U/S Physics (ch. 9, 10, 11)

rule: narrow beams create better images

beam width

as sound travels, the width of the beam changes:

• what size does the beam start out as?

• gets progressively ____ until it reaches its ____ diameter

• lastly, it ____

• same size as tranducer

• narrower; smallest

• diverges

The location where the sound beam reaches its minimum diameter

focus

the distance from the transducer face to the focus. Also called focal length or near zone length.

focal depth

The region or zone in between the transducer and the focus

near zone (fresnel zone)

The region or zone deeper than the focus, beyond the near field. The beam diverges.

far zone (fraunhofer zone)

The region surrounding the focus where the beam is “sort of narrow” and the picture is relatively good. Half of the focal zone is located in the near field and the other half is located in the far field

focal zone

At the transducer the beam diameter is ____ to the transducer diameter

equal

at the focus, the beam diameter is ___ the transducer diameter

1/2

at 2 near zone length, the beam diameter is ___ to the transducer diameter

equal

deeper than 2 near zone, beam diameter is ____ than the transducer diameter

wider

the focal depth is determined by:

1. ______

2. ______

1. transducer diameter

2. frequency

for a deeper focus:

• ___diameter

• ___frequency

large; higher

for a shallower focus:

• ___diameter

• ___frequency

smaller; lower

Describes the spread of the sound beam in the deep far zone

sound beam divergence

sound beam divergence is determined by

1. _____

2. _____

1. transducer diameter

2. frequency

in the far field, beam is _____ (lateral resolution is the ____) with large diameter, high frequency transducers

narrowest; best

In the far field, beam is ____ ( lateral resolution is ____) with small diameter, low frequency transducer

widest; worst

the ability to identify structures perpendicular to sound beam

Lateral resolution

less divergence:

• ____diameter

• ____frequency

large; higher

more divergence:

• ____diameter

• ____frequency

smaller; lower

which crystals produce higher frequency sound produce beams that diverge less in the far field

large diameter crystals

which crystals produce lower frequency sound produce beams that diverge substantially in the far field

smaller diameter crystals

diffraction pattern/spherical wave is ___ shaped, and also called _____

V-shaped; huygen’s wavelet

When produced by a tiny piece of PZT create a ____ pattern

v shaped

The V shaped wave is created when the source is about the size of sound’s ____

wavelength

Sound waves produced by imaging transducers are hourglass shaped

Huygen’s principle

Each tiny part of the surface of the large transducer face may be considered an individual:

sound source

The hourglass shape of a sound beam is the result of ____and ____interference of the many sound wavelets emitted from these numerous sound sources, each of these tiny particles is a ____

constructive; deconstructive; Huygen’s wavelets

The ability to image accurately ( accuracy, not merely quality)

resolution

The ability to distinguish two structures that are closed to each other front to back, parallel to, or along the beams main axis

axial resolution

synonyms for axial resolution

LARRD

• Longitudinal

• axial

• range

• radical

• depth

units of axial resolution and lateral resolution:

mm, cm, units of distance

can axial resolution be changed by a sonographer? what is needed?

no, a new transducer

shorter pulse” Mean a short ____ or a short _____

spatial pulse length; pulse duration

Transducers are designed by the manufacturers to have few cycles per pulse, so that the numerical LARRD resolution is ___and the image accuracy is ____

low; superior

typical values of axial resolution

0.1-1.0 mm

equation for axial resolution (mm) (LARRD) =

SPL (mm) / 2

axial resolution equation for soft tissue =

0.77 x # cycles in pulse / frequency

The spatial pulse length determined by ___and number of ___ in the pulse

wavelength; cycles

In soft tissue, sound with frequency of 2 MHz has a wavelength of ___ mm

0.77

when frequency is increased, axial resolution (LARRD) is ____. This means that we have improved LARRD resolution and higher quality images with ____ frequency transducers

decreased; high

what is the best measure of resolution for modern day ultrasound

axial resolution

The minimum distance that two structures are separated by side-to-side or perpendicular to the sound beam that produces two distinct echoes

lateral resolution

synonyms for lateral resolution

LATA

• lateral

• angular

• transverse

• azimuthal

for lateral resolution, the smaller the number, the more ____ the image is

accurate

lateral resolution is determined by:

width of the sound beam

where is the lateral resolution the best at:

focus or near zone length (focal depth)

pulses of sound at higher frequencies tend to have less ______ in the far field

divergence

do higher or lower frequency pulses have narrower beams

higher

what improves both LARRD and LATA resolution

high frequency

lateral resolution also improves with increasing the:

scan line density

front to back parallel beam =

side to side perpendicular beam =

axial resolution

lateral resolution

axial resolution is determined by:

pulse length

does axial resolution change at specific depths

no

in near and far field, axial resolution is best with ____ pulse

short

lateral resolution:

• smallest diameter crystal is best in:

• largest diameter crystal AND high frequency is best in:

• near field

• far field

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

focusing

three methods of focusing:

1. external

2. internal

3. phased array

Internal, external focusing may be used with _____transducer.(fixed,conventional or mechanical)

single element

Phased array focusing is reserved for array transducers with ______. (electronic focusing)

multiple active elements

external focusing ( fixed, mechanical or conventional) (focusing method)

lens

internal focusing,( fixed, mechanical, conventional) (focusing method)

curved piezoelectric crystal

Fixed internal focusing is done with _____ elements

Curved

A lens or curvature of the crystal can focus a wave produced by ____ PZT crystal. This is conventional, fixed, or mechanical focusing. The focal depth using either of these two methods ____ be changed

single; cannot

adjustable (discussed in “phased array”). Phased array technology provides dynamic, variable focusing or multi-focusing

electronic focusing

what means adjustable or multi focusing

phased array

best describes focal length divided by aperture

focal ratio or F number

single crystal transducers are always:

fixed focus

three basic modes of display:

1. amplitude

2. brightness

3. motion mode

a mode stands for:

b mode stands for:

m mode stands for:

amplitude mode

brightness mode

motion mode

a mode appears as a series of:

upward spike

the mode that provides very precise measurements of distance between the probe and the reflector

a mode

the mode that looks like a big city line

a mode

a-mode

the x-axis represents and is measured by:

the y-axis represents and is measured by:

reflector depth; measured by pulse’s time of flight

amplitude of echo; measured by echo strength

the mode that appears as a line of dots of varying brightnesses

b-mode

the stronger the returning echo is, the ____ the spot

brighter

in b mode, the brightness of the dot is ____ to the strength of the returning echo

proportional

which mode has the “invisible dot”

b mode

b mode

x axis represents and is measured by:

z axis represents and is measured by:

reflector depth; measured by pulse’s time of flight

amplitude of echos; measured by echo strength

the first form of grey scale imaging and is the basis for grey scale imaging

b mode

motion mode is also known as

T - M mode

which mode appears as a group of horizontal wavy lines

m mode

for m mode, the lines represent the motion of the _____ body surfaces as they occur in ____

reflecting; time

m mode is related to ____, NOT to _____

location; not echo amplitude

which mode is the only one that displays the movement of reflectors with respect to time

m mode

m mode

x axis represents:

y axis represents ___ and is measured by:

time

reflector depth; measure by pulse’s time of flight