Us Vocabulary 2

Front 1

Intensity Transmission Coefficient

Back 1

The percentage of intensity that passes in the forward direction when the beam strikes a boundary

Front 2

Refraction

Back 2

A change in direction of wave propogation when traveling from one medium to another, transmission with a bend

Front 3

Snell's Law

Back 3

A prediction of the amount of refraction that will occur, relates angle of transmission to propogation speed

Front 4

Time of Flight

Back 4

The elapsed time from pulse creation to pulse reception

Front 5

13-Microsecond Rule

Back 5

For every 13 microseconds of round trip time, the object creating the reflection is 1 cm deeper in soft tissue

Front 6

Axial Resolution

Back 6

The ability of a system to display two structures that are very close together when the structures are PARALLEL to the sound beam's main axis

Front 7

Resolution

Back 7

The ability to image accurately

Front 8

Mnemonic for Axial Resolution

Back 8

LARRD
Longitudinal
Axial
Range
Radial
Depth

Front 9

Transducer

Back 9

Any device that converts one form of energy into another

Front 10

Piezoelectric Effect

Back 10

The property of certain materials to create a voltage when they are mechanically deformed

Front 11

Piezoelectric Materials

Back 11

Materials which convert sound into electricity and vice versa

Front 12

Commonly Used PZT in US transducers

Back 12

Lead Zirconate Titanate

Front 13

Transducer Components (7)

Back 13

Case, electrical shield, acoustic insulator, PZT or active element, wire, matching layer, backing material

Front 14

Transducer Case

Back 14

Protects the internal components of the transducer from damage

Front 15

Electric Shield

Back 15

Thin metallic barrier that line case and prevents spurious electrical signals in the air from entering the transducer

Front 16

Acoustic Insulator

Back 16

A thin barrier of cork or rubber that prevents vibrations in the case from inducing an electrical voltage in the PZT of the transducer

Front 17

PZT or Active Element

Back 17

Piezoelectric crystal itself, shaped like a coin, PZT is one-half wavelength thick

Front 18

Wire

Back 18

An electrical connection between PZT and the US system

Front 19

Matching Layer

Back 19

In front of the PZT, increases the efficiency of sound energy transfer and protects the active element, ML is 1/4 wavelength thick

Front 20

Backing Layer (Damping Element)

Back 20

Bonded to the back of the active element, it reduces the "ringing" of the pulse, enhances axial resolution

Front 21

Bandwidth

Back 21

The range or difference between the highest and lowest frequencies in the pulse

Front 22

Resonant Frequency

Back 22

A long vibration at a single frequency

Front 23

Q Factor

Back 23

The main frequency divided by the bandwidth

Front 24

Curie Temperature

Back 24

The temperature at whick PZT is polarized

Front 25

Continuous Wave Transducers

Back 25

Frequency of sound emitted by probe is equal to the frequency of the electrical signal

Front 26

Pulsed Wave Transducers

Back 26

Frequency of sound created determined by (1) speed of sound in PZT and (2)thickness of PZT

Front 27

High Frequency Transducers

Back 27

Thinner PZT crystal
PZT with higher speeds
Thin & fast

Front 28

Low Frequency Transducers

Back 28

Thicker PZT crystal
PZT with slower speeds
Thick and slow

Front 29

Focus

Back 29

The location where the beam diameter is narrowest, width at focus is 1/2 the width of the beam as it leaves the transducer

Front 30

Near Zone (Fresnel Zone)

Back 30

Region from the transducer to the focus (beam narrows)

Front 31

Focal Length

Back 31

Distance from the transducer to the focus

Front 32

Far Zone (Fraunhofer Zone)

Back 32

Region starting at the focus and extending deeper (beam diverges)

Front 33

Focal Zone

Back 33

Region around the focus where the beam is relatively narrow, superior image detail

Front 34

Huygens' Principle

Back 34

A large active element may be thought of as millins of tiny, distinct sound sources

Front 35

Spherical Waves

Back 35

Sound waves produced by very small pieces of PZT diverge in the shape of a "V"

Front 36

Lateral Resolution

Back 36

The ability to distinctly identify two structures that are very close together when the structures are PERPENDICULAR or side by side

Front 37

Mnemonic for Lateral Resolution

Back 37

LATA
Lateral
Angular
Transverse
Aximuthal

Front 38

Three Types of Focusing

Back 38

External - with a lens
Internal - with a curved active element
Phased Array - with the electronics of the US system

Front 39

Hemodynamics

Back 39

Study of blood circulation (flow of blood)

Front 40

Pulsation

Back 40

Blood moves through the body due to the pumping action of the heart

Front 41

Heartbeat

Back 41

Rythmic contraction of the heart

Front 42

Heart Rate

Back 42

# of times heart contracts per minute

Front 43

Pressure Gradient

Back 43

Blood flows from high pressure to low pressure

Front 44

Resistance is affected by

Back 44

Length of vessel
Viscosity (thickness) of fluid
Radius of vessel

Front 45

Two Energy Concepts (capacity to do work)

Back 45

Kinetic - the energy of something in motion
Potential - stored energy or energy at rest

Front 46

Total Fluid Energy

Back 46

Kinetic + Potential

Front 47

Blood Flow Characteristics

Back 47

Laminar Flow - flow pattern arranged in layers

Front 48

Parabolic Flow Profile

Back 48

Bullet shaped pattern in vessel
fastest at center
slowest at vessel wall

Front 49

Flattened Plug Profile

Back 49

All layers travel at the same velocity

Front 50

Arterial Hemodynamics

Back 50

Pulsation
Heartbeat
Heart rate

Front 51

Venous Hemodynamics

Back 51

Pressure Gradient
Calf Muscle Pump
Valves
Respiration

Front 52

Hydrostatic Pressure

Back 52

The effect of gravity on veins while standing; measured above or below the heart

Front 53

Doppler

Back 53

Used to detect and evaluate blood flow by measuring (1) speed and (2) direction

Front 54

Types of Doppler (3)

Back 54

Spectral - waveform
Audio - hear flow
Color - Flow imaging

Front 55

Doppler Effect

Back 55

Change in the frequency of sound because of movement of RBCs

Front 56

Doppler Shift

Back 56

The difference between the frequencies that are transmitted and received; dependent upon cosine of the angle

Front 57

Positive Shift

Back 57

Received frequency is greater than transmitted frequency, RBCs moving toward transducer, seen as doppler shift above baseline

Front 58

Negative Shift

Back 58

Received frequency is less than transmitted frequency, RBCs moving away from transducer, seen as doppler shift below baseline

Front 59

Doppler Equation

Back 59

Doppler Shift = 2 X speed of blood X transducer frequency X Cosine / Propogation speed