Spectral CT-based 511 KeV for positron emission tomography
Inventors
Sahbaee Bagherzadeh, Pooyan • Saboury Sichani, Babak • Farhadi, Faraz
Assignees
Siemens Healthineers AG • US Department of Health and Human Services
Publication Number
US-11389127-B2
Publication Date
2022-07-19
Expiration Date
2039-09-30
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Abstract
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.
Core Innovation
The invention provides methods, systems, and non-transitory computer readable media for generating a virtual 511 KeV attenuation map from computed tomography (CT) data using spectral or multiple energy CT. This approach allows for more accurate extrapolation of the 511 KeV attenuation map by leveraging material decomposition or additional information from measurements at different energies. The generated attenuation map better accounts for all materials, including high density materials, improving the representation of actual attenuation at 511 KeV without requiring additional scanning with a 511 KeV source external to the patient.
This virtual 511 KeV attenuation map is used in positron emission tomography (PET) image reconstruction to provide more accurate attenuation correction. The method involves acquiring spectral CT data at different energies below 200 KeV and using various modeling techniques—such as machine-learned models, analytical simulations based on material decomposition, generalized linear models, or models tuned via ground truth comparisons—to generate the virtual attenuation map that corrects PET data for attenuation more precisely than conventional bilinear mapping from low energy CT data.
The problem addressed arises from the limitations of conventional PET/CT imaging where the 511 KeV attenuation map is derived from low-energy CT data using a simple bilinear mapping, which can lead to inaccuracies, especially near high density materials such as bone, implants, or contrast agents. These inaccuracies result from scatter and beam-hardening effects in CT data acquired at energies below 100 KeV, leading to bias in attenuation correction and reduced precision in PET quantification. The invention solves this by using spectral CT to better characterize tissue attenuation properties and thus generate a more accurate virtual 511 KeV attenuation map for PET attenuation correction.
Claims Coverage
The patent includes three independent claims covering a method, a system, and a non-transitory computer readable storage medium related to generating and using a virtual 511 KeV attenuation map from spectral CT data for PET attenuation correction.
Generating a virtual 511 KeV attenuation map from spectral CT data
A method for attenuation correction in PET involving acquiring spectral CT data at multiple energies, generating a virtual 511 KeV attenuation map in either image or projection domain from those spectral CT data, and using this map in PET image reconstruction.
Using spectral CT scanner and modeling for PET imaging system
A system comprising an x-ray scanner configured to obtain attenuation data at multiple energies below 200 KeV, rings of PET detectors, and a processor that generates the virtual 511 KeV attenuation map from these multiple energy attenuations and applies it in PET image reconstruction.
Instructions for estimating a virtual 511 KeV attenuation map and correcting PET data
A non-transitory computer readable storage medium with instructions executable by a processor to estimate a virtual 511 KeV attenuation map from CT data at different energies below 200 KeV, correct PET measured emissions based on the estimated attenuation, and generate a PET image from the corrected emissions.
The inventive features collectively provide a solution to more accurately estimate attenuation at 511 KeV for PET attenuation correction by using spectral CT data and various modeling approaches to generate a virtual attenuation map that improves PET image reconstruction and quantification.
Stated Advantages
More accurate attenuation correction for PET imaging by better representing actual attenuation at 511 KeV using virtual attenuation maps derived from spectral CT data.
Improved PET image quantification and reduction of errors caused by high density materials and beam hardening effects in CT data.
Avoidance of extra scanning with a 511 KeV source external to the patient since the attenuation map is virtually generated.
Ability to provide improved PET imaging in situations involving dense materials or attenuation ambiguity, such as prosthetic device infection evaluation or contrast-enhanced CT contexts.
Reduction in beam hardening effects, improved spatial resolution of CT images, potential x-ray dose reduction, and improved contrast in CT imaging.
Documented Applications
Use in attenuation correction for positron emission tomography (PET) imaging.
Application in PET scans where accurate quantification metrics such as standardized uptake value (SUV) or kinetic modeling parameters are required.
Improved PET imaging for evaluation of infections related to hip prosthesis, prosthetic aortic valves, and left ventricular assist devices.
Correction of quantification errors caused by contrast agents including enteric and intravenous contrast in oncologic patients.
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