Module 1: Transducer Evolution Flashcards
Old static B scanners and early real time units used how many crystals?
One
Some of the earliest probes were very basic in designed with what?
- A single disc element housed
- These probes were mechanically steered to obtain the field of view and were prone to breakdown
What was the evolution of the transducer?
Started from a single disc crystal > Mechanically steered > Electronic array
What kind of element does mechanical transducers have?
Thin disk shaped crystal 6-19 mm in diameter
Mechanical transducers have fixed focal zones with varying configuration such as
- Linear translation
- Wobbler
- Oscillating element
- Oscillating mirror
Linear translation is the oldest technology and simply moved how?
It moved the crystal assembly along a track to “sweep” the tissue
The wobbler probe fixed an element onto what?
Onto a motor that rotated back and forth to obtain the field of view
What kind of image did the wobbler probe produce?
Sector type image
The wobbler probe images were fluid filled and the moving parts risked the production of what?
Air bubbles
To achieve a linear Field of view, probes will use what?
A reflector or acoustic mirror to direct the sound into the patient
With the oscillating mirror, what is the difference?
It is the mirror that moves with a stationary element
What is the rotating wheel probe?
It has several crystals that spin and only pulse when the element passes the field of view
What is the annular array?
Uses concentric discs to allow for focusing of the beam
During the annular array, what happened when you change the disc that is fired?
You change the diameter which in turn varies the focal depth
The annular array still had the same limitations as what?
The mechanically steered
such as the production of grating lobes
In annular arrays what does the diameter of the crystal do?
Changes the focal depth
What did annular probes prove?
A probe with no moving parts was evident
Array probes are arranged how?
Multiple small elements aligned in linear rows
The two main types of arrays we will discuss are what?
- Phased sector array
- Phased Linear array (including the curved array)
Electronic array probes tend to have what kind of bandwidth? And why?
Wide bandwidth and need to have the flexibility to perform other applications such as
1. Colour/ spectral doppler
2. M mode
3. Power doppler
What is phasing?
Uses nanosecond time delays to change when the voltage excites the crystal
What is the purpose of phasing?
Allows use to control the beam and allow for beam focusing and steering
Focusing and steering are accomplished with what in electronic array probes?
Phasing of the voltages to the crystal in the electronic array probes
Steering of the beam can help with what?
Steering of the beam can help direct the sound out at an angle as is the case for the phased sector array, Doppler and vector scanning
What is another term for describing steering the beam?
Vector scanning
A good way to determine the direction of the beam is to assess what?
The slope of the delayed voltages
What is the FOV for phased array?
Can be as large as 90 degrees or as small as 30 degrees
What was the intention of phased array sector?
For the thought of scanning through the ribs as the reason for the shape
For a phased array probe how does it work?
All crystals (approx 128) are fired nearly at the same time to steer the beam across the face of the probe
What kind of footprint does the linear array have?
Tended to have relatively large footprint with approximately 64-200 elements arranged in a row
What is the FOV for a linear array probe?
It is a rectangular shape but can be trapezoidal if scanning in a vector mode
What does the FOV for linear array probes mean?
There is no scan line divergence
What were some of the applications of the linear array probe?
They tended to be used for exams associated with higher frequencies
Firing a single element will increase what? This will result in what?
It will increase divergence which equates to a broad beam resulting in poor resolution and sensitivity
Firing a single element takes away around ability to do what?
Electronically focus or steer the sound
The larger point source of sound would have what?
Less divergence and the resolution would improve as would the sensitivity
Firing in segments also enables what?
Electronic transmit focusing and steering
Having a larger point source or firing in segments has many benefits but at the cost of what?
Fewer scan lines which can degrade the images spatial resolution
What is segmental sequencing?
A group of crystals is fired to create a beam followed by a second group that is one crystal down in the row
The curved linear probe uses what kind of principles?
Similar to the linear array
What kind of elements are used in the curved linear probe?
Small rectangular shaped elements that are curved rather than straight
What is the major advantage of the curved linear probe?
Large footprint and FOV
** this means we see well in the near and far field**
What is the disadvantage of the curved linear probe?
The resolution in the far field can be degraded as the distance between beams is increased
Crystals can ring in an undesirable way along the length and width, This has the potential of creating what?
Off axis sound beams called grating lobes that will produce artifacts on the image
What is apodization?
Voltages to crystals are gradually weakened from the inside out
Obtaining 3D and 4D images can be done in two ways what are they?
- Freehand using a traditional array probe
- Volumetric probe
How can we obtain 3D and 4D images using volumetric probe?
Beam is swept over the area of interest (electronically or mechanically) to obtain the information for 3D reconstruction
Intravascular probes are capable for scanning what?
The Lumen of a vessel
What does a transesophageal echo probe do?
Probe that can help improve the visualization of the heart
What does the 1.5 probe do?
Allows us to focus in the Z axis
There are many specialty probes that exist for things like what?
- Biopsies
- Interventions
- Endocavitary exams
Transesophageal echo probes (TEE) can do what?
Improve visualization of the heart
Dedicated CW probes contain two crystals, what does each crystal do?
One transmits and the other receives
The two crystal CW probes are air backed and have what?
Continuous AC driving voltage
What is the pencil probe?
CW probes that contain two crystals that are air backed and have a continuous A driving voltage.
What is the pencil probe also referred to as?
Ped-off probe
