Chap 5 Lvl 2 Flashcards
What is one advantage of Pedof transducers?
Usually extremely sensitive in Doppler since designed specifically for Doppler
Pedof transducers are optimized for Doppler applications, enhancing their sensitivity.
What is a cost-related advantage of Pedof transducers?
Relatively inexpensive to make
This makes them accessible for various applications.
What is a physical advantage of Pedof transducers?
Small footprint allowing for insonation in smaller areas such as between ribs and suprasternal notch
Their compact design enables usage in confined spaces.
What does the term ‘mechanical’ refer to in the context of a transducer?
It refers to how the beam is steered to create the image.
How is a mechanical image produced?
By actuating the motor to point the transducer crystal in different directions over time.
What is the primary use of a mechanical curved array transducer?
Used for 2D imaging, M-mode, Doppler, and color Doppler
The mechanical curved array transducer is versatile in ultrasound applications.
What type of image does a mechanical curved array transducer create?
Creates a sector image with a ‘curved top’
This design allows for a wider field of view in imaging.
What is a characteristic feature of the mechanical curved array transducer?
Single crystal (sometimes split into two halves for CW Doppler or a second small crystal off to the side dedicated for Doppler)
The use of crystals enhances Doppler capabilities.
True or False: A mechanical curved array transducer can only be used for 2D imaging.
False
It is also used for M-mode, Doppler, and color Doppler.
What is the basic concept of an annular array?
The basic concept is to vary the diameter of the crystal to vary the focus.
How is the diameter of the transducer varied in an annular array?
The diameter is varied by turning on and off concentric rings.
What happens to the focus when only the center disc of an annular array is turned on?
The focus is very shallow.
What occurs when the next outer ring in an annular array is activated?
The diameter becomes larger and the focus becomes deeper.
Fill in the blank: In an annular array, if the _______ is activated, the focus becomes deeper.
next outer ring
What was the initial method used to produce images in an annular array?
The image was produced by mechanically steering the crystal.
True or False: An annular array consists of a single round crystal that is not diced.
False
What is created by dicing a single round crystal in an annular array?
A series of concentric rings.
What is the primary use of a mechanical annular array transducer?
Used for 2D imaging, M-mode, Doppler, and color Doppler
What shape does the sector image created by a mechanical annular array transducer have?
Curved top
How is a mechanical annular array transducer steered?
By a wobbling motor, rotating crystal, or mirrors
What are the main disadvantages of mechanical annular array transducers?
- Parts wear out
- Parts break
- Motion artifacts
- Limited temporal resolution
- Excessive grating lobe artifacts
- More expensive to make than single element mechanical transducers
What are the advantages of mechanical annular array transducers relative to single element mechanicals?
- Variable focus in the lateral direction
- Variable focus in the elevation direction
- Variable depth of field
True or False: Mechanical annular array transducers have a symmetric beam in elevation and lateral directions.
True
Fill in the blank: Mechanical annular array transducers are more expensive to make than _______ mechanical transducers.
single element
What is a common issue faced by mechanical annular array transducers due to their design?
Grating lobe artifacts
What type of motion artifacts are associated with mechanical annular array transducers?
Motion artifacts
What is the consequence of excessive grating lobe artifacts in mechanical annular array transducers?
Limited temporal resolution
What is a major limitation of mechanical transducers?
Lateral smearing effect degrading lateral resolution
This effect occurs due to the movement of the crystal in mechanical transducers.
What artifact is produced by motion in color Doppler?
Bright flashes of color
This motion artifact affects the clarity of the imaging.
What characteristic does a simple mechanical transducer have?
Fixed focus
This restricts the ability to adjust the focus dynamically.
What common issue do mechanical parts of transducers face?
Wear and breakage
Mechanical parts are prone to deterioration over time.
What happens to dome oil in mechanical transducers?
It can leak out and be replaced by air
This leakage can affect the performance of the transducer.
What desire led to the development of phasing in transducers?
To create a scan with no moving parts and a variable focus
This innovation aims to overcome the limitations of mechanical transducers.
Fill in the blank: The concept of _______ led to phased array transducers.
phasing
Phasing allows for dynamic focusing and improved imaging capabilities.
What is the term used for a subgroup of elements activated in large arrays?
Aperture
Why is only a subgroup of elements activated in large arrays?
To prevent the lateral beamwidth from becoming too large, resulting in poor lateral resolution.
How are the beams characterized in large arrays?
Each beam is narrow.
What is required to build up an image in large arrays?
Transmitting and receiving a sequence of beams over time.
What is a linear switched array?
A group of elements that can be turned on or off through electronic switches.
How many elements does a linear switched array typically have?
Generally 200 elements or more.
What type of image shape is produced by a linear switched array?
Rectangular.
What was the primary use of linear switched arrays?
Vascular 2D imaging, Doppler, and color Doppler.
Are linear switched arrays still in use today?
No, they are now obsolete.
What is the principle that is still used in newer transducers?
The principle of sequencing.
What arrangement do the crystals in a linear switched array have?
Multiple rectangular crystals arranged linearly.
