SPI Exam 4

What is the fundamental definition of a transducer?

Any device that converts one form of energy into another

During transmission, what type of energy conversion takes place

electric to acoustic

what type of energy conversion occurs during the reception phase of a transducer

acoustic to electric

what is the defining characteristic of a piezoelectric effect as described in the material

creating a voltage when they are mechanically deformed

How does the reverse piezoelectric effect function

it causes piezoelectric effect to change shape when a voltage is applied to them

Based of the principles of piezoelectricity, what dual conversion capability do these materials have?

convert sound into electricity and vice versa

what does piezo mean

pressure

If a hammer strikes a quartz crystal, what immediate physical and electrical response occurs inside the crystal

It mechanically deforms and generates a voltage

Piezoelectric materials are also commonly referred to by what alternative method

ferroelectric

Which of the following pairs consists entirely of naturally occurring piezoelectric materials

quartz and tourmaline

What is the primary man-made piezoelectric material commonly utilized in the construction of clinical ultrasound transducers

lead zirconate titantae (PZT)

Why are man made materials like PZT often preferred over natural piezoelectric crystals like quartz in modern clinical transducers

they can be engineered and tailored to have optimized electromechanical properties for specific ultrasound frequencies

In a clinical ultrasound transducer, how do piezoelectric materials convert electrical signals into ultrasound

by expanding their physical dimensions (expanding and contracting) when an alternating voltage is applied

Where is the matching layer located within an ultrasound transducer assembly relative to the PZT

in front of

What is the standard thickness of the matching layer in relation to the wavelength of sound within that layer

¼ wavelength thick

which of the following describes a key function of the matching layer in an ultrasound transducer

increases the efficiency of sound energy transfer

How does the acoustic impedance of the PZT active element generally compare to that of human skin

The impedance of PZT is about 20 times greater than the impedance of skin

What is the benefit of using multiple matching layers instead of just a single matching layer in a transducer design

it further increases the transmission of sound by reducing the acoustic impedance mismatch

what is an example of a coupling medium

gel

what eliminates air between the skin and transducer

coupling medium

Which of the following facilitates the transmission of sound by reducing the acoustic impedance mismatch

coupling medium

Without gel virtually all of a sound wave will be ___ at the tissue/transducer interface!

reflected

what is the unit for impedance

rayl (Z)

What is the number for PZT

1,000,000 Z

what is the number for matching layer

750,000 Z

what is the number for gel

500,000 Z

what is the number for patient

250,000 Z

The greater the difference in impedance, the more sound is going to ___

reflect back

what is another term for backing material

damping material

what is bonded to the back of the active element

backing material

what does backing material reduce

“ringing” (# of cycles in a pulse), dampens the emitted pulse

backing material shortens ___ and ____

duration; SPL

Backing material improves

axial resolution

what is made of epoxy resin impregnated with tungsten

backing material

backing material has a ____ ___ of absorption (sound)

high degree

what is similar to acoustic impedance

PZT

what are the consequences of backing material

decreased sensitivty, wide bandwidth, low q factor

what is less able to convert low level echoes into meaningful electrical signals; effects transmission and reception

decreased sensitivity

Pulse emitted by an imaging probe is a short duration “click” and Contains sound at many different frequencies

wide bandwidth

imaging probes are short pulse, __ ___

wide bandwidth

What is a unitless number related to bandwidth

low q factor

which bandwidth probes have a low q factor

wide

how is q factor related to the pulse length

directly

A shorter pulse has a ___ q factor

lower

what is the formula for q factor

main frequency/bandwidth

how is polarization achieved to create piezoelectric material like PZT

exposing the material to strong electrical field while heated to substantial temps

what is another term for curie temperature

curie point

what is the unit for which temperature PZT is polarized

curie

what also occurs at curie temperature

depolarization

what is the range for curie temperature

300-400 degrees C

can you put probes in an autoclave

no

what is destruction of all microorganisms by exposure to extreme heat, chemical agents, or radiation.

sterilization

application of a chemical to reduce or eliminate infectious organisms

disinfection

what are cleaning techniques for transducers

sterilization and disinfection

what should transducers be disinfected with

cidex or other cold germicides

Frequency of sound emitted by a __ probe is equal to the frequency of the electrical signal

CW

what depends on the characteristics of the active element

pw

what is the formula for frequency

sound speed in PZT/2 x thickness

what is pw determined by

speed of sound in PZT and thickness of the PZT

Increase PZT thickness=

decreased frequency

Increased speed of sound in PZT=

increased frequency

thickness of pzt is

0.2-1mm

thicker active elements =

lower frequencies

If I asked do thicker active elements have longer or shorter pulse lengths, what would you say?

longer

what is designed to enter the body

invasive transducers

what reduces sound transmission path lenth

invasive transducers

what allows for the use of higher frequencies which improve resolution

invasive transducers

how many crystals do modern transducers have that are not necessarily disk shaped

multiple

What is the basic shape of the crystal discussed in the introductory sound beam model?

disk shaped

How does the sound beam change as it travels deeper?

It narrows, reaches its smallest diameter, then widens

What are the four sections or features of the sound beam identified in the slides?

Near zone, focal zone, focal point, far zone

What is another name for the near zone?

Fresnel zone

What is another name for the far zone?

Fraunhofer zone

At what point is the sound beam's diameter narrowest?

focus point

According to the slides, the beam diameter at the focus point is what fraction of the original diameter?

One-half

Which statement best describes the focal zone?

The area where the beam is relatively narrow

How is the focal zone divided between the near and far zones?

Half in the near zone and half in the far zone

At the beginning of the near zone, the beam width is equal to what?

The transducer diameter

What happens to the beam in the far zone?

It diverges and becomes wider

When the beam is two near-zone lengths from the transducer, what is its diameter according to the slides?

The same as its original diameter

A transducer has a diameter of 6 mm. What is the beam diameter at the beginning of the near zone?

6 mm

If the original beam diameter is 6 mm, what is the diameter at the focus?

3 mm

The near zone is 4 cm long. What is the beam diameter at a depth of 8 cm, using the slide example?

6 mm

A focal zone extends from 3 cm to 5 cm. What is its length?

2 cm

If a 2 cm focal zone is divided equally between the near and far zones, how much lies in each?

1 cm each

Which two factors control focal depth with a fixed-focus transducer?

Transducer diameter and frequency

What is the relationship between transducer diameter and focal depth?

Direct

What happens to focal depth when frequency increases, according to the slides?

Focal depth increases

Which formula for focal depth is shown in the slides?

FD = (D² × F) / 61.6

If the question is about focal depth, what type of relationship should you remember from the slides?

Direct relationship

What happens to the sound beam at depths greater than the focus?

It spreads out or diverges

Which two factors determine sound beam divergence?

Transducer diameter and frequency

What effect does a smaller-diameter crystal have on beam divergence?

More divergence

What is the relationship between transducer diameter and beam divergence?

inverse

What happens to beam divergence when frequency decreases?

Divergence increases

Why can higher-frequency sound improve lateral resolution in the far field?

It reduces beam divergence

If the question is about beam divergence, what relationship should you remember from the slides?

Indirect relationship

What are spherical waves associated with in the slides?

Small PZT sources approximately the size of a wavelength

Which set of terms is used for the diverging wave pattern described in the slides?

Spherical waves, diffraction patterns, and Huygens' wavelets

According to Huygens' principle, a large active element can be thought of as what?

Millions of tiny, distinct sound sources