Cortical Thickness Mapping Visualisation

This page is used to visualise the results of the estimation of bone cortical thickness from CT data. This visualisation is automatically selected when the 'thickness' task page is selected.

In the middle of the visualisation controls are some text messages that show whether the current estimate was successful, what the various results are and what the average (least mean square) error was between the modelled and measured CT values along the displayed line, in HU.

At the top, there is a dropdown list for determining what is mapped to the surface, i.e. thickness, mass, density (CT value), trabecular density, joint width, endocortical, periosteal or soft tissue. If cortical thickness was estimated using the 'constant density' technique, the 'density' option will show a constant value over the entire surface. If cortical thickness was performed using FWHM (not fixing the density), then the actual peak CT value at each location will be mapped over the surface. 'Joint width' will only be available if the '+inner' or '+outer' checkboxes were ticked before estimation.

After this, there is another dropdown list which selects the colour map to be used to display this data. Various colour maps are available: the best choice will depend on the specific application.

The following four sliders control the range of values used for the colour scales when mapping these values. After this, the smoothing slider can be used to smooth any of these estimates over the surfaces. The 'fill missing data' slider controls to what extent this smoothing should be used to replace missing values as well.

The bottom three checkboxes control what is displayed in the visualisation window below the image and 3D windows. This contains a graph of CT values in HU against distance along the currently defined line in mm. The graph can display the 'original data' (in blue), which are just the CT values along the line through the data. It can also display the 'optimised blurred model' (in red), which is what the optimisation process attempts to match as closely as possible with the original data. The 'deconvolved model' (also in red) is the unblurred CT value distribution from which the optimised blurred model is created, and it is this which gives the cortical thickness. The default is to display all three graphs.

The range of CT values (in HU) on the vertical axis is the same as the range of CT values that can actually be seen in the CT image data. Hence to change this range, use the rotate tool to change the windowing parameters in the top left image window, and the graph will also be updated dynamically.

When cortical thickness is mapped over an entire surface, the results are updated dynamically as the calculation progresses, but at not more than 5 updates per second. It is likely that the actual calculation will proceed at a much faster rate than this.