Program Information
Theoretical and Empirical Investigation of 2D Anti-Scatter Grids for Improving Image Quality in a Small Animal Image Guided Therapy System
M Ranjbar*, P Sabouri , A Anvari , A Sawant , University of Maryland School of Medicine, Baltimore, MD
Presentations
SU-E-FS1-6 (Sunday, July 30, 2017) 1:00 PM - 1:55 PM Room: Four Seasons 1
Purpose: Small animal image-guided radiotherapy (SA-IGRT) systems are receiving increased interest for pre-clinical radiobiology studies. A major limitation of these systems is that they provide CT image-guidance using cone-beam geometry, which is prone to increased x-ray scatter and therefore reduced image quality. This is especially limiting for small animal studies where structures are both smaller and low-contrast. Here, we investigate pixel matched 2D anti-scatter grids aligned with the flat-panel imager in order to reduce the scatter-to-primary ratio (SPR).
Methods: Scanner geometry and x-ray source spectrum (XSTRAHL, Atlanta, GA) was simulated using the Monte-Carlo (MC) code PENELOPE, with a water phantom in the imaging path. For the XSTRAHL imaging detector (pixel-pitch=400µm, area=22.5×23cm2), the following ranges of grid parameters were simulated: wall-thickness (50µm–200µm), height (500µm–2500µm), pitch (200µm–1400µm), from steel, nickel, and tungsten; the SPR was calculated for each combination. An optimal grid- wall-thickness=75µm, height=2000µm, pitch=400µm was designed in 3D-CAD software and is under construction. As a proof-of-concept, an early, non-optimized prototype- wall-thickness=200µm, height=1000µm, pitch=1×103µm was constructed using the direct metal laser sintering technique. SPR with and without the prototype grid was simulated and also experimentally measured using a 4cm PMMA-phantom with a 1cm-thick lead block.
Results: For a 7cm-thick water phantom, an optimal grid (steel, wall-thickness=75µm, height=2000µm) was found to decrease SPR from 25% to 14%. For a 5cm-thick phantom, the measured (simulated) SPR values without and with the prototype grid were 14% (13.8%) and 9.4% (8.7%), respectively. Our MC simulations indicate that an optimal, pixel-matched steel grid would further reduce the SPR to 6%.
Conclusion: These early results indicate that image-quality can be significantly improved in SA-IGRT systems through the use of pixel-matched anti-scatter grids. While the use of grids increases the imaging dose, such increases are acceptable in the pre-clinical environment given the gain in CBCT image quality.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by NIH R01 CA169102.
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