Chap. 5 And 6 Level 1

Question 1

What is a transducer in ultrasound

Answer 1

A device that converts electrical energy into acoustic energy and back to electrical energy

Question 2

What is the piezoelectric effect

Answer 2

An electric field is created by certain crystal materials getting mechanically deformed through vibrations

Question 3

What material is commonly used in ultrasound transducers?

Answer 3

Lead zirconate titanate (PZT)

Question 4

What is poling

Answer 4

Poling is placing the crystal materials into a specialized oven at high temperatures. These high temperatures allow the positive poles to align in one direction and the negative poles the opposite direction

Question 5

What is the curie point

Answer 5

The temperature at which a crystal loses its poling and efficiency as a piezoelectric material

Question 6

What is the curie temperature for PZT

Answer 6

300 degrees Celsius

Question 7

Formula for operating frequency in PW

Answer 7

Fo (mhz) = C(mm/sec)/2 x thickness (mm)

Question 8

The thickness of the crystal determines what?

Answer 8

• A thinner crystal will imply a shorter period (higher frequency)
• A thicker crystal will imply a longer period (lower frequency)

Question 9

What determines the frequency in CW?

Answer 9

• The drive voltage frequency of the pulser
• Fo = drive voltage frequency = transmit signal

Question 10

What is the crystals impulse response

Answer 10

How a crystal responds to a single, short electrical impulse

Question 11

A long vs short crystal impulse response

Answer 11

• Long, many cycles leading to a long spl
• short, few cycles leading to a short spl
• shorter spl, better axial resolution

Question 12

What are the 2 physical dimensions of a transducer

Answer 12

Diameter and thickness

Question 13

What do diameter and thickness determine in terms of a transducer

Answer 13

• diameter determines beam width
• thickness determines operating frequency

Question 14

What is the beam shape view

Answer 14

The region in the patient that the sound wave propagates

Question 15

Attenuation occurs at deeper or shallower depths?

Answer 15

Greater attenuation at Deeper depths

Question 16

What is the shape of an ultrasound beam during CW?

Answer 16

The beam begins at the crystal and gets narrower as it reaches the center then diverges as it increases in depth

Question 17

What is the natural focus

Answer 17

• The depth at which the beam reaches its narrowest beamwidth.
• the center of the beam

Question 18

What is the “focal depth” or “near zone length”

Answer 18

The distance from the surface of the transducer to the natural focus

Question 19

Formula for near zone length

Answer 19

NZL = D^2 x operating frequency/6

Question 20

NZL is proportional and inverse to what?

Answer 20

-NZL is proportional to diameter squared and operating frequency
- NZL is inversely proportional to 4(wavelength)

Question 21

What crystals are good for superficial and deeper focus

Answer 21

• Smaller crystals are good for superficial imaging
• large crystals are good for deep imaging

Question 22

What beams produce better lateral resolution

Answer 22

Narrow beams

Question 23

Formula for axial resolution

Answer 23

Axial resolution = Spl/2

Question 24

Why do we have a matching layer

Answer 24

To minimize the acoustic impedance mismatch between the high impedance of the crystal and the low impedance of tissue

Question 25

What is the matching layer

Answer 25

A thin layer of material attaches to the front of the crystal

Question 26

Why is the matching layer a 1/4 wavelength

Answer 26

It prevents reverberation artifacts from energy ping ponging within the crystal

Question 27

What are the 3 imaging planes

Answer 27

Axial, lateral, and elevation

Question 28

What is lateral resolution

Answer 28

The ability to resolve 2 structures in the lateral dimension

Question 29

How to identify to separate structures side by side

Answer 29

If the beam is narrower, you can identify each structure individually

Question 30

What are the techniques for changing focus of the transducer

Answer 30

1) mirrors 2) lenses 3) curved elements 4) electronic focusing 5) retrospective gating

Question 31

What is elevation resolution

Answer 31

- The elevation resolution is determined by the beamwidth - the elevation resolution is best where the beam is narrowest

Question 32

Define transmit power

Answer 32

The amplitude or gain

Question 33

What is the dynamic range

Answer 33

- Dynamic range is the ratio of the maximum to the minimum amplitude - also known as the ratio of the biggest signal/smallest signal

Question 34

What are the 4 types of dynamic range

Answer 34

- input dynamic range: max/min input signal - output dynamic range: max/min output signal - display dynamic range: max/min display signal - gain dynamic range: max/min applicable gain

Question 35

Difference between receiver gain and transmit power

Answer 35

Both control gain, but transmit power affects the amplitude going into the patient where receiver gain affects the amplitude after it has returned to the receiver

Question 36

Define signal and noise

Answer 36

- Signal: any phenomenon desired to be measured - noise: any unwanted signals

Question 37

Define noise floor and signal-noise-ratio (SNR)

Answer 37

- noise floor: the amplitude level where no signals are visible because of the presence of noise - SNR: the amplitude of the signal/amplitude of noise

Question 38

What are the signals for Doppler and ultrasound

Answer 38

- The reflections from the tissues that are converted into images - signals for spectral Doppler are the Doppler shifts

Question 39

What is the SNR

Answer 39

SNR is what specifies the signal quality. A higher SNR gives better imaging while lower SNR gives poor imaging

Question 40

Give an ex: of a good signal to noise ratio and a bad

Answer 40

- Good: a high amplitude and low noise floor - bad: high amplitude and high noise floor

Question 41

In terms of SNR, what does increasing amplitude do

Answer 41

Increasing amplitude increases both signal and noise evenly. The true SNR may not change. But the apparent SNR could

Question 42

Define clutter

Answer 42

Large returning echoes from structures that obliterate weaker signals

Question 43

Pre processing vs post processing

Answer 43

- pre processing: a real time signal - post processing: imaging that can be changed after captured

Question 44

What can be changed in post processing?

Answer 44

Compression, colorization, and reject

Question 45

What are examples of analog in ultrasound?

Answer 45

Blood flow, EKG’s, pressure waveforms

Question 46

What is the NyQuist criterion

Answer 46

The minimum rate at which you must sample for an accurate reconstruction of an analog signal

Question 47

Equation for NyQuist criterion

Answer 47

NyQuist: F(max) = F (sampling)/2

Question 48

Basic system function

Answer 48

- transducer converts electrical to acoustic and acoustic to electric signals - receiver receives the echo - processor converts echo into images - displays real time image - image is stored and can perform required measurements

Question 49

What are the 5 operations the receiver performs

Answer 49

- amplification - compensation - compression - demodulation - rejection

Question 50

What is the job of the receiver

Answer 50

To receive signals from the transducer and apply the necessary processing before converting the signals into an image

Question 51

Compression in dynamic range

Answer 51

The dynamic range must be compressed in order for the human eye to be able to see it.

Question 52

What is demodulation

Answer 52

The process by which the modulations of the wave are removed or detected (signal detection)

Question 53

What is rectification

Answer 53

Converts the negative components of a signal into positive components (bipolar to unipolar)