Abstract:
Background Radiation imaging technology, as an important diagnostic, has been widely used in scientific devices such as inertial confinement fusion and flash photography. It has been found that unexpected low-frequency components usually exist in the point spread function (PSF) of radiation imaging systems, leading to the so-called low-frequency blur or long-range blur. Because of long-range blur, the image grayscale varies nonlinearly with the ray flux, which in turn interferes with the analysis of the object density or the source intensity. Experimental measurement of the low-frequency components is challenging because of their extremely low intensity. The specific sources of low-frequency components are not very clear currently.
Purpose This study aims to address these challenges by proposing a new experimental method for measuring the low-frequency components. The goal is to ensure the reliability of the measurement data on low-frequency components and to identify the main sources of low-frequency components.
Methods A series of experiments were conducted on different components of the imaging system. A collimator called ring-aperture was used to modulate the x-ray or optical photons into a circular pattern, which led to a significant increase in the signal strength from low-frequency components by orders of magnitude.
Results A direct measurement result of the low-frequency components was obtained for the first time, and the measurement lower limit was extended to 10−6 relative to the peak of PSF. Experiments showed that the surface state of scintillators can have a significant impact on low-frequency components. By blackening the non-light-emitting surface, the low-frequency components caused by scintillator can be reduced by 22% to 62%.
Conclusions The ring-aperture method provides a reliable experimental approach for measuring low-frequency components of the PSF. The research results indicate that optical photon transport is an important factor leading to long-range blur. By surface treatment of scintillators, such as blackening and polishing, long-range blur can be effectively suppressed.
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