Term
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Definition
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Term
| Average speed in soft tissue |
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Definition
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Term
| Average speed in fatty tissue |
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Definition
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Term
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Definition
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Term
| What is the relationship between speed, wavelength, and frequency? |
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Definition
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Term
| The speed of sound is dependent on the ____________. |
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Definition
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Term
| Speed of sound is a function of the __________ and the ____________ of the propagation medium. What is the formula? |
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Definition
bulk modulus (stiffness or compressibility) and the density.
c = √(Β/ρ) |
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Term
A highly compressible medium like air has a _____ speed of sound.
A less dense medium has a _______ speed of sound. |
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Definition
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Term
| What remains constant as the wave travels through different mediums. |
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Definition
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Term
| Higher frequency US has better/worse resolution. |
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Definition
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Term
| Higher frequency US penetrates deeper/shallower. |
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Definition
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Term
Intensity, I, is defined as
and the units are |
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Definition
power (energy per unit time) per unit area
milliwatts / cm2 |
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Term
| The relative intensity in dB is |
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Definition
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Term
| How many dB does the half value thickness (HVT) correspond to? |
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Definition
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Term
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Definition
| reflection, refraction, scattering, and absorption |
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Term
Acoustic impendance, Z, is defined as
and the units are |
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Definition
Z = ρc (density * speed of sound)
units kg/(m2s), aka the rayl |
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Term
| Intensity Reflection Coefficient is |
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Definition
| RI = Ir/Ii = ((Z2 - Z1)/(Z2 + Z1))2 |
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Term
| The rate of US attenuation is |
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Definition
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Term
| Refraction is governed by Snell's law, which is |
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Definition
| sin θt / sin θi = ct / ci |
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Term
| angle of incidence, reflection, and transmission are measured relative to |
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Definition
| the normal incidence on the boundary |
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Term
| The piezoelectric element is made of |
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Definition
| PZT - lead-zirconate-titanate |
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Term
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Definition
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Term
| The thickness of the transducer element is ___ the wavelength. |
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Definition
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Term
| The thickness of each matching layer is equal to ____ wavelength. |
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Definition
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Term
The "Q" factor describes what?
and the formula for "Q" factor is? |
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Definition
The "Q" factor describes the bandwidth.
Q = f0 / bandwidth |
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Term
| The bandwidth of the transducer is determined by |
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Definition
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Term
| What two effects result from the dampening block? |
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Definition
| It shortens the spacial pulse length (SPL), but it increases the bandwidth. |
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Term
| A high "Q" transducer has _______ |
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Definition
| a narrow bandwidth, but a longer spacial pulse length (SPL). |
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Term
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Definition
| a wider bandwith and a shorter spacial pulse length (SPL) |
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Term
| Two types of transducer arrays |
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Definition
1. Linear arrays
2. Phased arrays |
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Term
| Linear transducer arrays typically have how many elements. |
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Definition
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Term
| Phase-array transducers typically have how many elements? |
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Definition
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Term
| How does a linear array transducer produce a beam? |
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Definition
| By firing a subset of ~20 elements as a group at a time. |
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Term
| How does a phased array produce a beam? |
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Definition
| By activating all the elements nearly simultaneously to produce a single US beam. |
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Term
| The US beam is _________ in the near field and ________ in the far field. |
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Definition
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Term
| The near field is also know as |
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Definition
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Term
| The Far field is known as |
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Definition
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Term
| The near field length is given by |
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Definition
| near field length = r2 / λ |
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Term
| The far field beam divergence is given by |
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Definition
sin Θ = 1.22 * λ / d
d is the effective diameter of the transducer |
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Term
| Axial resolution is given by |
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Definition
| 1/2 the SPL (spatial pulse length) |
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Term
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Definition
| Number of cycles emitted during a pulse by the transmitter multiplied by the wavelength |
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Term
| Axial resolution is _____ with depth. |
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Definition
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Term
| Shorter pulse length results in ______ axial resolution. |
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Definition
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Term
| Two ways to achieve shorter pulse length. |
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Definition
1. Increase damping (fewer cycles)
2. Increase frequency (shorter wavelength) |
