Measure air outside the phantom
Sample valid external air, check mean/SD and export an air report.
On this page
Before you start
Open 2D CT with genuinely imaged air outside the phantom; black borders may be invalid padding.
What you will achieve
Sample valid external air, check mean/SD and export an air report.
1. Open the air group
Open Analysis → QA → External air. The first visit on this slice attempts to create a reliable air ROI; still inspect its position.
2. Add an ROI if needed
Click Add air ROI, then click imaged air; Esc cancels. Avoid the phantom, table, obvious artifacts and invalid padding. Move or resize as needed. A deleted ROI is not automatically recreated.
3. Calculate and inspect
Release an edit to calculate automatically or click Calculate. Check mean, SD and valid pixel count. Air does not enter water CT number, uniformity or normalized water noise. If no valid result is available, check position and size; padding is not air.
Troubleshooting
Wait while values show “—” during recalculation. On failure, read the reason, adjust the region and click Calculate. Each ROI requires at least 16 valid pixels. Regenerate current group ROIs replaces the group layout; use Calculate if you only need new values.
Save or export
Click Export report in the footer, preview, then save. Check the image, ROI placement and values in the PDF. Water reports contain CT value/uniformity and water-noise groups; air reports are separate. Save a workspace and retain the source images to continue editing. Reports do not automatically determine compliance.