Quantitative Soft Tissue Imaging of the Mouse Knee Joint using microCT

Medical imaging is a crucial tool for obtaining specimen specific anatomy and geometry for computational modeling. X-Ray based imaging such as microCT provide excellent resolution for imaging and quantifying hard tissues such as bone, and MRI has high soft tissue contrast. However, the spatial resolution of MRI or even microMRI is insufficient for imaging the soft tissues in the knee when using small animal models such as mice. The current study presents uses microCT imaging techniques in order to provide sufficient contrast and excellent resolution that allows for segmentation of the ligaments, tendons, menisci, and cartilage in the mouse knee. The ability to quantify both changes in morphology and tissue density provides a framework to perform detailed analysis of the entire joint, investigating both changes in soft tissues and bone resulting from joint injury and osteoarthritis. This new method increases the utility of using a mouse animal model for studying joint injury and degradation in applications including osteoarthritis and joint bleeding in hemophilia. Introduction: Magnetic Resonance Imaging (MRI) provides excellent image contrast for soft tissues such as ligaments, tendons, and cartilage. In addition to long scan times and high cost, one big limitation of MRI is the spatial resolution, which is on the order of 1.0 mm for high tesla clinical scanners, and around 0.1 mm resolution for microMRI small animal scanners [1]. This resolution is insufficient to resolve the small ligaments, tendon, meniscus, and cartilage in the knee joint when using small animal models such as mice, particularly when trying to quantify any morphological changes of these tissues due to injury or pathology. The ability to obtain high resolution imaging of these soft tissues has many applications including studying joint degradation and therapies in osteoarthritic mouse models [2] and joint bleeding and injury in hemophilic mouse models [3]. MicroCT, which is based on x-ray attenuation, is traditionally used for imaging hard tissues such as bone with spatial resolution on 5-10 μm [4;5]. However, x-ray based imaging typically has very poor soft tissue contrast. This paper presents novel methods, which are still currently under refinement, for using microCT to obtain higher soft tissue contrast in the mouse knee. Methods This study was not performed under a specific IACUC animal protocol as the mouse hind limbs were taken from the existing inventory of preserved tissues resulting from previous studies. All of these previous studies were conducted under and approved by the University IACUC. At the time of