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Quantitative optical densitometry with scanning-laser film digitizers.
J F Dempsey1, D A Low, A S Kirov
1Radiation Oncology Center, Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Medical Physics
|September 29, 1999
Summary
This study introduces a new method to remove two common artifacts from laser film digitizers, improving image precision and accuracy. The process effectively corrects interference patterns and light transmission errors in optical density measurements.
Area of Science:
- Medical Physics
- Image Processing
- Radiological Imaging
Background:
- Commercially available scanning-laser film digitizers exhibit two types of artifacts.
- These artifacts, interference-pattern fluctuations (up to 7%) and light-spreading (up to 50%), compromise precision and accuracy in optical density (OD) measurements.
- Such errors are critical in applications like brachytherapy and electrophoresis gel quantitation.
Purpose of the Study:
- To develop and validate a novel process for eliminating specific artifacts in transmission scanning-laser film digitizers.
- To enhance the precision and accuracy of optical density measurements from digitized films.
Main Methods:
- Characterized digitizer artifacts using test radiochromic and radiographic films exposed to a 6 MV photon beam and an 192Ir brachytherapy source.
- Eliminated interference-pattern artifacts by digitizing films on a masked diffusing ground-glass scanning bed.
- Removed light-transmission artifacts using discrete-fast-Fourier-transform (DFFT) deconvolution with measured digitizer line-spread functions, followed by noise filtering.
Main Results:
- The masking and diffusing ground-glass bed successfully eliminated interference-pattern artifacts.
- DFFT deconvolution, combined with prior artifact removal and Wiener noise filtering, effectively corrected light-transmission artifacts.
- The developed process demonstrated successful removal of significant OD distribution errors (15%-35%) in critical applications.
Conclusions:
- A robust method for artifact correction in laser film digitizers has been established.
- This process significantly improves the accuracy and precision of optical density measurements, crucial for medical and scientific imaging.
- The findings have direct implications for high-gradient OD distribution analysis in radiotherapy and gel electrophoresis.