Photon Counting Imaging Apparatus APD Undercharging Correction
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Solution Overview
Problem
The reliability of X-ray detection apparatuses using SiPMs is compromised due to undercharging of APD cells during high X-ray doses, leading to inaccurate energy resolution as it becomes impossible to distinguish between true low pulse heights and those caused by undercharging, resulting in unreliable energy measurements.
Innovation Solution
The X-ray detection apparatus switches the count data generation mode between the charging period and the charging completion period of the APD cells, ensuring that only energy signals from the charging completion period are counted, thereby avoiding the inaccuracies associated with undercharging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the SiPM is used to detect X-rays in Geiger mode, then the device can measure X-ray energy through pulse height, but undercharging of APD cells during high X-ray doses causes pulse height lowering that cannot be distinguished from true low energy signals, compromising measurement precision
Solution Approach 1:
The patent applies preliminary action by monitoring the voltage state of APD cells before they become undercharged. The system detects the voltage drop during the charging period and uses this information to identify and exclude potentially inaccurate pulse height measurements before they are recorded, thereby preventing measurement errors rather than correcting them afterward
Solution Approach 2:
The patent extracts and separates the charging period signals from the valid measurement signals. By identifying the time window during which APD cells are being recharged (when voltage is recovering), the system extracts these transient signals and excludes them from energy measurement, keeping only the stable post-charging signals for accurate energy resolution
2Productivity
If the APD cells are continuously operated in Geiger mode, then the detector can maintain high counting rate, but the charging time of APD cells causes delays during high X-ray doses, leading to undercharging and inaccurate measurements
Solution Approach 1:
The patent implements feedback by continuously monitoring the voltage state of APD cells and using this information to control the measurement process. The system measures the voltage across the APD cells during operation, compares it against reference levels, and adjusts the signal acceptance criteria accordingly, creating a closed-loop system that adapts to changing operating conditions
Solution Approach 2:
The system performs preliminary detection of the voltage recovery state before accepting measurements. By identifying the charging period through voltage monitoring in advance, the system can preemptively exclude signals that would be affected by undercharging, ensuring that only measurements taken when APD cells are properly charged are recorded
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 approach enhances the accuracy and reliability of energy resolution by excluding energy signals from the charging period, improving the correctness of count data and maintaining high energy resolution even under high X-ray doses.
Implementation Method 1
The scintillator converts incident X-rays into a plurality of scintillation photons
Implementation Method 2
The plurality of scintillation photons are received by the plurality of APD cells
Implementation Method 3
In a Geiger mode, each APD cell causes an electron avalanche (ignites) in response to one or more scintillation photons to generate a current pulse
Data Source
AI summary
According to one embodiment, a photon counting imaging apparatus includes an X-ray tube, an X-ray detector, and data acquisition circuitry. The X-ray detector includes a detector pixel including photoelectric conversion cells each configured to individually generate an electrical signal of a predetermined pulse height, and output circuitry configured to generate an energy signal having a pulse height corresponding to energy of the X-rays based on the electrical signals from the photoelectric conversion cells. The data acquisition circuitry corrects the energy signal based on a relationship between an amplification factor and an applied voltage to the detector pixel during a period until the voltage applied to the detector pixel recovers from a breakdown voltage to a reverse bias voltage.