The `Measurements' window displays quantitative information relating to 2D curves drawn in the `Reslice' window and 3D landmarks positioned by the user.
The window is divided into three panels. The top panel shows the numbers of the currently defined landmarks. By clicking with the left mouse button on the landmark numbers, you can select any three at a time. The three landmarks define a triangle: the middle panel shows a sketch of this triangle and displays the coordinates its vertices (in the coordinate system of the position sensor), the length of each side and the angle at each vertex. Lower down, there is a sketch of the 2D curve drawn by the user in the `Reslice' window. The curve's length and enclosed area are displayed. The area is arrived at by connecting the two end points of the curve to produce a closed contour. Note that drawing a curve in the `Reslice' window has a dual purpose: it can be useful for length and area measurements in conjunction with the `Measurements' window, and it can also be used to define a surface for non-planar reslicing in the `Manifold' window. Please refer to the documentation for the `Manifold' window for instructions on how to draw and edit the curve in the `Reslice' window. Finally, the bottom panel of the `Measurements' window has three text entry fields with which you can attach labels to the three selected landmarks. Right at the bottom there is a button to close the window.
Landmarks can be positioned using the `Review', `Reslice', `Manifold' or `Surface' windows. You can define up to 100 landmarks at a time. Landmarks 0-73 are associated with the current data set and saved in segmentation files. The remaining landmarks, labelled `a' to `z', are not saved in segmentation files and persist after you close the data file: they can, however, be saved in the fiducial registration file. Their intended use is to aid the registration of the 3D ultrasound data set with another 3D image volume. Click here for further details.
To place a landmark, move the cursor to the appropriate position in the `Review', `Reslice' or `Manifold' window and type the number of the landmark you wish to define (if it's a two digit number, be careful not to move the cursor between digits). The corresponding landmark immediately moves to the new position, and the landmark's number appears in the top panel of the `Measurements' window (if it was not there already). The landmarks are also displayed in the `Outline' window, though they are not drawn if you have chosen not to view segmentations using the `Seg' toggle button. Similarly, landmarks are only visible (and can only be defined) in the `Review' window if the `Segment' toggle button is selected. The three persistent landmarks, `a', `b' and `c', can also be defined in the `Preview' window.
As well as selecting landmarks, the top panel of the `Measurements' window can be used to delete or zero a landmark. Clicking with the right button on the landmark's number deletes the landmark. Clicking with the middle button resets the landmark's position to the origin of the position sensor's coordinate system. In conjunction with the `Outline' window (you may need to zoom out a lot), this facility allows you to see where the position sensor's transmitter was located relative to the B-scans.
You can attach a label to a landmark by selecting it (left mouse click in the top panel) and then typing the text into the corresponding field at the bottom of the `Measurements' window. Labels must commence with the number of the landmark, then a colon: Stradx will not let you delete the number and colon in the text entry field. After the colon, you can append whatever label you wish.
In the example above, landmarks 2 and 3 were positioned in the `Review' window. Landmark 2 happens to lie on the intersection with the reslice plane, so it is also displayed in the `Reslice' window. Landmark 1 was positioned in the `Reslice' window. The resulting measurements can be seen in the example of the `Measurements' window at the top of this page. The window displays the distances and angles defined by the landmarks, and also the length of the foetus' spine (the area measurement is, in this example, fairly meaningless).
Landmarks can also be placed in the `Surface' window. As with the other windows, you simply type the number of the landmark, which is then positioned below the mouse pointer. If the surface is fully opaque, the landmark is placed on the front surface; if it is semi-transparent, the landmark is placed midway between the front and back surfaces. You can change the opacity of the surface using the `Object Selection' panel. If you hold down the 'Control' key while placing the landmark, it will be positioned at the centroid of the first object under the mouse pointer.
The `Measurements' window also controls the display of calibrated rulers in the `Review', `Preview', `Reslice' and `Manifold' windows. These rulers are displayed when the `Measurements' window is open, but not when the `Measurements' window is closed. Here's an example of rulers displayed in the `Review' window.
The large tick marks correspond to centimetres, the small ticks are millimetres. For lower resolution scans, the millimetre ticks are not displayed.
You should take great care when using the rulers in the `Manifold' window: the vertical scale measures distance along the generating curve, not absolute distance. So features which are, say, 5cm apart vertically according to the ruler, may in fact be much closer together in 3D space. Similarly, be careful interpreting ruler readings when you're looking at a volume rendering in the `Reslice' or `Manifold' window.