Physics- Beam Shape

Front 1

what is the simplest kind of tx?

Back 1

single crystal

unfocused

disc shaped crystal

Front 2

Can an unfocused tx have a near and far field?

Back 2

YES

Front 3

Near field in regards to resolution?

Back 3

near field has the best resolution

Front 4

NFL?

Back 4

distance from tx face to transition between near and far field

Front 5

NFL in a focused tx?

Back 5

in a focused tx, NFL is the focal plane

Front 6

Can the angle of divergence be predicted?

Back 6

yes

Front 7

near field name?

Back 7

fresnel

Front 8

far field name?

Back 8

fraunhoffer

Front 9

beam shape of a single crystal, unfocused tx?

Back 9

near field- cylindrical

far field- conical

(both 3D, both look rectangular to us)

Front 10

Angle of divergence for single crystal, unfocused tx?

Back 10

theta 0

Front 11

Near field- distance?

Back 11

Distance from tx surface to where beam begins diverging

Front 12

Formula for NFL?

Back 12

diameter of crystal, squared / 4 x wavelength

Front 13

As diameter of crystal increases, the NFL?

Back 13

as diameter of crystal increases, the NFL increases

Front 14

As wavelength increases, the NFL?

Back 14

As wavelength increases, then NFL decreases

Front 15

As frequency increases, wavelength decreases = ___ NFL?

Back 15

As frequency increases, wavelength decreases = increased NFL

Front 16

As frequency decreases, wavelength increases = ____ NFL?

Back 16

As frequency decreases, wavelength increases = decreased NFL

Front 17

If diameter of crystal is constant, and frequency increases, then NFL ___?

Back 17

If diameter of crystal is constant, and frequency increases, then NFL increases

Front 18

Near field in regards to penetration?

Back 18

Near field is not about penetration, it is about the shape of the beam

Front 19

Which one has a higher frequency along with a shorter wavelength?

Back 19

This has a longer NFL, a shorter wavelength, and a higher frequency

Front 20

If frequency is constant, and diameter increases, then NFL ___?

Back 20

If frequency is constant, and diameter increases, then NFL increases

(bigger tx diameter, also increase NFL (not tied in with penetration or attenuation)

Front 21

Calculate NFL if you had an unfocused tx with a 2.25 MHz tx with a 13 mm tx diameter?

Back 21

wavelength = velocity (speed in soft tissue) / frequency

1540/2.25 x 10^6 = .68

NFL = diameter of crystal^2 = 13^2

___________________ ________

4 x wavlength = 4 x .68

Front 22

Angle of divergence for far field?

Back 22

sin 0= 1.22 x wavelength/ diameter of cyrstal

as wavelength increases that value increases

as diameter increases that value decreases

Front 23

The larger the diameter, the _____ angle of divergence?

Back 23

The larger the diameter, the smaller angle of divergence

Front 24

An increase in frequency = ______ angle of divergence?

Back 24

An increase in frequency = a decreased angle of divergence (& a shorter wavelength)

Front 25

Self focus in regards to an unfocused single element tx?

Back 25

An unfocused single element tx still has a natural occurring focus

Front 26

General definition and method for focusing?

Back 26

You want to use the method of narrowing the beam to concentrate the sound beam (AKA focusing)

You focus at area of interest

You need to minimize divergence- divergence means the beam is getting wider, so it is harder to separate small targets from each other, you want good lateral resolution to see those targets individually.

SonoSite and Zonare have an autofocus, much like a camera that will change it's focus depending on light.

Front 27

Which part of a focused beam has the best focus?

Back 27

the skinniest part (plane with narrowest beam width)- the focal plane

This is where you'll have the best image

The yellow line is the focal plane

Front 28

What does the focal zone include?

Back 28

Some near field and some far field

Front 29

Which part of a focused beam has the greatest intensity?

Back 29

The focal plane

-the same plane with the best image (plane with the narrowest beam width)

Lateral resolution is very good here

Focus creates an area of highest intensity in the middle of the beam instead of right after the tx face because the wavelets

Front 30

focal point in a focused tx?

Back 30

center of focal plane

point on central beam axis

CBA has greatest intensity and best image, as well as focal plane

Front 31

Focal distance? AKA

What area on beam?
Area of improving?

Back 31

Focal distance is the distance from tx to focal plane

AKA NFL

-area of improving resolution- the resolution is gradually improving

Front 32

Focal zone?

