Hardware, software, and scanning issues encountered during small animal imaging of photodynamic therapy in the athymic nude rat
2007
Small animal imaging devices are now commonly used to study gene activation and model the effects of
potential therapies. We are attempting to develop a protocol that non-invasively tracks the affect of Pc 4-mediated
photodynamic therapy (PDT) in a human glioma model using structural image data from micro-CT and/or micro-MR scanning and functional data from 18F-fluorodeoxy-glucose (18F-FDG) micro-PET imaging.
Methods: Athymic nude rat U87-derived glioma was imaged by micro-PET and either micro-CT or micro-MR prior to Pc 4-PDT.
Difficulty insuring animal anesthesia and anatomic position during the micro-PET, micro-CT, and micro-MR scans required adaptation
of the scanning bed hardware. Following Pc 4-PDT the animals were again 18F-FDG micro-PET scanned, euthanized one day
later, and their brains were explanted and prepared for H&E histology. Histology provided the gold standard for tumor
location and necrosis. The tumor and surrounding brain functional and structural image data were then isolated and coregistered.
Results: Surprisingly, both the non-PDT and PDT groups showed an increase in tumor functional activity
when we expected this signal to disappear in the group receiving PDT. Co-registration of the functional and structural
image data was done manually. Discussion: As expected, micro-MR imaging provided better structural discrimination of the
brain tumor than micro-CT. Contrary to expectations, in our preliminary analysis 18F-FDG micro-PET imaging does not readily
discriminate the U87 tumors that received Pc 4-PDT. We continue to investigate the utility of micro-PET and other methods
of functional imaging to remotely detect the specificity and sensitivity of Pc 4-PDT in deeply placed tumors.
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