The PACS Truth Engine
A practical screening check for dimensional scaling in projection radiography workflows
Author: Jarrid Henderson, J2 Medical
Date: March 2026
Version: 1.0
Contact: J2 Medical, Pittsburgh, PA — www.j2medical.com
Purpose
Measurement tools in PACS are widely used to quantify anatomy and pathology. In projection radiography, apparent size varies with geometry (source distance, object plane, detector distance). Without a known physical reference near the plane of interest, pixel-to-mm scaling can function as an inference rather than a verification.
The PACS Truth Engine is a simple screening approach to help teams check whether a given workflow’s size scaling is plausibly aligned with physical reality, and to prompt follow-up with medical physics or vendors when warranted.
Scope, limitations, and intent
This document describes a screening check, not a formal calibration method.
It is not a substitute for acceptance testing, periodic QA, or work performed under a qualified medical physicist.
Results should be interpreted as “investigate further” indicators, not as a standalone basis for clinical decisions or device performance claims.
Nothing here asserts that any specific PACS vendor or system is inaccurate.
Why do a screening check?
In orthopedic templating, teams commonly use a physical reference to reduce uncertainty in sizing. In many other workflows, measurements may be used longitudinally (e.g., tracking change over time) without a built-in, immediate “ground truth” feedback mechanism.
A quick verification-style screening check can help answer a practical question:
“In our workflow, are our measurements plausibly aligned with a known physical size under typical technique?”
The Five-Minute Coin Screening Check
Goal: Screen for potential systematic scaling mismatch in a specific room + protocol + PACS measurement workflow.
Recommended default: Use a US quarter (larger diameter tends to reduce measurement noise).
Steps
Place a coin flat on a foam pad (to reduce tilt) at an approximate “clinical depth” (e.g., 8–12 cm) on a table.
Keep the coin near the center of the field and use a consistent SID (use the same SID each time you repeat the check).
Expose using the same protocol you want to screen and send to PACS.
Measure the coin diameter in PACS.
Repeat 3 exposures and average the 3 measured values.
Coin diameters (US)
Penny: 19.05 mm
Nickel: 21.21 mm
Dime: 17.91 mm
Quarter: 24.26 mm
Half Dollar: 30.61 mm
Use the screening calculator
To keep the math simple, visit www.j2medical.com/pacs-truth-engine and use the Truth Engine Screening Calculator. Choose your coin and enter the diameter you measured in PACS. The calculator reports the implied scaling (magnification) factor and the percent difference from the coin’s known diameter.
Interpreting results (screening)
If repeated measurements differ from the known diameter by a few percent, that can indicate the workflow is worth reviewing with medical physics (positioning, SID, measurement tool behavior, protocol differences between rooms, etc.). As a practical screening threshold, repeated error greater than ~2–3% may justify a deeper review.
What to do if the screening check shows a discrepancy
If the check suggests a systematic mismatch:
Reconfirm the basics: coin flat, centered, consistent SID, same protocol, repeatability across exposures.
Consider whether object plane assumptions match the workflow.
Escalate to medical physics / PACS support for formal QA and documentation if needed.
Disclosure
The author is the founder of J2 Medical, which manufactures and sells radiographic scaling markers (Akucal). Mention of any product is provided as one possible approach for placing a consistent physical reference into the image field when appropriate.
Closing
This screening method is intended to be simple, practical, and non-disruptive—a quick way to check whether a measurement workflow is behaving as expected and to encourage formal follow-up when it is not.
Learn more: www.j2medical.com/pacs-truth-engine