Ch 7 Beam Former

Question 1

Differentiate principle 1 vs principle 2?

Answer 1

Principle 1:
-pulse echo technique
-phasing to focus

Principle 2:
-no more focus
-fewer pulses required

Question 2

List the 4 pulse echo instruments in order?

Answer 2

-Beam former
-Signal processor
-Image processor
-Display

Question 3

What is the beam former?

Answer 3

-Where the action originates
-Consists of 7 things (pulser, pulse delays, T/R switch, amplifiers, ADC, echo delays + summer)

Question 4

List functions of the beam former?

Answer 4

-Generates voltages
-Determines PRF, coding, frequency + intensity
-Amplifying echo voltages
-Compensates for attenuation using TGCs
-Digitizing the echo voltage stream
-Directing, focusing + apodizing the u/s beam on transmission + reception

Question 5

What does the pulser do?

Answer 5

-Generates the voltages that drive the probe
-Generates the production of a pulse
-Determines the PRF

Question 6

Sequencing + phasing operations of array probes are carried out by what 2 things?

Answer 6

The pulser + pulse delays

Question 7

What adjusts PRF?

Answer 7

The pulser - based on imaging depth

Question 8

Why is PRF automatically reduced?

Answer 8

To provide proper display of returning echoes, which avoids range ambiguity artifacts

Question 9

What are range ambiguity artifacts?

Answer 9

It places structures much closer to the surface than they should be

Question 10

What is output power?

Answer 10

-Aka transducer driving, transmit power, drive voltage
-Displayed as a % or in dBs relative to max output
-The greater voltage amplitude produced by the pulser, the stronger the signal that gets transmitted through the pt
-Creates increased penetration + higher amplitude of returning signals

Question 11

Is it assumed that for each pulse all echoes are received before the next pulse is sent out?

Answer 11

Yes! Although, echoes from deep structures created by a 1st pulse will arrive at the probe AFTER the 2nd pulse has been sent out

Question 12

How is output power related to bioeffects?

Answer 12

Can lead to heating of tissue for sustained time

Question 13

List 3 tasks that the pulser + pulse delays carry out?

Answer 13

-Sequencing
-Phasing
-Variations in pulse amplitudes (apodization)

Question 14

What is a channel?

Answer 14

-An independent signal path consisting of a probe element, delay + possibly other electronic components
-There are 64, 128 or 192 channels
- # of channels never exceeds the # of elements in the probe

Question 15

An increased # of channels allows for what?

Answer 15

More precise control of beam characteristics

(specifically sequencing + phasing of crystals)

Question 16

Explain the transmit/receive switch?

Answer 16

During transmission:
-T/R switch opens path from the pulser to the probe elements

During reception:
-T/R switch opens path from elements to the reception amplifiers

(the switch protects the sensitive input components of the amplifiers from the large driving voltages from the pulser)

Question 17

Define amplification?

Answer 17

To increase the amplitude of the returning signals

Question 18

What are our amplifiers?

Answer 18

Our gain + TGC controls

(these make our returning echoes brighter)

Question 19

The beam former has how many amplifiers for each channel?

Answer 19

1

Question 20

What are radio frequency signals?

Answer 20

-Sound energy that is converted back into electrical energy
-Low level RF signal is the returning electrical signal
-The returning RF signals are weak + need to be amplified with gains

Question 21

Explain time gain compensation (TGC’s)?

Answer 21

-Aka depth gain compensation
-Compensates for the effect of attenuation on an image (m/c about 60 dB of attenuation)
-Allows for compensation of signals that traveled a greater path length

Question 22

Can later echoes be amplified to the same level of brightness as the earlier echoes?

Answer 22

Yes

Question 23

What does lateral gain control do?

Answer 23

Adjusts gains laterally across image

(applied in cardiac scanning to help see ventricular walls)

Question 24

What are analog-to-digital converters (ADC)?

Answer 24

They convert the analog voltages representing echoes to numbers for digital signal processing + storage

Question 25

From the ADC, the digitized echo voltages pass through what?

Answer 25

Through echo delays + a summer

Question 26

Reception apodization + dynamic aperture functions are accomplished as part of what?

Answer 26

The summer