Chapters 9-12 Santanna Flashcards by Jessica Johnson

As sound travels

the width of the beam changes

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Narrow beams create

better images

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the location at which the beams= reaches its minimum diameter

focus or focal point

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the distance from the transducer to the focus

focal depth
focal length or near zone length

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near zone (fresnel zone)

the zone between the transducer and the focus

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far zone ( fraunhofer zone)

the zone deeper than the focus, beyond the near zone

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sound beams ____ in the near zone

coverge

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sound beams ___ in the far zone

diverge

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what is focal zone

the region surrounding the focus where the beam is kind of narrow and the picture is relatively good

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PZT diameter

transducer aperture (another name for the transducer diameter)

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at the transducer

beam diameter equals transducer diamter

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at the focus

beam diameter is one-half transducer diameter

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at 2 near zone lengths

beam diameter equals transducer diameter

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deeper than 2 near zone lengths

beam diameter is wider than transducer diameter

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focal depth is determined by

transducer diameter and frequency of the ultrasound

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shallow focus

small diameter, low frequency

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deep focus

large diameter, high frequency

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divergence of the beam describes

the spread of the sound beam in the deep far zone

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less divergence

larger aperture, high frequency, narrower beam in far field, improved lateral resolution in the far field

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more divergence

smaller aperture, low frequency, wider beam in far field, degraded lateral resolution in far field

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frequency (CW) is determined by

electronic frequency

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frequency (pulsed) is determined by

thickness in ceramic and speed of sound in ceramic

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divergence

aperture of active element and frequency of sound

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each tiny part of the surface of the transducer face may be considered

an individual sound source, this creates a huygens wavelet

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when all of these wavelets combine, they create an hourglass shaped beam

huygens principle

axial resolution

the ability to distinguish two structures that are close to each other front to back, parallel to, or along the beam's main axis

units of axial resolution can it be changed by sonographer

distance, mm, cm no

changing axial resolution means

changing transducers

SPL (mm) / 2

equation for axial resolution

Shorter pulses mean

shorter SPL and PD... meaning images are more accurate

axial resolution is BEST with

highest frequency and fewest number of cycles per pulse

axial resolution is WORST with

lower frequency and larger number of cycles per pulse

If we add more pulses, we

degrade our images

Better axial resolution

shorter SPL shorter PD higher frequencies fewer cycles per pulse lower numerical values

minimum distance that two structures are separated by side to side or perpendicular to the sound beam that will produce two distinct echoes

lateral resolution

units for lateral resolution

lateral resolution =

beams diameter

lateral resolution varies with

depth also known as beam width variation or point spread artifact

lateral resolution is best at

focus or one near zone length from transducer bc this is where the beam is narrowest

lateral resolution is ____ as axial resolution because sound waves are wider than they are short

not as usually good as

In the far field, higher frequency pulsed sound has _____ beams

narrower

higher frequency sound improves both axial and lateral resolution where?

in the far field only

higher frequency improves

image detail

LARRD

Longitudal Axial Range Radial Depth

LATA

Lateral Angular Transverse Azimuthal

Focusing concentrates the sound energy into a ________ beam and thus ______ the lateral resolution

narrower and improves

What are the three methods of focusing are

external focusing - using a lens internal focusing - using a curved active element phased array focusing- using the electronics of the ultrasound system

Fixed focus transducers have

poor lateral resolution bc the depth cannot be adjusted

Single crystal transducers

are always fixed focus

what is the only display mode that provides info regarding reflector motion with respect to time?

M-mode

with A- mode, what is displayed on the x-axis?

depth of the reflector

with m-mode, what is displayed on the y-axis?

depth of the reflector

which mode provides the foundation for real-time, gray scale anatomic imaging?

b-mode

with a-mode, what is displayed on the y-axis?

amplitude of the reflected signal

in m-mode, what is displayed on the x-axis?

time

with b-mode, which axis is related to the strength of the reflection?

the z-axis is related to reflection strength

a-mode

x-axis y-axis z-axis depth amplitude none

m-mode

x-axis y-axis z-axis time depth none

b-mode

x-axis y-axis z-axis depth none amplitude

ultrasound travels in a ______ line

straight

what is dynamic aperture

technique used to make the sound beam narrow over a greater range of depths which optimizes lateral resolution

The focus created by a _____ diameter element is shallow

small

the focus created by a _____ diameter element is

deep

apodization

the process of reducing the strength of the side and grating lobes

In apodization, ____ signals excite the inner crystals and the _____ electrical signals excite the outer crystals.

stronger and weaker This diminishes side lobes

Mechanical Scanning

contain one disc shaped element (like a coin)

array

a collection of active elements in a single transducer

element

a single slab of pzt cut into separate pieces called elements

channel

combination of electronic circuitry, the wire, and the element

linear array

a group of ringed elements (target bulls eye) with a common center

curvilinear array

elements arranged in an arc 2 types: curvilinear switched sequential array and curvilinear phased array

with a mechanical transducer

the PZT crystal is physically moved to create an image

Linear Array Transducers

active elements are arranged in a straight line

Annular Array Transducers

elements are arranged as a circular rings with a common center

Convex Array Transducers

active elements are arranged in a bowed or arched line. The transducer may be called curved or curvilinear

Electrical Patterns

electronic slope creates a beam steering, and an electronic curvature creates beam transmit focusing

slope

steering

curvature

transmit focusing

3D is more accurately at ?

measuring volumes of structures such as cysts

1 1/2 D arrays contain more elements side to side than up and down. This allows what?

focusing in the plane of the image, make thinner slices and improves elevational resolution

disc shaped crystals make

thinnest slices and have the best elevational resolution within the focal zone

the circle width in one direction is the ?

beam diameter (determines lateral resolution)

the height of the circle

beam thickness (determines elevational resolution)

at all depths the beam is much _____ than it is wide.

thicker