We agree with Dr Rez that there is considerable uncertainty involved in quantifying the doses emitted and absorbed when passengers are imaged with the backscatter scanners. This uncertainty could be reduced if the TSA allowed greater access to the scanners so that additional independent testing and direct measurements could be made. Ideally, every scanner in operation should be checked to ensure its proper functioning. However, it is not clear that estimating doses by reviewing images, or estimating the exposures based on the reported scattered dose, provides greater precision than using estimates that were derived from direct measurements reported by the Johns Hopkins University Applied Physics Laboratory1 and the NIST,2 who were given access to the scanners.
Smith-Bindman R, Mehta P. Uncertainties in the Dose From Full-Body Airport Screening—Reply. Arch Intern Med. 2011;171(12):1129-1130. doi:10.1001/archinternmed.2011.259