Technical Note: Assessment of scatter originating from the x-ray tube collimator assembly of modern angiography systems.

PURPOSE

While scatter from the patient is assumed to be the primary source of occupational radiation dose associated with fluoroscopically guided interventional procedures, the potential contribution of scatter from the x-ray collimator assembly is unknown. The purpose of this work was to survey clinical x-ray angiography systems to assess the potential contribution of collimator assembly scatter on occupational radiation dose.

METHODS

Experimental methods were designed to measure the relative contributions of scatter originating from within the collimator assembly of the x-ray tube to total scatter, which included scatter from a patient-simulating phantom. Measurements were acquired as a function of lateral distance from the x-ray beam center using a posterior anterior (PA) projection and at a fixed location for variable right anterior oblique to left anterior oblique projections in the range -90º to 90º. For one system, the collimator assembly was partially disassembled to assess the scatter contribution of individual components. For two systems, 0.5 mm Pb was added to the inner surface of the collimator assembly cover and tested for efficacy to block collimator assembly scatter.

RESULTS

Considering all x-ray systems and only the PA projection, collimator assembly scatter contributed 20-50% to total scatter. For x-ray projection angles of -90º to 90º, the relative contribution of collimator assembly to total scatter was dependent on projection angle and ranged from 5% to 56%. X-ray systems with kerma-area product meters demonstrated higher collimator assembly scatter than those without. Considering all projection angles, the addition of 0.5 mm Pb to the inside of the collimator assembly cover reduced collimator assembly scatter from 28% to 16% of total scatter for both systems.

CONCLUSION

Findings from this work suggest that contemporary radiation safety practices and guidelines should be revised to account for scatter originating from the collimator assembly of angiographic x-ray tubes.