Calibrating radiographs

Calibration tells the app the real-world size of one pixel. Every measurement and every implant template depends on this — without it, the rest of the app’s tools are locked.

Why it matters

Radiographic magnification varies between exposures. The same dog’s tibia may project as 130 mm on one X-ray and 142 mm on another. If you skip calibration and try to overlay a 65 mm implant, it’ll land at the wrong size — and you’ll plan with the wrong dimensions.

Every measurement and overlay in the app uses the calibration you set. Get this step right.

How to calibrate

Click Calibrate in the sidebar.
Auto-detection runs immediately. If it finds the marker and the confidence is high, calibration is set automatically.
If auto-detection misses or picks the wrong object, click near the calibration marker. The app re-runs detection in a window around your click.
If that still fails, the manual circle tool lets you fit the calibration circle by hand.

The calibration scale appears in the top of the canvas once set.

What you need in the image

A radiopaque reference of known dimension visible in the radiograph. The default is a 25 mm sphere placed in the same plane as the bone of interest — typically taped to the limb. Other reference sizes can be set in the calibration sub-panel before placing.

Common problems

Chained or stacked markers. Two or more spheres touching can look like one large blob to most detectors. The app’s auto-calibration handles stacked spheres, but verify the picked one is the correct individual marker.
Marker off-plane. A marker laid next to the bone but at a different distance from the X-ray plate has different magnification than the bone itself. Calibration will look right but the rest of your planning will be subtly off.
No marker visible. You can’t calibrate without one. The app won’t let you measure or place templates until a scale is set.

Auto-detection confidence

Auto-detection produces a confidence score. High-confidence detections are accepted automatically; lower-confidence ones prompt you to verify. Auto-detection is a starting point, not an authority — always visually confirm the picked marker is correct before relying on the calibration for surgical planning.

When to re-calibrate

New radiograph in the same case — every image needs its own calibration.
Suspicious measurements (a 6 kg dog’s tibia measuring 180 mm) — recalibrate before trusting the rest.