Technical evaluation of a prototype ratio 29:1 grid for adult patient cardiovascular angiography imaging conditions.

The purpose of this work was to assess technical performance of a prototype high-ratio (r29), 80 line cm-1grid for imaging conditions which mimic those for adult cardiovascular angiography. The standard equipment r15, 80 line cm-1grid was used as a reference. Plastic Water®LR phantoms with thickness in the range 20-44 cm were used to simulate adult patient attenuation and scatter. Grids were tested using x-ray field of view 20 and 25 cm and x-ray source to detector distance (SID) 107 and 120 cm. The primary transmission fraction (TP) was measured using both narrow beam geometry and a lead beam stop (BS) technique. Scatter transmission (TS) was measured with the lead BS technique. The quantum signal to noise ratio improvement factor (KSNR) was used to describe relative grid performance. The experimental conditions required revised theory to assess grid performance. Theory to account for the detector glare and underestimation of scatter intensity by the lead BS method was developed. Also, novelKSNRtheory was developed to allow direct comparison of two grids operated at different SID. MeanTPwas modestly lower for the r29 versus r15 grid (0.69 versus 0.75). When tested under equivalent scatter condition, TSof the r29 grid was approximately ½ that of the r15 grid (0.18 versus 0.34).KSNRof the r29 grid at SID 120 cm compared to the r15 grid at SID 107 cm increased linearly with phantom thickness (range 1.0 to ∼1.16). Findings of this work indicate that the r29 grid used at SID 120 cm is expected to provide improved image quality (or reduced patient radiation dose) when compared to the r15 grid used at SID 107 cm for adult cardiovascular patients and that the potential benefit of the r29 grid increases with patient thickness >20 cm.

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.

Effective use of radiation shields to minimize operator dose during invasive cardiology procedures.

OBJECTIVES: This study sought to measure the protection from scatter radiation offered to the primary physician by a variety of available shields and to provide best practice guidelines for shield use during invasive cardiology procedures. BACKGROUND: It is accepted that exposure to radiation includes a predicted increase in cancer risk. In the cardiac interventional laboratories, radiation shields are widely available; however, proper use of the shields to optimize protection during cardiac interventional procedures is not well understood. METHODS: The protection from scatter radiation offered by a variety of shields used alone and in combination was measured. Protection was assessed from air-kerma measurements of scatter radiation from a phantom performed without and with the shields. Protection was assessed for 3 patient- access locations (right jugular vein, right femoral artery, and left anterior chest) and for elevations ranging from 25 to 175 cm from the floor. The influence of precise placement of the ceiling-mounted upper body shield was specifically assessed. RESULTS: The utility and protection of shielding varied for the 3 access points and with elevation. For femoral artery access locations, the shields can provide at least 80% protection from scatter at all elevations; however, protection depends substantially on upper body shield position. A disposable radiation-absorbing pad can provide 35% to 70% upper body protection for procedures during which the upper body shield cannot be used effectively. CONCLUSIONS: Radiation shields can provide substantial protection from radiation during cardiac interventional procedures. Shields must be thoughtfully and actively managed to provide optimum protection. Best practice guidelines for shield use are provided.