modulation transfer function

Computed Tomography (CT) is one of the most widely used screening and diagnostic tools in medical imaging centers. Considering IAEA HUMAN HEALTH SERIES No. 19 and the American College of Radiology (ACR) Accreditation Program, quality assurance (QA) and quality control (QC) are mandatory programs to periodically monitor the system condition to promote the effective utilization of ionization radiation for a diagnostic outcome through obtaining and retaining appropriate image quality and reduction of patient dose. Computational phantoms (CPs) are the key tool to monitor system condition. The commercial QC phantoms are expensive products and are not flexible enough for user demands. Also, it has recently been reported that standard parameters based on IAEA and ACR, including noise magnitude, and resolution, are not accurate parameters for quantitatively evaluating system performance in terms of image quality. In this paper, we designed and fabricated a new CP along with a graphical user-friendly interface program integrally called “QCT” enabling to measure IAEA/ACR-based standard image parameters and beyond metrics including CT calibration curve, CT number of multiple objects, contrast-to-noise ratio, the edge spread function, the line spread function, the modulation transfer function, spatial resolution, noise power spectrum, image noise, and uniformity. The experimental assessment of QCT was tested on a GE LightSpeed VCT multi-detector CT scanner available in Emam-Khomeini hospital complex. In addition, we reported the details of fabrication process of our QC phantom, enabling readers to create flexible and affordable QC phantoms.

The usage of digital radiology systems with insufficient quality control of digital image detectors can efface inherent superiorities of digital systems in comparison with analogue radiology systems and even makes an increased level of patients’ radiation doses. Modulation transfer function (MTF) is one of the most important parameters related to image quality and digital detectors efficiency. In this study, MTFs of two digital radiology systems (namely, Swiss ray and Siemens) are measured using an edge reference block. The results then were used for the system evaluations. For MTF measuring, an edge reference block was constructed from a 0.8-mm-thick Cerrobend foil. The pre-sampled MTFs of the systems were measured using an edge method. The different MTF values were measured by changing dose levels at Siemens digital detectors surface. The Swiss ray digital detector slightly changed on that dose levels (less than 1%) and showed better results. These results are in good accordance with practical MTF measurements of Marshall et al research. Investigation showed that some quality control weaknesses existed in Siemens system. This is due to heavy work load and insufficient quality control of the system in proper time periods. Finally, this research showed the importance of quality control program and the importance of MTF parameter for quality control measurement of digital radiology systems.