Breast Ultrasound Physics Flashcards
Breast ultrasound systems require_____________ and ____________ for improved visualization
Spatial resolution
Contrast resolution
The linear array transducer contains ___________ ______________
Piezoelectric crystals
How does the linear array transducer activate piezoelectric crystals? What shape is the beam?
Crystals are activated in groups and sequenced to produce parallel scan lines to create a uniform image from near to far fields.
A rectangular image is created
Name 6 benefits of linear array transducer style for breast ultrasound
⏺Rectangular shape allows skin contact and even compression
⏺Beam is more perpendicular to the skin and chest wall
⏺Wide beam for near field structures
⏺Uniform image field
⏺Less beam divergence
⏺Narrow focusing improve needle visualization
Why is high frequency needed for breast imaging
To better visualize superficial structures of the breast
Key advantage of high frequency transducers
Improved axial resolution
Axial resolution
Ability to differentiate 2 closely spaced each interfaces lying in the direction of the sound beam (think of beam as an axis)
Most breast ultrasound systems use _______ MHz or higher
10
Disadvantage of using high frequency transducers
Reduced penetration due to rapid attenuation of the beam
A ___________ ___________ transducer produces a sound beam with more than 1 frequency
Pulsed-wave
Bandwidth and pulse length are _________ proportional
Inversely
Frequency and resolution are ________ related
Directly
Advantages of broad bandwidth transducers
Transducer can operate at different frequencies to optimize resolution and penetration
Can perform Doppler at a lower frequency when needed
Allows harmonic imaging with lower frequencies and reception of sound beam at higher frequency
The ultrasound beam of a transducer is ___ dimensional
3
A narrower sound beam improves
Resolution
A narrow sound beam intensifies sound energy at the
Focus
________ resolution is best where the sound beam is narrowest
Lateral resolution
Lateral resolution
The ability to resolve 2 closely spaced objects lying side-by-side in a direction perpendicular to the sound beam
6 Transducer features suitable for high resolution breast imaging
Linear array format High frequency Broad bandwidth Variable electronic focusing Near-field focusing Thin slice thickness
Variable electronic focusing
Focusing that occurs along the long axis of a linear array transducer
Focusing can be altered at various distances by altering or delaying the timing of excitation of the transducer elements
Multiple transmit foci create a narrow receive beam
Lateral resolution is improved
Fixed elevation focusing
Focusing along the short axis of the transducer
Fixed focal depth at 1.5cm
Corresponds to slice thickness
A shallow elevation focus of a linear array transducer with high frequency improves _________ and reduces ____________
Near-field resolution
Slice thickness
High-frequency, broad bandwidth transducers provide excellent _______________ and ______________
Spatial and contrast resolution
What is another word for spatial resolution. What is the definition?
Detail.
The ultrasound system’s ability to depict small anatomic structures at their correct location
___________ ___________is measured in 3 planes. What are they?
Spatial resolution
Axial plane
Lateral plane
Elevation plane
Define the 3 planes
Axial - along the direction of the sound beam (parallel to beam)
Lateral - perpendicular to the sound beam
Elevation - perpendicular to sound mean, also corresponds to slice thickness
Spatial resolution is affected by which transducer characteristics?
Frequency
Focusing
Scan lines
Axial resolution improves with ___________, ___________, __________
High frequency transducers Shorter pulse lengths
Broader bandwidth transducers
Contrast resolution
The ability of the ultrasound equipment to distinguish anatomic structures based on variations in echo brightness.
Factors that affect contrast resolution
Acoustic imprudence mismatch Transducer frequency Dynamic range Signal-to-noise ratio Artifacts
Example of what happens when a system has poor contrast resolution
2 closely spaced objects may appear as one
Temporal resolution
The ability of a system to distinguish moving objects (not affected I breast ultrasound because of limited depth of field)
_________ resolution is limited by the frame rate
Temporal
Equipment parameters that need to be optimized for a breast US exam
Output power Overall gain Time Gain Compensation (TGC) Dynamic range Focal zone placement Frame rate Image scale Monitor brightness and contrast
Brightness is affected by
Output power
Overall gain
TGC
Dynamic range
Output power affects the ______
of the transmit voltage and the intensity of the __________ __________.
Amplitude
Transmitted beam
The output power controls the excitation voltage that drives the _________ ____________
Transducer crystals
How output power affects the quality of US exam
⬆️Output power➡️ ⬆️Voltage to crystals➡️ ⬆️Oscillation of crystals➡️ ⬆️Amplitude/intensity of sound beam➡️ ⬆️Ultrasound energy to patient
A higher intensity sound beam produces a _______ ________ ___ _______ _________
Signal to noise ratio
The _______ ________ control provides uniform amplification of all echo signals returning to the transducer
Overall gain
Why is overall gain important?
