THE USE OF CARBON-FIBER MATERIAL IN RADIOGRAPHIC CASSETTES - ESTIMATION OF THE DOSE AND CONTRAST ADVANTAGES

A Monte Carlo simulation has been used to estimate the dose and contra st advantages of replacing radiographic cassette fronts fabricated fro m aluminium with cassette fronts fabricated from low atomic number mat erial (carbon fibre). The simulation used a realistic imaging geometry and calculations were made both with and without an anti-scatter grid . Account was taken of the scatter generated in the cassette front and the effect of beam hardening on primary contrast. Dose and contrast w ere evaluated for a range of cassette front thicknesses and tube poten tials (60-150 kV) as well as for four examinations representative of s ituations with varying amounts of scatter. The results with an anti-sc atter grid show a clear dose and contrast advantage in all cases when an aluminium cassette front is replaced with a low attenuation cassett e front. The contrast advantage is dependent upon the examination and is generally greater for imaging bony structures than for imaging soft tissue. If a 1.74 mm aluminium cassette front is compared with a 1.1 mm carbon fibre cassette front, then the dose advantages are 16%, 9%, 8% and 6% and the contrast advantages are 10%, 7%, 4% and 5% for the A P paediatric pelvis examination at 60 kV, the anteroposterior (AP) lum bar spine examination at 80 kV, the lateral lumbar spine examination a t 100 kV and the posteroanterior (PA) chest examination at 150 kV, res pectively. The results without an anti-scatter grid show an increased dose advantage when a low attenuation cassette front is used, but the contrast advantage is small and in some situations negative.