High resolution micro arthrography of hard and soft tissues in a murine model.

OBJECTIVE: Recent developments on high resolution micro computed tomography (µCT) allow imaging of soft tissues in small animal joints. Nevertheless, µCT images cannot distinguish soft tissues from synovial fluid due to their similar mass density, limiting the 3D assessment of soft tissues volume and thickness. This study aimed to evaluate a lead chromate contrast agent for µCΤ arthrography of rat knee joints ex vivo. DESIGN: Intact tibiofemoral rat joints were injected with the contrast agent at different concentrations and imaged using a µCT at 2.7 µm isotropic voxel size. Cartilage thickness was measured using an automated procedure, validated against histological measurements, and analyzed as a function of µCT image resolution. Changes in hard and soft tissues were also analyzed in tibiofemoral joints 4 weeks after surgical destabilization of the medial meniscus (DMM). RESULTS: The contrast agent diffused well throughout the whole knee cavity without penetrating the tissues, therefore providing high contrast at the boundaries between soft tissues and synovial fluid space. Thickness analysis of cartilage demonstrated a high similarity between histology and µ-arthrography approaches (R(2) = 0.90). Four weeks after surgical DMM, the development of osteophytes (Oph) and cartilage ulcerations was recognizable with µCT, as well as a slight increase in trabecular bone porosity, and decrease in trabecular thickness. CONCLUSIONS: A lead chromate-based contrast agent allowed discriminating the synovial fluid from soft tissues of intact knee joints, and thus made possible both qualitative and quantitative assessment of hard and soft tissues in both intact and DMM tibiofemoral joints using high resolution µCT.

The solid-state catalytic synthesis of tritium labeled amino acids, peptides and proteins.

New catalytic reaction between a solid bioorganic compound and activated spillover tritium (ST), based on High-temperature Solid-state Catalytic Isotopic Exchange (HSCIE) was examined. The HSCIE mechanism and determination of the reactivity of hydrogen atoms in amino acids, peptides and proteins was investigated. Quantum mechanical calculations of the reactivity of hydrogen atoms in amino acids in the HSCIE reaction were done. The carbon atom with a greater proton affinity undergoes a greater exchange of hydrogen for tritium in HSCIE. The electrofilic nature of spillover hydrogen in the reaction of HSCIE was revealed. The isotope exchange between ST and the hydrogen of the solid organic compound proceeds with a high degree of configuration retention at the carbon atoms. The HSCIE reaction enables to synthesize tritium labeled proteins with a specific activity of 20-30 mCi/mg and kept biological activity.