Conference Paper


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BACKGROUND: Conventional interpretation of methionine PET (Met-PET) scans in suspected brain tumors uses the ratio of the tracer uptake within the lesion to the corresponding contralateral area. The precise location at which the region of interest used to calculate the reference value is placed is vital, because local variations in methionine uptake may significantly alter the calculated ratio. Identifying a precise mirror region is complicated by the distorting effect of the tumor and the need for manual realignment of the image. METHOD: Patients with low-grade primary brain tumors or benignlesions were identified on the basis of a tissue diagnosis or surveillance neuroimaging that excluded a high-grade tumor. These conditions were selected because they primarily involve a single hemisphere, with methionine uptake in the unaffected hemisphere being essentially normal. A total of 180 Met-PET scans performed during 2003 – 2005 were identified from the database at the Max Planck Institute for Neurological Research, coded, and anonymized for analysis. Scans demonstrating midline lesions, significant mass effect, or evidence of substantial previous surgery were then excluded. A methionine template was prepared using data from patients who had undergone both FDG and Met-PET scans within eight weeks, with normalization to a previously developed FDG template. Methionine scans were coregistered to the template, after masking of any tumor, and the diseased hemispheres stripped. Mean uptake maps for each hemisphere were calculated on a voxel-by-voxel basis and merged to create the normal methionine uptake map. Scans unsuitable for inclusion into the normal map were reanalyzed using the contralateral hemisphere and the normal uptake map for reference values, allowing the methods to be compared. RESULTS: Good correlation was found between uptake ratios using reference values calculated by both methods. Reference values could be reliably calculated in tumors that were previously problematic to analyze, such as those that cross the midline. Coregistration of the normal map was impaired in some cases by loss of the normal architecture, but valid reference values were obtained despite this. CONCLUSION: Use of a normal uptake may facilitate calculation of PET uptake ratios in brain tumors. Further research is required to evaluate the correlation with histological findings and the accuracy of image coregistration in the presence of distorting tumors.

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Despite the inherent problems associated with in vivo animal models of tumor growth and metastases, many of the current in vitro brain tumor models also do not accurately mimic tumor-host brain interactions. Therefore, there is a need to develop such co-culture models to study tumor biology and, importantly, the efficacy of drug delivery systems targeting the brain. So far, few investigations of this nature have been published. In this paper we describe the development of a new model system and its application to drug delivery assessment. For our new model, a co-culture of DAOY cell brain tumor aggregates and organo-typic brain slices was developed. Initially, the DAOY aggregates attached to cerebellum slices and invaded as a unit. Single cells in the periphery of the aggregate detached from the DAOY aggregates and gradually replaced normal brain cells. This invasive behavior of DAOY cells toward organotypic cerebellum slices shows a similar pattern to that seen in vivo. After validation of the co-culture model using transmission electron microscopy, nanoparticle (NP) uptake was then evaluated. Confocal micrographs illustrated that DAOY cells in this co-culture model took up most of the NPs, but few NPs were distributed into brain cells. This finding corresponded with results of NP uptake in DAOY and brain aggregates reported elsewhere.
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