Effect of patient support pads on image quality and dose in fluoroscopy

An investigation was performed of the changes in image quality and patient dose as a result of increasing filtration for fluoroscopy performed under automatic brightness control. Filtration was added either at the x-ray tube housing (i.e., scatter-free geometry) or adjacent to a tissue equivalent phantom simulating the patient (i.e., with-scatter geometry). Patient doses were expressed in terms of the total energy imparted to patients simulated by either a 10 cm (i.e., pediatric) or 20 cm (i.e., adult) acrylic phantoms. Changes in image quality were determined by measuring the relative visibility of circular disks in a Leeds Test Object 10 contrast-detail phantom. In the scatter-free geometry, the addition of 4 mm Al filtration reduced the energy imparted by 27% (10 cm phantom) and 20% (20 cm phantom). In the with-scatter geometry, the corresponding reductions in energy imparted were 17% and 9% for the 10 and 20 cm phantoms, respectively. The visibility of low contrast disks generally decreased as the thickness of the added aluminum increased but the location of the added Al (i.e., with-scatter or scatter-free geometry) had no significant effect on the resultant image quality. These results demonstrate that the use of patient support pads with a thickness of ~4 mm Al will generally have an adverse impact on fluoroscopic image quality and result in modest reductions (~10%) of adult patient doses.