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22. 4D Surface Editor

22.1 Introduction

The 4D Surface Editor package (which predates the 3D version) is designed specifically for cardiac image analysis. As such it has additional functionality for this purpose, and it also provides graphical user interfaces to parts of the shape-based deformation analysis methods (see Papademetris et al. TMI 2002 [81].)

There are five major differences in the user interface of the 4D surface editor as compared to the 3D version, namely:

1. There is no objectmap functionality - there are only surface-based editing tools. The objectmap menu is replaced by a much simpler ``Edit Surface'' menu.
2. There is a ``Cardiac'' menu button in the menu bar which provides access to two additional controls.
3. There are four-tabs in the rightmost pane instead of three. The ``Multi'' tab corresponds mostly to the ``Surface+'' tab of the 3D editor, whereas the ``Segment'' tab has additional functionality for batch mode segmentation and curve interpolation
4. There is a cine-mode (if the loaded image has more than one time point) accessible using the ``Movie Control'' button in the ``Image'' tab.
5. The Spline Editor (which replaces the Spline/Objectmap Editor) has the ability to display what is termed ``ghost curves'', i.e. the curves of the same surface at the previous and next time frames to enable the construction of temporally smooth sequences. This is shown in Figure 22.3.

The rest of this description assumes familiarity with the 3D editor and simply focuses on the above 5 points.

22.2 Movie Controls (Cine Mode)

The movie control (shown in Figure 22.2) is accessed using the ``Movie Control'' button in the ``Image'' tab. It has functionality for playing cine-loops of the contents of the viewer (e.g. image, surfaces, tstacks, strain maps etc.). It has two distinct play modes ``Complete'' which is equivalent to simply incrementing the frame and ``Fast'' which uses cached versions all frames prior to playing to achieve higher performance at the loss of interaction during movie mode. The caching is performed by clicking the ``Prepare'' button.

Figure 22.1: The 4D Surface Editor - Similar to the 3D surface editor, but with slightly different control features.
Figure 22.2: The Movie Controls Popup.

22.3 The ``Multi'' and ``Segment'' Tabs

The ``Multi'' tab is closely related to the ``Surface+'' tab in 3D Surface Editor. The key difference is that the Load All/Save All functionality refers to the loading/saving of temporal sequences of surfaces instead of surface sets. In addition the ``Export'' button provides access to a more advanced export facility, for exporting temporal sequences of surfaces.

The ``Segment'' tab provides facilities for spatial and temporal interpolation. In the ``Spatial'' tab the user specifies the top and the bottom slice and curves in between are filled in. In the temporal interpolation, the assumption is that the user will first trace the ED and ES surfaces and then the interpolation algorithm can be used to generate good candidate segmentations by simple interpolations.

The ``Auto'' and ``Batch'' modes refer to automated segmentation using the snake algorithm, This is work in progress and should be used sparingly.

Figure 22.3: The Spline Editor is similar in spirit to the more advanced Spline/Objectmap editor used in the 3D Surface Editor. It does not have any ``objectmap'' functionality. The one additional feature is the ``Ghost Display'' option which enable the display of the previous and/or next curve(s) in the temporal sequence (the ghosts of the past and the future) to enable the easier construction of smooth temporal sequences.

Figure 22.4: Additional Functionality of The 4D Surface Editor

22.4 Changes in the menu and controls

The 4D viewer has a number of different menu choices and associated control windows from the those of the 3D viewer.

The Menu The Cardiac menu shows how to access the ``tstack'' control and the ``Abaqus post control''. The tstack control shown below has functionality for manipulating tstack (Triangulated Stack files). These are created from the surface .sur files and represent an explicit surface representation (in terms of points and triangles) as opposed to the implicit cubic polynomial representation of surfaces stored in the .sur files.

The Tstack Control The .tstack files can be generated using the ``Export'' button in the ``Multi'' tab of the main 4D surface editor window. These generates a series of files which can be Loaded/Saved using the Load/Save options in the T-stack control. Much of the rest of the functionality of the T-stack control mirrors closely that for the SplineStack control described earlier.

Figure 22.5: Additional menu choices in the 4D Surface Editor - The Cardiac menu is present here, containing two tools for working with cardiac images in the form of triangulated stack files, and output files from the Abaqus FEM package.
Figure 22.6: The various control windows that are accessible from the 4D Surface Editor.

One key difference is the presence of the ``Color Mode'' menu. This selects the function used to create a color scale for the surface. These measures are based on the different combinations of the two principal curvatures (e.g. Gaussian, Mean, 1st principal, 2nd principal, bending energy and shape index). These colorscales are aids to visualization.

Computing Curvatures The curvatures can be computed using the ``Computing Curvatures'' control (shown in the top right) which is accessed using the ``Curvatures'' button. There are two parameters to be set. The ``scale'' parameter controls the size of the neighborhood used for curvature computation and the ``smooth iterations'' the number of smoothing iterations applied prior to curvature computation.

Once curvatures are computed the can be used as an input to the shape tracking algorithm. This is done in the ``Shape-based .. tracking control'' which is accessed from the ``Shape-Tracking'' menu on the T-stack control. The options are involved are too technical for a brief overview of this kind. The same applies to the solid control which creates a finite-element mesh between selected endo-cardial and epi-cardial surfaces. The functionality captures in these controls (curvatures, shape-based tracking, create solid) represents most of the steps in the shape-based tracking deformation algorithm of [Papademetris et al , TMI 2002]. The one step missing is the finite element analysis step itself which requires the presence of the Abaqus Finite Element package.

The output of the Abaqus FEM package can be loaded into the ``Abaqus Post Control'' to visualize and quantify regional myocardial strains.

Webpage design by Marcello DiStasio.


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