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Immunohistological analysis of SPIO-labeled grafts performed with confo-
cal and Prussian blue staining confirmed the MRI data and demonstrated
the survival of the grafts and migration toward the stroke-damaged areas
(Daadi et al., 2009).
Cellular MRI is also useful in cell therapeutic approaches for brain tumor
as a sensitive method of assessing the efficacy of NSCs to target and eliminate
tumors in vivo . It has been reported that NSCs home toward brain tumors
(Arboody et al., 2000; Benedetti et al., 2000; Ehtesham et al., 2002; Shah et
al., 2005). As such, they could be used as a vehicle to deliver therapeutic
genes to the tumor. To generate animal models of brain tumor, GFP-labeled
gliomas were transplanted into the forebrain (Zhang et al., 2004). One week
later, SPIO-labeled NSCs were injected into the cisterna magna and tail vein.
MRI demonstrated the ability of the NSCs to migrate and infiltrate the tumor
mass. Immunocytochemistry and Prussian blue staining analysis confirmed
the tumor infiltration and the overlapping of Prussian blue-stained NSCs
over GFP + glioma cells.
Clinical studies have demonstrated the feasibility of MRI of grafted neural
cells labeled with ferumoxides into patients with traumatic brain injury in
China (Zhu et al., 2006). A second study, performed in Brazil (Callera and de
Melo, 2007) used magnetic bead-labeled bone marrow cells transplanted into
patients with spinal cord injury.
20.4 Positron Emission Tomography
In the past two decades, PET imaging has been a rapidly advancing tech-
nology in molecular imaging of neurological disorders. Due to accuracy
and noninvasiveness, PET is now routinely used for diagnosis and post-
therapeutic monitoring of patients. The most commonly used radiolabeled
probe to image brain activity is 18 18F-fluorodeoxyglucose ( 18 F-FDG). The bio-
logical parameter estimated in this molecular imaging modality is the rate of
regional glucose utilization. The regional concentration of the radioactivity
may be accurately measured and normalized to a reference region of the
brain. FDG-PET is approved by the U.S. Food and Drug Administration and
is currently the most commonly performed modality in the clinical arena.
FDG-PET has been used to image the transplantation of neurons into
stroke patients (Kondziolka et al., 2000). Patients were injected with 7 mCi of
18 F-FDG, and PET imaging was performed 40 minutes later. PET images were
normalized, and the 18 F-FDG uptake in the infarct and peri-infarct zones
was expressed as percentage of baseline. PET scans performed 6 months
after surgery revealed a 15% increase in 18 F-FDG uptake at the transplant
site or in the ipsilateral adjacent parenchyma. This was observed in 6 of 11
patients and was relative to pretransplant scans. Interestingly, 4 of these 6