Biomedical Engineering Reference
In-Depth Information
Specimen
Contrast
Agent
+90 deg.
Detector
2D Images
Data
Available
120 -140
Degrees
Emitter
−
90 deg.
(a)
(b)
Figure 8.22: (a) Transmission electron microscopy is used to image very small
specimens that have been set apart from the substrate by a contrast agent.
(b) TEM imaging technology provides projections over a limited set of angles.
8.6.5 Results
8.6.5.1 Transmission Electron Microscopy
Transmission electron microscopy is the process of using transmission images
of electron beams to reveal biological structures on very small dimensions. Typ-
ically transmission electron microscopy (TEM) datasets are produced using a
dye that highlights regions of interest, e.g. the interior of a microscopic structure,
such as a cell (see Fig. 8.22(a)). There are technical limits to the projection angles
from which data can be measured. These limits are due to the mechanical appa-
ratus used to tilt the specimens and the trade-off between the destructive effects
of electron energy and the effective specimen thickness, which increases with
tilt angle. Usually, the maximum tilt angle is restricted to about
±
60-70
◦
. Figure
8.22(b) shows an illustration of the geometry of this limited-angle scenario. The
TEM reconstruction problem is further aggravated by the degree of electron
scattering, which results in projection images (sinograms) that are noisy rela-
tive to many other modalities, e.g. X-ray CT. Finally, due to the flexible nature
of biological objects and the imperfections in the tilting mechanism, the objects
undergo some movements while being tilted. Manual alignment procedures used
to account for this tend to produce small misregistration errors.
We applied the proposed algorithm to 3D TEM data obtained froma3MeV
electron microscope. This 3D dataset consists of 67 tilt series images, each
corresponding to one view of the projection. Each tilt series image is of size 424
×
334. The volume reconstructed by FBP is of size 424
×
424
×
334. Figures 8.23(a)
