Optical Imaging - Correction Techniques in Emission Tomography - page 253

subject can be rotated while placed in the middle of the instrumentation, or
in a more advanced approach the instrumentation can be rotated instead. In
case of rotating instrumentation, the animal is assumed to be in a relatively
more comfortable position, which increases the possibilities of in vivo exper-
iments, with greater flexibility to anesthetize the animal, and the possibility
to monitor disease progression in an animal over time by repeated imaging.
This last approach is attractive for multimodal imaging solutions.

12.3.2 Multimodal optical imaging
The latest developments in the field of optical imaging include the de-
velopment of multi-modality systems. Before the development of hybrid sys-
tems, co-registration was achieved for example by using appropriate mouse
constrainers to transfer mice from one modality to another without chang-
ing their placement or shape. But because FMT is based on the use of safe,
non-ionizing energies, it is compatible with many different imaging modali-
ties, and can be integrated with other modalities in one hybrid system. The
simplest form of co-registration is by optically capturing the tissue outline
or surface. Knowledge of the boundary of the imaging volume is a great ad-
vantage in free-space imaging of arbitrary shapes, as it can be used to more
accurately calculate the forward model of light propagation which is used for
reconstruction of the fluorescent source distribution. Combination of fluores-
cence tomography modalities with three-dimensional imaging modalities such
as MRI or X-ray CT will yield even more benefit, since both modalities have
complementing features. Fluorescence tomography offers depth-dependent flu-
orescence contrast which is mainly functional or molecular, but it does not
give any anatomical information. Therefore co-registration with modalities
that reveal anatomy will help in positioning and understanding the source of
contrast. The images of the fluorescent source distribution can be superim-
posed for improved visualization. Furthermore, the anatomical modality can
be used to guide the inversion problem by offering a priori information to
facilitate the reconstruction of the fluorochrome distribution solution.

12.3.2.1 Optical tomography and MRI

The combination of near-infrared optical tomography and MRI has been
explored in the context of breast cancer detection and pre-clinical research
[6, 29, 30]. In breast cancer detection applications, imaging is focused on the
reconstruction of the optical property distribution of the breast, specifically of
absorption and scattering maps. Different optical coecients can be coupled
to different tissue types (tumor, background, etc.). The MRI image can sub-
sequently be used to create a segmentation of the structures indicated by the
optical property map in order to identify malignant regions. The MRI image
can also be used other way around, to guide the reconstruction of the optical
property distribution through regularization. In that case the MRI image is