Noninvasive Quantitative Functional Optical Imaging of Calvarial Defect Repair: Monitoring of Osteogenesis and Angiogenesis

INTRODUCTION In extreme situations in which the extent of bone loss or damage is too large, complete regeneration will not occur. Such bone defects in the craniofacial complex are often a result of trauma or cancer surgery. Approximately 1,600,000 bone grafts are performed each year to regenerate bone loss due to trauma or disease; 6% of these (96,000) are cranio-maxillofacial in nature. Autologous bone, usually used to treat these lesions, is not always available, and its harvest necessitates injury to another bone. Moreover, the repair achieved using this technique is not efficient. An alternative, allograft, is composed of dead bone, which at first glance appears to be a tremendous resource for craniofacial reconstruction. However, blood vessel growth into a cortical allograft is limited to 1 to 3 mm and the dead cortical bone is never replaced by new bone. The large potential supply of craniofacial allografts thus still requires the addition of cells or related genes to facilitate their biointegration in the defect site. To find the best therapeutic approach, fracture healing requires in vivo tracking and quantification. Optical imaging studies, performed using near-infrared fluorescence (NIRF) agents or bioluminescence-marked cells or genes, are widely used for many applications in small animal models. This is due to advantages these studies have relative to CT, MRI, and nuclear imaging, such as: 1) equipment cost is relatively low; 2) one may follow the distribution of more then one target simultaneously: and 3) nonionizing radiation is used. We previously published data on the fluorescence molecular tomography (FMT) of osteogenesis (1). New bone formation was shown in an ectopic site and in radial defects in mice during mesenchymal stem cell–based therapy. We hypothesized that functional fluorescence imaging (Functional FLI) would enable monitoring of osteogenesis and angiogenesis in calvarial defect repair. For this purpose criticalsize calvarial defects were created in mice. A comparison of the healing provided by autografts and allografts was analyzed using functional FLI specific to angiogenesis and osteogenesis.