ARDMS SPI Image Formation and Processing 3 — Questions and Answers
Question 1: Which type of resolution describes the ability to distinguish two closely spaced reflectors located side by side perpendicular to the beam axis?
- Axial resolution
- Lateral resolution (Correct answer)
- Elevational resolution
- Contrast resolution
Correct answer: Lateral resolution
Lateral resolution refers to the minimum separation between two targets in the plane perpendicular to the beam and is determined by beam width at a given depth.
Question 2: Axial resolution in ultrasound is primarily determined by:
- Beam width at the focal zone
- Spatial pulse length (Correct answer)
- Frame rate
- Dynamic range setting
Correct answer: Spatial pulse length
Axial resolution equals half the spatial pulse length; shorter pulses (higher frequency, fewer cycles) yield finer axial resolution.
Question 3: Elevational (slice thickness) resolution is most directly controlled by:
- The transmit frequency
- The fixed focusing of the transducer in the elevation plane (Correct answer)
- The dynamic range setting
- The number of focal zones selected
Correct answer: The fixed focusing of the transducer in the elevation plane
Elevational resolution depends on the fixed mechanical lens focus in the elevation dimension, which cannot be dynamically adjusted in most transducers.
Question 4: A hyperechoic artifact that appears as a bright line or band posterior to a highly reflective surface, caused by reverberation between two strong reflectors, is called:
- Acoustic shadowing
- Ring-down artifact
- Mirror image artifact
- Reverberation artifact (Correct answer)
Correct answer: Reverberation artifact
Reverberation artifacts result from echoes bouncing multiple times between two strong reflectors, creating equally spaced bright lines deep to the true interface.
Question 5: Acoustic shadowing posterior to a gallstone is caused by:
- Total reflection and high attenuation by the stone preventing sound transmission (Correct answer)
- Constructive interference of side lobes behind the stone
- Refraction of the beam around the calcification
- Increased transmission through the stone's interface
Correct answer: Total reflection and high attenuation by the stone preventing sound transmission
Calcifications strongly reflect and absorb sound, so little energy passes through to deeper tissues, producing a dark shadow posteriorly.
Question 6: Posterior acoustic enhancement (increased through-transmission) is seen deep to structures that:
- Have high acoustic impedance relative to surrounding tissue
- Attenuate sound less than surrounding tissue (Correct answer)
- Contain gas bubbles
- Reflect nearly all incident sound energy
Correct answer: Attenuate sound less than surrounding tissue
Fluid-filled cysts attenuate sound minimally, so echoes returning from deep to the cyst are stronger than expected, appearing brighter.
Question 7: Which artifact occurs when a strong reflector redirects the ultrasound beam so that a structure appears to exist on the opposite side of the reflector?
- Side-lobe artifact
- Mirror-image artifact (Correct answer)
- Comet-tail artifact
- Grating-lobe artifact
Correct answer: Mirror-image artifact
A mirror-image artifact is produced when a specular reflector (e.g., the diaphragm) acts as an acoustic mirror, reflecting the beam toward a real structure whose duplicate appears on the far side of the reflector.
ARDMS SPI Image Formation and Processing 3
Which type of resolution describes the ability to distinguish two closely spaced reflectors located side by side perpendicular to the beam axis?