Novel capsule imaging devices, systems and methods are provided for in vivo imaging applications, such as for gastrointestinal applications. A swallowable video imaging device, such as a capsule, can be used with a light filter for in vivo illumination of a target tissue that has absorbed a previously administered biological probe. The target tissue can be distinguished in images transmitted from the video imaging device. Quantification of the signal intensity of fluorescence can be used to assess how progressed the target tissue may be. The target tissue can be therapeutically treated to shrink or kill the target tissue.