Exam 2 Flashcards
what is a channel made up of?
Single PZT element in the transducer, the electronics in the beam former/pulser, and the wire that connects them
what are tissue harmonics?
As a sound wave travels in the body, a miniscule amount of energy is converted from the fundamental frequency to the harmonic frequency during transmission.
The strength of the harmonic waves _____ as the sound travels in the tissue
grows
where are tissue harmonics created?
are created in the tissue during transmission
-deeper in the tissue
-nonlinear behavior
-along the beam’s main axis
tissue harmonics are _____ present as sound leaves the transducer
NOT
What is apodization?
is the process of reducing the strength of the side and grating lobes
-alters the electrical spike voltages and reduces lobe strength
Axial resolution definition (3)
It measures the ability of a system to display two separate structures that are very close together when they are parallel to the sound beam’s main axis.
-NOT adjustable
-determined by spatial pulse length (sound source and medium)
Name the 4 other names for Axial Resolution
Longitudinal
Range
Radial resolution
Depth resolution
what are the 3 other names for Lateral resolution?
Angular
Transverse
Azimuthal Resolution
-improve with higher frequencies (diverge less due to narrow beam)
how to improve axial resolution?
shorter pulses that are associated with higher frequency sounds
which transducer would have the WORST axial resolution? MHz & Cycles/pulse given
lowest frequency
most ringing (more cycles/pulse)
long pulse
which transducer would have the BEST axial resolution? (5)
1) Shorter Spatial pulse length
2) Shorter pulse duration
3) Higher frequencies (shorter wavelength)
4) Fewer cycles per pulse (less ringing)
5) lower numerical values
In soft tissue, a 3 cycle, 1 MHz pulse has a pulse length equal to 4.5mm. What is the axial resolution?
a) 3 mm
b) 1 mm
c) 2.25 mm
d) 1.54 mm
c) 2.25
Axial resolution is one-half of the spatial pulse length (4.5mm /2 = 2.25mm)
what can you calculate as the axial resolution when given the number of cycles, MHz, and pulse?
Spatial pulse length (mm) /2
Wavelength x # cycles/pulse/ 2
Soft tissue= 0.77 # cycles/frequency
what are grating lobes?
-Are similar to side lobes; however, they are created by array transducers.
-These extra, off-axis sound beams are undesirable because they degrade lateral resolution, reduce image quality, and create artifacts.
what is stronger than the grading lobes?
the beam’s main axis
What are the essentials for the proper operation of a linear phased array? (7)
1) Footprint of array is small and uses 100 to 300 elements
2) Fan or sector-shaped
3) 2D image built with electronic steering called phasing
4) Beam focusing electronically
5) Phased array always means adjustable or multi-focus
6) Focusing may also occur during reception
7) Dynamic receive focusing is performed automatically by the ultrasound system and is NOT controlled by sonographer
which types of resolution improve frame rate?
Temporal resolution
-imaging depth
-number of pulses in each picture
Temporal resolution
pertains to the “accuracy in time” describes the ability to precisely position moving structures from instant to instant.
Imaging depth and frame rate are _________ related
inversely
Pulses per frame and frame rate are _____ realted
inversely related
Higher frame rate must consist of 4 things:
1) shallower imaging
2) single focus
3) narrow sector
4) low line density
what is A-mode?
(3)
appears as a series of upward spikes
-The height of the upward deflection is proportional to the amplitude of the returning echo
-Is accurate in determining the depth of reflectors
Strong echoes create ___ spikes
Weak echoes create ___ spikes
tall
short
what is B-mode?
appears as a line of dots of varying brightness that indicate the strength of the reflection
-Basis for all types of gray scale
-also called B scan
B mode
weak reflections appear as
strong reflections appear as
darker gray dots
brighter white dots
what is an M scan ?
appears as a group of horizontal wavy lines
-provides information about a reflector’s changing location with respect to time.
-A line that moves up and down on the display indicates that a reflector is moving closer to or farther away from the transducer.
