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Determination of the optimal conditions for dental subtraction radiography using a storage phosphor system
D S Brettle1, R Ellwood, R Davies
1Christic Hospital, Manchester, UK.
Objectives:
To determine the optimal kVp and exposure conditions for digital subtraction radiography system using a storage phosphor system.
Method:
Signal-to-noise (SNR) measurements were acquired using a Digora system (Soredex, Helsinki, Finland) of large area, low contrast, clinically realistic details against varying degrees of background attenuation for both single exposure unsubtracted and subtracted images. These results were combined with a measure of estimated thyroid dose to derive a figure of merit (FOM) for the unsubtracted and subtracted images.
Results:
For both unsubtracted and subtraction radiography, an exposure at 50 kVp and 250 muGy produce the best overall FOM. However, using the system at the 60 kVp maximum a FOM at 1000 muGy for unsubtracted radiography and 500 muGy for subtraction radiography gave the best SNR performance.
Conclusion:
Operating parameters have been derived which allow the user to choose between optimising SNR and dose (50 kVp, 250 muGy for unsubtracted and subtracted radiography) or SNR alone (60 kVp, 1000 muGy for unsubtracted and 60 kVp, 500 muGy for subtracted), for the visualisation of clinically representative details using the Digora system.