Ultrasound Physics Transducers I

Front 1

What is piezoelectric effect?

Back 1

The phenomen by which a mehanical deformation occurs when an electric field (voltage) is applied to a certain material or a varying electrical signal is produced when the crystal structure is mechanically deformed

Front 2

What is a transducer?

Back 2

Any device that converts one form of energy to another

Front 3

Why PZT is the material of choice for ultrasound?

Back 3

Because of its high coupling coeficient: high frequency of natural resonance and very good reproductible characteristics for a stable design

Front 4

What is Curie temperature?

Back 4

300 C, 572 F
If a material is overheated it can loose its poling and piezoelectric efficiency

Front 5

If the frequency doubles, the NZL
a) increases by a factor of 2
b) decreases by a factor of 2
c) increases by a factor of 4
d) decreases by a factor of 4

Back 5

a) increases by a factor of 2

Front 6

What is the relation between operating frequency and the thickness of a crystal?

Back 6

1.A thicker crystal has a slower compression and a lower frecquency
2.A thinner crystal has a higher compression rate and a higher frecquency

Front 7

If he diameter of a tx is increased by a factor of 2, the near zone lenght will:
a) increases by a factor of 2
b) decreases by a factor of 2
c) increases by a factor of 4
d) decreases by a factor of 4

Back 7

c) increases by a factor of 4

Front 8

Which of the following txs will give the shallowest focus?
a) D=2mm, f=2MHz
b) D=1mm, f=2MHz
c) D=2mm, f=10MHz
d) D=1mm, f=10MHz

Back 8

NZL=(D*D*F)/6
corect answer is b

Front 9

What is bandwidth?

Back 9

Bandwidth is described as the useful range of frequencies over which anything can operate

Front 10

What is fractional bandwidth?

Back 10

Fractional bandwidth is determined by dividing the bandwidth by the operating frequency

Front 11

What is a broadband transducer?

Back 11

Transducers are considered broadband
when they have a fractional bandwidth > 80%

Front 12

What is the quality factor ?

Back 12

Q factor is a unitless number
Q-factor=Operating frequency / bandwidth

Front 13

What techniques can be used to improve performance of a multi-Hertz Transducer?

Back 13

1.Dynamic Frequency Tuning
2.Harmonic imaging
3.Frequency Fusion (Compounding)

Front 14

How are the pulse duration and the bandwidth related?

Back 14

Shorter PD = Wider Bandwidth

Front 15

How can you decrease the impulse response?

Back 15

1. Dumping
2. Increasing the frequency

Front 16

What is the relation between axial resolution and the impulse response time?

Back 16

1. short impulse response = fewer cycles in the pulse ; improves axial resolution
2. longer impulse response = many cycles in the response; degrades axial resolution

Front 17

What is the beam shape for continous and pulse waves?

Back 17

For continuous waves, beamshape is consistent (as long as the signal is ON);
For pulse wave, the beamshape vary depending on the time it had been traveling

Front 18

What are the beam parammeters?

Back 18

1. Depth (Axial, Longitudinal, Radial)
2. Beamwidth: Lateral (Azimuthal, side by side, Transverse, Angular)

Front 19

What is elevation?

Back 19

For nonsymetrical crystals, the beamwidth will be different in 2 different planes which creates another dimensional definition: elevation

Front 20

What is the beamwidth for an unfocused transducer?

Back 20

For an unfocused tx. the beamwidth is 1/2 the diameter of the crystal at the focus

Front 21

Unfocused tx. do not have a focus point.

TRUE / FALSE

Back 21

FALSE

Front 22

What is natural focus?

Back 22

The depth where the beam reaches it's narrowest beamwidth

Front 23

For an unfocused tx, what is the approx. beamwidth at the focal ditance and twice the focal distance, given a crystal diameter of 5mm?
a) 5 mm, 10 mm
b) 2.5 mm, 10 mm
c) 5 mm, 5 mm
d) 2.5 mm, 5 mm

Back 23

d)

Front 24

How thick would a crystal have to be for 2 MHz pulsed mode operation given a propagation velocity through the crystal of 5,000 m/sec?

Back 24

fo = c / 2*thickness
thickness = c / 2 *fo = 5,000m/sec / 2*2*10power6 1/sec
thickness = 1.25 mm

Front 25

What is NZL ?

Back 25

1. Near Zone Lenght
2. Distance from tx to the natural focus
3.Fresnel Zone

Front 26

How do we calculate NZL?

Back 26

1. NZL = D*D/ 4λ
most frequently in its modified form
2. NZL = D*D * Fo / 6

Front 27

Which crystalis is better for superficial imaging; a smaller or a larger one?

Back 27

The crystal with smaller diameter

Front 28

If we increase the diameter of a crystal by 2, how much will increase the depth of natural focus (NZL) ?

