Biomedical Engineering Reference
In-Depth Information
(a)
(b)
(c)
(d)
(e)
Figure 8.23: 2D slice of dendrite data: (a) sinogram of one slice, (b) sinogram es-
timated by the proposed method, (c) back projection showing artifacts, (d) initial
model obtained by thresholding the back projection (white curve overlaid on
the back projection), and (e) final surface estimate.
and (b) show the sinogram corresponding to a single slice of this dataset and
the estimate of the same sinogram created by the method. Figure 8.23(e) shows
the surface estimate intersecting this slice overlaid on the back projected slice.
Some structures not seen in the back projection are introduced in the final
estimation, but the orientation of the structures introduced suggests that these
are valid features that were lost due to reconstruction artifacts from the FBP.
Also, the proposed method captures line-by-line brightness variations in the
input sinogram (as explained in Section 8.6.2.1). This suggests that the density
estimation procedure is correct.
Figure 8.24 shows the 3D initialization and the final 3D surface estimate. The
figure also shows enlarged initial and final versions of a small section of the sur-
face. Computing the surface estimate for the TEM dendrite with 150 iterations
took approximately 3 hours on a single 300 MHz processor of a Silicon Graph-
ics Onyx2 workstation. We consider these results positive for several reasons.
First, the biology is such that one expects the spines (small protrusions) to be
connected to the dendrite body. The proposed method clearly establishes those
connections, based solely on consistency of the model with the projected data.
The second piece of evidence is the shapes of the spines themselves. The re-
constructed model shows the recurrence of a characteristic shape—a long thin
spine with a cup-like structure on the end. This characteristic structure, which
