Virtual 511 KeV Attenuation Map from Spectral CT
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Solution Overview
Problem
Current PET imaging techniques using low-dose CT data for attenuation correction suffer from inaccuracies, particularly near high-density materials like bone or contrast agents, due to simple bilinear mapping and polychromatic photon sources, leading to errors in quantification.
Innovation Solution
Generating a virtual 511 KeV attenuation map from spectral or multiple energy CT data using dual energy or photon counting detectors, which allows for material decomposition and more accurate representation of attenuation, eliminating the need for external 511 KeV sources and improving PET image reconstruction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If low-dose CT data with polychromatic photon source is used for attenuation correction, then the need for external 511 KeV sources is eliminated, but measurement precision deteriorates due to inaccurate extrapolation of 511 KeV attenuation map
Solution Approach 1:
The patent changes the energy parameter of the photon source from polychromatic (below 100 KeV) to monoenergetic (140 KeV or 511 KeV). This parameter change allows accurate measurement of attenuation coefficients at the specific energy level needed for PET reconstruction, eliminating the need for complex bilinear mapping while maintaining high measurement precision.
Solution Approach 2:
The patent creates a virtual 511 KeV attenuation map by using a 511 KeV photon source to measure attenuation coefficients that directly represent the PET emission energy. This virtual copy of the actual PET attenuation conditions provides accurate correction data without requiring external 511 KeV transmission scanning.
2Device complexity
If simple bilinear mapping is used to extrapolate 511 KeV attenuation map from CT data, then device complexity is reduced, but manufacturing precision deteriorates due to inaccuracies near high-density materials
Solution Approach 1:
The patent changes the photon energy parameter from the polychromatic range (below 100 KeV) to specific monoenergetic values (140 KeV or 511 KeV). This parameter change enables accurate measurement of attenuation coefficients that properly account for the energy-dependent interaction of photons with high-density materials, eliminating the fundamental limitation of bilinear mapping.
Solution Approach 2:
The patent replaces the mathematical approximation system (bilinear mapping) with a direct physical measurement system using monoenergetic or 511 KeV photons. This substitution eliminates the need for complex mathematical corrections and directly provides accurate attenuation coefficients through physical measurement.
3Device complexity
If polychromatic photon source with energy below 100 KeV is used, then device complexity is reduced, but measurement precision deteriorates due to energy mismatch with 511 KeV PET emissions
Solution Approach 1:
The patent changes the energy parameter of the photon source from a polychromatic distribution (below 100 KeV) to monoenergetic (140 KeV or 511 KeV). This parameter change ensures that the measured attenuation coefficients directly correspond to the energy of PET emissions, eliminating energy mismatch errors and providing accurate attenuation correction.
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 provides more accurate PET image reconstruction by accurately accounting for attenuation across a broader range of materials, reducing quantification errors and enhancing image fidelity, especially in situations involving high-density materials.
Implementation Method 1
A computed tomography (CT) scanner acquires spectral CT data
Implementation Method 2
the attenuation of the photons through tissue is accounted for in reconstruction. The degree of attenuation is related to a cumulative attenuation coefficient of tissue across the LOR
Implementation Method 3
an unstable radionuclide emits a positron, which collides with an electron resulting in annihilation of mass and emission of energy in form of two photons (gamma radiation) with 511 KeV energy
Implementation Method 4
emission of energy in form of two photons (gamma radiation) with 511 KeV energy
Implementation Method 5
Since spectral or multiple energy CT may allow for material decomposition and/or due to additional information in the form of measurements at different energies, the modeling used to generate the 511 KeV attenuation map may better account for all materials including high density material
Data Source
AI summary
A virtual 511 KeV attenuation map is generated from CT data. Spectral or multiple energy CT is used to more accurately extrapolate the 511 KeV attenuation map. Since spectral or multiple energy CT may allow for material decomposition and/or due to additional information in the form of measurements at different energies, the modeling used to generate the 511 KeV attenuation map may better account for all materials including high density material. The extrapolated 511 KeV attenuation map may more likely represent actual attenuation at 511 KeV without requiring extra scanning using a 511 KeV source external to the patient. The virtual 511 KeV attenuation map (e.g., CT data at 511 KeV) may provide more accurate PET image reconstruction.