ARDMS SPI Image Formation and Processing 2 — Questions and Answers
Question 1: What is the primary function of the scan converter in a diagnostic ultrasound system?
- Amplify returning echoes before display
- Convert polar ultrasound data into a rectangular display format (Correct answer)
- Filter out high-frequency noise from the received signal
- Control the transmit pulse repetition frequency
Correct answer: Convert polar ultrasound data into a rectangular display format
The scan converter maps echo data from the polar coordinate geometry of the transducer sweep into the Cartesian (rectangular) format used by the video display.
Question 2: Which parameter directly determines the number of pixels used to represent a digital ultrasound image?
- Bit depth
- Matrix size (Correct answer)
- Frame rate
- Dynamic range
Correct answer: Matrix size
Matrix size (e.g., 512×512 or 1024×1024) defines the total number of pixels in the digital image grid.
Question 3: In digital ultrasound imaging, bit depth refers to:
- The number of image frames stored per second
- The maximum imaging depth in centimeters
- The number of bits used to encode the gray-scale value of each pixel (Correct answer)
- The lateral width of the scan plane
Correct answer: The number of bits used to encode the gray-scale value of each pixel
Bit depth determines how many distinct gray levels can be represented; 8-bit depth yields 256 gray levels.
Question 4: Frame rate in real-time ultrasound imaging is primarily limited by:
- The transducer element impedance
- The speed of sound and imaging depth (Correct answer)
- The analog-to-digital conversion speed
- The patient's body habitus
Correct answer: The speed of sound and imaging depth
Because sound must travel to the maximum depth and return before the next pulse is fired, greater depth forces a lower pulse repetition frequency and thus a lower frame rate.
Question 5: What happens to frame rate when the number of scan lines per frame is increased while imaging depth remains constant?
- Frame rate increases
- Frame rate decreases (Correct answer)
- Frame rate is unaffected
- Frame rate doubles
Correct answer: Frame rate decreases
More scan lines require more pulses per frame, which increases the time needed to build each image and therefore reduces frame rate.
Question 6: The process of reducing high-amplitude speckle noise while preserving edge detail in ultrasound images is best described as:
- Harmonic imaging
- Adaptive image processing (speckle reduction imaging) (Correct answer)
- Time-gain compensation
- Coded excitation
Correct answer: Adaptive image processing (speckle reduction imaging)
Adaptive speckle reduction algorithms analyze local image statistics to smooth homogeneous regions while retaining boundaries.
Question 7: Which of the following correctly describes interpolation as used in the scan converter?
- Removing redundant scan lines to speed processing
- Estimating pixel values between actual sample locations to fill the display grid (Correct answer)
- Compressing the dynamic range of echo amplitudes
- Applying a threshold to eliminate low-level signals
Correct answer: Estimating pixel values between actual sample locations to fill the display grid
Interpolation fills gaps between measured data points by estimating intermediate values, producing a continuous-looking image from discrete samples.
ARDMS SPI Image Formation and Processing 2
What is the primary function of the scan converter in a diagnostic ultrasound system?