M scan
a straight line indicates a ___
used primarily to assess ____
stationary reflector
the motion of cardiac walls and structures
Mode X-axis Y-axis Z-axis
A
B
M
A: depth (X) , amplitude (Y)
B: depth (X), Amplitude (Z)
M: time (X) , depth (Y)
What receives a single electrical spike from a pulser that distributes to numerous active elements?
Beam former
Receiver definition
transforms the electrical signals from the transducer. (produced by the reflected sound) into a form suitable for display.
Switch definition
-important during both transmission and reception
-Protects the delicate receiver from powerful signals
-Directs the electrical signals from the transducer to the appropriate electronic and processing components.
Beam former definition
-determines the firing delay patterns for phased array systems.
-sophisticated electronic device that receives the pulser’s single electrical spike and distributes it to the numerous active elements of the transducer.
Beam former operations (3)
1) Sets the correct time delays
2) controls dynamic aperture
3) Digital beam form use microprocessor to produce signals in a digital format
Which out of the 5 types of operations for the sound being received back, can NOT be adjusted by the sonographer?
Demodulation is NOT adjustable
what are the 5 operations of the receiver?
Amplification
Compensation
Compression
Demodulation
Rejection
Demodulation definition
Is a two part process that changes the electrical signals within the receiver into a form more suitable for display on a monitor.
-Rectification
-Smoothing
what are the 2 primary mechanical tissue biologic effects?
Thermal mechanism
-tissue temperature elevation
Nonthermal mechanism (mechanical mechanisms)
-cavitation (gas bubbles in tissue)
-radiation force (distortion of structures)
Static Scanning definition
process of displaying images one frame at a time
“photo”
Real-time imaging definition
all modern ultrasounds are capable of creating each frame and displaying them very quickly providing the impression of constant motion
“movie”
M mode scan definition
a line that moves up and down on the display indicates that a reflector is moving closer to or farther away from the transducer
-provide’s info about a reflector’s changing location with respect to time
-the sampling rate of M-mode is very high and equal to the pulse repetition frequency of the system
How is B mode ultrasound incorporated with the other mode scanning methods?
is the first form of gray scale imaging
-is the basis for all types of gray scale anatomic imaging including real-time imaging
Aliasing
is the most common error associated with doppler ultrasound
-the false identity in pulse doppler is that very high velocities in one direction are incorrectly displayed as going in the opposite direction.
-at the bottom of the spectrum
How is external focusing done with the transducer?
a lens is placed in front of the piezoelectric (PZT) material. As the arc of the lens becomes more prominent, the degree of focusing increases and the beam narrows in the focal zone.
Internal focusing definition
A curved piezoelectric crystal concentrates the sound energy into a narrower or tighter beam
-as the curvature of the PZT becomes more pronounced, the degree of focusing increases
-most common form of fixed focusing
-NO lens needed
Method : Lens
Name
Type
Transducer Type
external
fixed, conventional or mechanical
single element transducer
Method: Curved Active Element
Name
Type
Transducer type
internal
Fixed, conventional, or mechanical
Single element tranducer
Method: Electronic
Name
Type
Transducer Type
Phased array
Adjustable
Array transducers-those with multiple active elements
AIUM (American Institute of Ultrasound in Medicine)
…
The strength of the A mode is reluctant to the height deflection of what?
is proportional to the amplitude of the returning echo
-Strong echoes: tall spikes
-Weak echoes: short spikes
is accurate in determining the depth of relfectors
which mode is correlated to the height of deflection?
A mode
The ability of imaging to detect weak reflections is called what?
Sensitivity…
the height of a vertical spike on an A mode display corresponds to the strength of what?
Y-axis: represents strength or amplitude of the reflected signal
-proportional to the amplitude of the returning echo
Demodulation is the process of what?
The fourth function of the receiver that changes the electrical signals to make them suitable for display on a monitor.
-NOT adjustable
-No effect on image
which of the 5 different processes that occur when sound is returned to the receiver is NOT adjustable by the sonographer?
Demodulation
Pulser definition
creates and controls the electrical signals sent to the transducer that generate sound pulses.
-Determines the amplitude, pulse repetition period, and pulse repetition frequency.
Transducer definition
transmitting signal is changed electrical energy into acoustic energy.
