definitions Flashcards
a type of wave that carries energy , not matter from place to place
Sound
the effects of the medium upon the sound wave
acoustic propagation properties
the effects of the sound wave upon the biologic tissues
biological effects
acoustic variables
Pressure, density, distance
concentration of force within an area, Force/area
Units= Pascals (Pa)
Pressure
concentration of mass within a volume
Units= Kg/cm^3
Density
measure of particles in motion
Units=cm, feet, miles
Distance
particles move in a perpendicular direction (right angle) to the direction of the sound wave
Transverse waves
particles move in the same direction as the wave
Longitudinal wave
regions of higher density and pressure
compressions
regions of lower density and pressure
rarefractions
inform us of which waves are sound waves
acoustic variables
describe the features of a particular sound wave
acoustic parameters
the time required to complete a single cycle
can also be described as the time from the start of a cycle to the start of the next cycle
period
number of certain events that occur in a particular time duration
Frequency
waves with frequencies exceeding 20,000Hz (20KHz)
This frequency is so high that the sound is not audible
Ultrasound
infrasound
sound with frequencies less than 20Hz
audible sound
heard by man, frequencies between 20Hz and 20,000Hz
the difference between the average value and the maximum value of an acoustic variable. The variation of an acoustic variable
amplitude
the concentration of energy in a sound beam
the beams power divided by the beam’s cross-sectional area
Intensity
the rate that work is performed, or the rate of energy transfer
power
the length or distance of a single cycle
wavelength
the rate that sound travels through a medium.
Also called velocity and speed
Propagation speed
opposites of stiffness
compressibility and elasticity
same as stiffness
Bulk modulus
a collection of cycles that travel together
a pulse
the time from the start of a pulse to the end of that pulse
the actual time that the pulse is on
Pulse duration
the length or distance that an entire pulse occupies in space
The distance from the start to the end of one pulse
Spatial pulse length
the time from the start of one pulse to the start of the next pulse
It includes one pulse duration and one “listening time”
Pulse repetition period
the number of pulses created by the system in one second
Pulse repetition frequency
the percentage or fraction of time that the system transmits sound
Duty factor
the concentration of the power in a beam
intensity
a logarithmic scale
a relative scale
a comparison, therefore, two intensities are needed to calculate decibels
Decibels
the decrease in intensity, power and amplitude of a sound wave as it travels
This is unrelated to speed
attenuation
the amount of attenuation per centimeter
*a way to report attenuation without dealing with distance
attenuation coefficient
transmission with a bend
a change in direction as sound transmits from one medium to another
refraction
any device that converts one form of energy into another
transducer
when PZT is heated above this temperature (approximately 360C degrees or 680F degrees), it loses its piezoelectric properties, ( the PZT is depolarized)
Curie temperature / Currie point
the complete destruction of all living microorganisms by means of exposure to heat, chemical
sterilization
the application of a chemical agent to reduce or eliminate infectious organisms on an object, such as a transducer
disinfection
the piezoelectric crystal, also called the ceramic, PZT, or crystal
1/2 wavelength thick
Active element
the range of frequencies
bandwidth
a unitless number representing the extent of damping
Quality factor
the location where the beam reaches its minimum diameter
Focus or focal point
the distance from the transducer face to the focus. also called focal length or near zone length
focal depth
the region or zone in between the transducer and the focus
*sound beams converge here
Near zone (Fresnel zone)
the region or zone deeper than the focus, beyond the near field
*sound beams diverge here
Far zone (Fraunhofer zone)
the region surrounding the focus where the beam is “sort of narrow” and the picture is relatively good
Focal zone
V-shaped wave, also called a Huygen’s wavelet
Diffraction
explains the hourglass shape of an imaging transducer’s sound beam
Huygen’s principle
the ability to image accurately
Resolution
the ability to distinguish two structures that are close to each other front to back, parallel to, or along the beams main axis
axial resolution
the minimum distance that two structures are separated by side-to-side or perpendicular to the sound beam that produces two distinct echoes
Lateral resolution
a collection of active elements in a single transducer
array
a single slab of PZT cut into separate pieces called elements
element
combination of electronic circuitry, the wire and the element
channel
a collection or elements in a line
- linear switched (sequential) array
- linear phased array
Linear array
a group of ringed elements (bull’s eye) with a common center
annular array
elements arranged in an arc
- convex switched (sequential) array
- convex phased array
convex, curved, or curvilinear array
adjustable, or multifocus; achieved electronically
Phased arrays
creates electronic patterns. Delays are approximately 10 nanoseconds
beam former
phase delays during reception can be applied to the electrical signals from the transducer to the US system.
