ARDMS SPI Principles of Image Resolution 2 — Questions and Answers
Question 1: Which factor primarily determines the lateral resolution of an ultrasound beam?
- Pulse duration
- Beam width at the focal zone (Correct answer)
- Wavelength in tissue
- Receiver bandwidth
Correct answer: Beam width at the focal zone
Lateral resolution equals the beam width at any given depth, so it is best at the focal zone where the beam is narrowest.
Question 2: A transducer operating at 10 MHz will have _____ axial resolution compared to one operating at 5 MHz.
- Worse
- The same
- Better (Correct answer)
- Dependent only on focusing
Correct answer: Better
Higher frequency produces shorter wavelengths and shorter pulses, improving axial resolution.
Question 3: Elevational (slice-thickness) resolution is primarily controlled by:
- Dynamic receive focusing
- Fixed focus in the elevation plane (Correct answer)
- Pulse repetition frequency
- Time gain compensation
Correct answer: Fixed focus in the elevation plane
Most arrays cannot steer or focus electronically in the elevation plane, so slice thickness is fixed by the lens curvature.
Question 4: Increasing the number of focal zones in a linear array will:
- Improve lateral resolution throughout the image at the cost of frame rate (Correct answer)
- Improve axial resolution
- Reduce slice thickness
- Increase temporal resolution
Correct answer: Improve lateral resolution throughout the image at the cost of frame rate
Multiple transmit focal zones improve lateral resolution over more depths but require multiple firings, reducing frame rate.
Question 5: The spatial pulse length (SPL) is calculated as:
- Frequency × pulse duration
- Number of cycles × wavelength (Correct answer)
- Amplitude / frequency
- Wavelength / bandwidth
Correct answer: Number of cycles × wavelength
SPL = number of cycles × wavelength; shorter SPL yields better axial resolution.
Question 6: Which type of resolution describes the ability to distinguish two structures side by side perpendicular to the beam axis?
- Axial
- Lateral (Correct answer)
- Temporal
- Contrast
Correct answer: Lateral
Lateral resolution refers to resolving structures side by side (perpendicular to the beam direction).
Question 7: A heavily damped transducer will produce:
- Longer pulses and better axial resolution
- Shorter pulses and better axial resolution (Correct answer)
- Narrower beams and better lateral resolution
- Higher amplitude and better penetration
Correct answer: Shorter pulses and better axial resolution
Heavy damping reduces ringing, shortening the pulse and thus improving axial resolution.
ARDMS SPI Principles of Image Resolution 2
Which factor primarily determines the lateral resolution of an ultrasound beam?