Since returning echo signals are weakened due to attenuation, the returning signals need to be electronically amplified
Overall gain is the same as ______ _______
Receiver gain
⬆️overall/receiver gain ➡️
⬆️_________ and vice versa
Brightness
Gain and dynamic range settings should be set so that fat displays a _____ ________ ________ shade
Medium level gray
Excessive settings of the gain and dynamic range will introduce ______ _______ of breast tissues and cysts
False echoes
How would too low a setting of overall gain and dynamic range affect the appearance of solid masses
They would reduce the detection of real echoes with solid masses, making them appear cystic
The ________ control allows selective amp location of weaker signal from deep structures to compensate for attenuation loss
TGC (Time Gain Compensation)
TGC control makes the image more
Uniform
TGC should be adjusted so that echoes from similar structures are displayed with the same ________ or ________
Brightness
Amplitude
Dynamic range definition:
The ratio of the smallest to the largest strength level that a system can handle without distortion.
Increasing the dynamic range allows for a greater range of____________ to be displayed, thus increasing the __________.
Echoes
Grayscale
⬆️ dynamic range➡️
⬆️___________
Grayscale
Decreasing dynamic range leads to an image with greater _________, showing less differentiation of grayscale patterns
Contrast
Electronic focusing narrows the __________ along the ________ axis of the transducer.
Beam width
Long
A conventional linear array transducer does not allow manual adjustment of the _____ ______ _______
Fixed short axis plane
Incorrect focusing can cause ______ _______ from volume averaging
False echoes
How does using multiple focal zones affect breast ultrasound imaging? How many zones produce adequate focusing?
Multiple focal zones improve lesion clarity
3
Frame rate definition
The number of images displayed/second
Frame rate affects _______ resolution
Temporal
Which ultrasound functions or adjustments affects the frame rate
Changing
- Number of focal zones
- Image depth
- Frame size
- Doppler
Using multiple focal zones ⬆ or ⬇️ the frame rate
⬇️
How can a sonography the compensate for a slow frame rate?
Decrease depth
Decrease image size
Why would enlarging the field of view be helpful
To visualize margins and internal featured of a mass
What are the 3 Doppler modes used in breast imaging
- Pulsed-waved Spectral Doppler
- Color flow Doppler
- Power Doppler
Pulsed-waved Spectral Doppler
⏺Blood flow is sampled at a selected depth within a vessel segment
⏺Spectral waveform displays changes in flow velocity and direction of moving red blood cells
⏺Waveform differentiates arterial vs. venous flow
⏺Waveform differentiates turbulent vs. laminar (sliding)
⏺Measurement of peak, mean, and minimal velocities
Color Flow Dopplar
Superimposed display of blood flow over anatomic image
Identification of vessel blood flow
Demonstration of blood flow turbulence
Mosaic of colors with high velocities
Power Doppler
⏺Estimates total amplitude and intensity
⏺Less angle dependent
⏺Better sensitivity to low flow states
⏺Better demonstration of tortuous vessels
⏺No info on flow direction, velocity or turbulence
⏺More susceptible to motion artifacts
Which types of Doppler are more angle dependent? Which is not?
Angle dependent
- Pulse-waved
- Color Doppler
Not angle dependent
1. Power Doppler
Doppler settings should be optimized for _________ flow states
Low flow
T or F
Intravenous contrast is commonly used in breast ultrasound.
F
FDA does not approve intravenous contrast agents for breast ultrasound
Panoramic views are also known as
Extended Field of View
How does harmonic imaging work
The US system transmits at a given frequency
In general terms, how does ultrasound work
Conventional ultrasound imaging sends out a burst of sound and listens for that burst to echo off of structures in the body. The time it takes for the echo to return is proportional to the distance the sound wave traveled.
What are the benefits of harmonic imaging
Harmonic imaging has a number of potential clinical benefits including
- improved spatial resolution to permit visualization of smaller objects
- improved contrast resolution to improve demonstration of increasingly subtle differences in grayscale.
How does harmonic US imaging work as compared to conventional US?
With conventional imaging, the ultrasound system transmits and receives a sound pulse of a specific frequency The difference between the transmitted and returned signal is that the returned signal is less intense, losing strength as it passes through tissue.
With Harmonic Imaging, the signal returned by the tissue includes not only the transmitted frequency, but also signals of other
frequencies – most notably, the “harmonic” frequency, which is twice the
fundamental frequency. Once this combined fundamental/harmonic signal is received, the ultrasound system separates out the two components and then processes the harmonic signal alone.
Harmonic imaging reduces _______. How?
Artifacts. False echoes are eliminated.
Why is harmonics used?
