Sub-millimeter APD Array for PET Scintillator Readout
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Solution Overview
Problem
Current PET imaging systems face challenges with high noise and capacitance in large surface area avalanche photodiodes (APDs), leading to poor detector performance, and SiPM detectors operate in non-linear Geiger mode, limiting their ability to accurately detect multiple photons.
Innovation Solution
A high-density, highly integrated array of small sub-millimeter avalanche photodiode cells is used, arranged in an n×n configuration to match the scintillator surface area, with independent cell readout capability to minimize noise and capacitance, allowing for accurate energy and timing determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If one APD is coupled to one scintillation crystal in a one-to-one configuration to collect maximum light, then light collection efficiency is improved, but noise and capacitance increase due to larger surface area
Solution Approach 1:
The patent divides a large surface area photosensor into multiple smaller APD cells arranged in an array. Each cell has reduced surface area, which lowers its individual noise and capacitance, while the collective array maintains the total active area needed for efficient light collection from the scintillation crystal.
2Use of energy by moving object
If large surface area APDs are used to match scintillator area, then light collection is improved, but measurement precision deteriorates due to increased noise and capacitance
Solution Approach 1:
By segmenting the large photosensor area into multiple small APD cells, each cell provides accurate measurement with low noise and capacitance. The array configuration preserves total light collection area while enabling precise energy and timing determination through individual cell readout.
Solution Approach 2:
The patent transitions from a single large-area photosensor to a two-dimensional array of small cells. This dimensional reorganization allows simultaneous optimization of light collection (through total array area) and measurement precision (through individual cell characteristics).
3Reliability
If SiPM detectors operate in Geiger mode to provide high gain, then detection sensitivity is improved, but linearity is lost due to binary operation mode
Solution Approach 1:
The patent changes the operating parameter of the APD cells from Geiger mode (binary, non-linear) to proportional mode (linear). By biasing the APDs below breakdown voltage, they provide high gain while maintaining linear response to multiple photons, enabling accurate quantification of light intensity.
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 enhances the detection accuracy and linearity of PET imaging systems by reducing noise and capacitance while maintaining high gain, enabling better energy and timing resolution for PET imaging applications.
Implementation Method 1
avalanche photodiodes (APDs) are commonly used in such devices to provide the desired detection sensitivity. An APD is a semiconductor device that is biased near the breakdown region such that charge generated as a result of the absorption of an incident photon is amplified in the APD itself
Implementation Method 2
charge generated as a result of the absorption of an incident photon is amplified in the APD itself as a result of a cascading effect as charge is accelerated by the high bias potential applied across the p-n junction of the device
Implementation Method 3
Gamma photons produced by an annihilation event can be detected by a pair of oppositely disposed radiation detectors capable of producing a signal in response to the interaction of the gamma photons with a scintillation crystal, with which the photons interact to produce flashes of light or 'events'
Data Source
AI summary
The present invention is a photodetector including improved photosensors configured of an array of small (sub-millimeter) high-density avalanche photodiode cells utilized to readout a single scintillator. Each photosensor comprises a plurality of avalanche photodiodes cells arranged in an (n×n) array of avalanche photodiode cells (where, n>1) that are coupled to a single scintillation crystal. The overall (n×n) array area as the photosensor is the same as the area of a face of the scintillator and each avalanche photodiode cell has a surface area that is not greater than one square millimeter. The photosensor is also configured to facilitate reading the output of each avalanche photodiode cell in the array. By reading out each small avalanche photodiode cell independently, the noise and capacitance are minimized and thereby provide a more accurate determination of energy and timing.