Receiving signal is changed from acoustic energy into electrical energy.
Signal processor
…
Image processor
…
Display definition
presented processed data.
Maybe a flat screen monitor, a transparency, a spectral plot or a variety of other formats.
Preprocessing definition
manipulation of image data BEFORE storage in the scan converter
Post processing
manipulation of image data AFTER storage in the scan converter
Preprocessing 6 characteristics
Time gain compensation
Write magnification
Persistence
Spatial compounding
Edge enhancement
Fill-in interpolation
Post processing 4 characteristics
Black/white inversion
Read magnification
Contrast variation
3-D rendering
Analog signals “numbers” definition
are REAL world numbers
-signals from the transducer are changed to digital form and stored in computer memory
-A-D converter used
Digital signals
computer world (10011101)
only whole #
signals are converted back into analog form for display on a standard television screen
-D-A converter used
Pixel interpolation definition
image interpolation occurs when you resize or distort your image from one pixel grid to another.
-image resizing is necessary when you need to increase or decrease the total number of pixels.
Pixel density
the number of picture elements per inch
low density: few larger pixels in less detailed picture
higher density: more smaller pixels in a more detailed image
what does RAM stand for?
Random-access memory
what are the functions performed by the receiver?
1) Amplification
2) Compensation
3) Compression
4) Demodulation
5) Reject
What are the two parts of demodulation?
Rectification
Smoothing
Rectification definition
converts all negative voltages into positive voltages. It corrects for, or eliminates, negative voltages.
-changes the form of the electrical signal by eliminating
- the up and down wave is changed to just the top part above baseline
-NOT adjustable
-NO visual effect on image
Smoothing definition
(or enveloping) places a smooth line around the “bumps” and evens them out.
Compensation definition
second function of a receiver
Corrects for attenuation
creates an image that is uniformly bright from top to bottom
-Adjustable
-Time-gain comp (TGC)
-Depth gain comp (DGC)
-Swept gain…
what is attenuation?
sound waves weaken as they propagate in a medium
-decrease in intensity, power, amplitude of a sound wave
-measured in decibels
-determined by path length and frequency
Distance and attenuation are _____ related
Frequency and attenuation are ____ related
Directly
Pixel
the smallest building block of a digital picture
-at any instant in time, the entire pixel is a single shade of gray
Pixels characteristics (3)
Image element
Image detail
Spatial resolution
Bistable definition
images that are composed of only 2 shades
-Black
-White
Bits definition
smallest amount of computer memory
-has a value of 0 or 1
A group of __ bits of computer memory is called ___
A word consists of ___ bytes of ___ bits
A large number of ___ increases contrast resolution
8 bits is called byte
2 bytes of 16 bits
bits
Bits 3 characteristics
Computer memory
Gray shades
Contrast resolution
what are the units of Power?
-rate of energy transfer of the rate at which work is performed
-determined by: sound source only
-Adjustable
-Watts
what part performs the function of demodulation?
the receiver
Compensation definition
corrects for attenuation, makes the picture bright from the top of the bottom
-decibels
-treats echoes differently, depending upon the depth from which they arise
Compression definition
(6)
keeps the electrical signal levels within the accuracy range of the system’s electronics
-keeps image’s grayscale content within range of detection by the human eye
-Adjustable
-Decibels
-called log compression or dynamic range
-performed twice
Rejection definition
allows the sonographer to control whether low-level grayscale info within the data will appear on the display image.
Amplification definition
(5)
amplifies also called Receiver gain
-each signal undergoes an equal amount of amplification
-does NOT improve signal to noise ratio, both are amplified equally
-Adjustable
-Decibels
Master synchronizer definition
maintains and organizes the proper timing and interaction of the system’s components
Pulser transmitter
the pulser creates electrical signals that excite the transducer’s PZT crystals and create sound beams.
The pulser functions during transmission.
Transducer output
sonographer can adjust the magnitude of the pulser’s electrical voltage spike, which ranges from near 0 to approximately 100 volts.
Interpolator
is a method of constructing new simulated data points to fill in the gaps. The goal of fill-in interpolation is to fill in the gaps of missing data in a way that cannot be detected by the observer
