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Physical Image Quality Evaluation of X-ray Detectors for Digital Radiography and Mammography
Published in Paolo Russo, Handbook of X-ray Imaging, 2017
Nicholas W. Marshall, Pascal Monnin
One could use a direct measurement of the PSF from which the pre-sampling MTF is calculated to estimate the detector unsharpness; however, this is difficult for a number of reasons. The aperture used to generate the point source incident on the detector must be small compared to the PSF; fabrication of such a pinhole in a radio-opaque sheet is challenging. The resultant input signal to the detector is of very low intensity, and this can lead to noise influencing the measurement. Furthermore, using this method with pixelated detectors is problematic, as the measured PSF will depend on the position (i.e., the phase) of the aperture with respect to the pixel matrix. Some of these problems can be overcome by using line or knife-edge input sources to respectively assess the LSF or edge spread function (ESF), as these are somewhat easier to manufacture and yield greater intensities; however, the problem of position dependence remains. The solution to the phase dependence of stimuli used to digital imaging systems sharpness, first described by Judy (1976) for Computed Tomography (CT) scanners, and later by Reichenbach et al. (1991) and Fujita et al. (1992) for projection digital imaging devices, involves the angulation of the slit or edge test device against the pixel (or voxel) matrix to measure the pre-sampling MTF. While earlier work described the use of slit methods (Fujita et al. 1992; Dobbins et al. 1995), the edge method has become the preferred method for a number of reasons, including ease of manufacture and ease of positioning (Samei et al. 1998; Buhr et al. 2003).
Performance Testing of Dysprosium-Based Scintillation Screens and Demonstration of Digital Transfer Method Neutron Radiography of Highly Radioactive Samples
Published in Nuclear Technology, 2022
William Chuirazzi, Aaron Craft, Burkhard Schillinger, Nicholas Boulton, Glen Papaioannou, Amanda Smolinski, Kyrone Riley, Andrew Smolinski, Michael Ruddell
The spatial resolution of a neutron radiography system depends on a wide range of factors across the entire imaging system. The three major factors that fundamentally limit the spatial resolution are the following:The aperture diameter and associated L/D ratio of the beam introduce geometric unsharpness to the image based on the sample-to-detector distance.The neutron converter produces charged particles, the range of which in the detector medium deposits signals away from their point of origin, introducing some unsharpness.Light diffusion within the scintillator screen itself blurs the resulting image, which effectively increases with increasing screen thickness.
X-Ray and Neutron Radiography System Optimization by Means of a Multiobjective Approach and a Simplified Ray-Tracing Method
Published in Nuclear Technology, 2021
Robert Nshimirimana, Ajith Abraham, Gawie Nothnagel, Andries Engelbrecht
The overall unsharpness can be approximated using the edge method or using a duplex wire-type image quality indicator device designed according to the International Organization for Standardization such as ISO 19232-5:2018aISO 19232-5:2018, “Non-Destructive Testing – Image Quality of Radiographs – Part 5: Determination of the Image Unsharpness and Basic Spatial Resolution Value Using Duplex Wire-Type Image Quality Indicators,” International Organization for Standardization. (Refs. 65 through 68). The edge method measures the unsharpness in the image from the edge between two adjacent homogeneous structures of different attenuation. A grayscale line profile is taken perpendicular to and across the edge, and the unsharpness is derived from the information across the discrete boundary or an edge spread function,54,69,70 which approximates a step function in real position space. The overall unsharpness as adopted for this simulator is defined as the pixel distance over which the grayscale values are changing along the line profile, as indicated in Fig. 3. In practice, it is difficult and subjective to find the start of the no-change points A and B on the line profile, but once a definition (threshold grayscale value) has been set, comparisons and calibrations can be made consistently.
Spatiotemporal Evaluation of Bubble Characteristics in Sodium Using Real-Time X-Ray Imaging
Published in Nuclear Technology, 2023
Avinash Kumar Acharya, E. Hemanth Rao, M. Menaka, Sanjay Kumar Das, D. Ponraju, B. Venkatraman
Total unsharpness of the X-ray imaging system was the main source of error in the measurement of bubble size and displacement. Total unsharpness UT and image unsharpness UIm of the digital X-ray imaging system was calculated as given in Eq. (5) (Ref. 24):