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