front 11

LAARD

Back 11

Longitudinal, Axial, Range, Radial, Depth

Front 12

Image quality is better when axial resolution has a ________ numerical value

Back 12

lower

Front 13

Axial Resolution (mm) =

Back 13

Axial Resolution (mm) = spatial pulse length(mm) / 2

Axial Resolution (mm) = [wavelength (mm) x # cycles in pulse] /2

Front 14

In Soft Tissue: Axial Resolution(mm) =

Back 14

[0.77 x #cycles in pulse] / frequency(MHz)

Front 15

A short pulse is created in two ways:

Back 15

Less ringing

Higher frequency

Front 16

Less Ringing?

Back 16

A pulse is short if there are few cycles in the pulse.

Front 17

One way to reduce ringing is to_________________________________________

Back 17

dampen the crystal after it has been exited by an electrical signal from the signal

Front 18

Higher Frequency?

Back 18

A pulse is short if each cycle in the pulse has a short wavelength

Front 19

__________ wavelengths are characteristic of higher frequency sound

Back 19

Shorter

Front 20

Pulses made of higher frequency cycles have _________axial resolution

Back 20

Superior

Front 21

Better Axial Resolution Is Associated With The Following: (5)

Back 21

1) Shorter Spatial Pulse Length

2) Shorter Pulse Duration

3) Higher Frequencies (Shorter Wavelength)

4) Fewer Cycles Per Pulse (Less Ringing)

5) Lower Numerical Values

Front 22

Lateral Resolution?

Back 22

The ability to distinctly identify two structures that are very close together when they are side by side, or perpendicular to the sound beams main axis

Front 23

Lateral Resolution - Units?

Back 23

mm,cm, or any unit of distance

Front 24

Lateral Resolution - Determined By?

Back 24

the width of the sound beam

Front 25

Lateral Resolution:

__________beams have better resolution

Back 25

Narrower

Front 26

Beam diameter varies with ______

Back 26

depth

Front 27

Lateral resolution changes with _______

Back 27

depth

Front 28

Lateral Resolution - Synonyms?

Back 28

angular, transverse, or azimuthal resolution

Front 29

LATA

Back 29

Lateral, Angular, Transverse, Azimuthal

Front 30

Lateral resolution is best at the ______________

Back 30

focus (at the end of the near zone) where the beam is narrowest

Front 31

In clinical situations, is axial or Lateral resolution better?

Back 31

In clinical situations, axial resolution is better than lateral resolution because ultrasound pulses are shorter than they are wide. The numerical value for axial resolution is less than the value for lateral resolution

Front 32

When two side by side reflectors are closer to each other than the width of the beam______________________________

Back 32

only one reflection is observed on the image

Front 33

___________frequencies improve both axial and lateral resolution

Back 33

Higher

Front 34

Axial resolution is improved in the_____________ because shorter pulses are associated with high frequency sound

Back 34

entire image

Front 35

Lateral resolution is improved in the______________

Back 35

Lateral resolution is improved in the far field only because high frequency pulses diverge less in the far field than low frequency pulses. Higher frequency sound beams are narrower than lower frequency beams

Front 36

Axial - orientation?

Back 36

Front to back

Parallel to beam

Front 37

Axial- mnemonic?

Back 37

LARRD

Front 38

Axial - determined by?

Back 38

pulse length

Front 39

axial - best with?

Back 39

Shortest pulse

Highest frequency and fewest cycles

Front 40

Axial- does it change?

Back 40

Same at all depths, does not change

Front 41

Axial -In Near Field,Best With?

Back 41

Shortest pulse

Front 42

Axial - In Far Field, Best With?

Back 42

Shortest Pulse

Front 43

Lateral - orientation?

Back 43

Side by side

Perpendicular to beam

Front 44

Lateral - mnemonic?

Back 44

LATA

Front 45

Lateral - Determined By?

Back 45

Beam Width

Front 46

Lateral - best with?

Back 46

Narrowest Beam

Front 47

Lateral - Does it change?

Back 47

Changes with depth, best at focus

Front 48

Lateral - In near field, best with?

Back 48

Smallest diameter crystal

Front 49

Lateral - In far field, best with?

Back 49

Largest diameter and highest frequency (least divergence)

Front 50

Focusing?

Back 50

Concentrates the sound energy into a narrower beam and thus improves lateral resolution

Front 51

The 3 methods of focusing?

Back 51

1) External Focusing

2) Internal Focusing

3) Phased Array Focusing

Front 52

External Focusing?

Back 52

With a lens

Front 53

Internal Focusing?

Back 53

With a curved active element

Front 54

Phased Array Focusing?

Back 54

with the electronics of the ultrasound system

Front 55

Internal and external focusing may be used with ________________________

Back 55

single element transducers

Front 56

Phased array focusing is reserved specifically for __________________

Back 56

array transducers - those with multiple active elements

Front 57

Fixed Focusing, aka ______________

Back 57

conventional or mechanical focusing,

Front 58

Fixed Focusing, includes both ___________________

Back 58

external and internal techniques

Front 59

With fixed focusing, the focal depth and the extent of focusing are determined when ___________________________________

Back 59

the transducer is fabricated and cannot be changed

Front 60

External Focusing - A lens is placed _______________________

Back 60

in front of the piezoelectric material

Front 61

As the arc of the lens becomes more prominent, the degree of focusing ____________ and the beam ____________________

Back 61

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

Front 62

Internal Focusing :

A curved piezoelectric crystal ___________________________________________

Back 62

concentrates the sound energy into a narrower or tighter beam

Front 63

As the curvature of the PZT becomes more pronounced, the degree of focusing _______

Back 63

increases

Front 64

________________ is the most common form of fixed focusing

Back 64

Internal Focusing

Front 65

There is no lens with _________________

Back 65

internal focusing

Front 66

Electronic Focusing: Phased Array?

Back 66

-The systems electronics focus the sound beam

-The sonographer can adjust the focusing characteristics of a beam

Front 67

Electronic Focusing : Phased Array:

This technique may be used only on

Back 67

multi-element transducers, never on single crystal transducers

Front 68

When focused, The beam diameter in the near field and the focal zone ____________

Back 68

narrows

Front 69

when a sound beam is focused, The focus is________________________________

Back 69

moved closer to the transducer. (the near zone length is reduced)

Front 70

when a sound beam is focused, The beam diameter beyond the focal zone ____________. Focusing improves lateral resolution in the____________________, and degrades lateral resolution_____________

Back 70

The beam diameter beyond the focal zone widens. Focusing improves lateral resolution in the near and focal zones, and degrades lateral resolution beyond the focal zone

Front 71

4 Effects of Focusing

Back 71

1) Beam diameter in near field and focal zone is reduced

2) Focal depth is shallower

3) Beam diameter in the far zone increases

4) Focal zone is smaller

Front 72

Frequency - Continuous Wave : Determined By?

Back 72

Frequency of electrical signal from ultrasound system

Front 73

Frequency - Pulsed Wave: Determined By?

Back 73

Thickness of ceramic and speed of sound in ceramic

Front 74

Focal Length : Determined By?

Back 74

Diameter of ceramic and frequency of sound

Front 75

Beam Divergence: Determined By?

Back 75

Diameter of ceramic and frequency of sound

Front 76

Lateral Resolution: Determined By?

Back 76

Beam width