NZL

NZL = (D^2 * f) / 6

speed of crystal

c = fo * (2 * thickness)

Operating frequency formula

fo = c/(2*thickness)

thickness formula

thickness = c/(2*fo)

Axial Resolution formula

1/2 SPL

If a transducer diameter is doubled, what happens to the NZL?

If a transducer diameter is doubled, the near zone length will quadruple?

If a transducer diameter is doubled, what happens to the depth of the focus?

If a transducer diameter is doubled, the focus is 4 times as deep.

If the operating frequency is doubled, what happens to the NZL?

If the operating frequency is doubled, the NZL is doubled.

focus beamwidth formula

focus beamwidth = 1/2 transducer diameter

True or False?

The U/S beam is razor thin.

False

beam has
length
width
height (thickness)

Transducer

device that converts energy from one form to another

electric motor

electricity to kinetic

people

chemical to kinetic

light bulb

electricity to light (heat)

Sound transducer

converts electricity to sound & vice versa

Audible transducer

speaker - electricity to sound
microphone - sound to electricty

amber - fossilized plant resin
quartz
rochelle salts
tourmaline

naturally occurring Piezoelectric materials

ceramics - lead zirconate titanante (PZT)
barium titanate
polyvinylidene fluoride (PVDF)

Man-made piezoelectric material

ferroelectric material

piezoelectric material

Piezoelectric principle

applied pressure (echo) comes back to the transducer, converted to electric energy.

Reverse Piezoelectric principle

when a matter is deformed by an applied voltage it produces a pulse.

when you control the electricity going in, you control the strength of the pulse.

What is the most commonly used piezoelectric material in U/S?

ceramics - lead zirconate titanante (PZT)

PZT

Piezoelectric element

ceramic

Piezoelectric element

crystal

Piezoelectric element

element

Piezoelectric element

Creation of Piezoelectric material

Heat to currie point
polling
cool it

polling

placing a material in a very strong electrical field while the material is at a high temperature

curie point

360 degrees

the temperature where piezoelectric materail loses it's piezoelectric properties.

Heat sterilize

Never

element will lose it's piezoelectric properties

when electricity is applied to PZT

vibrates then creates a mechanical longitudinal wave

Increases & decreases in alternating current change the voltage within the crystal

Piezoelectric Effect

One cycle of the operating (drive) voltage creates how many U/S pulses

2 or 3

How many cycles of (drive) voltage is required for Doppler?

5 to 30

Placing a material in a very strong electric field while the material is at a high temperature.

A) poling
B) curie point
C) piezoelectric
D) autoclaving

A) poling

Frequency of the driving voltage

equals the voltage of the sound produce by the transducer

preferred frequency

voltage of the sound produce by the transducer

operating frequency

voltage of the sound produce by the transducer

resonant frequency

voltage of the sound produce by the transducer

natural frequency

voltage of the sound produce by the transducer

What 2 things determine operating frequency

propagation speed of material - 4 to 6 mm/μs

thickness of the transducer - .2 - 1 mm

propagation speed of material

4 to 6 mm/μs

thickness of the transducer

.2 - 1 mm

thickness formula

thickness = .5λ

wavelength formula

λ = c/f

thickness (f)

thickness = .5c/f

Relationship between thickness and frequency

inverse

Relationship between thickness and wavelength

direct

pulses per second

PRF

voltage pulses per second

VRF

relationship between PRF & VRF

PRF = VRF

formula Pd

pd = nt

SPL formula

SPL = nλ

*decrease the number of cycles = decrease SPL

Dampening

material placed behind the element which reduces # of cycles, Pd & SPL

What is dampening material made of

epoxy resin + tungstun
metal powder + plastic or epoxy.

What is the purpose of damping material?

short pulses create better images

damping material stops pulse

*think of grabbing a bell while it rings

dampening and axial resolution

dampening improves axial resolution

dampening and amplitude

dampening reduces amplitude

dampening and sensitivity

dampening decreases sensitivity

dampening and efficiency

dampening decreases efficiency

dampening and SPL

dampening decreases SPL

dampening and Pd

dampening decreases Pd

Which of the following is positive?

