Limitations
Several factors can affect the sensitivity and resolution of an in vivo optical imaging system. First, the signals used for molecular imaging are subject to the physical limitations inherent to light. For example, signals are emitted in all directions; some photons are scattered, while others are absorbed. Second, the signal levels generated during in vivo fluorescence imaging are low compared to more common light sources and detectors must be sensitive to low-light emissions. Third, mice are heterogeneous and light transport must be modeled correctly for heterogeneous media. Finally, fur and pigmented skin may interfere with signal detection.
Autofluorescence can also be a factor for some imaging applications. For example, collagen, elastin, and beta‑carotene fluoresce in the lower visible wavelengths and some commonly used markers, such as GFP, also fluoresce within this range. Ingested chlorophyll, which can be commonly found in animal diets, can also contribute to unwanted auto-fluorescent signals.