The Ultrasonic Field Flashcards by Kate Grimeau

Divergence

Spreading out of sound wave from a small source

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Smaller source = ____ divergence

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Focal zone has the best _____ resolution

Lateral

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Huygens principle taught us that to limit divergence we can fire a ____ of elements that together create a ____

Group
Wavefront

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Near fields have ____ beams as the result of of ______ between the wavelets

Non-uniform beams
Interference

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Far fields have _____ beams

Uniform

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The many Fs emitted from low Q probes also make _____ fields ____ uniform

Near
Less

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Another way to represent the non-uniformity of the near field is to relate it to the _____ differences

Intensity

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Low Q probes have (3)

Wide bandwidth
Short pulse
Lots of fs emitted

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What are off axis beams called

Grating lobes

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The main beam contains ____ of the energy and the grating lobes are ____

Most
Weaker

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In mechanical probes the grating lobes are called ____

Side lobes

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Intensity ____ as areas increases

Decreases

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Grating lobes are the result of ____ and ___ of the crystal resulting in ____

Length
Width vibration
Crosstalk

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Side lobes are the result of ____ in the single disc probes

Radial mode vibration

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Near field aka

Fresnal

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Far field aka

Fraunhofer

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____ improves grating lobes in regular probes. _____ helps with the single disc probes

Apodization
Insulator rings

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The near field is characterized by _____ beam width while the far field is charactered by a ______ beam width

Nearly constant
Divergent

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NZL

Near zone length

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Even with old flat discs there is a natural narrowing of the beam that occurs at the _______ (aka ______)

One near field length
Near zone length

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The natural narrowing of the beam of a single disc probe is called a ___

Transition zone

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Transition zone

The natural narrowing of the beam of an old flat disc that occurs at one near field length

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The beam is ___ the crystal diameter at the transition zone

1/2

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2 NZL has the same ____ as the first NZL

Diamter

The natural beam shape (with NZL) also helps to define the _____

Usable beam shape

The usable beam shape length, equal to ___ NZLs, is narrow enough to provide reasonable _____ resolution

2 Lateral

Near field length formula

NZL = (D^2) / (4 x wavelength) D= diameter of crystal

Formula to calculate the near field specifically for soft tissue

NZL = (D^2 x f)/6

As the f or diameter of the crystal increases = ____ NZL

Increases

The far field is the _____ part of the beam

Divergent

Formula to calculate the amount of divergence

Sin0= 1.22 x wavelength / D D=diameter of crystal

Increasing the frequency or diameter of the crystal = _____ the angle of divergence

Decrease

In the array probe the diameter is controlled by the ____ and called ____

Machine Aperture

As the depth of the focus increases = aperture ____ to maintain a relatively consistent beam width at the ____

Increases Focus

Increase f = _____ axial resolution

Improves

Near zone length = ____ (con/divergent) part of beam

Convergent

F increases = ____ wavelength = ____ angle of divergence

Decreases Decreases

narrow aperature = _____ focal distance

shorter

increase aperature = _____ focal distance (depth) + beam width ______

deepens widens

the prime reason for focusing is to improve _____ (_____ beam width)

lateral resolution decrease

different types of focusing (2)

mechanical (external/internal) electronic

internal (mechanical) focusing occurs when a ______ is applied to the crystal itself. We can only focus in the ____

curve near field

external (mechanical) focusing is accomplished with an _____ or ____

acoustic lens mirror

internal focusing is very _____ to do

hard (for the manufactures ex. applying a curve to a 1mm crystal is hard)

downside to external focusing

its a fixed focus

mechanical probes could be categorized into the following focal lengths (3)

short (1-4cm) medium (4-10cm) long (7-19)

electronic focusing is for the _____ transducers

array

electronic focusing is _____ and _____ controlled

variable operator

electronic focusing is more specifically referred to as ______

transmit focusing

if all the elements in an array are excited at the same time then they act as a ___ (____ focus (____ the aperture))

flat single disc natural 1/2

we learned that we can apply a delay to the crystals to steer the probe but the delays can also be used to _____ the probe

focus

the more focus i apply = the more _____ i get in the far field

divergence

when time delays are used to excite a group of elements then the wave fronts ____ toward the _____ region

converge focal

increasing delays = ______ focus

increase (closer)

transmit focus: lat resolutionis improved in the near field and focal point, the _____ in the far field will increase greatly and the ____ will decrease

divergence NZL

how can divergence and decreased NZL in a transmit probe be overcome (2)

dynamic aperture frequency

dual focusing

use of both mechanical and electronic focusing in the probe

the beam is ____ dimensional and there is a need to focus in what we call the _____ or _____

3 Z-axis elevational plane

3 planes of a beam

lateral (width), axial (length), elevational (thickness)

it is possible to have more than one _____ on the image

transmit focus

disadvantage to dual focusing (CHECK ITS NOT MULTIPLE FOCUSING)

elevational focused is fixed

multiple focusing _____ the focal regions of the transducer creating a ____ focus

expands long

multiple focusing requires ____ pulses per scan line with each pulse focused at a different ____

multiple depth

1.5 probes are able to focus the ____ dimension

elvational

in multiple focusing the _____ is reduced but ______ is optimized (only in the ___ dimension at the expense of our ____)

frame rate resolution lateral temporal resolution/frame rate

array transducers can also focus the _____ echo signals

recieved

time delays are applied to the received echoes to all for ____ interference

constructive

receive focus is the official name of the _____ in the beam former

echo delay

does receive focus effect the frame rate

is receive focus operator controlled

receive focus is done ______ as echoes come back from deeper depths (closer to probe require ___ delay, further away require ___ delay)

dynamically more less

the goal of receive focus is the bring the echoes into ___ so they dont ____

phase cancel each other out

receive focus AKA

dynamic receive focus

what is another way to describe the elevational plane

slice thickness

another way to describe the elevational plane

axial resolution is dependent on ___ and lateral resolution depends on ____

SPL beam width

slice thickness (elevational resolution) depends on the _____

beam width perpendicular to the image plane

cystic structures that are smaller than the slice thickness may demonstrate ____ since echoes are picked up from the off center part of the beam as well as the center

false debris

how to differentiate between lateral resolution (beam width) and elevational resolution (depends on)

depends on beam width vs depends on beam width perpednicular to image plane

slice thickness is fixed and requires a _____ or ___ to help reduce the thickness at a fixed depth

curved element lens

the following controls determine the sensitivity of the system and can change the effective beam shape (3)

gain power suppression (reject)