SPI Flashcards
Bioeffects
Effect of US waves on living organisms, including their composition, function, growth, origin, development, and distribution
Acoustic exposure
The amount of acoustic energy the patient receives
ALARA
As low as reasonably achievable. Used to reduce bio effects in humans and the fetus
Cavitation
Interaction of the sound wave with microscopic has bubbles found in tissues
Epidemiology
Studies of various factors determining the frequency and distribution of diseases in the human community
Ergonomic
Study of the human body at work.
In vitro
Outside living organism
In vivo
In or on living tissue (animal testing)
Mechanical Index (MI)
Describes the likelihood of cavitation occurring
OSHA
An act passed by congress to assure safe and healthful working conditions
Pulse Average (PA)
Average intensity throughout the pulse duration.
For continuous wave, pulse average is equal to temporal peak
Spatial Average (SA)
Average intensity across entire sound beam.
Equal to total power across the beam/ beam area
Spatial Peak (SP)
Peak intensity found across the sound beam
Center
Temporal Average (TA)
Average intensity during pulse repetition period.
Equal to (PA)x duty factor
Temporal Peak (TP)
Greatest intensity during the pulse.
Thermal index (TI)
Relates to the heating of tissue.
FDA regulates
Ultrasound instruments according to the application, output intensities, and thermal and mechanical indexes
AIUM recommends
Prudent use of Ultrasound in the clinical environment by minimizing exposure time and output power
ALARA principle uses
High receiver gain and low output power
Power should be decreased in OB and Pediatric exams
Exposure should be kept to a minimum and benefits must outweigh risks.
Intensity
Power/area
W/cm^2
Varies across sound beam
Intensity is highest
In the center of the sound beam and falls off near the periphery.
Intensity starts
High and decreases near the end of the pulse.
Intensity with pulsed wave Doppler
Is greater than with continuous wave Doppler.
SATA
Spatial Average-Temporal Average
Lowest intensity for a given sound beam
Heat is most dependent to this intensity
Measured during both pulse and receiving time (prp)
SPTA
Spatial Peak-Temporal Average
Used to describe pulse Ultrasound intensities and determine bio effects
Measured during PRP
SAPA
Spatial Average- Pulse Average
Measured during pulse duration
SPPA
Spatial Peak- Pulse Average
Measured during pulse duration
Intensity that occurs during pulse
SATP
Spatial Average- Temporal Peak
Used to describe pulse Ultrasound intensities
The average intensity within the beam at the highest intensity in time
SPTP
Spatial Peak - Temporal Peak
Highest intensity value for a given sound beam
Peak intensity of sound beam in both time and space
Instrument Output
Imaging instruments have lowest output intensity
PW Doppler has highest output intensity
Determined by a hydrophone
Stable cavitation
Involves microbubbles already present in tissue
When pressure is applied microbubbles will expand and collapse
Bubbles can intercept and absorb a large amount of acoustic energy
Transient cavitation
Dependent of the pressure of the ultrasound pulse
May occur with short pulses
Bubbles expand and collapse violently
Aliasing
A misrepresentation of the Doppler shift in a negative direction occurring when the pulse repetition frequency is set too low
Exceeds nyquist limit
Bernoulli effect
Pressure reduction in a region of high flow speed
Bruit
Auscultatory sound within an artery produced by turbulent blood flow.
Clutter
Noise in the Doppler signal caused by high-amplitude Doppler shifts.
Doppler effect
Observed frequency change of the reflected sound resulting from movement relative to the sound source or observer.
Doppler shift
Frequency shift created between the transmitted frequency and received frequency by an interface moving with velocity at an angle to the sound.
Energy gradient
Energy difference between two points.
Flow
To move in a stream, continually changing position and direction.
Gate
Electronic device controlling the transmission or reception of a Doppler signal; size of the gate is determined by the beam diameter, receiver gate length, and length of the ultrasound pulse.
Hemodynamics
Science or physical principles concerned with the study of blood circulation.
Hue color map
The perceived color; any one or a combination of primary colors.
Hydrostatic pressure
The pressure created in a fluid system, such as the circulatory system.
The hydrostatic pressure is zero in supine
When upright the pressure is negative above the heart and positive below the heart.
Nyquist limit
The highest frequency in a sampled signal represented unambiguously; equal to one half the pulse repetition frequency
Doppler packet
Positioning of multiple pulsed Doppler gates over the area of interest.
