MCQ Flashcards

What is the primary purpose of a matching layer on a transducer face?

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.

Frame rate in real-time ultrasound is most directly limited by:

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.

Which artifact is caused by the assumption that all echoes return along the central beam axis when they actually originate from a side lobe?

Answer: Side lobe artifact

Side lobe artifacts are misregistered echoes from off-axis reflectors that the system incorrectly places along the main beam axis.

Increasing the pulse repetition frequency (PRF) in color Doppler will:

Answer: Reduce aliasing by raising the Nyquist limit

A higher PRF raises the Nyquist limit, allowing detection of higher-velocity flow before aliasing occurs.

The mechanical index (MI) is used to estimate the risk of:

Answer: Non-thermal (cavitation) bioeffects

The Mechanical Index estimates the likelihood of cavitation and other non-thermal mechanical bioeffects from ultrasound exposure.

Which imaging mode provides the highest temporal resolution for evaluating rapidly moving structures like heart valves?

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.

Grating lobes in array transducers are caused by:

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.