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59 Cards in this Set

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Intensity Transmission Coefficient
The percentage of intensity that passes in the forward direction when the beam strikes a boundary
Refraction
A change in direction of wave propogation when traveling from one medium to another, transmission with a bend
Snell's Law
A prediction of the amount of refraction that will occur, relates angle of transmission to propogation speed
Time of Flight
The elapsed time from pulse creation to pulse reception
13-Microsecond Rule
For every 13 microseconds of round trip time, the object creating the reflection is 1 cm deeper in soft tissue
Axial Resolution
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
Resolution
The ability to image accurately
Mnemonic for Axial Resolution
LARRD
Longitudinal
Axial
Range
Radial
Depth
Transducer
Any device that converts one form of energy into another
Piezoelectric Effect
The property of certain materials to create a voltage when they are mechanically deformed
Piezoelectric Materials
Materials which convert sound into electricity and vice versa
Commonly Used PZT in US transducers
Lead Zirconate Titanate
Transducer Components (7)
Case, electrical shield, acoustic insulator, PZT or active element, wire, matching layer, backing material
Transducer Case
Protects the internal components of the transducer from damage
Electric Shield
Thin metallic barrier that line case and prevents spurious electrical signals in the air from entering the transducer
Acoustic Insulator
A thin barrier of cork or rubber that prevents vibrations in the case from inducing an electrical voltage in the PZT of the transducer
PZT or Active Element
Piezoelectric crystal itself, shaped like a coin, PZT is one-half wavelength thick
Wire
An electrical connection between PZT and the US system
Matching Layer
In front of the PZT, increases the efficiency of sound energy transfer and protects the active element, ML is 1/4 wavelength thick
Backing Layer (Damping Element)
Bonded to the back of the active element, it reduces the "ringing" of the pulse, enhances axial resolution
Bandwidth
The range or difference between the highest and lowest frequencies in the pulse
Resonant Frequency
A long vibration at a single frequency
Q Factor
The main frequency divided by the bandwidth
Curie Temperature
The temperature at whick PZT is polarized
Continuous Wave Transducers
Frequency of sound emitted by probe is equal to the frequency of the electrical signal
Pulsed Wave Transducers
Frequency of sound created determined by (1) speed of sound in PZT and (2)thickness of PZT
High Frequency Transducers
Thinner PZT crystal
PZT with higher speeds
Thin & fast
Low Frequency Transducers
Thicker PZT crystal
PZT with slower speeds
Thick and slow
Focus
The location where the beam diameter is narrowest, width at focus is 1/2 the width of the beam as it leaves the transducer
Near Zone (Fresnel Zone)
Region from the transducer to the focus (beam narrows)
Focal Length
Distance from the transducer to the focus
Far Zone (Fraunhofer Zone)
Region starting at the focus and extending deeper (beam diverges)
Focal Zone
Region around the focus where the beam is relatively narrow, superior image detail
Huygens' Principle
A large active element may be thought of as millins of tiny, distinct sound sources
Spherical Waves
Sound waves produced by very small pieces of PZT diverge in the shape of a "V"
Lateral Resolution
The ability to distinctly identify two structures that are very close together when the structures are PERPENDICULAR or side by side
Mnemonic for Lateral Resolution
LATA
Lateral
Angular
Transverse
Aximuthal
Three Types of Focusing
External - with a lens
Internal - with a curved active element
Phased Array - with the electronics of the US system
Hemodynamics
Study of blood circulation (flow of blood)
Pulsation
Blood moves through the body due to the pumping action of the heart
Heartbeat
Rythmic contraction of the heart
Heart Rate
# of times heart contracts per minute
Pressure Gradient
Blood flows from high pressure to low pressure
Resistance is affected by
Length of vessel
Viscosity (thickness) of fluid
Radius of vessel
Two Energy Concepts (capacity to do work)
Kinetic - the energy of something in motion
Potential - stored energy or energy at rest
Total Fluid Energy
Kinetic + Potential
Blood Flow Characteristics
Laminar Flow - flow pattern arranged in layers
Parabolic Flow Profile
Bullet shaped pattern in vessel
fastest at center
slowest at vessel wall
Flattened Plug Profile
All layers travel at the same velocity
Arterial Hemodynamics
Pulsation
Heartbeat
Heart rate
Venous Hemodynamics
Pressure Gradient
Calf Muscle Pump
Valves
Respiration
Hydrostatic Pressure
The effect of gravity on veins while standing; measured above or below the heart
Doppler
Used to detect and evaluate blood flow by measuring (1) speed and (2) direction
Types of Doppler (3)
Spectral - waveform
Audio - hear flow
Color - Flow imaging
Doppler Effect
Change in the frequency of sound because of movement of RBCs
Doppler Shift
The difference between the frequencies that are transmitted and received; dependent upon cosine of the angle
Positive Shift
Received frequency is greater than transmitted frequency, RBCs moving toward transducer, seen as doppler shift above baseline
Negative Shift
Received frequency is less than transmitted frequency, RBCs moving away from transducer, seen as doppler shift below baseline
Doppler Equation
Doppler Shift = 2 X speed of blood X transducer frequency X Cosine / Propogation speed