SPAD Photon Detector Layout for Cherenkov Time Stamping
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Solution Overview
Problem
Existing photon detectors, such as photomultiplier tubes and silicon photomultipliers, face limitations in high-speed and high spatial and time resolution, particularly in applications like PET and SPECT, due to bulkiness, high voltage operation, and low photon detection efficiency, with time resolution limited by scintillation processes and position-dependent photon spread.
Innovation Solution
A photon detector design combining a direct conversion detector with a single photon avalanche diode (SPAD) detector array and an electrode array, optimized for Cherenkov photon detection, integrated with digital silicon photomultipliers, where the SPAD detector array covers a significant surface area of the direct conversion detector, and the electrodes are made of transparent materials to enhance photon detection and time stamping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If photomultiplier tubes are used for photon detection, then high speed photon counting is achieved, but the devices become bulky and require high voltage operation
Solution Approach 1:
The patent replaces the mechanical/electronic multiplication system of photomultiplier tubes with a semiconductor-based avalanche photodiode system. The avalanche photodiode uses electrical field multiplication instead of electron cascade multiplication, enabling compact integration while maintaining high-speed photon counting capability.
Solution Approach 2:
The patent changes the operating parameters by using reverse bias voltage above the breakdown voltage of the avalanche photodiode, enabling single-photon detection through avalanche multiplication. This parameter change allows the device to achieve PMT-level performance in a compact form factor.
2Measurement precision
If scintillation processes are used for time stamp generation, then photon detection is achieved, but time resolution is limited to 100 ps-200 ps
Solution Approach 1:
The patent extracts the time stamp generation function from the scintillation process by using Cherenkov radiation instead. Cherenkov photons are emitted instantaneously when charged particles exceed the phase velocity of light in the medium, providing a time reference that is not limited by scintillation decay times.
Solution Approach 2:
The patent introduces Cherenkov radiation as an intermediary mechanism between gamma ray interaction and time stamp generation. The Cherenkov photons serve as a direct temporal marker of the interaction event, bypassing the time-consuming scintillation process.
3Measurement precision
If transparent semiconducting crystals are used for Cherenkov photon detection, then time stamp generation with picosecond precision is achieved, but the number of detected Cherenkov photons is low
Solution Approach 1:
The patent merges the charge readout electrodes with the SPAD detector array in a single integrated structure. The electrodes that collect charge from the direct conversion detector also serve as the light-sensitive elements for detecting Cherenkov photons, maximizing photon detection efficiency while maintaining time precision.
Solution Approach 2:
The patent makes the electrode array multi-functional by enabling it to perform both charge collection and photon detection functions. This universal structure eliminates the need for separate photodetector elements, increasing the number of detectable Cherenkov photons while preserving picosecond time stamping capability.
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
Improves time resolution and detection sensitivity by maximizing Cherenkov photon detection, reducing dark noise, and simplifying system design, enabling better spatial and temporal accuracy without needing depth-of-interaction corrections.
Implementation Method 1
a direct conversion detector configured to detect gamma radiation and generate direct conversion signals responsive to impingement of photons
Implementation Method 2
detect Cherenkov radiation generated in the direct conversion detector in response to impingement of photons and generate SPAD detection signals
Implementation Method 3
When biased above its breakdown voltage, the avalanche diode goes into break down responsive to impingement of a single photon. Such a device is sometimes called a single photon avalanche diode (SPAD) detector
Implementation Method 4
This current is quenched relatively quickly as voltage over the resistor due to the current flow lowers the reverse bias across the avalanche diode to a level below its break down voltage
Data Source
AI summary
The present invention relates to a photon detector, a detector device and an imaging apparatus for detection of radiation, in particular gamma radiation. The photon detector comprises a direct conversion detector (11) configured to detect gamma radiation and generate direct conversion signals responsive to impingement of photons, a single photon avalanche diode. SPAD, detector array (12) comprising a plurality of SPAD detectors (13) configured to detect Cherenkov radiation generated in the direct conversion detector in response to impingement of photons and generate SPAD detection signals, and an electrode array (14) comprising aurality of electrodes arranged on top of the direct conversion detector and between the direct conversion detector and the SPAD detector array and configured to read out the direct conversion signals. The SPAD detector array substantially covers a surface on one side of the direct conversion detector.