Principles of Image Resolution Flashcards

Increasing transducer frequency to improve resolution is limited primarily by:

Answer: Greater acoustic attenuation reducing penetration depth

Higher frequencies are attenuated more rapidly in tissue, limiting the usable imaging depth.

Which component in a modern ultrasound system performs dynamic aperture control?

Answer: The beamformer

The beamformer applies time delays and apodization across elements, enabling dynamic aperture and focusing.

In harmonic imaging, the image is formed from the _____ harmonic frequency.

Answer: Second (2f₀)

Tissue harmonic imaging uses the second harmonic (twice the transmitted frequency) generated by nonlinear propagation.

Tissue harmonic imaging improves lateral resolution compared to fundamental imaging because harmonic signals:

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.

The far field (Fraunhofer zone) of an unfocused transducer is characterized by:

Answer: Beam divergence and degrading lateral resolution

In the far field the beam diverges, widening the beam and worsening lateral resolution.

Which statement about slice-thickness (elevational) artifacts is true?

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.

Apodization in ultrasound beamforming refers to:

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.