Abstract
Spontaneous light emission from living animals can overcome the investigated light signals in small animal luminescence imaging. Despite autofluorescence emission is well studied the spontaneous luminescence background is less known and its importance is growing due to the new born imaging techniques like Cerenkov Luminescence Imaging and Radionuclide Luminescence Imaging in which faint sources are often involved. In order to investigate the spontaneous emission we studied the background luminescence in vivo from health Nu/Nu mice in optical imaging acquisitions and we related it with the optical properties of the diet of the animals. In particular luminescence images of mice feed with normal diet used in animal facilities were acquired using a commercial optical imager. The intensity and the spectral features of the luminescence emission from the animal surface after sunshine exposition and after normal lighting laboratory conditions were measured. The same was done with the pellets of food used to feed the animals. We found a background emission from the entire animal surface and localized light sources in the abdominal/lumbar region. Their intensity can be modulated by the light exposition of the animals before the imaging session and decreases along the time when they are put in darkness. The comparison of the luminescence time decay of animals and pellets suggests that the light sources are related to the persistent luminescence of the molecules contained in the food. So ambient exposure before imaging is important for luminescence imaging in order to keep down the background. The optical properties of food are also important and it necessary to check them before to feed the animals not only in fluorescence imaging but also in luminescence imaging.
Highlights
In vivo bioluminescence imaging (BLI) is a molecular imaging technique that offers important opportunities for investigating a wide variety of disease processes
BLI images of the animals revealed a luminescence background emission from the entire animal surface and localized high intensity sources in the abdominal/lumbar region; this emission can be seen both in mice placed in dorsal position (Figure 1) and in mice placed in ventral position (Figure 2)
In our study we demonstrated the sensitivity of the spontaneous luminescence emission both to the ambient exposure and to the optical properties of food
Summary
In vivo bioluminescence imaging (BLI) is a molecular imaging technique that offers important opportunities for investigating a wide variety of disease processes. BLI utilizes luciferase as an internal biological light source that can be genetically programmed to noninvasively “report” the presence or activation of specific biological events and it is used to demonstrate expression of celland tissue-specific promoters, label cell populations and detect protein-protein interaction. In order to increase the signal to noise ratio another approach can be based on the reduction of the spontaneous background emission from the animal surface that can be revealed during the imaging process. The origins of this emission needs to be investigated and despite they could be due to a large plethora of different experimental conditions, it is necessary to investigate the most important ones. On the contrary the autofluorescence at the living organisms is more investigated and the sources are considered endogenous cromophores in animal tissues and fluorochromes accumulated with the diet [9]
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