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WE‐DE‐207B‐08: Towards Standardization of X‐Ray Filters in Digital Mammography‐Enabled Breast Tomosynthesis Systems
Author(s) -
Shrestha S,
Vedantham S,
Karellas A
Publication year - 2016
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 - 10.1118/1.4957868
Subject(s) - fluence , optics , monte carlo method , digital mammography , materials science , mammography , imaging phantom , nuclear medicine , mathematics , physics , medicine , laser , statistics , cancer , breast cancer
Purpose: In digital breast tomosynthesis (DBT) systems capable of digital mammography (DM), Al filters are used during DBT and K‐edge filters during DM. The potential for standardizing the x‐ray filters with Al, instead of K‐edge filters, was investigated with intent to reduce exposure duration and to promote a simpler system design. Methods: Analytical computations of the half‐value thickness (HVT) and the photon fluence per mAs (photons/mm2/mAs) for K‐edge filters (50µm Rh; 50µm Ag) were compared with Al filters of varying thickness. Two strategies for matching the HVT from K‐edge and Al filtered spectra were investigated: varying the kVp for fixed Al thickness, or varying the Al thickness at matched kVp. For both strategies, Al filters were an order of magnitude thicker than K‐edge filters. Hence, Monte Carlo simulations were conducted with the GEANT4 toolkit to determine if the scatter‐to‐primary ratio (SPR) and the point spread function of scatter (scatter PSF) differed between Al and K‐edge filters. Results: Results show the potential for replacing currently used Kedge filters with Al. For fixed Al thickness (700µm), ±1 kVp and +(1–3) kVp change, matched HVT of Rh and Ag filtered spectra. At matched kVp, Al thickness range (650,750)µm and (750,860)µm matched the HVT from Rh and Ag filtered spectra. Photon fluence/mAs with Al filters were 1.5–2.5 times higher, depending on kVp and Al thickness, compared to K‐edge filters. Although Al thickness was an order higher than K‐edge filters, neither the SPR nor the scatter PSF differed from K‐edge filters. Conclusion: The use of Al filters for digital mammography is potentially feasible. The increased fluence/mAs with Al could decrease exposure duration for the combined DBT+DM exam and simplify system design. Effect of x‐ray spectrum change due to Al filtration on radiation dose, signal, noise, contrast and related metrics are being investigated. Funding support: Supported in part by NIH R21CA176470 and R01CA195512. The contents are solely the responsibility of the authors and do not reflect the official views of the NIH or NCI.