Calculation of the modulation transfer function from the square wave response function data with an interactive curve fitting software

• Main Author: Wan Hassan, Wan Muhamad Saridan
• Format: Article
• Language: English
• Published: University of Aberdeen, Foresterhill, Aberdeen 2002
• Subjects: QC Physics
• Online Access: http://eprints.utm.my/id/eprint/6750/1/Physica_Medica_18_2002_pp25-31.pdf; http://eprints.utm.my/id/eprint/6750/
• Institution: Universiti Teknologi Malaysia

Two ways to calculate the modulation transfer function (MTF) of radiographic screen-film systems from the measured square wave response function (SWRF) data were investigated with an interactive curve fitting software. The measured SWRF data obtained by digitising a radiographic image of a bar pattern test object were fitted to a curve, and the fitted curve was used to calculate the MTF. Satisfactory MTF was obtained by using 12 terms in the calculation. A second version of the calculation included a correction for the normalization at 0.25 cycles/mm of the SWRF data. Measurements from a screen-film combination showed that the MTF of the first version was higher than the second by an average amount of 0.02 units for spatial range 0-3.5 cycles/mm, and on average the MTF of the first version was higher than the second by 10%. Both the SWRF data fitting and the MTF calculation were done within an interactive curve fitting software which made the calculation relatively easy to perform.