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First published online July 28, 2008
British Journal of Radiology (2008) 81, 771-777
© 2008 British Institute of Radiology
doi: 10.1259/bjr/21963665
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British Journal of Radiology 81 (2008),771-777 ©2008 The British Institute of Radiology

Full paper

Investigation of optimum X-ray beam tube voltage and filtration for chest radiography with a computed radiography system

C S MOORE, BSc, MSc1, A W BEAVIS, BSc, PhD1,2,3 and J R SAUNDERSON, BSc, MSc1,2

1 Radiation Physics Department, Hull & East Yorkshire Hospitals, Princess Royal Hospital, Saltshouse Road, Kingston Upon Hull HU8 9HE, 2 Postgraduate Medical Institute, University of Hull, Kingston Upon Hull HU6 7RX and 3 Faculty of Health and Wellbeing, Sheffield Hallam University, City Campus, Howard Street, Sheffield S1 1WB, UK

Correspondence: C S Moore, Radiation Physics Department, Hull & East Yorkshire Hospitals, Princess Royal Hospital, Saltshouse Road, Kingston Upon Hull HU8 9HE, UK. E-mail: craig.moore{at}hey.nhs.uk

The purpose of this study was to determine the optimum tube voltage and amount of added copper (Cu) filtration for processed chest radiographs obtained with an Agfa 75.0 Computed Radiography (CR) system. The contrast-to-noise ratio (CNR) was measured in the lung, heart/spine and diaphragm compartments of a validated chest phantom using various tube voltages and amounts of Cu filtration. The CNR was derived as a function of air kerma at the CR plate and with the effective dose. As rib contrast can interfere with detection of nodules in chest radiography, a tissue-to-rib ratio (TRR) was derived to investigate which tube voltages suppress the contrast of rib. Although processing algorithms affect the signal and noise in a way that is hard to predict, we found that, for a given set of processing parameters, the CNR was related to the plate air kerma and effective dose in a logarithmic manner (all R2 ≥0.97). For imaging of the lung region, a low voltage (60 kVp) produced the highest CNR, whereas a high voltage (125 kVp) produced the highest TRR. In the heart/spine region, 80–125 kVp produced the highest CNR, while in the diaphragm region 60–90 kVp produced the highest CNR. For chest radiography with this CR system, the optimal tube voltage depends upon the region of interest. Of the filters tested, a 0.1 mm Cu thickness was found to provide a statistically significant increase in the CNR in the diaphragm region with tube potentials of 60 kVp and 80 kVp, without affecting the CNR in the other anatomical compartments.






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