Exposure rates during special procedures with C-arm type fluoroscopic systems.

Abstract

To test for regulatory compliance of free-in-air entrance air kerma rates (EAKR) in C-arm type fluoroscopic equipment, measurements are frequently made under minimum source-to-image receptor distance (SID) and at 300 mm from the image intensifier. However, this is not representative of normal patient geometry, and the automatic brightness controls on these units frequently increase tube output as SID increases. This study investigated effects of these circumstances on actual EAKRs. Typical patient geometries were observed and recorded for 23 consecutive body vascular procedures. EAKRs were measured under compliance and normal patient geometries with use of five modern C-arm type systems for special procedures. SIDs of 1 m were typical when rapid film changers were employed and the patient's entrance skin surface was typically 500 mm from the image receptor. Actual EAKRs were found to be up to 2.5 times those measured under compliance geometry. Actual patient geometries should be used to ensure correct estimates of EAKRs.