Anti-Scatter Grid Utilization In Pediatric Diagnostic Fluoroscopy
Abstract
Purpose
To determine the appropriateness of using an anti-scatter grid in pediatric diagnostic fluoroscopy.
Methods
An image quality phantom (Leeds Test Object 10) was imaged on a flat-panel based general fluoroscopy system (Siemens Luminos Agile Max). The phantom was elevated two cm above the table to allow positioning of a dosimeter underneath for entrance Air Kerma Rate (AKR) measurements. Radiolucent supports were used to hold acrylic blocks seven cm above the table. The source-to-image distance was fixed at 39.4 inches, matching the grid’s focal distance to avoid cutoff. Using a Pediatric Voiding Cystourethrogram protocol and the lowest automatic dose mode, 10-frame fluoroscopy exposures and three AKR measurements were taken with acrylic thicknesses ranging 0 – 11 inches at 1-inch intervals with and without the anti-scatter grid. To process the phantom, regions-of-interest (ROIs) were placed over the largest and highest contrast signal and an adjacent background region. Contrast-to-Noise Ratio (CNR) was calculated as CNR = (s-b)/std(b) where s and b are the average pixel values in the signal and background ROIs, respectively, and std(b) is the standard deviation in the background ROI. A figure-of-merit, denoted CNRn, was computed by normalizing CNR by the square-root of measured AKR.
Results
The averages and standard deviations of CNR across 10 frames and AKR of three exposures are reported at each acrylic thickness. At all acrylic thicknesses, CNR alone is higher when using the anti-scatter grid. However, use of a grid reduces CNRn for acrylic thicknesses 3 inches or less. At thicknesses greater than 3 inches, CNRn curves remain relatively similar, despite the 300% average increase of AKR with the grid in.
Conclusion
This work indicates that AKR can be significantly reduced by removing the anti-scatter grid without compromising on image quality at patient thicknesses equivalent to and less than 3 inches of acrylic.