A) reduced amplitude
B) decrease # of cycles
C) decrease sensitivity
D) decrease efficiency

B) decrease # of cycles

impedance

propagation speed * density

what is the purpose of gel?

without gel 80% of intensity of a pulse is reflected off the skin

gel eliminates loss from reflection at the surface of the skin

Matching layer

matching layer eliminates loss from reflection at the surface of the transducer

matching layer thickness formula

thickness = .25λ

or

thickness = .25c/f

list impedance from highest to lowest

element > matching layer > gel > skin

impedance of matching layer

halfway between element and skin

ex. if element is 16 rayls a skin is 1 rayl

matching layer is 8 rayls

What determines the matching layer λ?

A) c/f
B) f/c
C) c * f

A) c/f

Matching layer thickness .25λ.

What is f?

A) operating pulse
B) pulse repetition frequency
C) frame frequency

A) operating pulse

Matching layer thickness .25λ.

What is c?

A) soft tissue
B) piezoelectric element
C) matching layer material
D) gel
E) rubber

C) matching layer material

What type of transducers do not need damping?

continuous wave

therapeutic

what is most desirable to get the maximum sound into the tissue?

A) low impedance crystals
B) multiple matching layers
C) little damping

B) multiple matching layers

Bandwidth

range of frequencies the transducer produces

bandwidth determined by

transducer and the machine electronics

relationship between Pd and bandwidth

inverse

bandwidth formula

max frequency - min frequency

middle frequency

center frequency

fractional bandwidth formula

bandwidth/operating frequency

Q factor

operating frequency/bandwidth

relationship between Q factor and bandwidth

inverse

Quality factor

unitless # describing the degree of damping

approximately the # of cycles in a pulse

low Q transducers

imaging transducers

decrease Pd
low SPL
low Q
widebandwidth

How many pulses in Q factor

1-3

when are transducers broadband?

fractional bandwidth is greater than 80%

Broadband transducers are ___________ sensitive.

less

Why are broadband transducers less sensitive

due to damping

The highest frequency is 6 MHz. The lowest frequency is 2 MHz. What is the bandwidth?

A) 2
B) 3
C) 4
D) 6
E) 12

C) 4

6 MHz - 2 MHz = 4 MHz

The highest frequency is 6 MHz. The lowest frequency is 2 MHz. if the center frequency is 4 what is the fractional bandwidth?

A) 1
B) 2
C) 4
D) 8
E) 16

A) 1

bandwidth/operating f

4 MHz / 4 = 1

Advantages of Broad bandwidth

*Multi-Hz transducers can be used
*duplex can use low frequency for Doppler & higher frequencies for B-mode
*dynamic frequency tuning - decreasing frequency with increasing depth
* harmonics can be used if bandwidth includes both frequencies

Types of Resolution

Detail
*axial
*lateral

Contrast

Temporal

Detail resolution

ability to detail fine detail
- the smaller the machine can image the better it is

Axial - depth
lateral - side
section thickness - side

What is detail resolution dependent on?

axial resolution
lateral resolution
matrix size
instrument electronics
display device

Axial resolution

ability to distinguish between two objects that lie next to each other in the depth plane.

Which is frequently better axial or lateral resolution?

axial resolution

What is axial resolution dependent on?

SPL

Synonyms for axial resolution

longitudinal resolution
range resolution
radial resolution
depth resolution

Units of axial resolution

mm

How does SPL improve axial resolution?

shortening the pulse length prevents the echoes from combining as they return to the transducer

How to improve axial resolution?

higher frequency
Decrease SPL by decreasing cycle or wavelength

Lateral resolution

minimum distance that two objects can lie side by side and still be seen as two objects

synonyms for lateral resolution

angular resolution
transverse resolution
azimuthal resolution

What is the prime factor for lateral resolution

beam width

lateral resolution varies with depth.
Where is it best?

at the focus or near zone.

Units of lateral resolution

mm

Symbol for lateral resolution

R L

primary method of reducing beam width

focusing.

How does focusing improve lateral resolution?

by decreasing beam width

Contrast resolution

the ability to see structures with different reflection intensity values as separate items.

Detail resolution is dependent on?

amount of memory
pre & post processing
decibel range
display system
detail resolution

Does urine have low or high impedance mismatch?

