An optical common-mode rejection for improving the sensitivity limit of a radiochromic imaging film

We found out that the dosimetric sensitivity limit of a radiochromic film can be much improved through use of a set of color components, e.g. red R and green G, outputs from an RGB color scanner. The two light component lights suffer a common fate, with the exception of wavelength-dependent events, having passed together along common attenuation paths. The mathematical operation of creating a ratio of the two components (R:G) is analogous to the ‘common-mode rejection’ (CMR) in electronics. In the case of the GAFCHROMIC films, HS-14 and MD-55-2, the detection limit was found to be greatly improved with optical CMR, and the lowest detectable dose attained was 20 mGy for HS-14 and 50 mGy for MD-55-2.