Two-Dimensional Ultrasound Imaging and Transducers

This set of flashcards covers vocabulary and concepts regarding two-dimensional imaging, various transducer types, beam characteristics, and the effects of element damage as presented in the lecture notes.

Dynamic Aperture

A technique used to make a sound beam narrow over a greater range of depths by changing the number of crystals along the face of the probe used to transmit pulses and receive reflections.

Apodization

A process that reduces the strength of side and grating lobes by using stronger electrical signals to excite inner crystals and progressively weaker signals for outer crystals.

Subdicing

The division of a crystal in a linear array into smaller sub-elements that are electrically joined to reduce grating lobes.

Side Lobes

Off-axis sound beams created by single element transducers that extend outside the main beam in the far zone and degrade lateral resolution.

Grating Lobes

Extra, off-axis sound beams created by array transducers that degrade lateral resolution and create artifacts.

3-D Imaging

Volume imaging created by a 2-D array with thousands of elements arranged in a checkerboard pattern.

Rendering

A computer-generated post-processing step that constructs photo-like pictures with color, shadows, and texture from three-dimensional data.

Elevational Resolution

Also called slice thickness resolution; it is measured in a direction perpendicular to the imaging plane and determines if reflections are from structures directly in the imaging plane.

$1\frac{1}{2}$-D Array

A transducer with multiple crystals in the up-and-down direction (e.g., 100 wide by 7 high) designed to improve elevational resolution.

Mechanical Transducer

A transducer containing a single, circular, disc-shaped active element physically moved by a motor to create a sector-shaped image.

Transducer Array

A modern transducer design containing multiple active elements cut from a single slab of PZT.

Channel

The combination of the active element, wire, and system electronics in an array transducer.

Linear Phased Array

A compact transducer that uses an electronic technique called phasing to steer and focus the beam, creating a sector-shaped image.

Beam Former

The electronics within the ultrasound system that create the electrical spike patterns used to steer and focus the sound beam.

Phase Delays

Infinitesimal time differences, such as $10\,ns$, between electrical signals that steer or focus a sound beam.

Dynamic Receive Focusing

Focusing performed automatically during reception by introducing variable time delays to electrical signals based on the depth of the reflection.

Annular Phased Array

A transducer with ring-shaped elements that provides multiple transmit focal zones and uses mechanical steering.

Linear Sequential Array

A large-footprint transducer that fires small groups of crystals simultaneously to create parallel sound beams and a rectangular image.

Convex Array

Also called curved or curvilinear; it has elements arranged in a bowed line to create blunted sector-shaped images.

Vector Array

A combination of linear sequential and linear phased technologies that creates trapezoidal-shaped images.

Mechanical Transducer Damage

Malfunction of the single crystal results in the loss of the entire image.

Linear/Convex Array Damage

Malfunction of an element results in a dropout of image information from the top to the bottom of the image.

Annular Phased Array Damage

Malfunction of a ring results in a horizontal or side-to-side band of dropout at a particular depth.

Phased Array Damage

Malfunction of an element results in erratic steering and focusing.