Digital Event Timing for Nuclear Imaging Detectors
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Solution Overview
Problem
Conventional nuclear medicine imaging systems face challenges in accurately detecting valid scintillation events due to issues like pulse pile-up, signal noise, and inaccurate energy measurement, leading to discarded valid events and increased imaging time.
Innovation Solution
A method that calculates a second derivative of the digital sample from a nuclear imaging detector, determines when it passes through a zero crossing point, and uses this information to calculate a clock fraction to accurately determine the event start time, thereby improving the accuracy of event detection and reducing processing delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional energy window testing is used to detect valid scintillation events, then scattered events can be filtered out, but accurate detection of event start time is required to avoid discarding valid events
Solution Approach 1:
The patent replaces conventional analog signal processing methods with digital signal processing. Specifically, it uses a digital flash analog-to-digital converter (FADC) to sample the scintillation event signal at high rate (e.g., 200 MHz), then applies digital algorithms (second derivative calculation, zero-crossing detection) to precisely determine event start time. This substitution of digital for analog methods enables both accurate event detection and precise timing measurement.
Solution Approach 2:
The patent performs preliminary processing of the scintillation signal by calculating the second derivative of the sampled signal before detecting the event start time. By pre-processing the signal to enhance its features (the second derivative emphasizes the rising edge), the system can more accurately identify the event start point, thereby improving both detection reliability and timing precision.
2Reliability
If pile-up rejection circuitry is used to handle overlapping gamma events, then pulse pile-up can be rejected, but the deadtime of the imaging system increases
Solution Approach 1:
The patent replaces hardware-based pile-up rejection circuitry with software-based pile-up correction algorithms. The digital signal processing approach allows the system to identify and correct pile-up events through computational methods (such as analyzing the shape and timing of sampled signals) rather than using hardware circuits that would require extended deadtime. This enables faster processing and reduced system deadtime while maintaining pile-up rejection capability.
Solution Approach 2:
The patent enables continuous processing of scintillation events through high-rate digital sampling (e.g., 200 MHz FADC), which captures events without interruption. Unlike analog pile-up rejection circuits that must complete processing before accepting new events, the digital approach allows overlapping events to be sampled simultaneously and processed sequentially, maintaining continuous operation and minimizing deadtime.
3Measurement precision
If accurate energy integration is performed from the start of each pulse, then total energy can be accurately measured, but inaccurate event start detection causes energy signals to fall outside the energy window
Solution Approach 1:
The patent performs preliminary detection of the event start time using digital signal processing (second derivative and zero-crossing detection) before integrating the signal to calculate total energy. By accurately identifying the start point through pre-processing, the subsequent energy integration can begin at the correct moment, ensuring both accurate energy measurement and valid energy signals that fall within the expected energy window.
Solution Approach 2:
The patent replaces conventional analog timing circuits with digital timing detection methods. The digital FADC samples the signal, and software algorithms (second derivative calculation followed by zero-crossing detection) precisely determine the event start time. This digital approach provides both the timing accuracy needed for correct energy integration and the flexibility to adjust detection parameters without hardware changes.
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 of event detection, reduces the impact of noise and pile-up errors, and decreases the overall time required for imaging procedures by providing a more precise determination of event start times.
Implementation Method 1
Such scintillators are conventionally made of crystalline material such as Nal(Tl), which interacts with absorbed gamma photons to produce flashes of visible light.
Implementation Method 2
The photosensor devices convert the received light photons into electrical pulses whose magnitude corresponds to the amount of light photons impinging on the photosensitive area of the photosensor device.
Data Source
AI summary
Methods, computer-readable mediums, and a circuit are provided. In one embodiment, a method is provided which obtains a digital sample. The method calculates a second derivative of the digital sample and thereafter determines when the second derivative passed through a zero crossing point. A master clock value and the second derivative value before and after the second derivate passes through zero are used to calculate a clock fraction and add the clock fraction to the master clock value. Thereafter, an event start signal is triggered to initiates signal processing.