Chapter 12, 13, 14

Question 1

To create a 2-D image slice, the
probe sends out multiple scan
lines right next to each other. What issues does this resolve?

Answer 1

The issues that sound travels in a straight line and beams must be narrow to improve lateral resolution.

Question 2

What are characteristics of a mechanical transducer

Answer 2

Single crystal, sector shaped image, mechanical steering and focusing, and a damaged PZT loses the entire image.

Question 3

What does array mean in context of modern transducers?

Answer 3

a transducer with multiple active
elements or crystals

Question 4

How does an array transducer work?

Answer 4

Each active element is connected to its own wire

Question 5

What are characteristics of a linear phased array transducer

Answer 5

100-300 crystals, sector shaped, electronic beam steering and focusing, damaged crystals cannot be predicted.

Question 6

How does electronic steering/focusing work? What causes this?

Answer 6

Crystals do not move or change, the order they fire can be altered which is called phasing. The electronics that allow phasing is the beam former.

Question 7

What is transmit focusing?

Answer 7

When we focus the beam by using electronic means to send out the beam using an array.

Question 8

How do we focus a beam? Is the steepness of the curve directly or inversely related to the focus?

Answer 8

To focus the beam, the crystals are fired in a curved pattern. Steep curves create a shallow focus- they are inversely related.

Question 9

What happens with multiple transmit focal zones? How is this related to frame rate?

Answer 9

Multiple sound beams are sent down each line. More focal zones decreases the frame rate.

Question 10

What is dynamic receive focusing

Answer 10

The beam hits the transducer and the information is processed using the electronic spike lines. The information is virtually focused using delay patterns

Question 11

What are characteristics of annular phased array?

Answer 11

Multiple ring shaped crystals, mechanical steering, electronic focusing, sector shape, horizontal dropout when PZT is damaged.

Question 12

What are characteristics of linear sequential array?

Answer 12

120-250 rectangle crystals, electronic steering and focusing, rectangle image, damaged PZT leads to vertical dropout.

Question 13

What are the differences between linear phased and linear sequential?

Answer 13

Sequential has a larger footprint and crystals. Each crystal is about 1 wavelength width whereas a phased crystal’s width is 1/4-1/2 a wavelength. Sequential is rectangular and linear is sector shaped.

Question 14

What is a linear sequential array?

Answer 14

These transducers fire a sequence of groups of crystals to improve frame rate, axial resolution, and so there is no divergence (good lateral resolution).

Question 15

What are characteristics of a convex sequential array?

Answer 15

120 to 250 large rectangle crystals, electronic beam steering and focusing, blunted sector, vertical drop out if PZT is damaged.

Question 16

What are characteristics of a vector array?

Answer 16

120-250 large rectangle crystals, electronic steering and focusing, trapezoidal shape.

Question 17

Disc shaped crystals are found in mechanical and annular phased array transducers. What kind of beam do these produce?

Answer 17

They produce beams with equal lateral and elevational resolution

Question 18

What is elevational resolution? Where is it measured?

Answer 18

Another word for slice thickness. It is 3 dimensional and It is measured perpendicular to the imaging plane.

Question 19

phased array, linear array, and convex array transducers have rectangular elements. What effect does this have on the beam?

Answer 19

the beam is narrowed side-to-side, not top to bottom. This improves lateral resolution, but does not impact slice thickness.

Question 20

What do 1½ dimensional arrays do?

Answer 20

They decrease the slice thickness by decreasing the thickness of the crystal. They have multiple crystals stacked on one aonther.

Question 21

What is a side lobe?

Answer 21

Side lobes happen when single element transducers create extra lobes off to the side, these degrade lateral resolution.

Question 22

What is a grating lobe?

Answer 22

Grating lobes are essentially side lobes that are created by array transducers and can be fixed by apodization

Question 23

What is apodization?

Answer 23

Apodization alters the electrical spike voltages. Stronger spikes excite the inner crystals and weaker spikes excite the crystals on the
edge of the transducer.

Question 24

What does subdicing mean?

Answer 24

The crystal is divided into a group of
smaller crystals, these are all electrically joined so they act as one crystal.

Question 25

What should you change when your ultrasound imager displays reflectors far from the transducer but no reflectors close to the transducer? What is the purpoe of this button?

Answer 25

Compensation (TGCs). They compensate for attenuation.

Question 26

What is real time imaging

Answer 26

Each frame is created and displayed quickly so that we have an impression of real-time scanning

Question 27

What is a frame rate and what unit do we use to describe it.

Answer 27

the number of frames per second. Measured in Hz or Frames per Second

Question 28

What is frame rate determined by?

Answer 28

It is mostly determined by depth but is also determined by speed of sound in tissue.

Question 29

What is temporal resolution? Is good TR many or few frames/second?

Answer 29

Accuracy in time- how quickly a system can display frames to appear real-time. Good TR is many frames/second

Question 30

What is temporal resolution determined by and what units do we use to measure it?

Answer 30

It is determined by frame rate and measured in Hz or Frames per second.

Question 31

Frame rate and T-frame are inversely related. Why is this?

Answer 31

When a system creates one image in 1/100 of a second, the frame rate is 100 frames per second.

Question 32

What is a T-frame?

Answer 32

The time it takes to display a single frame.

Question 33

How would a sonographer adjust the frame rate?

Answer 33

Changing depth or the number of pulses in each picture

Question 34

How does depth impact frame rate and temporal resolution?

Answer 34

The farther away the beam travels, the more the system must process.

Question 35

What factors affect the number of pulses needed to create an image

Answer 35

Number of focal zones, sector size, and line density

Question 36

What happens when you increase the number of focal zones

Answer 36

More pulses get sent down each scan line. This creates more work for the machine and decreases the frame rate.

Question 37

What are the two main functions of an ultrasound system?

Answer 37

Preparation/Transmission and the Reception of electrical signals.

Question 38

What does a pulser do with transmission?

Answer 38

The pulser creates electrical signals that excite the transducer’s PZT crystal and create sound beams

Question 39

What is SNR

Answer 39

Signal/Noise ratio . It's the ratio of important to non important information.

Question 40

Low pulser output power is best for ALARA principles, when would we want high output power?

Answer 40

I creating output power improves and increases the SNR

Question 41

What does the beam former do

Answer 41

Received the pulser's electrical spike and distributes the voltage to the PZT

Question 42

What affect does bean former have on side lobes?

Answer 42

It reduces them with apodization

Question 43

Is a switch used for transmitting or receiving? Why?

Answer 43

Both. It protects components from the signal and also directs electrical signals

Question 44

What does a receiver do?

Answer 44

After pulses return and strike the PZT, an electrical signal is received. the receiver prepares the information from the received signals.

Question 45

What are the 5 steps of receiving a pulse?

Answer 45

Amplification, compensation, compression, demodulation, and reject

Question 46

What is amplification? Is it adjustable and does it affect SNR?

Answer 46

Each signal is made larger. It is adjustable but does not affect SNR

Question 47

What is compensation? What button is it?

Answer 47

It is the TGC button and it compensates for attenuation

Question 48

What is compression?