Dose assessment during the commissioning of flat detector imaging systems for cardiology

Incident air kerma (IAK) and entrance surface air kerma (ESAK) have been measured for a range of copper (Cu) absorbers (1-10 mm) and polymethylmethacrylate (PMMA) slabs (12-28 cm) with kilovolt values ranging from 61 to 120 during the commissioning of an X-ray system equipped with a flat detector used in interventional cardiology procedures. Numerical parameters on image quality have also been measured for different X-ray beam qualities using the plastic wall of the ionisation chamber. When moving from 1 to 10 mm of Cu, IAK per frame increased to a factor of 38 for cine and 27 for fluoroscopy. A cine frame requires 60-116 times more IAK than a fluoroscopy frame. As for PMMA, when the backscatter factor is included (simulating real conditions with patients), and when moving from 12 to 28 cm, the increases in ESAK are 16 times for cine and 10 times for fluoroscopy. Because of the differences in X-ray beam quality for cine and fluoroscopy modes, the Cu thicknesses necessary to drive the generator to equivalent kilovolts resulted in the following values (cine and fluoroscopy, respectively): 12 cm of PMMA (1 and 1.5 mm Cu), 20 PMMA (2.5 and 3.5 mm Cu) and 28 cm PMMA (4.5 and 8.5 mm Cu). With the analysis of IAK, ESAK and image quality, one can verify the appropriate settings of the X-ray system and obtain baseline information for constancy checks and help cardiologists in the management of patient doses by knowing the dose increase factors and image quality changes when increasing patient thickness or using different C-arm projections.