Chapter 3: Imaging Principles and Instrumentation

Question 1

What is the range equation formula?

Answer 1

d = c x t/2      or      d = 0.77t
c = propagation speed = 0.77
t = round trip time in microseconds
d = distance

Question 2

What is the 13 microsecond rule?

Answer 2

It takes 13 microseconds for sound to travel to a depth of 1cm and return to the transducer.

Question 3

Grating lobes

Answer 3

Artifacts caused by extraneous sound that lies outside the primary path. Reduced by apodization, subdicing and tissue harmonics.

Question 4

Apodization

Answer 4

A technique that varies the voltage to the individual elements to reduce grating lobes

Question 5

Beam former

Answer 5

• Controls the timing of the signals sent to the individual elements to shape and steer the beam
• The beam former works to decrease the risk of grating lobes through a process called apodization.

Question 6

Pulser

Answer 6

-Part of the beam former
-Generates the voltage that drives the transducer
-Directly controls the power entering the patient
(Note: increases amplitude, not frequency)

Question 7

Receiver

Answer 7

Processes the return echo coming back from the patient (ACCDR)

Question 8

Amplification

Answer 8

increases or decreases all echoes equally

Question 9

compensation

Answer 9

adjusts brightness of echoes to correct for attenuation with depth

Question 10

Compression

Answer 10

Decreases the range of amplitudes present within the system

Question 11

Demodulation

Answer 11

Makes signal easier for the system to process; includes rectification and smoothing

Question 12

Reject

Answer 12

Eliminates low-level echoes that do not contribute to useful information on the image

Question 13

Master synchronizer

Answer 13

The part of the machine responsible for controlling the timing of the echoes

Question 14

How many shades of gray are possible with 4 bits of memory?

Answer 14

2x2x2x2 = 16

Question 15

pixel vs voxel

Answer 15

picture element (used in 2D) vs volume element (used in 3D)

Question 16

Ring down artifact

Comet tail

Answer 16

• Caused by sound interacting with small air bubbles

- Caused by small structures like surgical clips

Question 17

Mirror image artifact

Answer 17

Occurs when sound is aimed toward a large specular reflector that acts like a mirror and directs some of the sound in a direction other than back to the transducer. (usually near the diaphragm and pleura)

Question 18

Spatial compounding

Answer 18

Eliminates edge shadowing because the object is imaged from different angles.

Question 19

Side lobes

Answer 19

Artifact produced when extraneous sound energy that is not along the main axis reflects back to the transducer.
Side lobes = single element transducers
grating lobes = array transducers