Back 28

Will increase 4 times

Front 29

Axial resolution is determined by ?

Back 29

Wavelenght

Front 30

Lateral resolution is determined by ?

Back 30

Beamwidth

Front 31

How thick should be a matching layer?

Back 31

A quarter wavelenght

Front 32

What is axial resolution ?

Back 32

Ability to distinguish between 2 structures that are along the same beam path, in axial dimensions

Front 33

What is the relation between SPL and axial resolution ?

Back 33

1.shorter SPL = better axial resolution
2. axial resolution = 1/2 SPL

Front 34

What is SPL?

Back 34

SPL = no. cycles * wavelenght

Front 35

What is lateral resolution ?

Back 35

Ability to resolve 2 structures in the lateral dimension

Front 36

What is backing material ?

Back 36

tunsgsten powder and epoxy resins

Front 37

How can you change the focus ?

Back 37

1. Lenses
2. Curved elements
3. Electronic focusing
4. Mirrors

Front 38

What are the disadvantage of using lenses for changing the focus?

Back 38

1. creates another impedance mismatch between the matching layer and patient
2. decrease efficiency of tx because it is very absorptive
3. cause some surface heating on the tx.

Front 39

What are the disadvantage of using curved surface focusing for changing the focus?

Back 39

1. PZT is very brittle
2. newer materials are flexible composites

Front 40

Near field (Fresnel)

Back 40

the area between the face of tx. and the beam focus

Front 41

Far fiels (Fraunhofer)

Back 41

the region past the focus

Front 42

Focal region
(Depth of field)

Back 42

Region over which the beam is most tightly focused

Front 43

Detail Resolution

Back 43

bility to distinguish between 2 objects in any of 3 dimensions; axial, lateral or elevation

Front 44

Operating frequency
fo

Back 44

The center frequency of the transmit bandwidth

Front 45

fo (pulsed mode)

Back 45

Determined by the crystal thickness and speed of sound in crystal material
fo=c / 2*(thickness)

Front 46

fo (continuous mode)

Back 46

Determined by the frequency of the drive (transmit) voltage

Front 47

The footprint of a tx has 2 dimensions. The beamwidth is associated with .......... dimension and slice thickness is determined by the ................dimension
a) axial, elevation
b)elevation, lateral
c)elevation, axial
d)lateral, elevation

Back 47

d) lateral, elevation

Front 48

Which of the following does not belong?
a) Axial
b)Longitudinal
c) Depth
d) Radial
e) Azimuthal

Back 48

e) Azimuthal resoluion is the same as lateral resolution

Front 49

Which of the following is not the same as lateral resolution?
a) Radial
b)Angular
c) Azimuthal
d) Transverse

Back 49

a) Radial is the same as Range or axial resolution

Front 50

In pulse mode what determines the operating frequency fo ?
Give the equation

Back 50

fo= c / 2 * thickness

Front 51

In continuous mode what determines the operating frequency fo ?

Back 51

fo is determined by the frequency of the transmitter (of the pulser)

Front 52

If the thickness of a crystal doubles, fo for PW mode will:
a) double
b)halves
c)quadruples
d) quarters

Back 52

b) halves
fo= c / 2*thickness

Front 53

A tx is anything which converts .......... from one form to another form

Back 53

energy

Front 54

An ........... tx converts voltage into sound above human hearing and sound into voltage

Back 54

ultrasound

Front 55

An ultrasound tx converts electropontential .............. into .............. and mechanical energy into electropotential energy

Back 55

energy, mechanical energy

Front 56

Ultrasound tx use the...... effect

Back 56

piezoelectric

Front 57

A commonly used material for ultrasound tx is ....... Zirconate Titanate (PZT)

Back 57

Lead

Front 58

If a tx is heated above its ............... temperature will lose its piezoelectric properties.

Back 58

Curie

Front 59

For PZT the Curie temperature is

Back 59

300 degree C
572 defree F

Front 60

When a tx is reffered as mechanical, it means that the ....... is performed mechanical

Back 60

steering

Front 61

A............ is used to help focus a beam in the elevation plane

Back 61

lens

Front 62

The primary purpose of dumping mateerial is to:
1. decrease the no of cycles in the pulse
2. to improuve the axial resolution
3. create broadband tx

Back 62

1. decrease the no of cycles in the pulse

Front 63

HIgher frequency tx will have a deeper natural focus.
TRUE / FALSE

Back 63

TRUE
because they alternate quicklier

Front 64

Lateral resolution is the best
1. in the far field
2. at the focus point
3. in the near field

Back 64

2. at the focus point

Front 65

Regarding beam formation, what occurs in the Fraunhoffer zone?
1. better resolution
2. increased difraction
3. increased attenuation

Back 65

2. increased difraction