Image Production · ARRT 2025
Computed Radiography and Digital Workflow
Photostimulable phosphor (PSP), CR readers, histogram analysis, windowing, and post-processing for the ARRT Radiography Boards.
Overview
Computed Radiography and Digital Workflow explains how a photostimulable phosphor plate becomes a viewable image and what happens during the post-processing pipeline that follows. CR systems are the bridge between film/screen and direct digital radiography. The ARRT registry tests CR concepts because most facilities still use CR alongside DR.
The CR cassette holds a photostimulable phosphor (PSP) plate (typically barium fluorohalide doped with europium). When the plate is exposed to x-rays, electrons are trapped in metastable energy states proportional to local exposure. The plate is then read by a laser scanner: a red laser stimulates the trapped electrons to release blue light, which is captured by a photomultiplier tube and digitized. The plate is erased by intense white light and recycled.
Histogram analysis is the core of CR image processing. The system identifies the values of interest (VOI) within the recorded data, the range of pixel values that correspond to diagnostic anatomy. Edge detection and exposure recognition algorithms identify the collimated field. The histogram is normalized to a target shape, contrast and brightness are adjusted, and the final image is displayed. Exposure index (EI): the system's estimate of receptor exposure. Each manufacturer has its own EI scale (Fuji S-number, Kodak EI, Agfa lgM). The international IEC EI is a standardized alternative. Underexposure produces quantum mottle. Overexposure produces dose creep, each technologist increases technique to ensure a clean image, doses gradually rise unmonitored. Windowing: window width controls contrast (wide = low contrast, long scale); window level controls brightness (high = darker overall image). Other post-processing: edge enhancement (unsharp masking), spatial filtering, latitude expansion. CR/DR-specific artifacts: dead pixels, ghost images (incomplete plate erase), histogram errors (failure of edge detection), Moiré patterns (interaction of grid lines with the digital sampling matrix).
What you’ll learn in this chapter
The 10 lessons in this chapter break down as follows. The full lesson content is unlocked when you start a free account.
CR Foundations
- CR: Filmless Imaging
- Inside the CR Reader
Histogram & Look-Up Table
- Histogram Analysis & the LUT
- Garbage In, Garbage Out
Post-Processing
- Windowing: Width & Level
- Beyond Windowing: Special Effects
Knowledge Check
- Question 1 of 4 Quiz
- Question 2 of 4 Quiz
- Question 3 of 4 Quiz
- Question 4 of 4 Quiz
Key terms in this chapter
These are the 7 terms most likely to appear on the ARRT registry from this chapter. Use them as a flashcard pre-quiz.
- Photostimulable Phosphor (PSP)
- Barium fluorohalide doped with europium. Traps electrons proportional to x-ray exposure. Read by laser scanner.
- Histogram
- Distribution of pixel values across the image. The CR system normalizes the histogram to a target shape during processing.
- Exposure Index (EI)
- Manufacturer-specific or IEC-standardized estimate of receptor exposure. Tracks under- and overexposure.
- Window Width
- Range of pixel values displayed as gray scale. Wide width = low contrast, long scale of grays.
- Window Level
- Center pixel value of the displayed window. High level = darker overall image.
- Dose Creep
- Gradual unmonitored rise in technique factors over time as technologists overexpose to avoid mottle.
- Moiré Pattern
- Interference pattern from interaction of grid lines with the digital sampling matrix. CR/DR artifact.
Sample practice question: Image Acquisition
One free sample from the 98-question Image Acquisition bank. See the format, the rationale style, and the difficulty before you sign up.
An adult chest x-ray is performed at 80 kVp and 4 mAs at 72 inches SID. To maintain density at 40 inches SID, what new mAs is required?
Show answer and rationale
A, Incorrect: 1 mAs would result in significant underexposure. Apply the density maintenance formula.
B, Incorrect: Distance is decreasing, so mAs should decrease, but not by half.
C, Correct: Correct. Density maintenance formula: mAs₂ = mAs₁ × (SID₂² / SID₁²) = 4 × (40² / 72²) = 4 × (1600/5184) = 4 × 0.309 ≈ 1.2 mAs. Closer distance means more intensity, so less mAs is needed.
D, Incorrect: 13 mAs would more than triple the exposure. Reversed formula error, increasing distance requires more mAs, not less.
Read the full chapter, free.
The free tier unlocks one complete chapter (10 lessons), 50 practice questions, and 1 sample timed exam. No credit card required.
Frequently asked questions
What does the ARRT Radiography Image Production category cover?
Computed Radiography and Digital Workflow explains how a photostimulable phosphor plate becomes a viewable image and what happens during the post-processing pipeline that follows. CR systems are the bridge between film/screen and direct digital radiography. The ARRT registry tests CR concepts because most facilities still use CR alongside DR.
How many lessons are in the Computed Radiography and Digital Workflow chapter?
This chapter contains 10 lessons across 4 sections, plus a knowledge-check quiz at the end. The full lesson content is unlocked with a Premium subscription. The free tier includes the first chapter complete.
Is this chapter aligned with the ARRT 2025 Content Specifications?
Yes. Every chapter on this site maps directly to the ARRT Radiography Content Specifications effective 2025. This chapter falls under the Image Production domain of the official ARRT exam blueprint.