Ultra sound instrumentation Flashcards

Terms Definitions
DF is ____when the system is imaging at shallow depths .
For a simple crystal there are 2 dimensions , they are:
Diameter and crystal thickness
Crystal diameter plays a huge role in determine .....?
Beam width
Crystal thickness plays a role in determine..
The transducers operating frequency.
Causes a decrease in the intensity with increasing distance from the transducer.
Divergence of the beam.
Divergence is responsible for ?
Intensity loss
2 factors combine to determine beam divergence:
Transducer diameter & frequency of the sound.
Crystal diameter and beam divergence are _____related.
Larger crystals improve lateral resolution in the ____field.
Frequency and beam divergence are ______related.
Higher frequency sound improves lateral resolution in the _____field.
The near field is called ____zone.
The far field is called the _____zone.
The lateral resolution deteriorates in the ____field.
The lateral resolution deteriorates in the far field region of the beam because of ____.
The diverging or spreading out of the wave as it propagates.
The more cycles present in and US pulse creates _______of the frequency US emission.
A long pure tone of sound at a single frequency.
Resonant frequency
Resonant frequency is determined by ...?
The transducer fabrication
The range of frequencies in an US beam.
The fewer cycles and US pulse contains the more ______it will contain.
Describes the purity of the vibration of the PZT crystal.
Q factor (quality factor)
Wide bandwidth probes = ____Q factor, and _____ring down.
Low, short
Narrow bandwidth probes = ___Q factor, and _____ring down.
High. Long
______ Q transducers are desirable.
Refers to how closely two reflector or scattering regions can be to one another and still be identified as separate reflectors on an image.
Spatial resolution
Spatial resolution symbol
Spatial resolution units
Sometimes called longitudinal , axial range, or depth resolution.
Axial resolution
LARD refers to......
Longitudinal , axial range , or depth resolution ( axial resolution) .
Axial resolution _____be changed by the sonographer.
Axial resolution depends on 3 characteristics of the US beam....
The SPL, US frequency , and damping factor.
________depends primarily on the length of the U S pulse in space.
Axial resolution
A pulse of US containing 6 complete cycles will result in _____AR than one containing 3 cycles for the same operating frequency.
The best axial resolution possible with an US imaging system is called ....
Limiting axial resolution
In the final analysis the AR is determined by the _____in the pulse _____ and ______.
Number of cycles, damping , & operating frequency.
The ability to image closely spaced interfaces perpendicular to the axis of the US beam.
Lateral resolution.
Lateral resolution symbol
Lateral resolution units
Lateral resolution is also called ____, _______, ________, or ______.
Lateral , angular, transverse, or azimuthal.
LATA refers to
( lateral resolution) lateral , angular, transverse, or azimuthal.
LR is determined mainly by _______.
Beam width
All of the subsystems in the ultrasound machine are controlled by?
A master synchronizer
Range equation( time of flight/ go return time ) round trip
1. The time from pulse creation to pulse reception.
Time of flight is _____related to depth.
Shorter wavelengths = ______ resolution.
Axial resolution
1. The ability to distinguish two objects that are close together as separate.
Piezoelectric effect
1. Generate sound waves and detect echo signals.
Naturally PZT materials
Quartz & tourmaline.
Material most commonly manufactured to exhibit the PZT effect?
Lead zirconate titanite
Quartz and tourmaline's physical constants result in?
Superior efficiency and higher sensitivity
Ceramic elements such as lead zirconate titanite consist of mixtures of.....
Microscopic crystals randomly oriented throughout the volume of the element.
To be useful for transmitting and receiving US waves, these ceramics must first...
Be polarized.
Polarization is done by...
Heating the material above the curie temperature.
What is the curie temperature?
365 degrees Celsius
A high voltage is applied across the element producing partial alignment of the microscopic crystals
Positive molecules toward the negative electrodes ______the crystal.
The critical dimension of the PZT crystal is its ...
To have constructive interference so a single wave moves back and forth between the 2 surfaces , the distance from one surface to the other must equal?
1/2 the wavelength
Thinner crystals have ____resonance frequency .
PZT thickness and frequency are ______related.
The speed of sound in PZT & the frequency of sound are ___related.
The resonance frequency is determined mainly by the ...
Thickness of the PZT element.
Usually plastic designed to accommodate rough handling and yet be easily gripped and manipulated.
The case.
A thin metallic barrier lining the inside of the case preventing electrical signals in the air that are unrelated to diagnostic information from entering the transducer , and also helps to prevent noise.