How does the firing of elements occur in a linear switched array?
Elements are fired in a specific sequence to create an image.
True or False: The beam produced by a linear switched array is symmetric in elevation and lateral planes.
False.
Fill in the blank: The large lateral dimension of the transducer was to provide a large field of _______.
[view].
What is a disadvantage of fixed transmit focus?
Fixed transmit focus
This limits the ability to adjust the focus during transmission.
What is a disadvantage of fixed receive focus?
Fixed receive focus
This restricts the ability to adjust the focus during reception.
What is a limitation regarding image steering capabilities?
No image steering capabilities (must look straight ahead)
This means the system cannot direct the imaging beam to different angles.
What is a cost-related disadvantage of multi-element transducers?
More expensive to make than single element mechanical transducers
The complexity of manufacturing increases the cost.
What type of electronics are necessary for multi-element transducers?
More expensive electronics necessary (potentially one channel for each element)
This adds to the overall system cost.
What is an advantage of multi-element transducers compared to single element mechanicals?
Allows for creation of a wide linear image in near field (good for vascular)
This improves the visualization of vascular structures.
What is an array in the context of transducers?
An array is a transducer comprised of multiple ‘elements’ which can operate together or be controlled separately to transmit and receive signals.
What is the process of cutting a piezoelectric crystal block into smaller elements called?
‘Dicing’
What is the gap generated by the dicing process referred to as?
‘Kerf’
What dual function can each element of an array serve?
Each element can serve as a transmitter and as a receiver.
What is a variable transducer?
A device that converts one form of energy into another, with each element acting as a mini transducer
Each element acts as an individual wave source.
What is electronic steering in transducers?
The use of small time or phase delays between excitation pulses to each transducer element within an array
This allows for the creation of many waves simultaneously.
What are the advantages of electronic steering over mechanical steering?
- Eliminates disadvantages of mechanical steering
- Ability to vary focus through changing the aperture
- Ability to perform parallel processing
- Supports advanced processing techniques
The aperture refers to the active area of the transducer being used.
What is a major disadvantage of a phased array transducer?
Cost
Creating a phased array transducer is considerably more complex and costly than mechanical transducers.
Fill in the blank: Electronic steering requires an _______ to function effectively.
[array]
True or False: Electronic steering allows for the simultaneous creation of many waves.
True
What does Figure 40 demonstrate?
The concept of applying a phased delay voltage profile to a group of elements within a transducer
The figure illustrates the voltage pulse for an individual transducer element.
How is time represented in Figure 40?
By the ‘distance’
This representation highlights the challenge of depicting time in a static image.
What does the zig-zagged line in Figure 40 represent?
The voltage pulse for an individual transducer element
This illustrates the application of phased delay in electronic steering.
What does the zigzagged line represent in relation to the voltage pulse?
Time differences or delays between the voltages driving each of the elements.
The farther away the zigzagged line is from the transducer element, the later in time the pulse will arrive.
What principle can be used to predict how individual wavefronts construct a beam?
Huygens’ principle.
Huygens’ principle states that all points on a wavefront can be treated as point sources producing spherical secondary wavelets.
What does Huygens’ principle help determine in addition to predicting wavefront positions?
The laws of reflection and refraction.
This principle allows for the understanding of how wavefronts behave when they encounter different media.
What does each transducer element act as according to the text?
An individual transducer producing a spherical wave.
This is due to the time delays resulting in each wave being at a different distance from the transducer face.
What happens to the spherical waves as they begin to overlap?
They produce more constructive interference.
The overlap of the spherical waves results in stronger wavefronts initially.
What occurs to the overlap of spherical waves with depth?
The overlap decreases, resulting in less constructive interference.
As the waves grow, they start to lose coherence over greater distances.
Fill in the blank: Huygens’ principle states that all points on a wavefront can be treated as _______.
[point sources]
These point sources produce spherical secondary wavelets.
True or False: Each transducer element produces a different spherical wave due to time delays.
True.
The time delays cause each wave to be at a different distance from the transducer face at a given moment.
What is electronic steering in ultrasound?
Electronic steering is achieved by using small phase delays between the excitation pulses that drive the elements of a phased array transducer.
This technique allows for precise control of the ultrasound beam direction.
How is electronic receiving accomplished in a phased array transducer?
Electronic receiving is achieved by applying phase delays to signals received by each of the active elements of the phased array transducer.
This process enhances the quality of the received signals.
What impact did the advent of electronic steering have on ultrasound?
The advent of electronic steering revolutionized ultrasound and is still the basis of many imaging techniques today.
It transformed how ultrasound imaging is performed and improved diagnostic capabilities.
What are the benefits of electronic steering in ultrasound imaging?
Benefits of electronic steering include:
* Varying incident angles
* Improved image acquisition
* Control of imaging artifacts
These advantages lead to enhanced diagnostic accuracy.
How does electronic steering affect Doppler performance?
Electronic steering allows for significantly improved Doppler and color Doppler performance when flow is parallel to the skin surface.
This is crucial for accurate blood flow measurements.