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Term
| Lateral resolution is determined by |
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Definition
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Term
| Lateral resolution varies with depth, T/F. |
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Definition
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Term
| Where is lateral resolution the best. |
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Definition
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Term
| Elevation resolution is dependent on |
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Definition
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Term
| The beam former does what |
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Definition
| controls the electronic delays for individual transducer elements to achieve transmit and receive focusing and beam steering. |
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Term
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Definition
| Provides the voltage to excite the PZT element. |
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Term
| The time between transmission pulse and echo detection is given by |
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Definition
T = 2*D / c
D - reflector depth, c - speed of sound (1540 m/s)
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Term
| The number of times the transducer is pulsed per second is known as |
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Definition
| Pulse Repetition Frequency (PRF) |
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Term
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Definition
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Term
| The time between pulses is the |
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Definition
| Pulse Repetion Period (PRP) |
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Term
| Relationship between PRF and PRP |
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Definition
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Term
| Maximal Range is given by |
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Definition
Max range = c * PRP * 1/2
c - speed of sound (1540 m/s), 1/2 - round trip
PRP -Pulse repetition period (s) |
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Term
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Definition
The number of cycles in a pulse divided by the transducer frequency. (Same as # of cycles in a pulse times the period of a transducer cycle) It equals the instantaneous "on" time. Typically a few μs. |
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Term
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Definition
| The fraction of on time. Equals the pulse duration divided by the PRP. Typically 0.2-0.4%. |
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Term
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Definition
| Time gain compensation - adjusts the amplification of returning signals as a function of time to compensate for beam attenuation. Objects farther away will have less signal due to increased attenuation. |
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Term
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Definition
| Stands for Amplitude Mode. Displays echo amplitudes during one pulse-echo period. |
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Term
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Definition
| Stands for Brightness Mode. The echo amplitudes are encoded into brightness modulated dots along the A-line trajectory. |
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Term
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Definition
| Stands for Motion Mode. Uses B-mode information to display echos from moving structures. The B-mode data is repeatedly acquired and dislayed as a function of time with time on the horizontal axis. |
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Term
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Definition
| Creates 2D images from echo information and converts it to be displayed on a video display monitor. |
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Term
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Definition
| A single 2D image is a frame. It is created from N number of A-lines acquired across the FOV (Field of View) |
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Term
What is the time required to obtain a frame?
What is the frame rate?
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Definition
Tframe = (2*D / 1540 (m/s) ) * N
D is the depth, N is the number of A lines.
Frame rate = 1 / Tframe
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Term
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Definition
The spacing between A lines. LD = N / FOV
N - number of lines per frame. |
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Term
| Name 5 interrelated factors that affect forming a 2D US image. |
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Definition
| Number of lines per image (N), frame rate, field of view (FOV), line density (LD), and penetration depth (D) |
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Term
| List 3 ways the frame rate can be increased. |
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Definition
1. decreasing the penetration depth (D)
2. decreasing the number of lines (N) which also reduces the line density (LD) for the same FOV
3. decreasing the field of view (FOV) which also reduces the number of lines (N) for the same line density (LD) |
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Term
| US images are typically how big? |
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Definition
Each image is 512x512 pixels with 8 bits of depth
which requires ~ 1/4 MB of data storage. |
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Term
| Doppler shift is given by |
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Definition
fd = 2·fi·v·cos(θ) / c
fi - incident frequency, v - velocity of blood, θ - doppler angle, c - speed of sound in soft tissue |
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Term
| What is the preferred Doppler angle? |
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Definition
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Term
| What can happen if the Doppler angle is too high, too low? |
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Definition
Too high - small errors in Doppler angle lead to large errors in velocity.
Too small - refraction and critical angle interactions can lead to aliasing in pulsed Doppler |
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Term
| Typical Doppler shift frequency |
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Definition
| 20 Hz to 20 kHz (the audible range) |
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Term
| What is required to do Continuous doppler operation? |
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Definition
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Term
| Advantages of continuous doppler operation |
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Definition
1) high accuracy in the Doppler shift measurement
2) no aliasing when measuring high velocities |
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Term
| Pulsed Doppler US combines what |
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Definition
1) Velocity determination of continuous wave
Doppler
2) Range discrimination of pulse-echo imaging |
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Term
| The maximum Doppler shift that can be determined without aliasing is |
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Definition
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Term
| The maximum blood velocity that can be accurately determined is given by |
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Definition
Vmax = c * PRF / (4 * fo * cos(θ))
This was done by putting PRF/2 in the Doppler shift equation for Δf. |
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Term
Color Flow Imaging:
What color is used for blood moving towards the transducer and away from the transducer? |
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Definition
red - blood moving towards the transducer
blue - blood moving away from the transducer |
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Term
A minimum of ___ samples per cycle of Doppler shift frequency are required to avoid velocity aliasing.