- False echoes are eliminated in cysts and masses.
2. Margins better visualized
What is spatial compound imaging
New type of transducer transmits multiple scan planes at different angles, producing a better, compounded image with more defined margins of masses, subareolar structures with reduced artifacts
Other technologies
Convex Linear - transducer can electronically chafe to trapezoid shape for wider field of view
3D/4D Imaging/ Multiplanar/Multi slice - can be viewed in multiple planes showing enhanced images of speculation
Elasticity Imaging - shows stiffness
What is a spectrum of frequencies?
Bandwidth
Dopplar and harmonic imaging are performed using ⬆️or ⬇️ frequencies
⬇️
Artifacts are caused by:
- Atypical sound interaction with body
- Equipment malfunction
- Interfering signals
- Image processing
- Operator error
- Patient motion
Reverberation artifacts court when
The beam encounters 2 strong parallel reflectors
Reverberation artifacts occur when the sound beam is _______ to the interface
Perpendicular
a sound beam that reflects back and forth between an object and the transducer causes ________
Reverberation artifacts
________ is a common cause of false echoes within a cystic structure
Reverberation
If present, where does the reverberation artifact appear in a cystic structure
Anterior portion
Similar to reverberation, this type of artifact appears as multiple small parallel echo bands.
Comet tail artifacts
What can cause comet tail artifacts
Imaging of surgical clips and biopsy needles
Another type of Reverberation artifact, produced by gas bubbles
Ring down artifact
During which exam do ring down artifacts occur
Vacuum assisted biopsies
What are 3 types of attenuation artifacts
- Enhancement (aka posterior enhancement
- Shadowing
- Edge shadowing
What causes shadowing
Sound beam travels through weak reflectors such as a cyst. The beam travel easily through these structures and the is more sound energy left after exiting the structure to “sonify” distal structures. These will appear bright or “enhanced”
What causes shadowing
Sound beam that travels through a strong reflector or absorber will be absorbed and sound beam intensity is decreased and shapes appear behind the structure
The greater the attenuation, the _________ the shadowing
Greater
____________ represents a change in direction of the sound beam as it passes from one medium to another.
Refraction
What are 2 types of refraction
- Edge shadowing
2. Critical angle shadowing
When does refraction occur
- When there’s significant difference in propagation speeds at an acoustic interface
- When sound beam is not perpendicular to the interface
When does refractive edge shadowing occur
When sound beam bends and loss of energy occurs causing a shadow. Sound beam is refracted and loses energy when it transmits across the interface on lateral edges of structure
When does critical edge shadowing occur
Oblique incidence with Cooper’s ligaments
________ represents incorrect registration of the depth of a structure on the image when sound velocity through the structure is different from the assumed velocity of ________ for soft tissue
Propagation speed error
1540 m/s
If propagation speed error occurs when imaging a cyst, what happens. Why? What happens with a solid mass?
The location of the cyst is registered more superficially because the sound beam travels thru cyst more quickly than thru soft tissue, thus the signal returning to the transducer is faster. This causes a time/distance error.
With a solid mass the system registers the location at a deeper level
What is axial resolution artifacts and how do they appear
Failure to resolve 2 separate reflectors in the direction of the sound beam
2 objects appear as 1
Transducer frequency and special pulse length is related to which type of artifact
Axial resolution artifact
What is the type of artifact where there is a failure to resolve 2 separate reflectors perpendicular to the sound beam
Lateral resolution artifact
Lateral resolution artifact is related to ______ and _____
Beam width and focusing
What are side lobes and grating lobes
Side lobes are weaker sound beams emitted from a single element transducer directed to regions other than the main beam axis
Grating lobes are extra sound beams emitted from a multi element transducer
How do side lobes and grating lobes artifacts occur
Reflections from these these beams in other areas than the main beam cause echoes that degrade the image
Where do side lobes appear and with when are they the most obvious
In the near field.
When imaging cysts
What is slice thickness artifact
Fill-in effect related to the fact that beam width is not razor thin
What is speckle/noise and what causes it
Granular false echoes caused by scattered beams that produce weak echoes. Appears as bright or dark spots
What system function is speckle/noise caused by
Excessive gain and electrical interference
What image quality does speckle and noise have an effect on
Detail and contrast resolution
What is B mode and M mode in ultrasound imaging
Brightness mode
Motion mode
What system function can cause Doppler artifacts
Excessive gain and low filter settings
A high filter setting will _____ detection of low velocity blood flow
Reduce
What is PRF
The number of pulses (or send/listen cycles) sent out by the transducer
________is an imaging error which occurs due to under-sampling. The ultrasound system is trying to image an event that is occurring ________ than the rate we are sampling it, and as a result the system is uncertain about the direction of the signal and displays this as heading in the opposite direction.
