ARDMS SPI Principles of Image Resolution 4 â Questions and Answers
Question 1: Increasing transducer frequency to improve resolution is limited primarily by:
- Increased lateral resolution
- Greater acoustic attenuation reducing penetration depth (Correct answer)
- Lower pulse repetition frequency
- Increased slice thickness
Correct answer: Greater acoustic attenuation reducing penetration depth
Higher frequencies are attenuated more rapidly in tissue, limiting the usable imaging depth.
Question 2: Which component in a modern ultrasound system performs dynamic aperture control?
- The pulser
- The beamformer (Correct answer)
- The time gain compensator
- The digital scan converter
Correct answer: The beamformer
The beamformer applies time delays and apodization across elements, enabling dynamic aperture and focusing.
Question 3: In harmonic imaging, the image is formed from the _____ harmonic frequency.
- Fundamental (transmitted)
- Second (2fâ) (Correct answer)
- Third (3fâ)
- Sub-harmonic (fâ/2)
Correct answer: Second (2fâ)
Tissue harmonic imaging uses the second harmonic (twice the transmitted frequency) generated by nonlinear propagation.
Question 4: Tissue harmonic imaging improves lateral resolution compared to fundamental imaging because harmonic signals:
- Are generated at higher amplitude near the transducer face
- Are strongest near the beam axis where pressure is highest, reducing side lobes (Correct answer)
- Travel at higher speed in tissue
- Use a wider aperture
Correct answer: Are strongest near the beam axis where pressure is highest, reducing side lobes
Harmonic energy is concentrated near the beam axis, reducing clutter from side lobes and grating lobes.
Question 5: The far field (Fraunhofer zone) of an unfocused transducer is characterized by:
- Beam convergence and improving lateral resolution
- Beam divergence and degrading lateral resolution (Correct answer)
- Constant beam width
- Improved axial resolution
Correct answer: Beam divergence and degrading lateral resolution
In the far field the beam diverges, widening the beam and worsening lateral resolution.
Question 6: Which statement about slice-thickness (elevational) artifacts is true?
- They appear as multiple reflections in the axial direction
- They cause structures outside the image plane to be superimposed on the image (Correct answer)
- They only occur with high-frequency transducers
- They are eliminated by dynamic receive focusing
Correct answer: They cause structures outside the image plane to be superimposed on the image
Because the elevation beam is relatively thick, off-plane structures contribute echoes that create partial-volume artifacts.
Question 7: Apodization in ultrasound beamforming refers to:
- Varying element excitation amplitude across the aperture to reduce side lobes (Correct answer)
- Increasing transmit power to all elements equally
- Adjusting time gain compensation at each depth
- Setting the pulse repetition frequency
Correct answer: Varying element excitation amplitude across the aperture to reduce side lobes
Apodization applies a weighting window (e.g., Hanning) to element amplitudes to suppress side lobes at a slight cost to main-lobe width.
ARDMS SPI Principles of Image Resolution 4
Increasing transducer frequency to improve resolution is limited primarily by: