Involved people : Zouina Aktouf, Gilles Bertrand, Didier Scellier (Sopha Medical)
A radioactive substance (tracer) is injected by intravenous way to a patient. Using a scintillation camera, and by the use of reconstruction techniques, one can obtain a 3-dimensional image made up of voxels (elements of volume) in which the "brightness" of each voxel represents the concentration of the tracer in the corresponding element of volume. In the case of the heart, the radioactive tracer has the characteristic to concentrate in the viable zones of the myocardium. Our goal is to obtain quantitative information on the healthy and pathological parts, which implies a segmentation of the myocardium in its entirety.
The figure fig. 13 illustrates the processing sequence: the original image (a) is initially segmented coarsely by a simple thresholding (b). A 3D skeleton (c) is then obtained starting from (b). When the myocardium presents a defect, the skeleton can be disconnected or have some holes. To reconstitute the supposed shape of the heart, the skeleton has to be patched in accordance with a geometrical model (d). An algorithm based on fuzzy logic use the patched skeleton as well as the original image to create a new image in which the level of gray of a point represent its degree of membership to the myocardium (e). The degree of membership image can be segmented simply by some local thresholding (f). The myocardium can then be analysed, and a percentage of activity in each sector can be calculated.
Our principal contribution was to propose and establish a new skeletonization algorithm adapted to this application. In particular, our algorithm allows the elimination of some nonsignificant branches in the skeleton. It is necessary to filter these branches, because their presence distorts the reconstruction of the myocardium. The second specificity of our algorithm relates to the preservation of the topology of the 2D cross-sections. The fuzzy segmentation algorithm applies to a series of 2D cross-sections, and must necessarily work on skeletons which preserve both the 3D topology of the object and the topology of the 2D cross-sections [ Akt97 ].
This study was financially supported by the company "Sopha Médical".
 |
 |
 |
| (A) | (b) | (c) |
 |
 |
 |
| (d) | (e) | (f) |