MicroCT: An Essential Tool in Bone Metastasis Research

Abstract

Microcomputed tomography (microCT) is an essential tool for the study of small animal osseous and soft tissue structures. While several other technologies can be used to image bone, vasculature, and other soft tissues, microCT alone provides high spatial resolution of both hard and soft tissues. Prior to the development of microCT imagers, small animal research was conducted in clinical CT scanners; however, a consequence was poor resolution of the smaller tissues. The development of microCT permitted enhanced small animal imaging resolution and increased use of microCT in preclinical studies. Recent improvements to X-ray detector sensitivity have resulted in the ability of microCT, in combination with contrast agents, to be used in soft tissue studies. In clinical scanning, barium or iodine are typically used for soft tissue assessment; while in small animals, intraperitoneal injections of non-ionic water-soluble contrast medium or intravenous injections of a barium/gelatin mixture can be used for the visualization of soft tissues and vasculature (Paulus et al., 2000). This chapter will focus on the use of microCT to scan osseous tissues. The use of microCT has been well characterized in the study of bone development, fracture repair, biomaterial integration, osteoporosis, and, more recently, cancer bone metastasis. MicroCT allows for the creation of three-dimensional images of the bone which can be processed both qualitatively and quantitatively. MicroCT analysis quantifies several bone structural indices: bone mineral density (BMD), bone volume to total volume ratio (BV/TV), bone surface area (BSA), trabecular number (Tb.N), trabecular thickness (Tb.Th), and trabecular spacing (Tb.Sp). In addition, since microCT is non-destructive, the same specimens can then be used for mechanical testing, histological analysis, or further experiments. MicroCT scanning is the ideal method for assessing bone structure compared with magnetic resonance imaging (MRI), positron emission tomography (PET), X-rays, or bone histomorphometry (Table 1). Magnetic resonance imaging (MRI) is non-ionizing and ideal for soft tissue scanning, but not for osseous tissue. Although overall changes in the bone architecture can be seen, MRI cannot provide a structural analysis of bone tissue (Jiang et al., 2000). In addition, small animal MRI devices have micrometer spatial resolution, similar to microCT, but low sensitivity compared with highly sensitive microCT (Mayer-Kuckuk & Boskey, 2006). Overall, MRI has been used extensively for bone research and can provide some information on the bone structure and its level of mineralization, but is not as quantitative as microCT