Back 32

region where the start and stop of focal zone is 2 x the diameter of the focal plane

For an example: If focal plane is 2mm, then the focal zone is at 4mm.

If focal plane was 3mm, then the focal zone is 6mm.

The focal plane is the center yellow line, the focal zone is the pink lines

Front 33

Depth of focus is aka?

Back 33

Focal zone

Front 34

External focus singe element tx?

Back 34

a device is added to the tx. The crystal itself does not focus.

- a mirror could be used to redirect the beam (patents would lay on the mirror)

-a lens outside of the crystal

If crystal is curved then it is internal focus, devices were added to curve and focus the beam.

Front 35

Internal focus for a single element tx?

Back 35

The crystal itself does curve and that is focusing the beam (changes the curvature of the crystal)

Front 36

Internal focus for a multi-element tx? (today's)

Back 36

Electronic focusing to change shape of wavefront

We can vary how we pulse the tx to the shape the wavefront we want for that set of crystals or elements

Front 37

Benefit of a focused tx?

Back 37

You get a narrower beam width at the focal plane which effects the beam diameter, it goes from wider to narrow to focus at the focal plane, then widens again (diverges)

Front 38

Disadvantage of a focused tx?

Back 38

NFL decreases

-focal plane shifts closer to crystal

Front 39

In a single element, internally focused tx , the focal plane can't go farther than?

Back 39

The focal plane can't go farther than the center of the curvature of that crystal for that tx

-focal plane will always be at the center of the curvature

*the focal plane is like the radius of the curvature (HALF of the circle)

with multi element tx, you can vary the curvature on how we pulse the crystal, we have more flexibility on where the focal plane can go

Front 40

If the element or crystal has a greater curvature then?

Back 40

then the radius will be decreased, but there will be a stronger focus

Front 41

Does a focused tx or a non-focused tx have a shorter NFL?

Back 41

The NFL of a FOCUSED tx is shorter than for a non-focused tx (assuming same MHz and diameter)

A non focused is flat so the curvature of the radius is father from the tx, when you have that curve you are more focused closer to the tx.

Unfocused tx will be farther into tissue than that of a curved single element tx

Front 42

What is depth of focus?

Back 42

It is the length of the focal zone

NOT EQUAL TO THE NFL

Front 43

Effective beam width?

Unit?

based on?

demonstrated in?

Back 43

Use dB (decibels)

-demonstrated in cross section of beam

-based on beam energies

Front 44

Any intensity less than _____ is considered insignificant for _____?

Back 44

Any intensity less than 6.25 (-12 dB) is considered insignificant for our beam shape to define our beam margins

Front 45

I1 (I sub 1) ?

Back 45

= 0dB (reference point)

Center of cross section

This is defined as the intensities at our CBA- as the beam moves away from tx, fluctuations of intensities occur b/c it is not always uniform and it is predictable in some areas.

Front 46

I2 (I sub 2)?

Back 46

= 0 to -12 dB

Boundary of cross section

This is defined as all points on periphery or boundary of the cross section- points that define the boundary. -12 dB to define that beam boundary.

Front 47

I3 (I sub 3)?

Back 47

= beyond -12 dB

Energy beyond the boundary line

This is defined as non-specific energies, anything beyond the -12 dB/anything less than 6.25% of the original beam energy/beam axis.

Front 48

Pulse-echo beam cross sectional area?

Back 48

Pusle echo is PW, cross section of beam if beam is carrot then you cut the carrot and you look at the cross section of it, center of carrot or beam is the CBA as we move away from that center we have lower and lower intensites

CBA- maximum intensity

Maxium response is I1 = reference point to where -12 dB is being compared to, measured in crosss sectional area all the way out the beam

-infinite amount of slices, measure 1 cm increments to get shape of beam

Front 49

Pulse-echo focal plane?

Back 49

Cross sectional area

Pulse echo that uses PW, focal plane is the boundary between near and far field, focal point in between that.

Has narrowest diameter- has smallest area of all cross section cuts of beam

Smallest cross sectional area occurs at focal point

Front 50

Cross sectional planes are ____ to beam axis?

Back 50

perpendicular

Front 51

Pulse-echo focal length?

Back 51

distance along beam axis from center of the tx face to the focal plane

AKA

focal distance

NFL

distance to the near field boundary

Front 52

Pulse-echo focal zone?

