IN VIVO MICRO-CT/MICRO-PET IMAGING OF BONE REGENERATION INDUCED BY HUMAN-STEM-CELLS IN RAT MODEL: FEASIBILITY STUDY

Objective: The aim of the study was to evaluate the efficacy of an imaging system that integrates Positron Emission Tomography(PET)with x-ray Computed Tomography(CT),allowing simultaneous in vivo anatomic and molecular imaging, for quantitative and qualitative evaluation of bone regeneration induced from periosteal stem cells(PeSC)associated with biomaterials in critical size mouse calvarial defect. Materials and Methods: PeSC isolated from permanent human teeth, were cultured and treated to enhance differentiation activity toward the osteoblastic phenotype,and then combined with two different scaffolds:1) deproteinized bovine bone with 10% porcine collagen block;2)granular β-tricalcium phosphate. Two bilateral critical-size defects(5mm)were created in the parietal bones of 8 adult nude rats and implanted with:(1)a scaffold seeded with stem cells;(2)a scaffold without cells. The animals were housed for a total period of 12 weeks post-surgery and underwent longitudinal micro CT/PET an

Objective: The aim of the study was to evaluate the efficacy of an imaging system that integrates Positron Emission Tomography(PET)with x-ray Computed Tomography(CT),allowing simultaneous in vivo anatomic and molecular imaging, for quantitative and qualitative evaluation of bone regeneration induced from periosteal stem cells(PeSC)associated with biomaterials in critical size mouse calvarial defect. Materials and Methods: PeSC isolated from permanent human teeth, were cultured and treated to enhance differentiation activity toward the osteoblastic phenotype,and then combined with two different scaffolds:1) deproteinized bovine bone with 10% porcine collagen block;2)granular β-tricalcium phosphate. Two bilateral critical-size defects(5mm)were created in the parietal bones of 8 adult nude rats and implanted with:(1)a scaffold seeded with stem cells;(2)a scaffold without cells. The animals were housed for a total period of 12 weeks post-surgery and underwent longitudinal micro CT/PET analysis with the following schedule.In vivo micro-CT scans were made at 2,4,8 and 12 weeks in order to evaluate:the bone mineral density(BMD)of non-seeded scaffolds;the correct placement of biomaterials into the defects;the bone mineral density(BMD)of seeded scaffolds. At 4 and 12 weeks post-surgery,[18F]-NaF-PET were performed:this analysis allowed the evaluation of maximum standard uptake value(SUVmax)for each voxel;the standard uptake value(SUV)and the standard deviation of SUV. Results: The measurements showed that the presence of stem cells increase values of BMD when compared to those of scaffolds alone;the speed of regeneration is more pronounced in the first few weeks post-surgery(T4=45% - T12=18%)and appears to be not yet complete after 12 weeks;the onset of mineralization appears to occur preferentially in proximity of the parietal bone and it is not homogeneous in the biomaterials. This imaging system, which integrates in the same frame,micro-CT and micro-PET analysis,produces accurate spatial registration of the three-dimensional image volumes. Moreover,in vivo measurements allow tracking changes over time in the same living subjects,so that each animal acts as a longitudinal control, thus enhancing measurement accuracy and reducing the number of animals needed. This is an improvement over traditional cross-sectional, where many of the time-based information may be compromised by the variability in time within the group to each separate point. Conclusions: Integrated micro-CT/PET in vivo longitudinal analysis appears to be an ideal strategy for pre-clinical research on bone regeneration,since it provides a fast and accurate tool for measuring bone mineral density in critical calvarial defect of the rat.