There are two main performance indicators to evaluate the imaging quality of flat panel detectors: quantum detection efficiency and spatial resolution.
Quantum detection efficiency determines the ability of flat panel detectors to distinguish the density difference of different tissues, while spatial resolution determines the ability to distinguish the fine structure of tissues. The imaging capability of flat panel detectors can be evaluated by investigating the quantum detection efficiency and spatial resolution.
In the indirect conversion of flat panel detectors, there are two main factors affecting the efficiency of quantum detection: the coating of scintillators and the transistor that converts visible light into electrical signals.
In direct conversion flat panel detectors, the conversion of X-ray into electrical signals depends entirely on the pairs of electron holes produced by amorphous selenium layer, and the quantum detection efficiency depends on the charge generation ability of amorphous selenium layer. Generally speaking, the limit quantum detection efficiency of indirect conversion flat panel detectors with CSI+T FT structure is higher than that of a-Se direct conversion flat panel detectors.
In direct conversion flat panel detectors, there is no scattering due to the absence of visible light. The spatial resolution depends on the size of the thin film transistor matrix per unit area. The larger the matrix, the more the number of thin film transistors, the higher the spatial resolution. With the improvement of technology, the higher spatial resolution can be achieved.
In indirectly converted flat panel detectors, there exists scattering due to visible light. The spatial resolution depends not only on the size of thin film transistor matrix per unit area, but also on the control technology of scattering light. Generally speaking, the spatial resolution of indirectly converted flat panel detectors is not as high as that of directly converted flat panel detectors.
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