Photoelectric Conversion Panel Continuous Reset for X-ray Afterimage Suppression
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Solution Overview
Problem
Existing radiography devices suffer from afterimages due to leak currents from photodiodes, which persist even after reset operations, especially during the generation of X-ray moving images.
Innovation Solution
A photoelectric conversion panel is designed with a specific configuration including transistors, a photodiode, a capacitive element, and a control circuit that accumulates charge during irradiation, reads it during a designated period, and continuously resets the photodiode outside irradiation periods, thereby minimizing leak currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If reset operations are performed before read operations in conventional radiography devices, then photodiodes are temporarily reset, but leak currents persist and afterimages continue to occur
Solution Approach 1:
The patent implements continuous periodic reset operations during the entire irradiation period rather than single reset before readout. The control circuit repeatedly performs reset operations at predetermined intervals during irradiation, ensuring that any leak currents generated are continuously cleared. This periodic action during the harmful period effectively suppresses afterimage formation while maintaining image quality.
Solution Approach 2:
The patent performs reset operations in advance during the irradiation period itself, before the readout operation. By continuously resetting the photodiodes during irradiation, the system prevents accumulation of leak currents that would otherwise persist into the readout phase. This preliminary continuous resetting eliminates the need for additional post-irradiation reset operations.
2Measurement precision
If photodiodes are configured to suppress recombination of remaining carriers, then variance in current magnitude is reduced, but remaining carriers continue to leak and generate afterimages
Solution Approach 1:
The patent maintains continuous reset operations throughout the irradiation period, ensuring that the photodiodes remain in a cleared state continuously rather than intermittently. This continuous action prevents the accumulation and persistence of remaining carriers that cause afterimages, while the photodiode configuration maintains current consistency during the irradiation period when useful signal generation occurs.
Solution Approach 2:
The patent extracts and removes the harmful remaining carriers from the photodiodes through continuous reset operations during irradiation. By actively removing these carriers as they are generated, the system prevents their accumulation and subsequent leakage that causes afterimages, while preserving the useful photoelectric conversion function.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively reduces the effects of leak currents from photodiodes, minimizing afterimages and improving the quality of X-ray moving images by suppressing delay and ghosting artifacts.
Implementation Method 1
slight amounts of light emitted from scintillators at the time of irradiation by radiation (at the time of irradiation by X-rays) are input to reverse-biased photodiodes, thereby generating current
Implementation Method 2
a scintillator that converts X-rays into light, and also performs irradiation of the photodiode by light
Implementation Method 3
a capacitive element that is connected to a second electrode, which is another electrode out of the source electrode and the drain electrode of the first transistor
Data Source
AI summary
A photoelectric conversion panel accumulates charge in a capacitive element during a period in which a photodiode is irradiated by light, by conducting electricity to a first transistor in a state in which a second transistor is interrupted and also in which a third transistor is interrupted, reads the charge accumulated in the capacitive element during a read period, by conducting electricity to the second transistor in a state in which the first transistor is interrupted, and continuously resets the photodiode during a period other than the period in which the photodiode is irradiated by light, by conducting electricity to the third transistor in a state in which the first transistor is interrupted.