Aliasing
Faster
How are filters used in Doppler imaging
All types of Doppler ultrasound equipment employ filters to cut out the high amplitude, low-frequency Doppler signals resulting from tissue movement, for instance due to vessel wall motion. Filter frequency can usually be altered by the user, for example, to exclude frequencies below 50, 100 or 200 Hz. This filter frequency limits the minimum flow velocities that can be measured.
What will happen if Doppler angle is perpendicular to flow
No flow will be detected
Too low a Doppler filter setting can cause ______
Aliasing
Aliasing makes it look like blood flow is traveling _________
In the opposite direction
How to reduce Cooper’s ligament shadowing
Increase transducer pressure
Angle transducer do that scan is more perpendicular to the ligaments
What happens to PZT crystals when they are stimulated by electric current
Vibrate
__________ __________ change size when stimulated by electrical current
Change size
What is the unit used for measuring pressure
Pascals
What is the definition of period
The time it takes to complete one cycle
______ is the distance of one cycle
Wavelength
________ is the number of cycles over a specific period of time
Frequency
Ultrasound is measured in_____ ______ _________
Cycles per second
Breast imaging is ______ to ________ MHz
10-17
The speed of sound is _________
1540 m/s
What type of ultrasound is it when crystals are pulsing and receiving
Pulse wave
What does PRF stand for and what is it
Pulse Repetition Frequency
The PRF is the number of pulses (send and listen cycles) of ultrasound sent out by the transducer per second.
Increased depth increases/decreases PRF
Decrease
Increased transducer frequency allows more/less depth and increased/decreased resolution
Less depth
Increased resolution
Decreased transducer frequency allows more/less depth and increased/decreased resolution
More depth
Decreased resolution
What is redirection of a portion of the beam back to the transducer called
Reflection
What is the relationship between amplitude, power and intensity
Direct - as on increased the others increase
What is the wave equation
The wave equation: product of wavelength (λ) and frequency (f) represents the velocity (c) of the sound wave.
Wavelength X frequency = velocity
c = λ f
Triangle depiction of relationship between wavelength (λ), frequency (f), and velocity (c)
c
λ f
λ X f = c
Speed of sound wave through different mediums
Velocity (m/sec) Air 330 Fat 1450 Water 1480 Soft tissue 1540 Kidney 1560 Blood 1570 Muscle 1580 Bone 4080
How are power and amplitude related
Power = amplitude squared
Increased stiffness of medium allows increased/decreased speed
Increased
What is the bending of the beam called
Refraction
Edge shadowing is a type of
Refraction
Attenuation is measured in ________
Decibels
Sound waves strengthen/weaken as it propagates
Weaken
The propagation of sound waves is called
Attenuation
What does TCG stand for
Time gain compensation
What does TCG compensate for
Attenuation
What does gain adjust
Overall brightness
The ultrasound system needs to set fat to
Medium gray
The beam is narrowest at the
Focal point
The beam is relatively narrow at the
Focal zone
Where is the near zone
From the crystals to the focal point
What is the far zone
The focus to the deeper tissue
The ability to distinguish 2 structures that are parallel to the beam
Axial resolution
The ability to distinguish 2 structures that are side by side
Lateral resolution
What is doubling the fundamental frequency called
Harmonics
Color Doppler detects
Direction
Power Doppler detects
Flow
What is the purpose of the backing layer of the transducer
Reduces ringing
Where is the backing layer located
Behind the crystal
How are the crystals positioned in a linear array transducer
In a straight line
Where is the dead zone
Area close to transducer showing artifacts
T/F - Never autoclave or sterilize with heat a transducer
T
What is the problem when the screen shows a blacked out area fro top to bottom
Broken crystal
What is a testing object that contains tissue mimicking material that simulates properties of tissue, such as solidity, cystic, axils and lateral resolution
Phantom
A shorter pulse length results in wider/narrower bandwidth
Wider
Optimal resolution and penetration results from a transducer that is able to operate at different _________
Frequencies
The ability to resolve 2 closely spaced objects lying side-by-side in a direction perpendicular to the sound beam
Lateral resolution
What type of focusing is used by a linear array transducer
Variable electronic focusing
Focusing along the short axis of the transducer
Focusing along the short axis of the transducer
Which transducer is rectangular shaped and allows skin contact and even compression
Linear array
Which transducer produces less beam divergence
Linear array
Which transducer has narrow focusing and improves needle visualization
Linear array
Ability to differentiate 2 closely spaced each interfaces lying in the direction of the sound beam (think of beam as an axis)
Axial resolution
The ability to resolve 2 closely spaced objects lying side-by-side in a direction perpendicular to the sound beam
Lateral resolution
