Taking measurements
The Measurement section of the sidebar holds two different sets of tools, and which one you see depends on the toolset the film is open in — switch with the chevron beside the Librevet wordmark at the top left. Orthopaedic films get Line, Angle, Circle, TPA, CORA and Norberg; soft tissue films get VHS, VLAS and six ratio tools instead. Line, Angle and Circle are on both.
Anything that reads in millimetres needs a calibrated radiograph. Anything that reads a ratio or an angle does not, which is why every soft tissue tool works on a plain chest or abdomen film. All of them scale automatically with zoom and rotation.
Measurement modes
How do I measure a length?
Distance between two points. Used for fragment length, plate span, bone width, and any general linear measurement.
Click once to place the first point, click again to place the second.
How do I measure an angle?
Measure an ad-hoc angle between any two arms. It drops a V, and you drag the vertex or either arm to fit it. It reads the interior angle (0–180°) and each arm’s length in millimetres, so it needs a calibrated radiograph.
How do I measure a circle?
Diameter or radius of a circular feature — joint surfaces, medullary canals, or bone fragments.
Click and drag to define the circle, then release.
TPA (tibial plateau angle)
A two-line construction used in TPLO planning: the mechanical axis of the tibia, and the tibial plateau line. The TPA reading appears in degrees, just past the caudal end of the plateau line, so it stays off the joint whichever way the film faces.
Refer to your standard TPLO planning references for target angles.
CORA
Centre of rotation of angulation. Draw the proximal and distal axes; the construct reads the deformity angle and marks the CORA where the axes cross.
Norberg
The Norberg angle, both hips at once. Drop both femoral head centres and both craniolateral acetabular rims; it reads each hip live, with 105° or more shown as normal.
The L and R labels follow the patient, not the screen. A lead side marker on the film, where the app has read one, decides which hip is which. Without one, the app goes by how the view is usually hung, and mirroring the radiograph tells it the film had been stored back to front. Flipping the film top to bottom never changes the labels — see How do I flip an X-ray?.
LBL sits on the same grid but is greyed out — it is in development and not available yet.
Soft tissue measurements
Switch the toolset to Soft tissue and the Measurement grid changes. None of these needs a calibrated film: every one is a ratio, or a count of vertebrae, so the magnification cancels out.
Each tool drops all its handles at once. Drag each onto its landmark — the panel lists them in order while nothing has been placed yet, and no reading appears until you have moved at least one handle. Where the patient’s species is recorded on the case, the normal range is shown under the figure and the number turns amber when it falls outside.
VHS (vertebral heart score)
On a lateral thorax. Drop the long axis from the ventral border of the carina to the cardiac apex, the short axis across the widest part of the heart, and the two spine handles on the cranial edges of T4 and T9.
Each axis is counted in vertebrae and the two are added. The panel shows both halves as well as the total, so you can check it against the film. Normal is 8.5–10.6 v in the dog — with a lot of breed variation — and 6.7–8.1 v in the cat.
VLAS (vertebral left atrial size)
Also on a lateral thorax, and usually placed beside a VHS on a mitral valve case. From the ventral border of the carina to the caudodorsal angle of the left atrium, counted in vertebrae from T4. 2.3 v or less is normal; 3.0 v and above is marked enlargement.
Trachea
Tracheal diameter against the thoracic inlet, on a lateral. Across the tracheal lumen at the inlet, then from the ventral border of T1 to the dorsal edge of the manubrium.
This one prints no verdict, deliberately: the threshold is a breed figure, not a species one — about 0.20 in an ordinary dog, 0.16 in a non-bulldog brachycephalic and 0.13 in an English Bulldog — so all three are shown and you apply the right one.
Bowel
The widest small intestinal loop against a vertebral body, for suspected mechanical obstruction. In a dog measure the height of the body of L5 at its narrowest; in a cat the height of the cranial endplate of L2. The two are not interchangeable, and the tool uses the right normal for the species on the case.
Colon
Colon diameter against the length of L5 — not its height. The megacolon figure, under 1.48 being normal. A cat measurement; there is no canine equivalent.
Kidney
Kidney length against the length of L2, on a ventrodorsal view. 2.5–3.5 × L2 in the dog, 2.4–3.0 × L2 in the cat. It flags a small kidney as readily as a large one.
Prostate
Prostate against the distance from the cranial edge of the pubis to the sacral promontory, on a lateral. Under 0.7 is normal. The reference distance is what makes it independent of the dog’s size.
CVC:Ao
Caudal vena cava against the aorta, measured at the same level on a lateral. Under 1.5 is normal; a distended cava is the radiographic face of right-sided congestion.
How do I place the points accurately?
- Magnification loupe. Toggle it from the top bar for precise endpoint placement on bony landmarks.
- Snapping. Dragging an endpoint close to an existing measurement point snaps to it.
How do I hide the measurements on the film?
Measurements on the film in the top bar hides every measurement at once if they are cluttering the view. It hides them from the picture only; nothing is deleted, and the surgical report still lists them.
Do measurements stay on the film?
- They remain on the radiograph until you delete them, and the case auto-saves.
- They live in image coordinates, not screen coordinates — they zoom, pan, and rotate with the radiograph.
- As many as you like can sit on the same radiograph.
How do I move or delete a measurement?
- Move an endpoint: click and drag the small handle at either end.
- Move the whole measurement: click and drag the line body.
- Move its number out of the way: drag the reading itself. It stays where you put it through zoom, rotation and flipping, and when the case is opened again, with a dotted line back to what it measures. Double-click it to put it back.
- Delete: select and press Delete or Backspace.