Peak velocity
Maximum velocity at any given time
Plug flow
Speed is constant across the vessel
Pressure gradient
Difference in pressure required for flow to occur.
Pulsatility index
A parameter used to convey the pulsatility of a time-varying waveform.
Reynolds number
Predicts the onset of turbulent flow
Resistant index
Difference between the maximum and minimum Doppler frequency shifts divided by the maximum Doppler frequency shift.
Sample volume
Electronic device that controls the region of Doppler flow detection.
Saturation color map
Degree to which the original color is diluted with white; the paler the color (or less saturated it is) the faster the flow velocity; the purer the color, the slower the flow velocity.
Spectral broadening
Increase in the range of Doppler shift frequencies displayed resulting in a loss of the spectral window; usually seen with stenosis.
Stroke volume
Amount of blood moving in a forward direction; blood being ejected.
Variance mode
The average velocity is calculated, with the colors placed side by side
Velocity
Rate of motion with respect to time.
Velocity mode
All measured velocities for each gate are averaged, then the colors are arranged up and down.
Volume flow rate
The quantity of blood moving through the vessel per unit of time.
Blood flows from
Higher pressure to lower pressure
Types of blood flow
Low-resistive
High-resistive
Low resistive flow
Slow upstroke in systole and large amount of diastolic flow
ICA
High resistive flow
Sharp upstroke in systole
Very little diastolic flow
ECA
Laminar flow
Flow where layers of fluid slide over each other
Max flow velocity located in center of the artery
Min flow velocity located near arterial wall
Found in smaller arteries
Parabolic flow
Type of laminar flow
Average flow velocity is equal to 1/2 the max flow speed at center
Plug flow
Constant velocity across the vessel
Found in large arteries (aorta)
Pulsatile flow
Steady flow with acceleration and deceleration over the cardiac cycle.
Includes added forward flow and or flow reversal throughout cardiac system
Turbulent flow
Chaotic flow
Characterized by eddies and multiple flow velocities
Onset predicted by a Reynolds number greater than 2000
Caused by a curve in a vessel’s course or decrease in vessel diameter
Venous flow
Little resistance to flow
Low-pressure, non pulsatile flow
Lowest when patient is laying flat
Phasic flow
Flow variation during respiration
Inspiration
Increases abdominal pressure,
Decreases venous flow from lower extremities, decreases thoracic pressure, increases flow from upper extremities
Expiration
Increases thoracic pressure, decreases venous flow to upper extremities, decreases abdominal pressure, increases venous flow to lower extremities
Doppler Shift
The change in frequency caused by motion. Difference between the emitted frequency and the echo frequency returning from moving scatters.
Doppler shift is proportional to
The flow speed and source frequency
Doppler shift is dependent on
Doppler angle
Cosine values are
Inversely related to Doppler angle
Doppler shift equation
Doppler shift= 2 x frequency x velocity x cosine Doppler angle / propagation speed
Doppler effect
Units- Hz
Result from motion of blood
Observed frequency or wavelength change of the reflected sound is a result of reflector movement relative to the source or observer
Doppler effect is used to
Determine flow velocity and direction of moving reflectors
Doppler shift occurs in
Audible range
Rayleigh scattering results from?
RBC’s being smaller than the wavelength of the sound beam
There is no doppler shift if
The received and transmitted frequencies are the same
Positive Doppler shift
Occurs when the received frequency is greater than the transmitted frequency
Negative Doppler shift
Occurs when the received frequency is is lower than the transmitted frequency
Doppler shift is inversely related to
The angle and source of reflector
What may directly affect the intensity of the Doppler shift?
Concentration of red blood cells
Doppler shift is directly related to
Operating frequency
What may be necessary to achieve Doppler shifts at deeper depths?
