ARDMS SPI Transducer Construction and Function 5 â Questions and Answers
Question 1: A 2D matrix array transducer differs from a standard phased array primarily in that it:
- Has elements arranged in rows and columns enabling steering in both lateral and elevation planes (Correct answer)
- Operates exclusively at higher frequencies above 15 MHz
- Uses only mechanical steering for 3D acquisition
- Has fewer total elements to reduce cost
Correct answer: Has elements arranged in rows and columns enabling steering in both lateral and elevation planes
A 2D matrix array arranges thousands of elements in a grid, allowing full electronic steering and focusing in both the lateral and elevation dimensions for real-time 3D imaging.
Question 2: The Curie temperature of a piezoelectric material is important clinically because:
- It determines the maximum safe output intensity
- Above this temperature the material permanently loses its piezoelectric properties (Correct answer)
- It sets the upper frequency limit of the transducer
- It defines the temperature at which crystal resonance is optimal
Correct answer: Above this temperature the material permanently loses its piezoelectric properties
The Curie temperature is the threshold above which the polarization of piezoelectric domains is disrupted, permanently destroying the crystal's piezoelectric behavior.
Question 3: In harmonic imaging, the transducer transmits at frequency fâ and receives at:
- fâ / 2
- fâ
- 2fâ (Correct answer)
- 4fâ
Correct answer: 2fâ
Tissue harmonic imaging transmits at the fundamental frequency fâ and selectively receives the second harmonic at 2fâ, which is generated nonlinearly in tissue.
Question 4: Which statement about annular array transducers is TRUE?
- They provide electronic beam steering in all directions
- They focus symmetrically in all planes but require mechanical steering for scanning (Correct answer)
- They have lower near-field resolution than linear arrays
- They are preferred for cardiac imaging due to their small footprint
Correct answer: They focus symmetrically in all planes but require mechanical steering for scanning
Annular arrays provide symmetric (round) electronic focusing in all planes but cannot steer electronically, requiring mechanical wobbling or rotation to sweep the beam.
Question 5: Subdicing (dicing grooves cut partway through) of transducer elements is performed primarily to:
- Increase the resonant frequency of the crystal
- Reduce lateral coupling between elements and improve element flexibility (Correct answer)
- Separate individual elements for independent electrical connections
- Increase acoustic output power
Correct answer: Reduce lateral coupling between elements and improve element flexibility
Subdicing cuts partially through the crystal to reduce mechanical coupling between adjacent elements and allow the element to flex more efficiently, especially for curved arrays.
Question 6: The effective radiating area (ERA) of a transducer is always:
- Equal to its geometric face area
- Greater than its geometric face area due to fringing effects
- Less than its geometric face area (Correct answer)
- Determined solely by the frequency of operation
Correct answer: Less than its geometric face area
The ERA is the area that actually produces ultrasound energy and is always somewhat less than the total geometric area of the transducer face because edge regions vibrate less effectively.
Question 7: Which transducer design characteristic MOST directly determines axial resolution?
- Element diameter
- Spatial pulse length (Correct answer)
- Focal depth
- Number of elements in the array
Correct answer: Spatial pulse length
Axial resolution equals half the spatial pulse length; shorter pulses (fewer cycles, higher frequency, greater damping) yield better axial resolution.
ARDMS SPI Transducer Construction and Function 5
A 2D matrix array transducer differs from a standard phased array primarily in that it: