Speaker
Ms
Elodie Breton
(Service de Biophysique et Médecine Nucléaire, CHU Hautepierre, 1 av. Molière, 67098 Strasbourg, France)
Description
Small animal imaging techniques provides the possibility to follow non invasively and
in vivo the morphological or functional evolution of a particular organ or tissue
over time. The aim of dual imaging is to combine morphological and functional
information. Among multimodality imaging techniques for co-registration of mutual
information, SPECT/MRI has not, to our knowledge, be applied practically due to
complex interactions between magnetic field and nuclear instrumentation. We describe
and illustrate our practical experience in small animal sequential SPECT/MR images
acquisition and fusion. For SPECT imaging we used a small animal dedicated rotating
single head gamma camera with a 1.5mm diameter tungsten pinhole collimator and 12cm
in focal distance (Gaede, Freiburg, Germany) and an algebraic reconstruction method
able to achieve isotropic millimeter 1x1x1mm3 spatial resolution [1, 2]. MRI was
performed on a low field 0.1T open system (Bouhnik SAS, Vélizy-Villacoublay, France)
with an homogeneous (10-6) imaging volume of 10x10x6cm3 [3]. 3D MR sequences are
developed on a SMIS (Guilford, UK) console to achieve isotropic resolution of
0.4x0.4x0.4mm3, or high in plane resolution of 0.25x0.25mm² and 1mm slice thickness,
in less than 2h acquisition times. As sizes of our dual imaging devices (SPECT
103x80x140cm, low field MRI 72x40x118cm) fits in a single room and as the 5 Gauss
line is located at a few centimeters from the magnet, pinhole SPECT camera and
anesthesia set were located directly next to the MR magnet, without interfering.
Small animal (mouse or rat) is maintained under gaseous anesthesia (isoflurane
0.5-1.5%, 0.3L.min-1) in a warmed-up and non-magnetic technical cell dedicated to
small animal imaging (CTI, Minerve, Esternay, France) and adapted for both SPECT and
MRI devices. This imaging chamber isolates the animal during its transport and
imaging thanks to a bite bar warranting the animal positioning from one imaging
experiment to the other. After sequential SPECT and MRI acquisitions, co-registration
of images is obtained with the AMIDE [4] software (UCLA, California) helped by
location phantoms placed on the cell bed. Advantage of the cell concerns transport of
the anesthetized animal from one imager to another minimizing therefore the delay
between acquisitions without requiring any more manipulation. During the dual imaging
experiments in mice, we were able to keep the animals under anesthesia inside the
cell up to 10h without consequences.
As a proof of experience of this dual imaging modality, we performed sequential
SPECT/MRI of implanted glioma brain tumors in adult swiss nude mice (Transgene S.A.,
Strasbourg, France). Intra-peritoneal administration of 1mL of 0.5mmol of Gadolinium
(Dotarem, Guerbet, France) was followed by IV injection of 0.2mL of 700MBq of
99mTc-Sestamibi (BMS, Rueil-Malmaison, France) before dual imaging. For SPECT, 48
projections of 1min in a 64x64 format and 4.5cm radius of rotation was used. For MRI,
3D T1 and T2 weighted images were acquired, with the high in plane resolution
specified previously, in less than 4h. Co-registration of brain SPECT/MR images
was then applied after dual modality image reconstruction allowing for
differentiation of brain edema and tumor metabolism.
[1] Israel-Jost V, Choquet P, Salmon S, Blondet C, Sonnendrucker E, Constantinesco A.
Pinhole SPECT imaging : compact projection/backprojection operator for efficient
algebraic reconstruction. IEEE Trans Med Im 2006, 25: 158-67
[2] Constantinesco A, Choquet P, Monassier L, Israel-Jost V, Mertz L. Assessment of
left ventricular perfusion, volumes, and motion in mice using pinhole gated SPECT. J
Nucl Med 2005; 46: 1005-11
[3] Arbogast-Ravier S, Xu F, Choquet P, Brunot B, Constantinesco A. Dedicated low
field MRI: a promising low-cost technique. Med Biol Eng Comp 1995, 33: 735-9
[4] Loening AM, Gambhir SS, AMIDE: A free software tool for multimodality medical
image analysis. Mol Imaging 2003, 2: 131-7
Author
Ms
Elodie Breton
(Service de Biophysique et Médecine Nucléaire, CHU Hautepierre, 1 av. Molière, 67098 Strasbourg, France)
Co-authors
Prof.
Andre Constantinesco
(Service de Biophysique et Médecine Nucléaire, CHU Hautepierre, 1 av. Molière, 67098 Strasbourg, France)
Dr
Christian Goetz
(Service de Biophysique et Médecine Nucléaire, CHU Hautepierre, 1 av. Molière, 67098 Strasbourg, France)
Dr
Philippe Choquet
(Service de Biophysique et Médecine Nucléaire, CHU Hautepierre, 1 av. Molière, 67098 Strasbourg, France)
Dr
Ronald Rooke
(Transgene S.A., 11 rue de Molsheim, 67082 Strasbourg Cedex, France)