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Fluoroscopy Xray Field to Image Receptor Alignment Comparing 3 and 4% SID Requirement to 80% Overlap Requirement

Weiyuan Wang*, University of Oklahoma Health Science Center, Oklahoma City, OK


(Monday, 7/30/2018) 1:15 PM - 1:45 PM

Room: Exhibit Hall | Forum 1

Purpose: FDA has different requirements for fluoroscopy systems’ X-ray field (XRF) to image receptor (IR) alignment due to its shape and the date of manufacture: less than or equal to 3&4% of the SID, or 80% overlap. This study compares the two requirements for circular and square XRF/IR to determine which requirement is stricter.

Methods: Firstly, assuming that both of the XRF and IR are round and have the same diameter, the equations to calculate the overlap are derived. When XRF is mis-aligned with IR along the A/C (anode/cathode) direction, the mis-alignment angle (MLA) is zero degree, and when the mis-alignment is along 90 degrees to A/C direction the MLA is 90 degrees. The equations to calculate the mis-alignment along the A/C direction, and 90 degrees to the A/C direction are derived for different MLAs. Secondly, the same evaluations are done for the square XRF/IR.

Results: For round XRF/IR, when the MLA increases from 0 to 90 degrees, the maximum mis-alignment to meet the 3&4% requirement changes from 1.5cm (at 0 degree, SID=100cm) to 1.414cm (at 45 degree), and to 1.5cm (at 90 degree). The corresponding percentage overlaps are 92.49 (at 0 degree), 92.92 (at 45 degrees), and 92.49 (at 90 degrees). This shows that the 3&4% requirement is stricter than the 80% overlap requirement for all MLAs. In case of a square X-ray field/IR, suppose the mis-alignment along A/C direction is equal to the mis-alignment along 90 degree to A/C direction, when the two mis-alignments are equal to 2cm (SID=100cm), it just passes the 3/4% criteria, and it is 85% overlap. This shows that the 3/4% rule is stricter than the 80% overlap for square XRF/IR.

Conclusion: The 3&4% of SID requirement is stricter than the 80% overlap requirement for both circular and square XRF/IR for all MLAs.


Fluoroscopy, Quality Assurance


IM- X-ray: Quality Control

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