ARTIKLID LÕPUTÖÖDEST
FOOKUSTÄPI SUURUSE, ÜLESVÕTTEGEOMEETRIA JA KUJUTISE LAHUTUSVÕIME VAHELINE SEOS LASTE RINDKEREÜLESVÕTETEL The Relationship Between Focal Spot Size, Imaging Geometry and Image Resolution in Paediatric Chest Imaging Egne Kürsa, Erik Landõr, Kalle Kepler Abstract In conventional paediatric radiography, it is recommended to use small focal spot for thoracic imaging, which limits the use of larger X-ray tube currents. A longer exposure time is necessary to obtain images at lower currents, which can cause motion artefacts. The aim of the study was to find out the relationship between the focal spot size, imaging geometry and image resolution in paediatric chest imaging and explore the possibility to use large focal spot in paediatric chest images. The experiments were carried out using Siemens Ysio radiograph. A pinhole diaphragm was used to image the focal spot and the resulting image was used to take its measurements. Maximum resolution was determined using a bar pattern at various focus to receptor distances (FRD). Doses of the performed exposures were recorded. The focal spot sizes (both 0.6 mm and 1.0 mm) corresponded to the dimensions declared by the manufacturer. For the small focal spot, the determined image resolution was 3.4 line pairs per mm (lp/mm) at FRD of 100, 150, 180 and 250 cm, limited by the maximum resolution of the image receptor, 3.47 lp/mm. As for the large focal spot, the image resolution increased from 2.8 lp/mm at 100 cm FRD to 3.4 lp/mm at 180 cm FRD. While additional filtration of 0.1 mm Cu did not significantly affect the resolution of the images, the entry skin 51
