Improved Multimodality Imaging Using Alginate Molding in Xenograft Tumor Models

Purpose: To allow for reproducible rodent positioning using molding in multimodal tomographic imaging (positron emission tomography (PET), magnetic resonance imaging/spectroscopy (MRI/MRS)), minimization of magnetic field inhomogeneity during MRI investigations of peripheral structures, and reproducible positioning for subsequent histological sectioning of the separated tumor.
Materials and Methods: Chemical shift imaging (CSI) studies were carried out using phantoms and NMRI nu/nu mice bearing subcutaneous tumors. For embedding, three different materials were used: i) alginate, ii) gelatin, and iii) a mixture of wheat flour and salt. The animals were placed in an animal chamber including position markers visible by MRI and PET. The frozen embedded explanted tumors were sliced and examined autoradiographically as well as histologically.
Results: Alginate showed a substantial improvement of magnetic field homogeneity and histological sectioning was superior to the other methods. This embedding led to a significant reduction of the full width at half maximum (FWHM) of the water peak in the peripheral rim of the tumor in comparison to the same peak FWHM without embedding (41+-10 Hz vs. 80+-20 Hz).
Conclusions: Our research shows that animal positioning in an imaging chamber together with alginate embedding allows high quality multimodality investigations including coregistration of MRI/MRS, PET, and histological images.