Back 52

distance along beam axis of a focused tx

boundary of the focal plane- 2 x the focal plane, symmetrical on both sides of focal plane

Front 53

Focal zone resolution?

Back 53

good resolution at focal zone

good focus at focal zone

BUT NOT AS GOOD AS FOCAL PLANE/POINT

Keep area of interest in focal zone

If liver, put focal zone at diaphragm

if GB, put focal zone at posterior wall

Front 54

Focal strength-

strong focus?

Back 54

Strong focus is a shorter focus

-depth of focus or focal zone length is not very long

Front 55

Focal strength-

weak focus?

Back 55

Weak focus is a longer focus

- long focus refers to a beam with a long focal zone length

Front 56

For a strong focus, you should have a _____ NFL & the focal point should be _____ to tx?

Back 56

For a strong focus, you should have a short NFL, & the focal point closest to the tx.

Front 57

For a strong focus, you should have?

Back 57

narrow beam

focal point close to tx- short NFL

extreme beam divergence

-use to image small parts

Front 58

For a medium focus, you should have?

Back 58

medium focus 50%

usable beam width

-1/2 of unfocused beam width

-improves lateral res by 1/2

-1/2 beam length is useful

Intermediate focal length

Some beam deterioration- divergences

Front 59

Weak focus, you should have?

Back 59

weak focus 66%

beam width

-2/3 unfocused beam width

Has longest near field length

Mild beam divergence

Front 60

Short focus may refer to?

Back 60

may refer to a strong focus tx

not always

Front 61

Long focus may refer to?

Back 61

may refer to weak focus tx

not always

Front 62

For small parts?

Back 62

tx = 7.5 MHz

short, strong focus

-decreases penetration

-increases resolution

Front 63

Deep imaging?

Back 63

tx = 2.25 MHz

Long, weak focus

-decreased resolution

-increased penetration

Front 64

wavefront signifcant?

Back 64

we need devices that generate and US beam of uniform intensity

-huyguins- moves out and becomes planar- predictable and parallel to each other- alignment is perpendicular to beam axis

Front 65

If tx diameter has one wavelength?

Back 65

produces spherical wavefront

rapid divergence

regions of rarefaction and compression

creates non-uniform beam

Front 66

If tx diameter has multiple wavelengths?

Back 66

each small area is individual sound source with spherical wavefront

wavefronts undergo constructive and destructive interference

results in complex wavefront

Front 67

Lateral resolution?

Back 67

-ability to resolve two adjacent objective

-perpendicular to beam axis

When beam shape is larger than object itself, then object isn’t only thing that is generating reflections

-if smaller than beam width, the beam interacts with things around cyst, you get relection from the tissue around the cyst within that beam width. Inferfaces around cyst are source for reflections (so fill in cyst, not completely anechoic)

Front 68

Things that effect lateral resolution?

Back 68

focal zone

diameter of tx

beamwidth- beam shape

tx frequency

wavelength

Front 69

Is beam width uniform?

Back 69

No

You have a wide area for the NFL

then the focal zone and then focal plane, it then widens from divergence

Front 70

Decreased beam width = decreased or increased lateral resolution?

Back 70

decreased beam width = improved lateral resolution

Front 71

Increased frequency, ______ lateral resolution by ______ beam width?

Back 71

improved lateral resolution by decreasing beam width (although you have less penetration)

Front 72

slice thickness?

Back 72

thickness of the section of tissue that contributes to echoes visualized on an image

dimension of the beam perpendicular to the image plane

-rather than in the image plane

depends on beam size

THICKNESS OF IMAGE PLANE

Front 73

Other name for slice thickness?

Back 73

elevation resolution

azimuthal resolution

scan plane thickness

realted to lateral resolution, not same as

-lateral resolution and slice thickness are not uniform along a beam

Front 74

Annuluar array tx?

Back 74

for this tx, the slice thickness and lateral resolution were the same b/c the beam is symmetrical

Front 75

Linear and phased array tx?

Back 75

today's txs

slice thicnkess is not = to the lateral resolution, this is due to electronic focusing

Front 76

electronic focusing for a multi element tx?

Back 76

narrows in plane width of the beam to improve lateral resolution

Front 77

Slice thickness is the worst resolution value for ?

Back 77

array scanners