Optimization of image quality and patient dose in radiographs of paediatric extremities using direct digital radiography

Objective: The purpose of this study was to evaluate the effect of beamquality on the image quality (IQ) of ankle radiographs of paediatric patients in the age range of 0-1 year whilst maintaining constant effective dose (ED). Methods: Lateral ankle radiographs of an infant foot phantom were taken at a range of tube potentials (40.0-64.5 kV(p)) with and without 0.1-mm copper (Cu) filtration using a Trixell Pixium 4600 detector (Trixell, Morains, France). ED to the patient was computed for the default exposure parameters using PCXMC v. 2.0 and was fixed for other beam qualities by modulating the tube current-time product. The contrast-to-noise ratio (CNR) was measured between the tibia and adjacent soft tissue. The IQ of the phantom images was assessed by three radiologists and a reporting radiographer. Four IQ criteria were defined each with a scale of 1-3, giving a maximum score of 12. Finally, a service audit of clinical images at the default and optimum beam qualities was undertaken. Results: The measured CNR for the 40kVp/no Cu image was 12.0 compared with 7.6 for the default mode (55 0.1mm Cu). An improvement in the clinical IQ scores was also apparent at this lower beam quality. Conclusion: Lowering tube potential and removing filtration improved the clinical IQ of paediatric ankle radiographs in this age range. Advances in knowledge: There are currently no UK guidelines on exposure protocols for paediatric imaging using direct digital radiography. A lower beam quality will produce better IQ with no additional dose penalty for infant extremity imaging.