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Transmission characteristics of a two dimensional antiscatter grid prototype for CBCT
Cem Altunbas1, Brian Kavanagh1, Timur Alexeev1
1Department of Radiation Oncology, University of Colorado School of Medicine, 1665 Aurora Court, Suite 1032, Mail stop, F-706, Aurora, CO, 80045, USA.
Medical Physics
|May 18, 2017
Summary
A new two-dimensional antiscatter grid (2DASG) significantly reduces scattered radiation in cone-beam CT (CBCT) imaging. This 2DASG prototype improves signal-to-noise ratio and contrast, leading to more accurate CT numbers and better visualization.
Area of Science:
- Medical Physics
- Radiological Imaging
- Radiation Therapy Technology
Background:
- Scattered radiation in cone-beam CT (CBCT) degrades image quality, affecting CT number accuracy and the visualization of low-contrast objects.
- Antiscatter grids (ASGs) are used to reduce scatter, but conventional one-dimensional ASGs (1DASGs) have limitations in performance.
Purpose of the Study:
- To develop and evaluate a focused, two-dimensional antiscatter grid (2DASG) prototype for scatter suppression in CBCT systems.
- To compare the primary and scatter transmission characteristics of the 2DASG prototype against a conventional 1DASG.
Main Methods:
- The 2DASG was fabricated using additive manufacturing with tungsten septa and a focusing geometry for offset detector CBCT.
- Scatter-to-primary ratio (SPR) and scatter transmission fraction (Ts) were measured using the beam stop method with varying phantom thicknesses.
- Primary transmission fraction (Tp) and signal-to-noise ratio (SNR) improvement were calculated; contrast-to-noise ratio (CNR) was assessed using a low-contrast object.
Main Results:
- The 2DASG reduced SPR by 3-6 times and Ts to 5-14% compared to 1DASG (21-29%).
- 2DASG maintained lower SPR and Ts with increased air gap and bow tie filter.
- 2DASG provided up to 1.7 times greater SNR improvement and enhanced visualization of low-contrast objects.
Conclusions:
- The 2DASG prototype demonstrates superior scatter suppression compared to conventional 1DASG.
- Higher average primary transmission (84.7% vs 70.6%) in 2DASG is attributed to optimized geometry and absence of spacers.
- The 2DASG shows potential for improving CT number accuracy and contrast resolution in CBCT imaging.
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