The measurement and evaluation of the modulation transfer function (MTF) of mammography systems at a major teaching hospital in Malta

Abstract

Background: Modulation transfer function (MTF) is a quantitative metric of image quality in evaluating the spatial resolution of a medical imaging device. The MTF describes the loss in contrast between neighboring objects being imaged across different spatial frequencies. This allows for a quantitative assessment of the resolving ability of the imaging device, without the involvement of subjectivity, allowing detailed description of the performance of the imaging system via spatial resolution and allows comparison of performance between different mammography systems. Objectives: The scope of the project was to evaluate and study the variation of the MTF of a mammography system across different acquisition parameters i.e., tube voltage and current-time product with/without the aluminium filter. Research Methodology: The study involves imaging of the MTF phantom at different tube voltages and current-time product with and without the aluminium filter. The MTF placed at 40 mm above the breast support table via the polymethyl methacrylate (PMMA) blocks in the absence of the compression paddle. The MTF curves were obtained using the MTF plugin in the software ImageJ. The MTF curves were then, analyzed using Python to evaluate the spatial resolution of the mammography systems at different acquisition parameters and the associated errors, such that their significance could be studied. Results: The study showed the variation of the MTF curves at various acquisition parameters. The spatial resolution decreased with the increase of the tube voltage. The spatial resolution was shown to have very little, or no, effect from the current-time product. The application of filter on the mammography system enhanced the spatial resolution of the imaging device whilst reducing the magnitude of error associated with the MTF curves. Conclusions and recommendations: Results of the MTF show the possibility of an optimization process using the MTF as a metric to improve the sharpness in the acquired image whilst reducing the dose delivered to the patient as part of the optimization process of the medical physicists and medical physics experts.