This provides focusing at many depths during reception
Dynamic receive focusing
the production of a motion picture
Real time imaging
the ability to accurately locate moving structures at any particular instant in time
Temporal resolution
communicates with all of the individual components of the ultrasound system
organizes and times their functions, so as to operate as a single integrated systems
Master synchronizer
converts electrical into acoustic energy during transmission and acoustic into electrical during reception
transducer
Controls the electrical signals sent to the active elements for sound pulse generation
determines the pulse repetition period, PRF, and pulse amplitude
creates the firing pattern for phased array systems
(called the beam former)
Pulser
the electronics associated with processing the electronic signal production by the transducer during reception and producing a picture on a display device
Reciever
the device associated with the presentation of processed data for interpretation
> > monitor, audio speakers, a paper record
Display
any number of devices and “media” that are used to permanently archive the US data
> > computer memory, hard drive, (NAS, network attached storage)
Storage
increases the strength o f all electronic signals in the receiver prior to further processing
Amplification
used to create image of uniform brigthness from top to bottom
compensation
reducing the total number of signals, from the smallest to the largest
compression
changes the signal’s form to one more suitable for display
demodulation
Displays low level echoes only when they are clinically meaningful. Very low level echoes are not always important.; eliminates Low-level noise in our images
Reject
also called “micro-bubbles”
have different acoustic fingerprint than blood or tissue,
create strong reflections
contrast agents
affects brightness by adjusting the strength of the sound waves sent to the body from the transducer. affects patient exposure
output power
affects the brightness by changing the amplification of the electronic signals after returning to the receiver
Receiver gain
creates ultrasound scans from sound reflections at twice the transmitted frequency
harmonic imaging
the frequency of the transmitted sound wave
fundamental frequency
twice the transmitted frequency also called the second harmonic
harmonic frequency
changes the data format from penetrations (spokes) to horizontal lines of a display . Made gray scale displays possible
Scan converters
a microprocessor digitizes images. This converts the image into numbers which are stored in memory. The numbers can be processed and then retranslated for display as an image
Digital scan converter
the smallest element of a digital picture
pixel
the more pixel per inch, the more detail in the image, spatial or detail resolution
Pixel density
the smallest amount of digital storage
Bit
a group of bits,
a series of zeroes and ones
binary number
a group of 8 bits, 2__________ equal a word
byte
manipulating the data before storage in the scan converter, it carrot be reversed or “undone”
preprocessing
related to the ability of humans to see the gray scale differences in anatomic structures. Lowers the high level echoes and boosts the low level echoes.
log compression
manipulating the data after it has been stored in the scan converter memory but prior to display . increases versatility of the display process.
can be undone
Postprocessing
images can be improved by filling in gaps between lines
is pre-processing
Fill-in interpolation
Scan lines are steered by the transducer in different directions or views, so structures are interrogated by multiple pulses from several different angles
Spatial compounding
a form of electronic receive focusing
dynamic aperture
creates an element of realism to a 3-D or 4-D image
rendering
the ratio of the largest to the smallest signal strength that each component processes, the number of choices indicated the number of gray shades on an image
Dynamic range
Picture Archiving and Communications System
PACS
Digital Imaging and Communications in Medicine
Provides standards or guidelines for imaging networks
DICOM
Network storage devices
high storage capacity disc drives, economical, used in PACS systems
NAS (Network Attached Storage)
the movement of a fluid from one location to another
flow
Fluid moving at a constant speed or velocity
steady flow
blood moves with a variable velocity
pulsatile and phasic flows
flow streamlines are layered, aligned and parallel
plug or parabolic patterns
laminar flow
chaotic flow in many directions and speeds
turbulent flow
a unitless number indicating whether flow is laminar or turbulent
Reynold’s number
Blood flows when the total fluid energy at one location differs from the total fluid energy at another location
energy gradient
Motion energy, associated with an objects speed and mass
Kinetic energy
a form of potential or stored energy that has the ability to perform work
Pressure energy
the conversion of other forms of energy into heat
friction
describes the thickness of a fluid
viscosity
relates to the tendency of a fluid to resist changes in its velocity
inertia
a narrowing or irregularity in a lumen
stenosis
equals the weight of blood pressing on the vessel from heart level to the point of measurement
hydrostatic pressure
a change or variation in the frequency of sound as a result of motion between the sound source and the receiver (a moving interface)
Doppler shift
or
Doppler frequency
extracts the Doppler frequency from the transducer frequency and is preformed by a demodulator.
Demodulation
magnitude only
speed
magnitude and direction
velocity
the Doppler frequency at which aliasing occurs, equal to half the PRF
Nyquist frequency
