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Monte Carlo evaluation of scatter mitigation strategies in cone‐beam CT
Author(s) -
Lazos Dimitrios,
Williamson Jeffrey F.
Publication year - 2010
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3488978
Subject(s) - imaging phantom , monte carlo method , cone beam computed tomography , physics , contrast to noise ratio , subtraction , optics , image quality , nuclear medicine , computer science , mathematics , artificial intelligence , medicine , radiology , image (mathematics) , computed tomography , statistics , arithmetic
Purpose: To investigate the efficacy of two widely used scatter mitigation methods: antiscatter grids (ASGs) and beam modulating with bowtie filters (BTFs), in combination with subtractive scatter correction or zeroth order normalization phantom calibration, for improving image noise, contrast, contrast‐to‐noise ratio (CNR), and image uniformity for on‐board cone‐beam CT (CBCT) imaging systems used for image‐guided radiation therapy. Methods: PTRAN Monte Carlo CBCT x‐ray projections of head and pelvic phantoms were calculated for combinations of beam‐modulation and scatter rejection methods and images were reconstructed by in‐house developed software. In addition, a simple one‐dimensional analytic model was developed to predict scatter‐to‐primary ratio (SPR) and CNR as a function of cylindrical phantom thickness, ASG transmission, and beam modulation with bow‐tie filters. Results: ASGs were found to have slightly negative or no effect on head phantom image CNR and to modestly improve CNR (10%–20%) in pelvic phantom images. However, scatter subtraction and norm‐phantom calibration perform better when applied on data acquired with ASGs. Scatter subtraction improves CT number accuracy, but increases noise, and in high SPR/low primary‐photon transmission scenarios can dramatically reduce CNR and introduce streaking artifacts. The BTF is found to reduce SPR and image noise, resulting in a better trade‐off between CNR and imaging dose, but introduces a circular band artifact. Conclusions: Our study shows that ASGs have a modest positive impact in pelvic scans and negative in head scans, scatter subtraction improves the HU accuracy but reduces CNR, while BTF has a clearly positive effect.