Ultrasound Physics and Instrumentation II - Displays and Image Storage

Flashcards covering ultrasound instrumentation, digital and analog scan converters, image processing techniques (preprocessing vs. postprocessing), and archive protocols like PACS and DICOM.

Scan Converter

Commonly thought of as the 'memory' of the ultrasound system, it stores images while the scan is being created (write) and converts data so it can be viewed on a video monitor (read).

Analog Scan Converter

An older form of technology using a vacuum tube with an electron gun and a dielectric matrix to store image data, limited by image fading, flickering, and instability.

Digital Scan Converter

A device that uses computer technology to digitize images into numbers (binary code $0$ and $1$) for storage and manipulation.

Pixel Density

The concentration of pixels in an image; higher density provides better spatial resolution and detail.

Bit

A binary digit, representing the smallest amount of computer memory; used in scan converters to determine the number of shades of gray in an image.

A-to-D Converter (ADC)

A device that converts electrical signals created by the transducer from the real world (analog form) into the computer world (digital form).

D-to-A Converter (DAC)

A device that translates digital signals back into analog form so they can be presented on an analog video display for interpretation.

Preprocessing

Any processing of the reflected signals that occurs before the information is stored in the scan converter's mental memory; examples include adjustments made before 'freezing' the image.

Postprocessing

Any image processing that occurs after the information has been stored in the digital scan converter.

Write Magnification

A preprocessing technique used before the image is 'frozen' that rescans the region of interest using smaller pixels to improve resolution.

Read Magnification

A postprocessing technique performed after the image is 'frozen' that enlarges the existing pixels of the stored data.

Coded Excitation

A process occurring in the pulser that uses very long pulses with wide bandwidth to distribute energy over broad frequencies, shortening the pulse and improving resolution.

Spatial Compounding

A technique where scan lines are directed in multiple directions to reduce speckle, minimize clutter artifacts, and improve visualization beneath highly attenuating structures.

Frequency Compounding

An imaging method that divides the reflected sound's range of frequencies into sub-bands to reduce speckle and noise artifact.

Pixel Interpolation

A method used for sector displays that assigns brightness values to 'missed' pixels based on the average brightness of adjacent pixels.

PACS

Acronym for Picture Archiving and Communication; a large computer network where digital images are stored with instant access and no data degradation.

DICOM

Acronym for Digital Imaging and Computers in Medicine; a set of protocols that allows for digital sharing on a network and is necessary for PACS to work.

Bi-stable

A display containing only two shades: black and white.

Gray Scale

A display that uses multiple levels of brightness to represent different echo amplitudes.