Measure water CT number and uniformity

1. Choose the group

Open Analysis → QA → CT number and uniformity. After detection, check the center and four peripheral ROIs. Without successful detection, only ordinary sampling is available; no phantom summary is produced.

2. Inspect and adjust ROIs

Initial diameter is 10% of the phantom diameter, with peripheral outer edges 10 mm from the boundary. Move a circle or select it and drag a handle; release to calculate. Match sampling to your test protocol. Additional copied ROIs do not enter fixed-position uniformity metrics.

3. Read metrics

Water CT number is the center mean; uniformity is the largest absolute difference between a peripheral mean and the center, in HU. Consistency is the range of the five means, not repeatability.

For water noise, switch to its separate group instead of using these five ROIs.

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.