ARDMS SPI Image Formation and Processing 5

Question 1

Demodulation in ultrasound signal processing refers to:

Accepted Answer

Removing the radiofrequency carrier to extract the envelope of the echo signal

Answer

Demodulation (envelope detection) extracts the amplitude envelope from the high-frequency RF echo signal, which represents tissue reflectivity and is used to build the gray-scale image.

Question 2

What is the purpose of time-gain compensation (TGC) in ultrasound imaging?

Accepted Answer

To amplify echoes from deeper structures to compensate for attenuation

Answer

TGC applies progressively increasing gain with depth to offset the depth-dependent attenuation of sound in tissue, making echoes from similar structures appear equally bright regardless of depth.

Question 3

In a phased-array transducer, electronic focusing is achieved by:

Accepted Answer

Applying time delays to the firing sequence of individual elements

Answer

Precise time delays introduced across phased-array elements cause the wavefronts to converge at a desired focal depth, creating electronic focusing without moving parts.

Question 4

Dynamic receive focusing (dynamic aperture) in ultrasound systems:

Accepted Answer

Continuously adjusts receive delays to focus at the depth from which echoes are returning

Answer

As echoes return from progressively greater depths, the system continuously updates the receive time delays so the beam is always focused at the current echo depth, improving lateral resolution throughout the image.

Question 5

Grating lobes in array transducers are caused by:

Accepted Answer

Constructive interference from equally spaced element spacing greater than half a wavelength

Answer

When element spacing exceeds half a wavelength, spatial aliasing causes grating lobes — additional beams fired at off-axis angles that can produce spurious echoes in the image.

ARDMS SPI - ARDMS Sonography Principles and Instrumentation Practice Test

ARDMS SPI - ARDMS Sonography Principles and Instrumentation Practice Test

ARDMS SPI Image Formation and Processing 5