Electrical shield
Made of rubber or cork preventing the transmission of US energy into the casing .
Acoustic insulator
The heart of the transducer, it is shaped like coin..
The crystal
PZT is _____the wavelength.
Provides an electrical connection between the PZT and the US system.
Positioned in the front of the PZT at the face of the transducer increasing the efficiency of sound energy transfer between the active element and the body. It also protects the active element...
Matching layer
The matching layer is _____wavelength thick
1/4 one quarter
Immediately behind the crystal is _____usually a combination of epoxy resin and tungsten powder, designed to damp the US pulse. It also reduces ringing and enhances axial resolution.
Damping/ backing material
Damping reduces the sensitivity of the transducer because it..
Lowers the intensity of the output signal
Air has a very low acoustic impedence. Any air trapped between the transducer and skin will result in nearly total _____
Diagnostic US uses _____that allows time to listen for returning echoes
The time it takes for a pulse to ocvur. The time the transducer is generating one pulse.
Pulse duration / temporal pulse length
Pulse duration/ temporal pulse length units
Pulse duration/ temporal pulse length is determined by?
The sound source
PD _______ as the number of cycles decrease.
PD _______if the frequency is increased.
The time from the start of one pulse to the start of the next..
Pulse repetition period (PRP)
PRP units
Seconds and milliseconds
PRP = reciprocal of. _____
PRP is determined by _____
The sound source
The PRPbis altered when the ____is adjusted
Number of pulses occurring in one second
Pulse repetition frequency (PRF)
PRF units
Hz &KHz
Shallow depths = ____PRF
Deeper depths = _____PRF
Maximum PRF is used for ____only
Soft tissue
Increased velocity in the medium= _____PRF
Decreased depth of interest = ____PRF
PRF is determined by?
The sound source
The length of this short duration pulse can be estimated and called?
Spatial pulse length(SPL)
SPL units
SPL is determined by?
The source and the medium
SPL _____be changed by the operator
The fraction of time (%) the US unit is transmitting a pulse.
Duty factor
DF units
For CW the DF =
A typical unit with a pulse duration of 1 microsecond and a PRF of 1KHz is transmitting only..
0.1% of the time . 99.9% is spent listening
Is the DF operator adjustable ?
Changing _____also changes the DF
Depth of view
DF is _____related to depth
DF is _____when imaging at deplore depths
Us transducers with ____PZT crystals create sound beams that are shaped like an hour glass
_____sound sources create beams that are V shaped
A large element may be thought f as millions of tiny distinct sound sources, each of the particles is a source and creates a wavelet with a V shape
Huygens principle
Secondary projections of ultrasound energy that radiate away from the main beam
Side lobes
The beam is narrowest & the most intensity is at the focal zone
The electronics of the US system focus the sound beam. With _____you can alter the characteristics of the beam.
Electronic focusing ( phased array)
A lens is placed in front of the PZT focusing this way is similar to focusing light rays with a lens fixed focus
Acoustic lens
Concentrates the sound energy into a narrower beam
Curved crystal
Most common form of fixed focusing
Curved crystal
More curvature= _____focusing
Transforms electrical energy into acoustic energy, during reception converts acoustic energy into electric energy
Creates and controls the electrical signals sent to the transducer . Determines amplitude , PRP and PRF
Pulser ( beam former)
Transforms electrical signals from the transducer into a form suitable for display
Presents processed data, can be CRT or other formats
Archives the US studies . (Videotape , printouts , photographs, CD's and hard drives)
Maintains and organizes the proper timing and interaction of the system componets
Master synchronizer
Ratio of the smallest detectable input signal to the largest input signal that does not exhibit distortion
Units for amplification
The receiver corrects for attenuation with ____. It creates an image that is uniformly bright from top to bottom.
TGC's , depth gain , and swept gain, aka.....
Units for compensation
Alters the gray scale mapping of an US image
2 part process that changes the electrical signals within the receiver into a form more suitable for CRT display . Has no effect on the image
Demodulation_____be changed by the sonographer
Places an envelope around the bumps to even out rough edges.
Allows the sonographer to control whether low level grayscale information within the data will appear on the displayed image
Reject______be changed by the sonographer
Also called smoothing , is a filtering process that is carried out after demodulation.
The signal must be ____to prevent the display from regarding the signal as resulting from several different echoes.
Refer's to the output or power control
Transmit power
It is always best to use ____power / _____gain.
Low, high
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