(Sunday, 7/29/2018) 3:00 PM - 6:00 PM
Room: Exhibit Hall
Purpose: The purpose of this work was to characterize the relative quantum efficiency of air gaps (AGs) versus an anti-scatter grid for scatter rejection during cardiac catheterization angiography.
Methods: The scatter to primary ratio (SPR) associated with a set of 30x30 cm² Solid Water phantoms of thickness 5–35 cm was measured using a graduated lead beam stop method and fixed x-ray technique. Primary (PTF) and scatter transmission fractions (STF) of the anti-scatter grid (15:1, 80 in�¹, 105 cm) and scatter transmission fraction of 5-25 cm AGs were measured. From these parameters, the SNR improvement factor (SNRIF) of the grid and AGs was calculated. X-ray fields of view (FOV) 20 and 25 cm were tested.
Results: Findings for the 20 and 25 cm FOV were similar and results for 25 cm FOV are detailed herein. For the 10 cm AG, non-grid technique, the SPR ranged from 0.30-2.06 for the 5-35 cm phantoms. The non-grid SPR decreased rapidly with increasing AG. The grid PTF was 0.64-0.68 for all conditions. For AG = 10 cm, grid STF was 0.26-0.35 and decreased with increasing phantom thickness. Considering AG = 10 cm as a reference condition, the grid SNRIF increased with phantom thickness through the range 0.88-1.06. The non-grid AG STFs ranged from 1.3-0.50 for the 5-25 cm AGs. The corresponding SNRIF increased with phantom thickness and AG length through the range 0.94-1.18.
Conclusion: The relative benefit of an air gap versus a grid for efficient scatter rejection is dependent on phantom thickness, SPR, grid transmission fractions, and AG length. For all phantom thicknesses, the AG technique provides for higher quantum efficiency than the grid if AG > 20 cm can be achieved.
Funding Support, Disclosures, and Conflict of Interest: Mayo Clinic receives funding from Siemens Medical Systems for unrelated work performed by authors KAF and BAS.
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