The sample rate is given by: |
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Definition
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Term
Power Doppler is based on _______,
giving better __________,
but sacrificing ___________ |
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Definition
total signal strength of the Doppler signal
sensitivity to motion
directional information |
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Term
| US Contrast Agents contain what and are how big? |
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Definition
Encapsulated microbubbles of air, nitrogen, or perfluorocarbons
3-5 μm in diameter |
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Term
| Harmonic Imaging measures |
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Definition
| Integer multiplies of the center frequency, fo; so 2fo, 3fo, etc. |
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Term
| Harmonic imaging will enhance __________. |
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Definition
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Term
| Measurements of US Image quality includes |
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Definition
spatial resolution
contrast resolution
image uniformity
noise characteristics |
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Term
Axial resolution is determined by _____
Which is a function of |
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Definition
the Spatial Pulse Length (SPL)
frequency (wavelength) and dampening |
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Term
| Lateral and elevational resolution are strongly dependent on |
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Definition
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Term
| What is a refraction artifact and how do you tell? |
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Definition
| An object appearing in different places or not appearing due to refraction (change in pulse direction at a non-perpendicular boundary). The object may appear and disappear with small changes in beam orientation. |
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Term
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Definition
| A hyopintense signal area distal to an object. |
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Term
| What is an enhancement artifact? |
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Definition
| Hyperintense signals from objects distal to areas of very low attenuation. |
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Term
| What is a reverberation artifact? |
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Definition
| Occurs when the signal reflects multiple times from two closely spaced interfaces. The artifact appears as multiple, equally spaced boundaries. |
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Term
| What is a speed displacement artifact. |
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Definition
| Caused by a variability in the speed of sound in different tissues. It causes edge discontinuities in organ borders that are distal to fatty tissue. |
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Term
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Definition
| Multiple beam reflections that cause anatomy to be placed in a more distal location. |
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Term
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Definition
| Seen as a rapidly changing mixture of colors in Doppler mode, typically seen distal to a strong reflector. |
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Term
| Biological effects in US are primarily related to the ____________ |
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Definition
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Term
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Definition
| TI - The ratio of the acoustical power produced by the transducer to the power required to raise tissue in the beam by 1°C. |
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Term
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Definition
| A consequence of the negative pressure (rarefraction) that induce bubble formation from the extraction of dissolved gases in the medium. |
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Term
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Definition
| MI - expresses the likelihood of cavitation |
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Term
| Bioeffects in US have not been shown below an intensity of |
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Definition
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Term
| What are the NCP recommendations for considering a risk-benefit decision when TI exceeds _____ and MI exceeds ____? |
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Definition
When TI exceeds 1 and
MI exceeds 0.5 |
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Term
| What is a linear probe typically used for? Why? |
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Definition
| It uses high frequency, so it is good for structures near the surface like vascular imaging. |
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Term
| What is a curvilinear probe typically used for? |
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Definition
| It uses lower frequency US, so it penetrates more. It's good for intra-abdominal imaging. |
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Term
| What is a phased array probe typically used for? |
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Definition
| It has a smaller footprint, so it is good for viewing structures through small acoustic windows. It is good for chest viewing because it can go between the ribs. |
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Term
US intensity is measured over both _____ and ______.
Measurments can either be _____ or _______. |
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Definition
space and time
peak or average |
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Term
| Spatial average intensity is measured over? |
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Definition
| the area of the transducer |
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Term
| Temporal peak intensity is measured ? |
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Definition
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Term
| Thermal effects are best predicted using the _____ ______ and _____ ______ intensities. |
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Definition
| spatial peak and temporal average |
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Term
| Mechanical bioeffects and cavitation are best indicated by the ____ ____ and _____ _______ intensity. |
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Definition
| spatial peak and pulse average |
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