Measurements live under the Measurements toolbar group. This article covers the everyday ones: length (ruler), angle, rectangular or elliptical ROI, area, and volume. Each measurement persists with the study if you save it as a Presentation State.
Step 1: Measure a length
Click Line (or use the Ruler tool). Click the start point, then the end point. The distance in mm appears next to the line. For a multi-segment length, use Polyline and click each vertex; double-click to finish.
Step 2: Measure an angle
Click Angle. Click three points in order: first arm, vertex, second arm. The angle in degrees shows at the vertex. For Cobb angles and similar specialist measurements, use the dedicated tools described in the radiology measurements article.
Step 3: Measure an ROI
Click Ellipse or Rectangle. Click and drag to draw. The ROI label shows area (mm^2), mean HU (for CT), standard deviation, min, and max.
Step 4: Measure area or volume
Area uses a freehand (Pencil) or closed polygon to outline irregular regions. Volume extends this across multiple slices: outline on each slice, and the viewer sums the enclosed volume in cm^3.
Step 5: Save measurements
Use Save in the toolbar to write measurements as a Presentation State. They will display whenever the study is reopened. See the annotations article for detail.
Tips
- HU values depend on correct CT calibration. If you read a CT from an uncalibrated scanner, treat absolute HU with caution.
- Deleting a measurement is reversible only in the current session. Once you reload the study, deletions are permanent unless you restore from a saved Presentation State.
Related articles
- Radiology-specific measurements
- Annotations, text and arrows
- Calibration