1. Principals and Technology of 2D Echo

Question 1

What is intensity?

Answer 1

The level of sound energy in an area of tissue

Question 2

What is rarefaction?

Answer 2

Areas where molecules of a sound wave are dispersed (opposite of compression)

Question 3

Maximum intensity of cardiac ultrasound systems?

Answer 3

720 W/cm^2

Question 4

What are the determinants of the propogation velocity of sound?

Answer 4

Only the medium through which it passes

Question 5

What is the velocity of sound through soft tissue?

Answer 5

1540 m/s

Question 6

Velocity Equation

Answer 6

Velocity = Wavelength (mm) x Frequency (MHz)

In human tissue, velocity is constant = 1540 m/s

Question 7

Acoustic Impedance Equation

Answer 7

Acoustic Impedance = Density x Velocity

Question 8

What is acoustic impedance?

Answer 8

The capacity of a tissue to transmit sound
Higher acoustic impedance = greater ability to transmit sound
(Air = 0.00004; Water = 1.52)

Question 9

What determines the percentage of ultrasound energy reflected from a tissue interface?

Answer 9

The absolute difference in the levels of acoustic impedance between two materials
(When difference is large, more energy is reflected back to the transducer)

Question 10

Reflection Coefficient Equation

Answer 10

RC = (Z2-Z1)^2/(Z2+Z1)^2

Question 11

What is Specular Reflection?

Answer 11

= normal reflection back to probe

Greatest when beam encounters large object with smooth surface

Question 12

What angle of incidence maximizes specular reflection?

Answer 12

90 degrees (or beam perpendicular to surface)

Question 13

What is Scattering Reflection?

Answer 13

Ultrasound energy is scattered in multiple directions when encountering small or irregular shaped surfaces
- Basis of Doppler

Question 14

What is refraction

Answer 14

Ultrasound beam that is not reflected, but propagates through the medium with an altered direction

Question 15

At what angle of incidence is refraction minimized?

Answer 15

90 degrees

Question 16

What are the two types of attenuation?

Answer 16

1) Dispersion: ultrasound beam diverges over a greater area

2) Absorption: frictional forces convert ultrasound energy to heat

Question 17

Components of Transducer

Answer 17

1) Ceramic piezoelectric crystal
2) Electrodes: conduct electric energy
3) Backing: dampens crystal vibrations
4) Insulation: prevent unwanted vibration
5) Faceplate: Optimizes contact between crystal and esophagus

Question 18

What is the near field of ultrasound?

Answer 18

Area of highest beam manipulation and image resolution before area of focus

Question 19

Characteristics of near field

Answer 19

1) Ultrasound beam is narrow
2) Proportional to diameter of transducer face
3) Inversely proportional to wavelength

Length = Diameter^2/4*Wavelength

Question 20

What is the far field of ultrasound?

Answer 20

Distal to the near field zone the ultrasound beam diverges, forming the far field zone

Question 21

Characteristics of far field

Answer 21

1) Angle of divergence inversely related to diameter of transducer face

Question 22

What type of transducer produces the most desirable beam profile?

Answer 22

Large transducers with high-frequency (low wavelength) signals

= A long, narrow field with less divergent far field

Question 23

Definition of Axial Resolution

Answer 23

Ability of the ultrasound to identify two separate objects that lie along the path of the ultrasound beam axis

Improved by high bandwidth pulses (ie high frequency of short duration)

Question 24

Axial Resolution Equation

Answer 24

Axial resolution = 1.5 * Wavelength

Question 25

Definition of Lateral Resolution

Answer 25

Ability of the ultrasound to distinguish between objects that are horizontally aligned perpendicular to the path of the ultrasound beam

Question 26

Lateral Resolution Equation

Answer 26

Lateral Resolution = Depth/50

Question 27

Definition of Elevational Resolution

Answer 27

Ability of the ultrasound to distinguish between objects that are vertically aligned and perpendicular to the ultrasound beam

Question 28

Types of Resolution

Answer 28

1) Axial
2) Lateral (Azimuth)
3) Elevational

Question 29

Gain

Answer 29

Allows amplification of the electrical signal

Question 30

Time Gain Compensation

Answer 30

Selective amplification of structures of varying distance from the transducer

Question 31

Distance Equation

Answer 31

Distance = Velocity * Time

Question 32

Display Formats

Answer 32

1) Amplitude Mode
2) Brightness Mode
3) Motion Mode (M-Mode)

Question 33

Amplitude Mode Display

Answer 33

Amplitudes of the returning signals are represented as a series of horizontal spikes along a vertical axis

Question 34

Brightness Mode Display

Answer 34

Amplitudes of returning echo are represented as pixels of varying brightness. Brightness corresponds with signal strength.

Question 35

Motion Mode (M-Mode)

Answer 35

1) Applies temporal information to B-Mode
2) Frame rate >/= 2,000 frames/sec
3) Most superior display of dynamic motion
* Best mode for examining timing of cardiac events when displayed with ECG
4) Displays only axial motion

Question 36

Pulse Repetition Frequency

Answer 36

Rate at which sound pulses are transmitted per second

1) Greater pulse repetition frequency = greater number of scan lines emitted in a given period of time
2) PRF inversely related to sector depth

Question 37

Frame Rate

Answer 37

Frequency at which a sector is rescanned

Dependent on:

1) Sector depth
2) Sector width