Use of nuclear medicine imaging for diagnosis of spontaneous disease conditions in laboratory animals

Abstract

The laboratory animals constitute an integral part of preclinical studies and many key factors govern the outcome of experimental results. Healthy animals are important for preclinical testing, hence early detection and diagnosis of subclinical disease conditions is crucial before initiating an experiment. Nuclear imaging technology is explored for identification of disease status in laboratory animals. Physical examination was made and suspected animals were segregated and investigated by whole-body CT or PET-CT scan using [18F] FDG. The activity was injected intravenously with doses of 100 µCi and 1mCi in mice and rabbits, respectively. Based upon PET-CT findings and subsequent histopathology, observed lesions were categorized as inflammation, infection and tumor lesions in animals. One New Zealand white rabbit (n=1) had penile skin growth with site bleeding. PET-CT showed local inflammation (SUV max: 0.5) which was supported by cell cytology, presented more population of heterophils and was also corroborated by histopathology findings. Second New Zealand rabbit (n=1) had circling and torticollis. PET-CT scan showed local brain uptake (SUV max: 2.6) and liver uptake (SUV max: 2.4), indicative of inflammation and infection which was also supported by histopathology findings, which demonstrated degenerative changes, infiltration of inflammatory cells with spores of E. Cuniculi in liver and kidney. Skin infection reported in mice (n=2) and rabbit (n=1) was ruled out by obscure contrast of CT scan of the skin surface compared to the control mice population (n=2). In rabbits, increased cartilage thickening is due to mange infection. Skin scraping and histopathology confirmed the mange infection in both the animals. BALB/c mouse with laboured breathing (n=1) was suspected for lung infection with increased uptake of radiotracer (SUV max: 10.8) as compared to the control (SUV max: 3.2) animals (Fig. 1). Lung histology showed infiltration of polymorphonuclear cells and congestion indicating the pneumonic changes. Salivary gland tumor observed in BALB/c mice (n=1) having subcutaneous skin nodules displayed uptake of [18F] FDG at intense peripheral uptake at site with no uptake at major marked area. Histopathology showed cribriform morphology of epithelial cells with dilation of duct and accumulation of secretions with variable mitotic activity indicative of cystic adenocarcinoma of salivary gland in mice.