Computer-Aided and Digital Radiography Lecture

This flashcard set covers the history of computing, computer generations, the mechanics and construction of Computed Radiography (CR) and Digital Radiography (DR), image quality characteristics, exposure indicators, and digital image processing.

Abacus

The first counting tool, invented in China thousands of years ago.

Analytical Engine

A machine designed by Charles Babbage in 1842 intended to perform general mathematics.

Colossus

The first working electronic computer, made by the British in 1943 to crack secret German codes during World War II.

ENIAC

A general-purpose computer made in 1946 using $18,000$ vacuum tubes; it was fast for its time but lacked memory and frequently broke down.

Transistor

A tiny on-off switch for electricity created at Bell Labs in 1948, which marked the beginning of second-generation computers.

Integrated Circuits (ICs)

Also called microchips or chips, these are tiny electronic circuits where many components are fabricated together on a single piece of semiconductor, usually silicon.

Fourth Generation Computers

Computers starting from 1975 that used microprocessors and $VLSI$ (Very Large-Scale Integration).

Computed Radiography (CR)

Also known as cassette-based digital radiography, it uses storage phosphor plates to capture X-ray images.

Photostimulable Phosphor Plate (PSP)

The imaging plate ($IP$) used in $CR$ that captures X-ray energy and can be reused for several hundred exposures.

Barium fluorobromide with Europium ($BaFBr:Eu^{2+}$)

The most commonly used phosphor material in the phosphor layer of a $CR$ imaging plate.

Conductive Layer

A layer in the imaging plate construction that absorbs and reduces static electricity to prevent image quality degradation during transport in the reader.

High Resolution IP

An imaging plate with a thinner phosphor layer and lower speed settings, providing sharper detail for extremity examinations.

Latent Image

The invisible recorded image on the phosphor plate that exists after exposure but before processing.

Raster Pattern

The zig-zag pattern in which a red laser beam sweeps across the imaging plate to release trapped energy during the readout process.

Photomultiplier Tube (PMT)

A component that converts light emitted from the phosphor plate into electrons, amplifies the signal, and sends it to the analog-to-digital converter ($ADC$).

Ghosting

An image artifact caused by leftover signals from previous exposures appearing on a new image when a plate is not properly erased.

Digital Radiography (DR)

A modern way of taking X-rays without using cassettes, utilizing flat panel detectors or $CCD$ to create images almost instantly.

Indirect Capture

A $DR$ process where X-rays are first converted into light via a scintillator before being turned into an electrical signal.

Secondary Quantum Sink

A disadvantage in $CCD$ systems where the number of light photons reaching the sensors is less than those emitted by the scintillator, reducing spatial resolution.

Scintillator

A material used in indirect $DR$ to convert X-rays into light; commonly made of Cesium Iodide ($CsI$) or Gadolinium oxysulfide ($Gd_2O_2S$).

Amorphous Silicon (a-Si)

A photodiode array material that converts light emitted by a scintillator into an electrical signal in indirect capture systems.

Direct Capture

A $DR$ process that uses a photoconductor to change X-rays directly into an electrical signal without an intermediate light-conversion step.

Amorphous Selenium (a-Se)

The most common photoconductor material used in direct conversion detectors to create electron-hole pairs from X-ray photons.

Pixel

The smallest element of a digital image; smaller sizes result in higher spatial resolution.

Pixel Bit Depth

Determined by $2^n$, this value specifies how many gray shades each pixel can represent.

Voxel

A pixel with a numerical value in $3D$ space, representing volume rather than just a flat area.

Window Level

A post-processing control used to adjust the overall brightness (lightness or darkness) of the digital image.

Window Width

A post-processing control used to adjust the image contrast or the range of gray levels displayed.

Spatial Resolution

The ability of an imaging system to display small structures and fine detail clearly, often measured in line pairs per millimeter ($lp/mm$).

Detective Quantum Efficiency (DQE)

A measurement of how efficiently a detector converts X-ray photons into a useful image signal; higher efficiency allows for lower patient dose.

Exposure Indicator (EI)

A numerical value provided by digital systems that reflects the amount of radiation reaching the image receptor.

S-number (Sensitivity number)

The exposure indicator system used by Fuji, Philips, and Konica Minolta, which has an inverse relationship with the radiation exposure.

ALARA Principle

The ethical standard of maintaining radiation exposure "As Low As Reasonably Achievable" for patients and staff.

Histogram

A graphical representation showing the number of pixels at each gray level or brightness value in an image.

Look-Up Table (LUT)

A digital table used to control contrast by mapping each pixel value to a specific output shade.

Nyquist Theorem

A principle stating that the detector's sampling rate must be at least $2$ times the highest frequency (smallest detail) to record the signal accurately.

Aliasing

A phenomenon that occurs when a signal is sampled less than twice its highest frequency, resulting in a "folded" or striped pattern in the image.

Edge Enhancement

A high-pass filtering function that averages signals from neighboring pixels to emphasize differences and sharpen edges.

Veil Glare

Eye strain or temporary glare caused by the bright white borders of unexposed areas on a digital radiograph.

Image Stitching

A software process used to combine several individual images into one large image, typically for full spine or leg examinations.

Quality Assurance (QA)

A planned system focused on the personnel and processes within a radiology department to ensure service quality.

Quality Control (QC)

A specific set of tests and checks performed on radiology equipment to ensure it functions safely and produces high-quality images.

RAID 5

The most common storage configuration in $PACS$ short-term storage, utilizing data striping and error-checking across disks for speed and reliability.

Complementary Metal-Oxide Semiconductor (CMOS)

An image sensor where each pixel processes its own signal; it is faster and consumes less power than a $CCD$.