ARDMS SPI Transducer Construction and Function 3 — Questions and Answers
Question 1: Which of the following BEST describes the piezoelectric effect as used in diagnostic ultrasound transducers?
- Conversion of heat energy to mechanical vibration
- Conversion of electrical energy to mechanical energy and vice versa (Correct answer)
- Conversion of light energy to sound energy
- Conversion of magnetic energy to acoustic energy
Correct answer: Conversion of electrical energy to mechanical energy and vice versa
The piezoelectric effect allows certain crystals to convert electrical signals into mechanical (acoustic) vibrations and incoming pressure waves back into electrical signals.
Question 2: A phased array transducer steers and focuses the beam primarily by adjusting:
- The physical curvature of the array
- Time delays applied to individual element firings (Correct answer)
- The frequency of each element independently
- The size of the active aperture only
Correct answer: Time delays applied to individual element firings
Phased arrays use programmable electronic time delays across all elements to steer and dynamically focus the beam in real time.
Question 3: Increasing the diameter of a single-element unfocused transducer will:
- Decrease the near-field length
- Increase the near-field length (Correct answer)
- Have no effect on the near-field length
- Decrease the far-field divergence angle and shorten near field
Correct answer: Increase the near-field length
Near-field length = r²/λ; a larger radius (r) increases the near-field length, keeping the beam collimated for a longer distance.
Question 4: Side lobes in ultrasound transducers are most problematic because they:
- Increase axial resolution
- Create artifact echoes that appear to originate from the main beam (Correct answer)
- Improve lateral resolution at depth
- Reduce the dynamic range of the system
Correct answer: Create artifact echoes that appear to originate from the main beam
Side lobes radiate energy off-axis; reflectors in their path produce echoes that the system incorrectly places along the main beam axis, creating artifacts.
Question 5: What distinguishes grating lobes from side lobes in array transducers?
- Grating lobes only occur in phased arrays
- Grating lobes arise from the periodic spacing of array elements, not from the element aperture (Correct answer)
- Side lobes are more intense than grating lobes
- Grating lobes improve frame rate
Correct answer: Grating lobes arise from the periodic spacing of array elements, not from the element aperture
Grating lobes result from constructive interference due to the regular inter-element spacing of array transducers, while side lobes are inherent to any finite aperture.
Question 6: The resonant frequency of a piezoelectric crystal is primarily determined by its:
- Diameter
- Thickness (Correct answer)
- Electrical capacitance
- Surface area
Correct answer: Thickness
Resonant frequency is inversely proportional to crystal thickness: f = c / 2t, where c is the propagation speed within the crystal.
Question 7: Which transducer type provides the SMALLEST footprint and is therefore best suited for cardiac imaging between rib spaces?
- Linear array
- Curvilinear array
- Phased array (Correct answer)
- Mechanical sector
Correct answer: Phased array
The phased array has a small footprint that fits between ribs and uses electronic steering to produce a wide sector image from that small window.
ARDMS SPI Transducer Construction and Function 3
Which of the following BEST describes the piezoelectric effect as used in diagnostic ultrasound transducers?