5th EuropEan MolEcular IMagIng MEEtIng - ESMI

5th EuropEan MolEcular IMagIng MEEtIng – EMIM2010
A system for 4D (3D+Kinetics) molecular imaging in bioluminescence and fluorescence
Maitrejean S. (1) , Kyrgyzov I. (1) , Bonzom S. (1) , Levrey O. (1) , Le Masne Q. (1) , Hernandez L. (1) , Raphael B. (2) .
(1) Biospace Lab,
(2) CEA/DSV/ I2BM / SHFJ / LIME.
smaitrejean@biospacelab.com
Introduction: Several technologies and systems are
now capable of delivering tri-dimensional data in Bioluminescence
and Fluorescence imaging. However, all
are based on sequential acquisitions, and therefore any
of them allow the production of real kinetic data in
3D. In this work we demonstrate a new device which
is able to acquire Bioluminescence and Fluorescence
data from several views simultaneously, allowing the
reconstruction of tri-dimensional images while keeping
all kinetic properties of the acquisition.
Methods: Multiple views of Bioluminescence and Fluorescence
data are acquired simultaneously using a photon
counting device (Photon ImagerTM) in which a
specific add-on with four mirrors is installed. This device
(named 4Views) allows the concurrent acquisition
of the ventral, dorsal, right, and left views of the animal
in a single image. The size and intensity of the four subimages
(i.e. the four views) are corrected by taking the
true optical path into account. The corrected photon
counting data are recorded in a list mode file with time
information (43 frame/s) as can be seen in Fig1.
In a second step a micro video projector is used to
project a moving spot on the animal. For each position
of the spot, the
height of the animal
is calculated
by triangulation
and a map of the
surface of the animal
is produced.
As the chosen
reconstruction
Fig1: simultaneous acquisition of four views
in bioluminescence imaging.
method is based
on the finite elements
method,
the volume of the animal is represented by a tetrahedral
mesh (about 30 000 tetrahedrons) using the Delaunay
algorithm, while the surface is approximated
by triangles, using a marching cube method. Then, the
forward problem is solved for given light sources that
are placed at the nodes of tetrahedrons and the light
intensities on the surface of the triangles are computed.
The forward problem is based in this first version on a
diffusion model with average constant absorption and
diffusion parameters. In a next version, a registration of
the surface of the animal with an anatomical atlas will
allow to use optical parameters associated with each
organ. In the following step measured data is extracted
from the list mode file and mapped on the triangulated
surface. Since the detected events are stored separately,
any time interval from 22 ms (one frame) up to the
total scan duration can be used to create the data. In
the last step of the process, the inner light sources are
estimated as the result of the inverse problem using a
least square criterion with a Tikhonoff regularization
term. This regularisation term is chosen as an entropic
term in order to favour connected solution. The two
last steps can be performed using any time interval of
the list mode file and therefore 3D kinetic data can be
computed for times scales larger than 22 ms.
Results: The validity of the method has been first tested
using light beads (Microtek) inside a half cylinder of a
scattering material (delrin). It has been demonstrated
that two light beads as close as three millimetres could
be separated, at a depth of one centimetre. A second
set of tests has been realised on an animal (nude mice)
by placing the light beads in the rectum of the animal.
On the second image (Fig 2) , two beads 9 mm far from
each other were placed in the rectum. It was possible to
reconstruct the two positions of the light sources. The
distance between the two reconstructed sources is 9.77
mm in good agreement.
Fig2: Reconstruction of two light sources based
on the four views data of fig1.
Conclusions: 3D optical reconstruction is known to
be approximate, but can give useful and satisfactory
results in a large number of applications. We have
demonstrated that this four view approach is able to
provide 3D kinetic molecular imaging data with a
spatial accuracy similar to other methods.
Acknowledgement: This work was supported in part
by the DIMI and ENCITE networks.
EuropEan SocIEty for MolEcular IMagIng – ESMI
day1
Parallel Session 3: TECHNOLOGY