Image Formation and Processing Flashcards

Which type of resolution describes the ability to distinguish two closely spaced reflectors located side by side perpendicular to the beam axis?

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.

Axial resolution in ultrasound is primarily determined by:

Answer: Spatial pulse length

Axial resolution equals half the spatial pulse length; shorter pulses (higher frequency, fewer cycles) yield finer axial resolution.

Elevational (slice thickness) resolution is most directly controlled by:

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.

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:

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.

Acoustic shadowing posterior to a gallstone is caused by:

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.

Posterior acoustic enhancement (increased through-transmission) is seen deep to structures that:

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.

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?

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.