Snapshot spectral images viewing down the axis of the esophagus are processed to identify eosinophils. The snapshot images are based on fluorescence emitted in response to excitation optical radiation at two or more wavelengths. Ratio of spectral powers between snapshot images can be used in identification. In some examples, a relative abundance or density eosinophils is obtained, and processed to perform an in vivo assessment of tissue, such as esophageal tissue.
