Chapter 3 Sonography Principles & Instruments I

Transudcer

Any device that converts energy from on form to another

3 construction parts to transucer

1.)Damping, "back layer" 2.) Piezoelectric elements, "crystals" 3.) "face" matching layer

Piezoelectric effect

A property of certain materials to create a voltage when pressure is applied or when the material is mechanically deformed

How do Ultrasound transducers use the piezoelectric effect?

They convert electricity into ultrasound pulses ad the returning u/s pulses from the body back into electricity.

operating frequency is also called

Resonate frequency

What is the most used material in piezoelectricity?

PZT- lead zirconate titanate

What is the Curie point?

the temperature at which a crystal will lose PE properties

Advantages of CMUTS vs PZT?

It has broader bandwidth that improves detail resolution

What is a sequenced array?

A small group of crystals if "fired" simultaneously to produce the ultrasound beam.

What is a phased array(steering)?

the voltages are applied to all the elements but at different times. This allows the bean to be steered.... Pulse goes left, beam goes right

What is a Convex Array?

Curved voltages that produce a sector image.

What is operating frequency?

the natural or preferred frequency of the element

How does thickness effect operating frequency?

Thinner elements operate at higher frequencies.

What determines operating frequency?

Propagation speed and thickness of element

What must fractional bandwidth be, ATLEAST?

At-least 70%

How does focus increase resolution?

it creates a longer pulse, giving us a longer focal region

Greater Curve vs. Lesser Curve

Greater- puts the focus closer to the transducer and Lesser puts it deeper.

What is axial resolution determined by?

the ability to accurately identify reflectors that are arranged parallel to the ultrasound beam

What is lateral resolution?

Ability to distinguish reflectors in the direction perpendicular to beam propagation

What determines axial resolution?

Spatial Pulse Length (SPL)

What is a phased linear array?

A linear array that is sequenced

Disadvantages to electrical focus?

Slow frame rate

What helps give the beam the hourglass shape?

What is variable aperture?

short focal length

uses fewer elements

How ever wide the transducer is =

Width of

Grating Lobes

created by array transducers

How are grating lobes created?

By array transducers

how are grating lobes eliminated?

apadoization

Apodication

reduces the strength of side beams ie: reducing side lobes and grating lobes

apodication sends stronger electronic signals to the elements in what region?

The middle

Vector array

pulses sent in different directions from different starting points

True or False: Transducer face of vector array is flat

True

Dynamic focusing

continuously variable reception focusing that follows the increasing depth of the transmitted pulse as it travels

Dynamic aperture

Aperture that increases with increasing focal length (to maintain constant focal width)

3 types of imaging resolution

detail, contrast and temporal

2 types of detail resolution

axial and lateral

what is the useful frequency range

2-20 MHz

lower frequency=

longer wavelength so it images deeper

higher frequency=

shorter wavelength so shallower imaging

How are pulse length and pulse duration related?

directly

What determines the resonance frequency of an element?

Element thickness & propagation speed

How many pulses do u/s transducers typically generate?

2 to 3 cycles long

What does the matching layer do?

The matching layer is an intermediate layer that functions to reduces the reflections at the skin boundary.

What does the gel do?

Reduces the amount of reflection in the matching layer

Where are the damping layer and matching layer located in relation to the element?

matching is closest to the skin and damping is closer to the sonographer

What relationship is there between PRF & frequency of the transducer?

There is not one

How are the transducer frequency and wavelength related?

directly

How are wavelength and near zone length related?

directly

How are elements shaped in a convex array?

curved

How are elements shaped in a linear array?

rectangle

Narrow bandwidth vs. broad bandwidth

Broad bandwidth has more frequencies to choose from and creates a clear image

Beam Regions

How is ultrasound focused?

with a lens

Which principle explains why a sound bean is hour glass shaped?

Huygen's principle

Synonym for near zone?

Fresnel zone

Synonym for far zone?

Fraunhofer zone

What is lateral resolution equal to?

beam width

What frequency is useful for ultrasound transducers?

2mHz - 20mHz

Difference between Huygen's principles, piezoelectric effect, and ALARA?

H: why sound beams are hourglass shaped. P: abiltiy to take voltage and deform the crystal A: lowest intesity to protect patient

Know the difference between resolutions- Detail, Special(first two go hand in hand), Angular(lateral), and depth(axial)

Detail and Spatial are the regular ones and interchangeable.

How does that transducer frequency influence imaging depth?

lower frequency= deeper image

How much of the beam is reflected back with and without compensation?

c/= dependent on other factors & w/o= 80% of sound beam will be reflected back

How do pulses travel in a curved array?

Come from the same origin and travel in different directions

How do pulses travel in a linear array?

the have different origins but travel parallel in the same direction

What 3 things does phasing do?

focus, steer and improve resolution

Whats the impedance value of a matching layer?

Its a value between the impedance of the skin and the elements

Damping materials in CW vs. PW transducers?

CW has NO DAMPING

Focused vs. unfocused transducers beam profile?

All have a focus, but unfocused transducers are natural whereas focused is man made.

How does intensity change in the beam or does it?

It loses intensity as it travels further from the element

What can 3D ultrasound be used to diagnose?

Heart defects and fetal abnormalities

Match Transducer types with their display formats?

Rectangle

Which location is the deepest?

end of fraunhofer zone

T or F: Transducer frequency beam and divergence are inversely related

True

T or F: Large transducer diameters produce a beam with less divergence

True

T or F: Transducer frequency and near zone length are directly related

True

T or F: Active element diameter and near zone length are directly related

True

T or F: Damping increases efficiency

False

Using a fixed focus transducer, what 2 factors combine to determine focal depth?

Frequency of the sound and transducer diameter

The focal depth is the same as the length of?

Near Zone

What is the size of the sound beam at the beginning near the transducer element?

Same as diameter of the element

Transducers are usually *blank* bandwidth

Wide/broad

A low Q-Factor transducer is used more often that a high Q-Factor transducer

True

A transducer's damping material increases pulse length

False

How is pulse duration related to bandwidth?

inversely

Where is the matching layer located in a transducer assembly?(in relation to the element)

Front

Which convex transducer would you use to image a kidney deep in the body?

3 MHz