Computed Radiography & Digital Radiographic Technique

72 question-and-answer flashcards covering the major concepts, definitions, processes, and image-quality factors presented in the lecture notes on computed radiography and digital radiographic technique.

Who developed the first electronic digital computer?

Dr. John Atanasoff and Clifford Berry.

What years define the First Generation of computers?

1946–1959.

What electronic component characterized First-Generation computers?

Vacuum tubes.

Which device replaced vacuum tubes in Second-Generation computers?

The transistor.

What electronic advancement marks Third-Generation computers?

Integrated circuits fused onto a chip plus operating systems as the user interface.

What invention launched the Fourth-Generation of computers?

The Intel microprocessor (VLSI / microprocessor technology).

Give one key feature of Fifth-Generation computers.

They are faster, smaller and incorporate advances in semiconductor technology and artificial intelligence.

What major difference defines Sixth-Generation computers?

Greatly reduced size with increased speed and multitasking abilities.

Name the two principal parts of a computer system.

Hardware and Software.

Define computer hardware.

The physical components of the system, including input and output devices.

Define computer software.

Programs that tell the hardware what to do and how to manipulate or store data.

In what number system do computers operate?

The binary system (combinations of 0 and 1).

What is an operating system?

Instructions that organize data flow through the computer to solve problems (e.g., Windows, macOS, UNIX).

Give two examples of application programs.

Excel, iTunes (others include Word, tax software, etc.).

What computer element manipulates data and executes software instructions?

The Central Processing Unit (CPU).

List the three components of an analog (film/screen) imaging system.

Cassette, intensifying screen, and film.

In conventional radiography, what converts x-rays into light photons?

The phosphor of the intensifying screen.

How does CR differ from DR regarding cassette use?

CR requires the technologist to move a cassette/plate to a reader (indirect); DR has a permanently integrated detector with no cassette (direct).

Define digital imaging.

Any imaging process that produces an electronic image viewable or manipulable on a computer.

Why is a large dynamic range important in digital imaging?

It allows the image receptor to respond to a wide range of exposure values and still create diagnostic images.

Unlike analog systems, what type of values do digital systems produce?

Individual discrete (binary) values.

Name four types of digital image receptors.

PSP (CR), flat panel with TFT, CCD, and CMOS.

What older term is synonymous with Photostimulable Phosphor (PSP)?

Computed Radiography (CR).

Why is PSP called an indirect digital system?

Because the image is first stored on the plate, then read in a separate reader before display.

List the four basic steps of creating an image with PSP.

Metastable state (expose), stimulate, read, and erase.

During PSP exposure, what percentage of excited electrons return immediately to ground state?

Approximately 50%.

Why must a PSP plate be read soon after exposure?

If delayed, trapped electrons return to ground state and the latent image fades.

What does the PSP reader’s data-recognition program locate before processing the image?

Collimation edges to eliminate scatter outside the exposure field.

Which PSP layer traps electrons and is called the active layer?

The phosphor layer.

What is the purpose of the backing (light-shield) layer in a PSP plate?

To prevent external light from erasing plate data and to protect the cassette back.

What does the conductive layer in a PSP plate do?

Facilitates transportation through the reader and prevents static-related artifacts.

What compound is the typical PSP phosphor layer made of?

Barium fluorohalide doped with europium.

What is a photoconductor?

A material that absorbs x-rays and directly emits an electrical charge without needing a light step.

Give one example of a photoconductor material.

Amorphous selenium.

Define scintillator.

A phosphor that glows (emits light) when struck by high-energy photons.

Differentiate indirect and direct flat panel capture.

Indirect uses a scintillator to convert x-rays to light, then to an electrical signal; direct converts x-rays straight to an electronic signal via a photoconductor.

What material is commonly used for direct-capture flat panels?

Amorphous selenium.

State the primary role of a Thin-Film Transistor (TFT).

Collect released electrons (or light-generated charges) at each pixel and rapidly switch them for readout.

What are detector elements (DELs)?

Individual charge-collecting areas within the TFT array that correspond to image pixels.

A CCD requires which component to convert x-rays into detectable charges?

A scintillator such as cesium iodide or gadolinium oxysulfide.

Why are CCD detectors good for low-dose imaging?

They are highly sensitive and respond well to low light levels.

What special memory chip with battery support characterizes CMOS detectors?

Complementary Metal Oxide Semiconductor technology.

Name one advantage CMOS has over CCD.

Uses very little power and is cheaper to manufacture.

What does PACS stand for?

Picture Archiving and Communication System.

Give two typical PACS components.

Reading stations and archive servers (others: QC stations, web access, etc.).

List two key patient demographic items that must be entered with each exam.

Patient name and identification/medical record number (others: DOB, examination date).

How is digital image capture response described compared with film/screen?

Digital capture is linear, using all x-ray photons; film/screen response is logarithmic.

What was the speed class of the first PSP system?

200.

What is a pixel?

The smallest picture element in a digital image.

How does image resolution change when pixel size decreases?

Smaller pixels provide greater spatial resolution (detail).

What does bit depth determine?

The number of gray shades available for each pixel.

Define pixel pitch.

The distance from the center of one pixel to the center of the next pixel.

As matrix size increases while FOV stays the same, what happens to pixel size?

Pixel size decreases.

Does changing the Field of View (FOV) alter matrix size?

No; FOV changes do not affect matrix size, but matrix changes affect pixel size.

What information does the Exposure Index provide?

Feedback on the estimated exposure the image receptor received.

Define spatial resolution.

The ability to display small objects distinctly; described by spatial frequency and measured in line pairs per millimeter.

In what units is spatial frequency expressed?

Line pairs per millimeter (lp/mm).

How does a thinner phosphor layer affect CR spatial resolution?

It increases resolution.

What is noise in digital imaging?

Any unwanted signal interference; excessive noise lowers contrast resolution.

What term describes the efficiency with which a detector converts x-ray input into a useful image?

Detective Quantum Efficiency (DQE).

Which detector material currently shows the highest DQE?

Amorphous selenium (direct detectors).

What is an image histogram?

A graphical representation of an image’s gray-scale distribution.

Define aliasing in digital imaging.

Loss of digital information due to undersampling; also called fold-over or wraparound.

What is automatic rescaling?

Computer adjustment that corrects images with over- or under-exposure to provide uniform density and contrast.

Explain dose creep.

Progressive increase in patient dose when technologists raise technique (especially mAs) to avoid exposure errors rather than optimize factors.

What is a Look-Up Table (LUT)?

Stored data that substitutes new pixel values during processing to achieve proper brightness and contrast.

What does window level control?

The overall brightness (light or dark appearance) of the displayed image.

What does window width control?

Image contrast; a wider width produces lower contrast.

What is imaging stitching?

Digitally sewing multiple images together when the area of interest is too large for one cassette.

Why is background removal (shuttering) applied?

To blacken white collimation borders and reduce veil glare.

What is the function called “manual send” in digital imaging?

A computer command that forwards selected images to specified reading stations.

What does an archive query allow a user to do?

Retrieve images from PACS using criteria such as patient name, exam date, or anatomic area.