A lower frequency transducer
Continuous Wave Doppler
2 crystals- on transmitting, one receiving
Displays only waveforms
Large sample volume in region where transmitting and receiving sound beams converge
Sound is transmitted 100% of the time
Advantages of Continuous Wave Doppler
Ability to measure high velocities (no aliasing)
Use high frequencies
Sensitive to low flow velocities
Small probe size
Simplest form of Doppler
Disadvantages of Continuous Wave Doppler
Lack of imaging ability
Interrogates all vessels in the sampling area (range ambiguity)
Pulse Wave Doppler
Single crystal to transmit and receive Doppler info
Displays image of the vessel and Doppler info
Sample volume (gate) is placed within a specific vessel
Minimum of 5 cycles per pulse and up to 30 cycles per pulse
Advantages of Pulse Wave Doppler
Operator- adjusted placement of the sample volume (range resolution)
Allows smaller sample volume
Duplex imaging capabilities
Disadvantages of Pulse Wave Doppler
Maximum detectable Doppler shift determined by aliasing
Duplex imaging
Combination of 2-D gray scale and Doppler information
Electronic scanning permits switching between imaging and doppler functions several times per seconds, giving the impression of simultaneous imaging
Imaging frame rates are decreased to allow for interlaced acquisition of Doppler info.
Advantage of Duplex Image
Ability to place sample volume in a specific vessel
Disadvantage of Duplex Imaging
Decrease in gray-scale imaging frame rate
Spectral analysis
Allows visualization of the Doppler signal
Provides quantitative data used for evaluating the Doppler shift
High and low impedance conditions downstream give rise to different spectral displays
Spectral analysis axis
Vertical- frequency shift (velocity)
Horizontal- time
Spectral analysis uses
Fast Fourier Transform to convert Doppler shift information into a visual spectral analysis
Fast Fourier Transform
Breaks down the complex signals of the Doppler shift into individual frequencies
Advantages of Spectral Analysis
Allows measurement of peak, mean, and minimum flow velocities, flow direction and characteristics of blood flow
Presents Doppler shift frequencies in frequency order
Disadvantage of Spectral Analysis
Cannot accurately measure high velocities without aliasing
Color Flow Doppler
Presents 2-D color coded info of motion imposed over a gray scale image
Displays color coded flow velocity and direction
Color maps
Velocity and Variance modes
Doppler packets
*
Color info is obtained in?
Packets
Positioning of multiple sample gates over the area of interest
Increasing the length of the color box does what?
Decreases frame rate
Changing the Doppler angle in an image does what?
Produces various colors in different locations
Autocorrelation is necessary for?
Rapid obtainment of Doppler shift frequencies
Advantages of Color Flow Doppler
Detect flow quickly
Aids in distinguishing low flow velocities
Determines blood flow direction
Non vascular motion (urethral jets)
Increasing Doppler packet size will do what?
Increase sensitivity and accuracy
Decrease temporal resolution and frame rate
Disadvantages of Color Flow Doppler
Displays mean velocity
Over-gaining of gray scale image decreases color sensitivity
Less accurate that spectral analysis
Color Flow Doppler and aliasing
Occurs at lower velocities compared to pulse and continuous wave Doppler.
Power Doppler
Real time image of the amplitude of the signal.
Displays 2-D color image representing blood flow imposed over a gray scale image
Advantages of Color Doppler
Increases sensitivity to Doppler shifts in slow low flow within deep vessels
Insensitive to Doppler angle effects and aliasing
Better wall definition
Disadvantages of Power Doppler
Does not demonstrate flow direction, speed, or character information.
Doppler artifacts
Aliasing
Flash
Mirror imaging
Range ambiguity
Causes of Aliasing
Doppler shift exceeds one half PRF
Undersampling of the Doppler shift
What does aliasing look like?
Improper representation of the information sampled
Wrap around of the pulse wave or color Doppler display
Incorrect flow direction
How to fix aliasing
Increase PRF (scale) Increase Doppler angle Adjust baseline to zero Decrease operating frequency Decrease depth of the sample volume Change to continuous wave
Flash artifact
Sudden burst of Color Doppler extending beyond the region of blood flow.
Flash artifact is caused by
Tissue or transducer motion
How to fix flash artifact
Increase PRF
Decrease color gain
Increase filtering of low flow velocities
Mirror imaging artifact
Duplication of a vessel or Doppler shift in the opposite side of a strong reflector
What causes mirror artifact
Doppler gain too high
How to fix mirror imaging
Decrease color gain
Use a different acoustic window
Range ambiguity
Doppler shift received are not all from the same vessel
What causes range ambiguity?
Improper placement of the sample volume
How to fix range ambiguity
Readjust placement of a sample volume
Pulsatility index
Most sensitive ratio
Used to convey the pulsatility of a time varying waveform
Equal to peak systole - end diastole / mean velocity
ABD and OB imaging
Resistive index (Pourcelot index)
Index of pulsatility and opposition to flow
