Radiology, Vol 191, 849-852, Copyright © 1994 by Radiological Society of North America
Exposure rates during special procedures with C-arm type fluoroscopic systems
S Glaze, LK Wagner, BR Archer and SC Bushong
Department of Radiology, Baylor College of Medicine, Houston, TX 77030.
PURPOSE: 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. MATERIALS AND
METHODS: 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. RESULTS: 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. CONCLUSION: Actual
patient geometries should be used to ensure correct estimates of EAKRs.
