ARDMS SPI MCQ 4 — Questions and Answers
Question 1: What is the primary purpose of a matching layer on a transducer face?
- To increase transducer bandwidth by absorbing excess vibrations
- To improve energy transfer by reducing acoustic impedance mismatch between crystal and tissue (Correct answer)
- To prevent electrical interference from the patient
- To cool the piezoelectric element during operation
Correct answer: To improve energy transfer by reducing acoustic impedance mismatch between crystal and tissue
The matching layer reduces the large acoustic impedance difference between the piezoelectric crystal and soft tissue, improving energy transmission.
Question 2: Frame rate in real-time ultrasound is most directly limited by:
- Transducer frequency
- The speed of sound and imaging depth (Correct answer)
- Focal zone placement
- Dynamic range setting
Correct answer: The speed of sound and imaging depth
Because the system must wait for echoes to return from maximum depth before firing the next pulse, imaging depth and the speed of sound directly limit frame rate.
Question 3: Which artifact is caused by the assumption that all echoes return along the central beam axis when they actually originate from a side lobe?
- Shadowing
- Side lobe artifact (Correct answer)
- Enhancement
- Comet tail artifact
Correct answer: Side lobe artifact
Side lobe artifacts are misregistered echoes from off-axis reflectors that the system incorrectly places along the main beam axis.
Question 4: Increasing the pulse repetition frequency (PRF) in color Doppler will:
- Improve sensitivity to slow-flow states
- Reduce aliasing by raising the Nyquist limit (Correct answer)
- Decrease frame rate significantly
- Increase thermal bioeffect risk
Correct answer: Reduce aliasing by raising the Nyquist limit
A higher PRF raises the Nyquist limit, allowing detection of higher-velocity flow before aliasing occurs.
Question 5: The mechanical index (MI) is used to estimate the risk of:
- Thermal damage to tissue
- Non-thermal (cavitation) bioeffects (Correct answer)
- Grating lobe formation
- Image aliasing
Correct answer: Non-thermal (cavitation) bioeffects
The Mechanical Index estimates the likelihood of cavitation and other non-thermal mechanical bioeffects from ultrasound exposure.
Question 6: Which imaging mode provides the highest temporal resolution for evaluating rapidly moving structures like heart valves?
- B-mode with high frame rate
- M-mode (Correct answer)
- Color Doppler
- 3D volumetric imaging
Correct answer: M-mode
M-mode records a single scan line repeatedly at very high sampling rates (up to 1000 times/sec), giving superior temporal resolution.
Question 7: Grating lobes in array transducers are caused by:
- Excessive gain settings
- Periodic spacing of array elements at or near the wavelength (Correct answer)
- Refraction at tissue interfaces
- Thermal noise in the electronic circuitry
Correct answer: Periodic spacing of array elements at or near the wavelength
When element spacing equals or exceeds one wavelength, constructive interference produces off-axis grating lobes that can create artifacts.
ARDMS SPI MCQ 4
What is the primary purpose of a matching layer on a transducer face?