Visualization of blurring process due to analog components in a digital radiography system using a simple method
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SCIENTIFIC NOTE
Visualization of blurring process due to analog components in a digital radiography system using a simple method Sho Maruyama1 Received: 1 June 2020 / Accepted: 18 October 2020 © Australasian College of Physical Scientists and Engineers in Medicine 2020
Abstract To obtain useful medical X-ray images for diagnosis, it is necessary to accurately evaluate the characteristics and fully understand the features of the system to determine the imaging target and conditions. This study describes the performance of a digital radiography (DR) system in detail and proposes a method for characterizing the blurring process due to the presence of analog components in an imaging system. Our method does not involve any specialized technique, such as a simulation that requires long computing time on a high-performance computer. The method is based on the concept of the modulation transfer function (MTF). The functions that corresponded to the MTF of the analog components of the system when the Fourier transform was performed were examined. Indirect conversion type flat-panel detectors (FPD) in the general radiography energy range and direct conversion type FPD in the mammography were used for verification. A Gaussian function and Lorentz function were synthesized for modelling the blurring process of the indirect type FPDs. The spreads and shapes of the modeled functions depended on the systems. For the direct conversion type FPD, a combination of a Lorentz function with a narrow width and an impulse function characterized the results. Furthermore, based on the structure of each detector and the signal transfer process, the visualized results were considered reliable. The results of these experiments will aid in the detailed understanding of the image quality characteristics of the DR system by the feasible approach. Keywords X-ray imaging · Image quality · Flat panel detector · MTF · Modelling
Introduction In the medical X-ray imaging, various types of detectors have been used until now. To operate them appropriately, the users are required to accurately evaluate the performance of each system [1–7]. For example, evaluation of the system can help in optimizing the imaging condition [8] and can also predict the suitability of the system for imaging a given target [2]. Resolution characteristics and noise characteristics are commonly used to evaluate a digital radiography (DR) system performance [9–14]. The modulation transfer function (MTF) is an established method [15–17] for evaluating the resolution characteristics of a system. It estimates the amount of the input impulse signal blurred by the system in the spatial frequency domain. In * Sho Maruyama [email protected] 1
School of Radiological Sciences, Faculty of Health Science, Gunma Paz University, 3‑3‑4 Tonyamachi, Takasaki, Gunma 370‑0006, Japan
DR systems, shift-invariance does not hold, and the effect of aliasing cannot be ignored [15]. Therefore, a method called presampled MTF [16] was developed and has commonly been used since. By comparing the
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