In defence of optical density ratios in 2-deoxyglucose autoradiography.

The use of optical density ratios to describe changes in [14C]2-deoxyglucose uptake in neuroanatomical mapping experiments has recently been criticized. It has been argued that a fixed ratio of tissue isotope concentration does not yield a constant optical density ratio but is dependent on the exposure time and the absolute amounts of isotope used. Here it is demonstrated that such variations in optical density ratios are due to an artifact in calculating the optical density ratio, which can easily be corrected provided that the film is not approaching saturation and not due to the non-linearity of an exposure-density curve as has previously been suggested.