Ultrasound Physics: Axial & Lateral Resolution, Display Modes, and Transducers

Vocabulary flashcards covering key ultrasound physics concepts from Chapters 10, 11, and 12, including axial/lateral resolution, display modes, transducer array types, and beam artifacts.

Resolution

The ability of an ultrasound system to create an accurate image and distinguish structures from one another.

Axial Resolution

The ability of an ultrasound system to distinguish two structures positioned parallel (front-to-back) to the sound beam's main axis.

LARRD

An acronym for the synonyms of axial resolution: Longitudinal, Axial, Range, Radial, and Depth.

Spatial Pulse Length (SPL)

A primary determinant of axial resolution along with pulse duration, where shorter length results in better resolution.

Ringing

The continuous vibration of a PZT crystal after excitation, which is reduced through damping to produce fewer cycles and shorter pulses.

Lateral Resolution

The ability of an ultrasound system to distinguish two structures positioned side-by-side (perpendicular) to the sound beam's main axis.

LATA

An acronym for the synonyms of lateral resolution: Lateral, Angular, Transverse, and Azimuthal.

Beam Width

The primary determinant of lateral resolution, where a narrower width produces better resolution.

External Focusing

A fixed focusing technique that uses a lens placed in front of the PZT crystal to narrow the sound beam.

Internal Focusing

A fixed focusing technique that uses a curved PZT crystal to create a narrow, tight sound beam without a lens.

Electronic Focusing

An adjustable focusing technique used in phased array transducers that relies on electronic timing delays.

A-mode (Amplitude Mode)

An ultrasound display mode that shows returning echo amplitudes as vertical spikes, where the X-axis represents reflector depth and the Y-axis represents amplitude.

B-mode (Brightness Mode)

An ultrasound display mode that represents returning echo strength as dots of varying brightness, forming the basis of 2D images with X-axis as depth and Z-axis as amplitude.

M-mode (Motion Mode)

An ultrasound display mode that tracks structural motion over time, displaying time on the X-axis and depth on the Y-axis.

Mechanical Transducer

A transducer containing a single, circular disc-shaped PZT crystal that physically moves to produce a sector or fan-shaped image.

Transducer Array

A transducer constructed from a single slab of PZT cut into multiple individual active elements.

Channel

A combination consisting of a single active PZT element, its connecting wire, and the system electronics.

Linear Phased Array

A transducer with approximately 100 to 300 narrow rectangular elements in a straight line that electronically steers and focuses to produce a fan/sector image.

Phase Delays

Tiny electrical timing differences created by the beam former to electronically steer and focus the sound beam.

Beam Former

The ultrasound system component that creates spike patterns and timing delays used to steer and focus the beam.

Dynamic Receive Focusing

Continuous electrical delay adjustments made by the system during echo reception to achieve variable focusing at different depths.

Annular Phased Array

A transducer with multiple circular ring elements arranged concentrically like a bullseye, using mechanical steering and electronic focusing.

Linear Sequential Array

A transducer with approximately 120 to 150 rectangular PZT elements in a straight line that fires small groups simultaneously to create a rectangular image.

Convex Array

A transducer with 120 to 150 rectangular elements arranged in an arched line, producing a blunted sector-shaped image.

Vector Array

A hybrid transducer combining linear sequential and linear phased technologies to produce a trapezoid-shaped image.

Elevational Resolution

Resolution measured perpendicular to the 2D imaging plane (slice thickness) that contributes to overall image quality.

1½D Transducers

Transducers with multiple side-by-side crystal rows designed to improve slice thickness and elevational resolution.

3D Imaging

Volume imaging created using 2D arrays with thousands of elements arranged in a checkerboard pattern.

4D Imaging

Real-time 3D ultrasound imaging.

Rendering

A post-processing step that creates a visual image from 3D volume data collected during an exam.

Side Lobes

Unwanted off-axis sound beams produced by single-element transducers that degrade lateral resolution.

Grating Lobes

Unwanted off-axis sound beams produced by array transducers that degrade lateral resolution and create artifacts.

Apodization

The process of altering electrical signal strengths across array elements to reduce side and grating lobe intensity.

Subdicing

The division of each PZT element in an array into smaller sub-elements to reduce grating lobes.

Dynamic Aperture

A system technique that varies the number of active receiving elements with depth to keep the sound beam narrow and improve lateral resolution.