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Quantitative optical densitometry with scanning‐laser film digitizers
Author(s) -
Dempsey James F.,
Low Daniel A.,
Kirov Assen S.,
Williamson Jeffrey F.
Publication year - 1999
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 - 10.1118/1.598664
Subject(s) - optics , materials science , artifact (error) , deconvolution , interference (communication) , laser , dosimetry , stray light , transmission (telecommunications) , physics , computer science , nuclear medicine , artificial intelligence , medicine , computer network , telecommunications , channel (broadcasting)
A new process for eliminating two types of artifacts inherent in commercially available transmission scanning‐laser film digitizers is presented. The first kind of artifact results in nonreproducible interference‐pattern fluctuations as large as 7%. The second kind results in spreading of transmitted light from low‐to‐high optical density (OD) in regions with rapidly varying ODs, producing errors as large as 50%. These OD artifacts cause the loss of precision for films with low‐OD regions (first type) and the loss of accuracy for films with regions of high‐OD near high‐OD gradients (second type). Test radiochromic films, produced by uniform exposure to a 6 MV photon beam and a high dose rate192 Ir brachytherapy source, along with test radiographic films were used to characterize the artifacts of a commercially available scanning‐laser film digitizer. The interference‐pattern artifact was eliminated by digitizing the films on a masked diffusing ground‐glass scanning bed. The light‐transmission artifact was eliminated through discrete‐fast‐Fourier‐transform (DFFT) deconvolution of transmission profiles with measured digitizer line‐spread functions. Obtaining precise OD distributions after the DFFT deconvolution required prior removal of the interference‐pattern artifact and application of a low‐pass Wiener noise filter. Light‐transmission artifacts are particularly significant for applications requiring measurement of high‐gradient OD distributions, such as brachytherapy or conformal photon‐beam film dosimetry and quantitation of two‐dimensional electrophoresis gels. Errors as large as 15%–35% occur in OD distributions representative of these applications. The data collection and correction process developed in this study successfully removes these artifacts.