6 · Measuring and annotating
Measurement and annotation live on the MPR slice panes. All distances are true millimetres computed in volume geometry, and all density statistics are raw HU (section 5.1's calibration caution applies). The MPR guide (chapter 8.1) covers the reading workflow; this chapter is the tool reference.
6.1 The tool palette
The active tool runs on the left mouse button. Keys 1 to 9 and 0 select
tools in palette order, and W selects the window/level tool (it sits at the
end of the palette so the number keys keep their historical meaning):
| Key | Tool | What it does |
|---|---|---|
| 1 | Crosshairs | Click spots the crosshairs to that point in all planes; drag pans the pane |
| 2 | Pan | Drag moves the slice in the pane |
| 3 | Length | Two points, distance in mm |
| 4 | Angle | Three points, angle in degrees |
| 5 | Arrow | An arrow with a text label (prompted) |
| 6 | Text | A text label (prompted) |
| 7 | Rect ROI | A rectangle with density statistics |
| 8 | Ellipse ROI | An ellipse with density statistics |
| 9 | Freehand | An open stroke measures a curved path in mm; closing the loop makes a region with density statistics |
| 0 | 3D ROI | A rectangle extended through the slice by the box-depth slider (1 to 60 mm), returning volume and density statistics, outlined in the 3D pane |
| W | W/L | Window/level by dragging on any slice: up/down moves the window center, left/right changes its width. The sidebar Window section follows live |
6.2 Selecting and deleting
Select an annotation by shift-clicking it on a pane, or by clicking its row in
the objects panel. Del (or Backspace) deletes the selection.
6.3 The objects panel
The objects list, in a strip under the four MPR panes, lists every annotation and measurement on the current volume with its values, alongside the saved views (section 3.5). Each row names its kind in words, as the tool palette does (Length, Angle, Arrow, Text, Rect ROI, Ellipse ROI, Freehand, 3D ROI), then its value. The eye icon hides or shows one object, the cross deletes it. Rows select, restore, and delete in one click. The selected row is solid blue, as every selection is. A 3D ROI row also carries a small orange square beside its label, the colour of the 3D ROI hint on the slice pane, so it stays recognisable whether or not it is selected.
6.4 Persistence
Annotations, saved views, and 3D ROIs persist per volume across sessions. They are stored as small text sidecars in the app-data folder on this machine (labels, world-mm coordinates, HU statistics; never pixels; section 10.2), so reopening the same export finds them again, and the scan itself is never modified.