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A practical demonstration of improved technique factors in paediatric fluoroscopy

¹ Department of Medical Physics and Clinical Engineering, Royal Hallamshire Hospital, Glossop Road, Sheffield S10 2JF, ² Medical Physics Department, County Hospital, Greetwell Road, Lincoln LN2 5QY and ³ Radiotherapy Physics, Derbyshire Royal Infirmary NHS Trust, London Road, Derby DE1 2QY, UK

View larger version (25K): [in a new window]   Figure 1. Equipment set-up. The display monitor shows a representation of the Leeds N2 phantom; a ring of discs of diminishing contrast. The ionization chamber is inserted into the beam for dose rate measurements. Added copper filtration is on the couch since it was impractical to attach it to the tube for the purposes of this experiment.

View larger version (30K): [in a new window]   Figure 2. Measured image quality as a function of copper (Cu) filtration and water phantom thickness. The grey band is a qualitative fit to the data and highlights the trend ofdecreasing image quality with increasing Cu and phantom thickness. For reasons of clarity, no error bars are shown. Phantom thickness error approximates ±0.1 cm. Image quality error approximates ±0.5 discs. +, normal dose rate setting, no Cu; , high dose rate setting, 0 mm Cu; , high dose rate setting, 0.1 mm Cu; , high dose rate setting, 0.2 mm Cu; x, high dose rate setting, 0.3 mm Cu; , high dose rate setting, 0.4 mm Cu; •, high dose rate setting, 0.5 mm Cu.

View larger version (36K): [in a new window]   Figure 3. Percentage change in absorbed dose rate against change in image quality compared with the same measurements at the normal setting without added filtration. The four points in each group come from the four phantom thicknesses used (5 cm, 10 cm, 14.7 cm and 19.7 cm) at each copper (Cu) thickness. Errors in percentage dose change are not shown but equate to ±4%. , high dose rate setting, 0 mm Cu; , high dose rate setting, 0.1 mm Cu; , high dose rate setting, 0.2 mm Cu; x, high dose rate setting, 0.3 mm Cu; , high dose rate setting, 0.4 mm Cu; •, high dose rate setting, 0.5 mm Cu.

View larger version (11K): [in a new window]   Figure 4. The standard () and modified () high dose-rate tube potential/tube current automatic exposure control curves of the equipment used in our experiment. Their similarity is a result of limitations in equipment programmability. ---, idealized response, given a 2 mA tube current limit.