DYNAMIC IMAGING FOR STUDIES OF INFECTIOUS DISEASES
Conventional pre-clinical studies of infections, host responses to infection and therapy in small animal models hasa lot of limitations and weaknesses. These serial studies require animalsacrifice after infection or treatment at multiple time points to identifysites of infection and quantify pathogen infection burdens. This doesn’tmakeit possible to follow diseaseprogression in the same animal. It also demands a large numbers of animals to obtain quantitative, statisticallymeaningful data by tissue sampling.Moreover, as the studied tissues are chosen in advance, unexpected site may be missed because the infected tissue is not among the standard ones collected for analysis.
In vivo Optical Imaging is a highly sensitive, non-invasive technique based on the detection of visible light, produced by luminescence or fluorescence. Among the many small animal imaging instruments that recently have been developed, this imaging modality is a very suitable, high-throughput and cost-effective alternative to these conventional studies of infectious diseases and treatments in small animal models. OI has several advantages that make it a powerful technique for studiesof infection in mice.
Real-time, high-throughput longitudinal studies of infection
Many of the obligate steps of disease are dynamic in time and space, and thus, endpoint assays do not provide a full understanding of these processes. Unlike conventional methods that analyze infection and host response by euthanizing groups ofanimals at multiple time points, optical imaging techniques allow longitudinal,real-time studies of infection and disease progression. The non-invasive nature of optical imaging allows the high-throughput monitoring of the course of an infection within thesame group of animals. Importantly, multiple imaging of the same animal duringan experiment allows disease progression to be followed with better accuracy, while allowing each animal to act as its own control.
With the PhotonIMAGER™ system, it is possible to image more animals per hour than with other small animal imaging modalities. As a result, several subgroups can be analyzed in the context of one experiment, accelerating the studies.Thus, reducing the number of animals needed to generate statisticallysignificant data. In addition, by avoiding the need for invasive sampling procedures, OI can also result in a reduction inthe levels of stress and discomfort experienced by animals.
Improved detection and localization of small infection sites
One of the key advantages of the in vivo imaging is that besides accounting for animal-to-animal variations within experimental groups, imaging allows investigators to identify unexpected sites of infection orhost response that might be missed by analyzing only selected tissues at chosentime points. Until recently, the weak spatial resolution of in vivo imaging systems presented a real limitation in studies of infection. Today, it ispossible to obtain a spatial resolution of 2.5µm with the PhotonIMAGER™Macrolens module. This makes possible the identification of small infections andthe differentiation between closely spaced pathogen sites, either in vivo or exvivo. The 4-View module provides asolution for multi-view imaging so all the signals can be imaged from all sidesof the animal, in one single acquisition.
Zebra fish adults (age: 5 months) 10 days after intraperitoneal infection with GFP - Mycobacterium marinum (10 000 CFU/fish).
Improved quantification of pathogen burden
When constitutively expressed, bioluminescence isrelated to microbial numbers and can therefore be used for quantification of pathogen burden. A limitation of in vivo optical imaging is signal attenuation due to theabsorption and scattering of light by tissues presenting challenges inprecisely mesure infection burden and localize infection sites. Now, these limitations can be overcome by the 3Dmodule of the PhotonIMAGER™ which provides 3D reconstruction of the animalsurface and the optical signals deeper in tissues. This technology takes inaccount tissue absorption and scattering by recalculating signal intensity according to the depth and localization of the signal, making it possible tobetter localize signals and quantitate signal volumes. Integration ofother imaging modalities into optical imaging systems can further ameliorate the anatomical localization of pathogens. The X-Ray module of the PhotonIMAGER overlays a high-resolution x-Ray image with optical signal, while the StereoCT module offers further 3D anatomical data. Taken together data from different modalities can offer a better view on disease progression.