ARDMS SPI - ARDMS Sonography Principles and Instrumentation Image Formation and Processing Questions and Answers — Questions and Answers
Question 1: A sonographer is trying to improve the temporal resolution while imaging the fetal heart. Which of the following adjustments would be most effective?
- Increasing the number of focal zones
- Decreasing the imaging depth (Correct answer)
- Widening the sector size
- Increasing the line density
Correct answer: Decreasing the imaging depth
Temporal resolution is determined by the frame rate. To increase the frame rate, the time it takes to acquire each frame must be reduced. Decreasing the imaging depth reduces the pulse-return time (go-return time), allowing the system to listen for a shorter period and thus acquire lines faster, which increases the frame rate. Increasing focal zones, widening the sector, or increasing line density would all require more time to build a frame, thereby decreasing temporal resolution.
Question 2: Which of the following functions is considered a preprocessing function because it can only be performed on a live image before the data is stored in the scan converter?
- Read Magnification
- Adding caliper measurements
- Adjusting the grayscale map
- Write Magnification (Correct answer)
Correct answer: Write Magnification
Preprocessing functions manipulate the image data before it is stored in the scan converter memory. Write Magnification (or Write Zoom) is a classic example of preprocessing; it rescans the selected region of interest with a higher line density to generate a new, higher-resolution image. This can only be done on a live image. Read magnification, caliper placement, and grayscale map adjustments are postprocessing functions that can be applied to a frozen image.
Question 3: The primary function of the scan converter in an ultrasound system is to:
- Convert electrical signals into acoustic pulses.
- Amplify the weak returning echo signals.
- Format the echo data from the spoke format into a video format for display. (Correct answer)
- Calculate the Doppler shift from moving red blood cells.
Correct answer: Format the echo data from the spoke format into a video format for display.
The scan converter, or image processor, is a digital memory component that receives echo data from the receiver. Its main job is to reformat this data, which is acquired in a spoke or line-by-line format (like polar coordinates for a sector transducer), into a standard raster scan or video format (Cartesian coordinates) that can be displayed on a monitor.
Question 4: An ultrasound system's ability to display many shades of gray is most directly related to which of the following?
- The number of bits per pixel (Correct answer)
- The number of active channels
- The transducer frequency
- The pulse repetition frequency
Correct answer: The number of bits per pixel
The number of shades of gray an ultrasound system can display is known as its contrast resolution. This is determined by the bit depth of the digital memory (scan converter). The number of possible gray shades is calculated as 2 to the power of the number of bits (2^n). For example, a system with 8 bits per pixel can display 2^8, or 256, shades of gray.
Question 5: A sonographer freezes an image and then activates the zoom function to enlarge a specific area of interest. This action results in larger pixels and does not improve spatial resolution. Which type of magnification was used?
- Write magnification
- Focal magnification
- Read magnification (Correct answer)
- Acoustic magnification
Correct answer: Read magnification
Read magnification is a postprocessing function that is applied to a frozen image. It takes the existing pixel data stored in the scan converter and simply enlarges it, making each pixel bigger. Because no new data is acquired, the spatial resolution is not improved and may even appear degraded. Write magnification, a preprocessing function, would rescan the area live to create a new image with more pixels, thereby improving spatial resolution.
Question 6: During an abdominal ultrasound, a sonographer decides to increase the line density to improve lateral resolution. Which of the following is an expected trade-off for this adjustment?
- Increased penetration depth
- Decreased frame rate (Correct answer)
- Improved axial resolution
- Decreased contrast resolution
Correct answer: Decreased frame rate
There is an inverse relationship between line density and frame rate. Increasing the number of scan lines (line density) in a single frame improves lateral resolution by sampling the tissue more finely. However, because each line requires a pulse-listen cycle, adding more lines increases the total time needed to build one frame. This increase in frame acquisition time results in a lower frame rate, thus degrading temporal resolution.
ARDMS SPI - ARDMS Sonography Principles and Instrumentation Image Formation and Processing Questions and Answers
A sonographer is trying to improve the temporal resolution while imaging the fetal heart.
Which of the following adjustments would be most effective?