PET Scanner Detector Normalization Without Solid Angle Correction
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Solution Overview
Problem
Current 3D positron emission tomography (PET) scanner efficiency normalization methods are complex and require multiple component factors, which can be impractical for all PET scanner designs, especially those with pixilated detector modules, and often necessitate solid angle corrections that complicate calibration processes.
Innovation Solution
A method and apparatus for calibrating PET scanners using phantom sinogram data from solid cylinder and plane phantoms, determining crystal efficiency and detector geometry factors without solid angle corrections, and applying iterative smoothing techniques for accurate normalization, allowing for reduced complexity in 3D component efficiency normalization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional 3D component efficiency normalization methods are used, then detector normalization accuracy is improved, but device complexity and calibration difficulty increase due to multiple component factors and solid angle corrections
Solution Approach 1:
The patent extracts and eliminates the solid angle correction component from the traditional 3D component efficiency normalization method. By using a plane source phantom instead of a point source, the solid angle variation is removed, leaving only the detector efficiency factors to be determined. This simplification maintains normalization accuracy while reducing calibration complexity.
Solution Approach 2:
The patent changes the phantom geometry parameter from a point source to a plane source configuration. This parameter change fundamentally alters the measurement geometry to eliminate solid angle corrections, transforming the normalization process from requiring multiple complex factors to needing only detector efficiency factors.
2Measurement precision
If multiple component factors are used for 3D normalization, then normalization accuracy is improved, but ease of operation deteriorates due to impracticality for certain scanner designs
Solution Approach 1:
The patent creates a universal calibration method using plane source phantoms that works for all PET scanner designs, including pixilated detector modules. The plane source geometry provides a uniform response across all detector types, making the calibration process universally applicable without requiring design-specific modifications.
Solution Approach 2:
The patent removes the need for scanner design-specific calibration procedures by extracting the solid angle correction requirement. The plane source phantom approach provides a universal solution that works across different scanner geometries and detector configurations, greatly improving ease of operation.
3Loss of time
If direct efficiency normalization is used, then calibration speed is improved, but measurement precision deteriorates due to statistical accuracy concerns with large sinogram sizes
Solution Approach 1:
The patent segments the normalization process into two distinct parts: (1) determining detector efficiency factors using plane source phantoms with sufficient statistics, and (2) applying these factors to correct patient data. This segmentation allows the calibration phase to use larger phantom counts for accuracy while keeping patient scan times short.
Solution Approach 2:
The patent performs the statistically intensive normalization factor determination in advance using plane source phantoms. Once these factors are determined with high statistical accuracy, they can be applied repeatedly to patient data without requiring additional acquisition time, thus resolving the time-accuracy tradeoff.
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 simplifies the calibration process by reducing the number of component factors needed for 3D PET scanner detector calibration, improving statistical accuracy and practicality across various PET scanner designs without requiring solid angle corrections, thus enhancing the efficiency and reliability of PET scanner image reconstruction.
Implementation Method 1
The PET detectors typically comprise crystals and photomultiplier tubes (PMT's), wherein the detector crystals, referred to as scintillators, convert the energy of a gamma ray into a flash of light that is sensed by the detector PMT.
Data Source
AI summary
A method and apparatus for calibrating a PET scanner is provided. First phantom sinogram data is acquired from a scan of a solid cylinder phantom within a PET scanner imaging FOV; second phantom sinogram data is acquired from a scan of a second solid plane or scanning line phantom within the PET scanner imaging FOV; and a PET scanner detector component scanner efficiency normalization is determined from at least one of the first and second sinogram data. In one aspect a crystal determining efficiency factor is determined as a function of phantom sinogram data without a solid angle correction, and a detector geometry factor is determined as a function of the crystal efficiency factor and phantom sinogram data. In one aspect a smoothed crystal efficiency normalization factor is determined from a noisy crystal efficiency factor through an iterative smoothing technique.