An assessment of exposure indices in computed radiography for the posterior-anterior chest and the lateral lumbar spine

Studies have indicated that computed radiography (CR) can increase radiation dose to the patient, leading to potential biological effects. Although manufacturers have set parameters to safeguard against overexposure, it is unclear whether these are being used by radiographers or if their recommended values are consistent with the ALARA principle. The research aims are to investigate (i) whether radiographers are producing images with exposure indices within the manufacturers recommended range (MRR); (ii) the phenomenon of exposure creep, and (iii) the relationship between exposure indices (EIs) and radiation dose. A retrospective analysis of exposure indices over an 18-month period for the posteroanterior (PA) chest and lateral (LAT) lumbar spine at two centres using Kodak 800 and 850 CR systems was conducted. A phantom study was performed to assess the relationship between El and entrance surface dose (ESD) for fixed and varying tube potentials. Kodak recommends that images have EIs between 1700 and 1900. Thirty percent of LAT lumbar spine examinations at hospital B and 38% of PA chest examinations at hospital A were produced with EIs below 1700. In the phantom study, when using a varied tube potential (70-125 kVp) and maintaining a constant El of 1550, ESD was reduced by 56%. All clinical and phantom images were assessed to be of a diagnostic quality. The retrospective results indicate that there is a potential to reduce the MRR and optimize patient dose. There is also evidence to suggest that El is not a reliable indicator of patient dose. The authors recommend that staff training is essential on these newer systems.