Quantitative optical densitometry with scanning-laser film digitizers

James F. Dempsey, Daniel A. Low, Assen S. Kirov, Jeffrey F. Williamson

Research output: Contribution to journalArticlepeer-review

51 Scopus citations


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 rate 192Ir 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.

Original languageEnglish
Pages (from-to)1721-1731
Number of pages11
JournalMedical physics
Issue number8
StatePublished - Aug 1999


  • Electrophoresis gel quantitation
  • Film densitometry
  • Film digitization
  • Film dosimetry
  • Laser film digitizer


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