FULL CHARACTERIZATION OF THE X-RAY SYSTEM IN ORDER TO EVALUATE PATIENT DOSE IN INTERVENTIONAL CARDIOLOGY

Resumo

The purpose of the present paper is to evaluate interventional radiology x-ray system performance in order to analyze its influence on patient dose. Entrance air kerma rate in fluoroscopy modes and air kerma per image in cine modes were measured at the entrance of PMMA slabs (10 to 30 cm) in two interventional x-ray systems. Air kerma evaluation was performed in all image intensifiers (II) diameters and in all fluoroscopy and cine modes used in the clinical practice with an ionization chamber. High and low contrast resolution was evaluated for all PMMA thickness, II and modes, with two quality image tests (NEMA XR 21 and Leeds TOR-18FG). Significant differences were found in air kerma rate and air kerma per image in both x-ray systems for comparable II and modes. For example, for 24 cm PMMA thickness in fluoroscopic high dose mode, in one x-ray system delivers 0.49 mGy/s and the other one 1.87 mGy/s. However, differences in image quality were not significant. In the same conditions described above, Leeds test showed: 0.032 (low contrast) and 1.25 lpmm (spatial frequency). In addition, when phantom thickness increase, image quality decreases in x-ray systems, but in one of them, the difference is high. Results show that patient dose and image quality depend on the x-ray system characteristics. Due to this it is essential to perform a complete evaluation of the x-ray system in order to help interventional cardiologists (radiologists) to learn possibilities of dose reduction with no lose of image quality.