Low

Does bone have low or high impedance mismatch

high

SPL a function of

pulse duration
frequency
wavelength

SPW a function of

crystal diameter

Partial thickness artifact

partial volume artifact

(thickness) due to 3D aspect of transducer

Temporal resolution

the ability to accurately located moving structures at any particular instant in time.

resolution pertaining to time

Temporal resolution is dependent in time

Frame rate
depth of penetration
sector size
lines per frame
number of focuses
pulse repetition frequency

SPL

A) The ability to see two items side by side as separate
B) The ability to see two items above and below each other as separate items
C) The ability to see two separate events as separte events

B) The ability to see two items above and below each other as separate items

Huygens Wavelet

Produced by a tiny source
wave diverges into this shape

Huygens Principle

According to Huygens the hourglass shape of a sound beam is the result of constructive and destructive inference of many sound wavelets

Aperture

width of the beam

AKA width of the element

near zone

is the area from the transducer to the focus.

the area of convergence

focus

the smallest part of the beam

1/2 size of element

far zone

the area of divergence

is the area from the focus to the end of the beam.

What shape are sound waves produced by imaging transducers?

hourglass

What is the Fresnel zone?

Near zone

What is the Fraunhofer zone?

far zone

When does the beam stop divergence?

when it reaches its original size

What does width determine?

lateral resolution

What changes top to bottom?

lateral resolution

The width perpendicular to the scan plane determines what?

section thickness artifact.

Formula for axial resolution

1/2 SPL

Grating lobes

Significant intensity that travels out in some direction not included in the beam

What type of transducer causes grating lobes?

Array

What type of transducer causes side lobes

single element transducers

What are some other names for near field?

focal length
focal depth

What happens to the near field when you increase diameter?

increases

What happens to the near field when you increase frequency?

increases

NZL formula

Focal zone length

(f*d^2)/6

f 5 MHz d 5mm? 1 NZL

A) 4 mm
B) 4 cm
C) 125 mm
D) 125 cm
E) 2 mm
F) 2 cm

F) 2 cm

=(5*5^2)/6
=(5*25)/6
=125/6
=20 micrometer
=.02 cm

What is the relationship between near zone length and diameter?

direct

What is the relationship between near zone length and frequency?

direct

For and unfocused beam where are the intensities the highest?

at the focus

For and unfocused beam at any given point, Beam diameter is dependent on what?

frequency
element diameter
depth

When frequency is low beam divergence is __________.

wide

When frequency is high beam divergence is __________.

narrow

When diameter is high beam divergence is __________.

narrow

When diameter is low beam divergence is __________.

wide

Does a smaller frequency gives a shorter or longer near zone?

shorter

variable aperture

increases # of elements fired

What is the relationship between Beam divergence and frequency?

indirect

What is the relationship between Beam divergence and diameter?

indirect

Name the 3 way to focus a transducer

* curve the face
* add a lens
* phase the firing sequence electronically

What type of focusing are the following?

* curve the face
* add a lens

fixed
conventional
mechanical

Focal region

an area on either side of the focal point which is within 25& or 6 dB of SPL

Focused transducers and lateral resolution

worst lateral resolution due to mechanical focusing

what is the value of focusing?

to improve resolution

What improves lateral resolution?

decrease size of focal zone
decrease width of beam

Automatic scanning

method by which transducers rapidly collect information

*creating multiple adjacent scan lines
*rapidly
*repeatedly
*real time scanning - depends on frame rate

What are the two ways rapid motion is accomplished in real time scanning?

Mechanically
* motor unit
* fluid inside

Electronically
* no motor
* no moving parts
* no fluid

Mechanical Motion in fixed focus

mechanical steering has to fo with curvature of PZT

1. linear array
2. sector steered
3. curved linear
4. vector

Electronic scanning sequence

because elements are fixed focus is fixed

all elements fired at once act as one pulse

fires element in sequence until one frame is built.

During electronic scanning phasing
If delay is from left to right pulse angle to the ___________.

right

What does phasing control?

beam direction
focus level

Haygens law

multiple spherical wavelengths create a wave form produce a wave and the wave travels in a direction - orthogonal to the wave form.

where are electronic phased delay patterns produced?

in the beam former

how does phasing control aperture?

some electricity is turned off. This changed the size of the element

How is focus changed with phasing?

by curving the pattern

phasing

When focus is great the focus is ___________.

shallow

Vector

sector with flat top

vector converted from a linear rectangular format into a vector format

Annular array

multiple circular elements with wobble motor sweeps across

What format are annular arrays displayed in?

sector

Annular arrays

Steering is mechanical or electronic?

mechanical

Annular arrays

focus is mechanical or electronic?

electronic

dynamic apodization

changing the amplitude as focusing & steering changes to decrease grating lobe

dynamic focusing

delay correction is changed "on the fly"

transducer sets listening focus, as you cnage the depth

dynamic aperture

using more or less elements to change the diameter of the entire face.